Great question! Not one I've ever heard on YT. Finishing up on PT2399 project and working on Thomas Henry's 8038 VCO that's getting ready to smell smoke in the very recent future. Can't wait as I'm down to the last few connections on my printed circuit board. I etched the board myself, but the etchant was purchased in 1996 as is getting a little tired.
Please crimp the wires to connectors instead of soldering on top of the crimps. The soldering wicking into the wire makes it brittle at one spot where it ends and the insulation is not held to support it. The proper crimping tools have two-level dies, which crimp the smaller wings around the wire tighter and the larger ones around the insulation with larger size. Although the connector manufacturer tools are priced usually as if they were made of gold, there are good enough third party universal alternative tools, for example IWS3220. These have multiple sizes of positions to choose from and usually one of them is as good as the manufacturer tool, with a bit of fiddling around it works very well. A crimped connection can be as good as soldered one if done correctly.
I used to go to the Maplin store in Southend when I was a teenager and they were always very welcoming in there - until I kept asking them if I could try the 4600 in the window, to which they repeatedly refused. When I got irritated by their refusals and asked WHY I couldn't try it, one of the guys said, "Because it's just a display, dipstick! There's no synthesizer in it!"
One look at those circuit diagrams and I would have normally run away. But I think you did a really good job of explaining them as you worked your way thought them systematically. I really feel I have learnt a lot. Good job.
Excellent video - yes please lets have more - PART 3! I remember the Southend shop well. My Dad built the ETI synth and every so often he's say on a weekend "Err do you fancy a bit of a long drive?" - which meant hoping on the motorbike and toodling off to Southend to pick up some parts. I distinctly remember my Dad leaping out of the armchair when the ETI mag came on a Saturday, he was very excited about the white noise circuit - he thought it was a brilliant design. iI believe the guys that designed the Synth took some patents out including the white noise generator. Cheers.
47:15 Those connectors are not attached properly. The wider part should be crimped over the wire insulation to provide strain relief. Then your wires wouldn't keep breaking off.
I never made it to the Maplin store in Southend, but I used to spend an inordinate amount of my pocket money on mail-order components from Maplin. This was long before other regional Maplin stores opened. I bought some of the 4600 PCBs and associated components and brackets. Sadly, my pocket money never stretched to completing the whole thing. The circuit boards that I did complete, stored in the roof of my parents' house, suffered from serious corrosion from damp, and were beyond repair when I rediscovered them many years later. Would love to see a Part 3 where you get the rest of the circuits going.
This synth and the Transendent were the two synths I would ogle over in the old electronic magazines I'd get back in the day. I was lucky in that I did the same ogling over the first computers and got on (a NASCOM), but for years I lusted after these synths and never got anywhere near owning one. It wasn't until the late 1980s until I bought a new Juno1. I had no idea what these sounded like, or how good they were or anything. It was just purely ignorant desire. I'm so glad these are being saved.
Mate, I can't tell you how many bits of old kit I've fixed with wires breaking off plugs. I'd suggest getting new plugs and simply repining them and adding a small bit of heat shrink over the connection where the wire meets the pin. It adds a bit of strain relief and elevates loads of headaches. As far as the rest of the fixes, I'd love to see them. Cheers!
I'm enjoying these so much! Please continue until it's done, I love watching. I know you're only showing us the interesting parts so we don't see the drudgery, but even so, I have to say you have a lot of patience. I'd probably quickly get grumpy, having to keep soldering that ribbon cable! Anyway, I'll go and make a small donation shortly. By the way, I used to work in the Southampton Maplin shop (not Southend), but it was after these synths' time was over: around 1987/88. I got 25% staff discount though, and I did build a few kits, including a sound-to-light controller, which I wired up to three coloured spotlights in my bedsit so I could have "disco lights" when I played music. Fun times :) Electronics was always a bit of a dark art to me, I preferred software and after leaving Maplin I began a software career - but I still love looking at circuit diagrams!
@50:00....channeling your inner Mike Oldfield there ;) Synth is sounding really good after all that work. As you are finding, there can be pretty massive differences between apparently identical components, so careful selection of specific type to application is vital. A circuit diagram can be misleading and give a false sense of security. Point of order re Maplins store, it was Westcliff-on-Sea, not Southend. Apologies for the pedantry. As I commented elsewhere on this vid and on your last one, I used to work for E&MM and spent many a lunch break down in the Maplin shop playing with the toys. I looked at the Wiki entry for Maplin and they mentioned the speech synthesis module that Maplin sold, and that featured in E&MM. We visited TI to look at their speech chip and they were running it on a 16 bit platform. My humble Mictrotan 65 was the first 8 bit machine to ever make one of those modules 'talk'. Nerd claim to fame there ;)
I have been utterly captivated by this series. Please make part 3 if resources allow. What a labour of love and a brilliant result.... (did I hear another wire popping off?)
Great job on this! I learn a lot from your videos. As far as parts go, ALWAYS CHECK EVERYTHING! I've bought some blue resistors and are marked for 200 ohm and actually measure 20 K! All of the resistors on the tape were marked the same and measured the same. I've seen this on smd capacitors as well. Of course they come from an online discount site, which are great, but beware! ALWAYS wear a condom! And always socket your ic's! There is a lot of fake- ees! Take care!
Maplins in Southend - wow! They started the UK's first music mag - Electronics & Music Maker, also in Southend. I worked on the mag down there )depending on your geographical location) for a few months and wrote for it for many years. Really sad to see Maplins go. I never did make any of the projects 🤔😊
Ian…. I worked at E&MM from shortly before the launch for about 6 months or so. The pay was so crap I quit as soon as I had to pay tax because it cost me more to get to work than I was getting! I have a crap memory for names…were we there at the same time? Never forget the magazine launch at the Princess Anne Theatre with Magnus Pike as the star turn… with his notes scribbled on his shirt cuff. Not to he picky, but technically it was Westcliff on Sea, not Southend ;)
I was an avid reader of that magazine for the first few years of its life. Never built anything from it but it was a great way to test my understanding of electronics.
The staff in the original Maplin shop (technically Westcliff-on-Sea) were great - really helpful and knowledgeable. On one occasion I was in the shop, skint as usual, trying to memorize a circuit for a fuzz box from a Babani book (I couldn't afford the book.) Doug Simmons, one of the founders, came out of the back room and took the book from my hands. I thought he was going to throw me out. Instead he said, "Wait there" and walked into the office at the back. One minute later he came out, gave me a photocopy of the circuit and components list and put the book back on display. When I thanked him, he said "Do me a favour, lad - when you've saved up your pocket money for the parts, buy them from us!" I did! Later, I was a loyal mail order customer and built several of the E&MM circuits, but gave up when they got (a) too expensive and (b) sloppy, leaving items out of mail orders and accusing me of trying to steal from them when I had to complain for the third time.
@@chrissavage5966 Names, faces and places - I forget them all 😄 And it was sooooo long ago. I was not there at the start but followed Chris Jordan. I'd done acouple of pieces for Mike Beecher and he asked me to fill in for a while. Don't remember the pay exactly but it must have been OK for a Northern boy 😊
You might be able to eliminate the slight portamento effect on the high octave by reducing the value of the sample & hold capacitor. A smaller value will charge faster, eliminating the glide effect with the glide control set to its minimum. The downside is that the charge will bleed away faster than with a largeer capacitor, but if the buffer opamp has a high enough input impedance (TL071 etc will be perfect for this as these have a very high impedance FET input stage), then this shouldn't be a problem in practice. Since the original capacitor is specified as 0.47uF (470nF), you might try 220nF (0.22uF) and see if this improves things a bit :) I'm really enjoying this series of videos - Myself and a couple of mates built the Maplin 3800 synth back in the early 80s, which has very similar circuitry (although it used a digital keyboard controller which was a good bit more stable) We actually wanted the 5600S but that was out of our budget range so we had to settle for the lite version instead :)
Thank you so very much, I could understand what you were saying, most people would have put it as everyone else should understand how it all starts, you did it in the most simple way possible, and for that, thank you so much.
The circuit board printing is very similar to that of a machine from the same time period I picked up recently, which is a single loop Buddha machine. This one is different from the newer, multi song ones, which play actual music samples from a Rom chip. It has a built in speed adjustment pot which, when you turn it all the way down, the sounds are still perfectly crisp and clear even though they are slowed down to almost nothing, because the original sample loop was carefully dissected so it could be recreated from scratch inside the machine.
This is great, thankyou. Just found a part built, but with all components 4600 on ebay (Jan 2025) going for £2,495 - so I'm still drooling. Suppose I could sell my car or wife. 😂
I love that you guys are doing this, only downside is you're on the wrong side of the Atlantic from me so I can't visit. So I get to live vicariously through RUclips.
What is really remarkable is that the schematic and circuitry actually works as it should! Magazine based articles for construction often had errors and issues that made the end result disappointing for the builders but ETI seems to have done a good job with that one. It also, of course, makes repairs that much easier. PS - run a bead of hot glue across where the wires exit the sockets on those multiway connectors. Strain relief......
The rarity of your practical knowledge and experience alone could be enough to distinquish you as a relative expert, in the absence of an existence of many others.
That noise generator schematic will be a fine addition to my collection... I'm currently in the process of designing one, so I wanna check all the sources I can! LFSRs are fascinating for sure
These things can be fixed if one is willing to put the work in for it and look around. I fixed a TV for my mother this week by popping the back off. I'm no EE, but it seems like the visibly corroded electrolytic capacitors on the power supply were a good place to start. (Just watch out for the resident angry pixies. ⚡) Good going, Mitch! 👍
As youngish boy I had a go at building this kit. PSU went phut fairly early on an dI never really got going again before bits started getting lost. What a silly chap I was. Should ask parents if they've still got any of the bits.
Keyboard sample & hold acquisition time can be reduced by reducing the value of the hold capacitor (0.47µF). This would, of course, make any leakage into the buffer amplifier more critical since note droop would be easily discernable. A good FET input OP-amp would then be necessary (I think I used RS 305-456 in the Museum's "Riggysynthi" but they are well old now).
@@TheVirtualWatcher think it’s a good solution, the range on the glide pot is really big so loosing a bit won’t matter too much. Riggysynthi is going strong!
yep couple people mentioned they'd like to see more of the repair work in action. From my perspective it was just more of the same we did last time, but i see now how it adds to the journey of fixing it! Will include more
Really enjoying these videos, reminds me of my analog electronics class (but better). One thing for feedback, please put a bit more of the "THis is what it sounds/looks like when wrong" and "this is right" be it audio or voltmeter/oscilloscope. This way we get little rewards watching it as well too!
Another excellent video, thanks, I learned a lot. I'm working on a self designed & built valve amp, as a maker of videos I know how much work goes into them & how hard it is to articulate complex electronic concepts etc. Sorry not in a position to chuck you a few quid at the moment but would love another video please.
A friend of mine built one of these back in the day, and I remember fixing it on a number of occasions. The problem is the power supply design was both underpowered, and of poor quality. It either failed, or it was so unstable it would blow chips and boards up. In the end, I ripped out the lot and put a decent switch-mode PSU in there. I would strongly recommend doing the same, it's really not to be trusted.
V/Hz systems are interesting. I"m using it on my synth. Rather than adding signals together in the V/Oct system, you multiply signals, because log(a*b) = log(a) + log(b). This is easy enough with op-amps, because you can just use a potentiometer as a multiplier. It gets tricky if you want to multiply two (or more) control voltages together. Tuning is different as well. In the V/Hz system you need the oscillators to be at exactly 0Hz for 0V input, so a DC offset needs to be used to tune the *bass* frequencies. V/Oct systems need the treble notes tuned. I don't think the resistors needed to be matched on the op-amp, as that would just change the relative pitch of the oscillators. No doubt you're aware the ratio between the two resistors determines the gain (i.e. multiplication). Regarding the glide control, an RC time constant doesn't care about the voltage difference. It's a time constant after all. I'm thinking the flat C at the top is caused by the TL071, which have terrible output swing. The output voltage might be hitting the limit of the op-amp running off a +/- 14V rail. Looking forward to the next video! Cheers.
cheers for this. My brain mustve been foggy to forget the rc time constant, ill correct that in the next vid and try your op amp suggestion. Failing that swap out that cap. Im sure youre right the resistor change wasnt strictly necessary but doing that meant the tune knob could be set correctly at the 0 position on the panel which is easier for people to understand at the museum
@bobskool haha I do have noisy fingers it’s true even if they’re cold. Just proved the clock was the issue and the circuit only consisted of that quad NOR so had to be it.
Buy 100, only find 3 that match.... Yes, I'm working on an audio circuit as well. What the frack, can we see a close up and a circuit of those trimmer/switch/jobbies? You have almost got a set of Digital Bagpipes there!
The first video in the series was more a mix of theory and checking the circuit. This second one was a bit more theory and less the work on the circuit. I personally liked the first video more. But I understand it's a lot more work to get all the shots working on the boards
sorry the tripod is annoying to set up! ill try more in the next one. The full schematics are linked in the description if you wanna take a closer look
I don't think you needed to match R52 and R53. Since all the frequency controlling voltages are derived by voltage dividers from the voltage at the output of IC2 (adjustable with the 50K TUNE trimmer RV12 top left of Fig. 11 Keyboard controller circuit), if R52 and R53 are a bit different, you just need to adjust RV12 to compensate.
its true but that RV12 tune adjustment is a pot on the panel not an internal trimmer. I preferred calibrating it so that tune knob is correct at the 0 position so we can easily retune it when people fiddle with it all at the museum. To compensate for that in the oscillators was also not possible because of the range of the scaling available
@hackmodular the 4600, having four VCOs does lend itself to basic polyphony but it would need a slightly more complex keyboard controller. Nothing too complex, but it would need a counter/decoder driven by the keyboard trigger output (a CD4017 should be a perfect candidate here) with seperate sample&hold switch/buffer for each VCO, so each time you press a key, the counter moves one step and sends each subsequent voltage to the appropiate VCO, if that makes sense. It's not actually all that complicated, but the problem will be getting all the oscillators to track the keyboard accurately - that's a decent enough challenge with a 1V/octave setup, and it'll be a good bit tougher with this sort of arrangement. I built a very basic polysynth in the 80s using this idea - also with non-standard VCOs (in my case they were based on 555 timer ICs with BC108 transistor buffers for the ramp wave on pin2, giving a very basic Square and (sort of) sawtooth output. It worked fine, but tuning stability was a bit hit and miss at times :)
What can't the whole collection of boards not be implemented using a DSP processor and EPROM containing the firmware and a Dual channel ADC and dual channel DAC.
Marcusfuller did a repair series on a similar Maplin synth a few years ago with an entirely different set of problems. ruclips.net/video/7Wy5X4IGozc/видео.html
What are you repairing/making at the moment?
Seeing as you asked, holographic cameras for imaging plankton
I'm building up boards for the "WaveMaker", my 16 voice polyphonic Fourier synthesis based additive synthesiser.
Working on some Kosmo modules
Great question! Not one I've ever heard on YT. Finishing up on PT2399 project and working on Thomas Henry's 8038 VCO that's getting ready to smell smoke in the very recent future. Can't wait as I'm down to the last few connections on my printed circuit board. I etched the board myself, but the etchant was purchased in 1996 as is getting a little tired.
@@W1RMD Have you visited the museum? There's a couple of 8038 based VCO's in the 'Riggysynthi' ...
You guys need to get some central heating in there! I’m shivering just watching you!🥶
Yeah when you can see your breath, that's not a good working environment
I'm sure they'd heat the place if you donated £100 a week to the museum
@ I’m American, we don’t have any money 😑 but we do have expectations for our homes and workplaces to have heat and AC. The weather can kill you here.
Please crimp the wires to connectors instead of soldering on top of the crimps. The soldering wicking into the wire makes it brittle at one spot where it ends and the insulation is not held to support it. The proper crimping tools have two-level dies, which crimp the smaller wings around the wire tighter and the larger ones around the insulation with larger size. Although the connector manufacturer tools are priced usually as if they were made of gold, there are good enough third party universal alternative tools, for example IWS3220. These have multiple sizes of positions to choose from and usually one of them is as good as the manufacturer tool, with a bit of fiddling around it works very well. A crimped connection can be as good as soldered one if done correctly.
I used to go to the Maplin store in Southend when I was a teenager and they were always very welcoming in there - until I kept asking them if I could try the 4600 in the window, to which they repeatedly refused. When I got irritated by their refusals and asked WHY I couldn't try it, one of the guys said, "Because it's just a display, dipstick! There's no synthesizer in it!"
A bit like the TV's and computers in Ikea!
One look at those circuit diagrams and I would have normally run away. But I think you did a really good job of explaining them as you worked your way thought them systematically. I really feel I have learnt a lot. Good job.
Excellent video - yes please lets have more - PART 3! I remember the Southend shop well. My Dad built the ETI synth and every so often he's say on a weekend "Err do you fancy a bit of a long drive?" - which meant hoping on the motorbike and toodling off to Southend to pick up some parts. I distinctly remember my Dad leaping out of the armchair when the ETI mag came on a Saturday, he was very excited about the white noise circuit - he thought it was a brilliant design. iI believe the guys that designed the Synth took some patents out including the white noise generator. Cheers.
Love this kind of content - longer form and interesting circuits
Would love to see a video about common "building blocks" to help look at schematics
That was fascinating, thank you.
47:15 Those connectors are not attached properly. The wider part should be crimped over the wire insulation to provide strain relief. Then your wires wouldn't keep breaking off.
yeah none of them were bent over. Not just the wires on that connector either there are loads more in the back!
I never made it to the Maplin store in Southend, but I used to spend an inordinate amount of my pocket money on mail-order components from Maplin. This was long before other regional Maplin stores opened. I bought some of the 4600 PCBs and associated components and brackets. Sadly, my pocket money never stretched to completing the whole thing. The circuit boards that I did complete, stored in the roof of my parents' house, suffered from serious corrosion from damp, and were beyond repair when I rediscovered them many years later.
Would love to see a Part 3 where you get the rest of the circuits going.
Brilliant Stuff, looking forward to Part 3, You are excellent at getting across how this all hangs together, Nice repair work too. :)
I really appreciate when people share their process thinking about and repairing electronics on RUclips.
This synth and the Transendent were the two synths I would ogle over in the old electronic magazines I'd get back in the day.
I was lucky in that I did the same ogling over the first computers and got on (a NASCOM), but for years I lusted after these synths and never got anywhere near owning one. It wasn't until the late 1980s until I bought a new Juno1.
I had no idea what these sounded like, or how good they were or anything. It was just purely ignorant desire.
I'm so glad these are being saved.
I built a Transcendent. They were cool little machines for the day at under £200.
Yay I've been waiting for this follow up, great work dude!
Is that Sam destroying the Mini in the background? 😄
I just watched his last video and by the look of it, the mini is already destroying itself :)
Thoroughly enjoying this series on the Maplin synth!
Well done , persistence paid off, a great analog synth recreation lives ..good work.😊
The wires wouldn't break so easy if you bent the "Crimp" wings over to hold the sleeving.
Nice to have the odd long video like this to get an idea of the whole machine. Well explained :)
Mate, I can't tell you how many bits of old kit I've fixed with wires breaking off plugs. I'd suggest getting new plugs and simply repining them and adding a small bit of heat shrink over the connection where the wire meets the pin. It adds a bit of strain relief and elevates loads of headaches. As far as the rest of the fixes, I'd love to see them. Cheers!
Fantastic job. Really enjoyed the episodes.
That looks so effin cold 🥶
I'm enjoying these so much! Please continue until it's done, I love watching. I know you're only showing us the interesting parts so we don't see the drudgery, but even so, I have to say you have a lot of patience. I'd probably quickly get grumpy, having to keep soldering that ribbon cable! Anyway, I'll go and make a small donation shortly. By the way, I used to work in the Southampton Maplin shop (not Southend), but it was after these synths' time was over: around 1987/88. I got 25% staff discount though, and I did build a few kits, including a sound-to-light controller, which I wired up to three coloured spotlights in my bedsit so I could have "disco lights" when I played music. Fun times :) Electronics was always a bit of a dark art to me, I preferred software and after leaving Maplin I began a software career - but I still love looking at circuit diagrams!
@@macronencer thank you for the donation! It’ll go to synth parts 👍
Nice to hear it sounding so good hope to see more
@50:00....channeling your inner Mike Oldfield there ;) Synth is sounding really good after all that work. As you are finding, there can be pretty massive differences between apparently identical components, so careful selection of specific type to application is vital. A circuit diagram can be misleading and give a false sense of security.
Point of order re Maplins store, it was Westcliff-on-Sea, not Southend. Apologies for the pedantry. As I commented elsewhere on this vid and on your last one, I used to work for E&MM and spent many a lunch break down in the Maplin shop playing with the toys.
I looked at the Wiki entry for Maplin and they mentioned the speech synthesis module that Maplin sold, and that featured in E&MM. We visited TI to look at their speech chip and they were running it on a 16 bit platform. My humble Mictrotan 65 was the first 8 bit machine to ever make one of those modules 'talk'. Nerd claim to fame there ;)
I would so love one of these. I remember when they were for sale originally. I would really treasure one.
Awesome diag and repair. Loved it.
I have been utterly captivated by this series. Please make part 3 if resources allow. What a labour of love and a brilliant result.... (did I hear another wire popping off?)
Great job on this! I learn a lot from your videos. As far as parts go, ALWAYS CHECK EVERYTHING! I've bought some blue resistors and are marked for 200 ohm and actually measure 20 K! All of the resistors on the tape were marked the same and measured the same. I've seen this on smd capacitors as well. Of course they come from an online discount site, which are great, but beware! ALWAYS wear a condom! And always socket your ic's! There is a lot of fake- ees! Take care!
Maplins in Southend - wow! They started the UK's first music mag - Electronics & Music Maker, also in Southend. I worked on the mag down there )depending on your geographical location) for a few months and wrote for it for many years. Really sad to see Maplins go. I never did make any of the projects 🤔😊
Ian…. I worked at E&MM from shortly before the launch for about 6 months or so. The pay was so crap I quit as soon as I had to pay tax because it cost me more to get to work than I was getting!
I have a crap memory for names…were we there at the same time?
Never forget the magazine launch at the Princess Anne Theatre with Magnus Pike as the star turn… with his notes scribbled on his shirt cuff.
Not to he picky, but technically it was Westcliff on Sea, not Southend ;)
I was an avid reader of that magazine for the first few years of its life. Never built anything from it but it was a great way to test my understanding of electronics.
The staff in the original Maplin shop (technically Westcliff-on-Sea) were great - really helpful and knowledgeable. On one occasion I was in the shop, skint as usual, trying to memorize a circuit for a fuzz box from a Babani book (I couldn't afford the book.) Doug Simmons, one of the founders, came out of the back room and took the book from my hands. I thought he was going to throw me out. Instead he said, "Wait there" and walked into the office at the back. One minute later he came out, gave me a photocopy of the circuit and components list and put the book back on display. When I thanked him, he said "Do me a favour, lad - when you've saved up your pocket money for the parts, buy them from us!" I did!
Later, I was a loyal mail order customer and built several of the E&MM circuits, but gave up when they got (a) too expensive and (b) sloppy, leaving items out of mail orders and accusing me of trying to steal from them when I had to complain for the third time.
@@chrissavage5966 Names, faces and places - I forget them all 😄
And it was sooooo long ago. I was not there at the start but followed Chris Jordan. I'd done acouple of pieces for Mike Beecher and he asked me to fill in for a while. Don't remember the pay exactly but it must have been OK for a Northern boy 😊
@@tinplategeektoo I never built anything either but I liked the music content. It was the only UK synthy read for a long while...
Part 3 plz
You might be able to eliminate the slight portamento effect on the high octave by reducing the value of the sample & hold capacitor. A smaller value will charge faster, eliminating the glide effect with the glide control set to its minimum. The downside is that the charge will bleed away faster than with a largeer capacitor, but if the buffer opamp has a high enough input impedance (TL071 etc will be perfect for this as these have a very high impedance FET input stage), then this shouldn't be a problem in practice. Since the original capacitor is specified as 0.47uF (470nF), you might try 220nF (0.22uF) and see if this improves things a bit :)
I'm really enjoying this series of videos - Myself and a couple of mates built the Maplin 3800 synth back in the early 80s, which has very similar circuitry (although it used a digital keyboard controller which was a good bit more stable) We actually wanted the 5600S but that was out of our budget range so we had to settle for the lite version instead :)
Thank you so very much, I could understand what you were saying, most people would have put it as everyone else should understand how it all starts, you did it in the most simple way possible, and for that, thank you so much.
Definitely a 3rd Part! Please!
Agreed- I'm already looking forward to part 3
The circuit board printing is very similar to that of a machine from the same time period I picked up recently, which is a single loop Buddha machine. This one is different from the newer, multi song ones, which play actual music samples from a Rom chip. It has a built in speed adjustment pot which, when you turn it all the way down, the sounds are still perfectly crisp and clear even though they are slowed down to almost nothing, because the original sample loop was carefully dissected so it could be recreated from scratch inside the machine.
This is great, thankyou. Just found a part built, but with all components 4600 on ebay (Jan 2025) going for £2,495 - so I'm still drooling. Suppose I could sell my car or wife. 😂
Allowing for inflation, that's probably not far off the original cost when it first came out in the early 1970s
I love that you guys are doing this, only downside is you're on the wrong side of the Atlantic from me so I can't visit. So I get to live vicariously through RUclips.
Great way to see how you diagnose , thanks
Really enjoying this series. Many thanks again for making it.
What is really remarkable is that the schematic and circuitry actually works as it should! Magazine based articles for construction often had errors and issues that made the end result disappointing for the builders but ETI seems to have done a good job with that one. It also, of course, makes repairs that much easier. PS - run a bead of hot glue across where the wires exit the sockets on those multiway connectors. Strain relief......
Great stuff - as soon as I saw all those presets clustered on the range knobs I had terrible calibration flash backs.
The rarity of your practical knowledge and experience alone could be enough to distinquish you as a relative expert, in the absence of an existence of many others.
That noise generator schematic will be a fine addition to my collection...
I'm currently in the process of designing one, so I wanna check all the sources I can! LFSRs are fascinating for sure
Great video, thank you for making and sharing it.
Part 3, yes please!
These things can be fixed if one is willing to put the work in for it and look around. I fixed a TV for my mother this week by popping the back off. I'm no EE, but it seems like the visibly corroded electrolytic capacitors on the power supply were a good place to start. (Just watch out for the resident angry pixies. ⚡) Good going, Mitch! 👍
As youngish boy I had a go at building this kit. PSU went phut fairly early on an dI never really got going again before bits started getting lost. What a silly chap I was. Should ask parents if they've still got any of the bits.
Bagpipe emulator? That drone..
Keyboard sample & hold acquisition time can be reduced by reducing the value of the hold capacitor (0.47µF). This would, of course, make any leakage into the buffer amplifier more critical since note droop would be easily discernable. A good FET input OP-amp would then be necessary (I think I used RS 305-456 in the Museum's "Riggysynthi" but they are well old now).
@@TheVirtualWatcher think it’s a good solution, the range on the glide pot is really big so loosing a bit won’t matter too much. Riggysynthi is going strong!
Thanks for this very entertaining hour. I'd like to see part 3. and maybe some of the actual repair action! keep it up🦾
yep couple people mentioned they'd like to see more of the repair work in action. From my perspective it was just more of the same we did last time, but i see now how it adds to the journey of fixing it! Will include more
Outstanding
Awesome video part 3 is a nust ... Please😊
18:54 Can see your breath condensing into steam! Need to run the propane gas organ again!
Really enjoying these videos, reminds me of my analog electronics class (but better). One thing for feedback, please put a bit more of the "THis is what it sounds/looks like when wrong" and "this is right" be it audio or voltmeter/oscilloscope. This way we get little rewards watching it as well too!
yeah good feedback will do!
I look forward to part 3 and 4!
Nice. Bit of a "Big Clive" vibe about bits of this. good stuff.
Another excellent video, thanks, I learned a lot. I'm working on a self designed & built valve amp, as a maker of videos I know how much work goes into them & how hard it is to articulate complex electronic concepts etc. Sorry not in a position to chuck you a few quid at the moment but would love another video please.
Those were the days! I made one of those but never got the spring thing working. I think it was the reverb.
We've already had 1st and 2nd part, but what about 3rd part? Yes please!
@@projekt6_official a synth repairman is never late, nor is he early, he posts videos exactly when he means to ;)
Ooooh, I've been looking forward to this! Cool as hell.
I'm working on getting my act together. It's not going great. 🥴
one step at a time
@hackmodular thanks man.
I made one of those in the 70s as a teenager!
There may be a practical use of that tone if it only exists passively, or that is in the absence of keyboard activity.
Drink more Newcastle Brown that's the answer .....it gives you wings 😂😂
A friend of mine built one of these back in the day, and I remember fixing it on a number of occasions.
The problem is the power supply design was both underpowered, and of poor quality.
It either failed, or it was so unstable it would blow chips and boards up.
In the end, I ripped out the lot and put a decent switch-mode PSU in there.
I would strongly recommend doing the same, it's really not to be trusted.
The interior looks cool, what would have costed the pcb's back than or what jl... already around?
Cool video man,will be cool when sorted ..peas on all planets.
V/Hz systems are interesting. I"m using it on my synth. Rather than adding signals together in the V/Oct system, you multiply signals, because log(a*b) = log(a) + log(b). This is easy enough with op-amps, because you can just use a potentiometer as a multiplier. It gets tricky if you want to multiply two (or more) control voltages together.
Tuning is different as well. In the V/Hz system you need the oscillators to be at exactly 0Hz for 0V input, so a DC offset needs to be used to tune the *bass* frequencies. V/Oct systems need the treble notes tuned.
I don't think the resistors needed to be matched on the op-amp, as that would just change the relative pitch of the oscillators. No doubt you're aware the ratio between the two resistors determines the gain (i.e. multiplication).
Regarding the glide control, an RC time constant doesn't care about the voltage difference. It's a time constant after all. I'm thinking the flat C at the top is caused by the TL071, which have terrible output swing. The output voltage might be hitting the limit of the op-amp running off a +/- 14V rail.
Looking forward to the next video! Cheers.
cheers for this. My brain mustve been foggy to forget the rc time constant, ill correct that in the next vid and try your op amp suggestion. Failing that swap out that cap. Im sure youre right the resistor change wasnt strictly necessary but doing that meant the tune knob could be set correctly at the 0 position on the panel which is easier for people to understand at the museum
Great work makes me happy, your cold workshop makes me sad.
Edit: Are you sure it's an issue with the NOR gate, you might just have a noisy finger.
@bobskool haha I do have noisy fingers it’s true even if they’re cold. Just proved the clock was the issue and the circuit only consisted of that quad NOR so had to be it.
will there be a part three to this synthesiser?
Buy 100, only find 3 that match....
Yes, I'm working on an audio circuit as well.
What the frack, can we see a close up and a circuit of those trimmer/switch/jobbies?
You have almost got a set of Digital Bagpipes there!
hope you get the heating going
The first video in the series was more a mix of theory and checking the circuit. This second one was a bit more theory and less the work on the circuit. I personally liked the first video more. But I understand it's a lot more work to get all the shots working on the boards
"Entertainin'!"
A heating maybe as support😮
I'm really loving this series but could you go easier on the zooming in/out on the schematic? Fanks!
sorry the tripod is annoying to set up! ill try more in the next one. The full schematics are linked in the description if you wanna take a closer look
I don't think you needed to match R52 and R53. Since all the frequency controlling voltages are derived by voltage dividers from the voltage at the output of IC2 (adjustable with the 50K TUNE trimmer RV12 top left of Fig. 11 Keyboard controller circuit), if R52 and R53 are a bit different, you just need to adjust RV12 to compensate.
its true but that RV12 tune adjustment is a pot on the panel not an internal trimmer. I preferred calibrating it so that tune knob is correct at the 0 position so we can easily retune it when people fiddle with it all at the museum. To compensate for that in the oscillators was also not possible because of the range of the scaling available
Sam doesn’t let you have heat?
Ha can either have heat or synths?! It’s my workshop i chose my priorities
Does lack of heat - cold temperatures have an effect on electronics?
Is this polyphonic or just one note at a time
only monophonic this one, much more complex to make poly unfortunately!
@hackmodular the 4600, having four VCOs does lend itself to basic polyphony but it would need a slightly more complex keyboard controller. Nothing too complex, but it would need a counter/decoder driven by the keyboard trigger output (a CD4017 should be a perfect candidate here) with seperate sample&hold switch/buffer for each VCO, so each time you press a key, the counter moves one step and sends each subsequent voltage to the appropiate VCO, if that makes sense. It's not actually all that complicated, but the problem will be getting all the oscillators to track the keyboard accurately - that's a decent enough challenge with a 1V/octave setup, and it'll be a good bit tougher with this sort of arrangement. I built a very basic polysynth in the 80s using this idea - also with non-standard VCOs (in my case they were based on 555 timer ICs with BC108 transistor buffers for the ramp wave on pin2, giving a very basic Square and (sort of) sawtooth output. It worked fine, but tuning stability was a bit hit and miss at times :)
Damn it looks chilly in that room.
You fogged up the camera 😅
What can't the whole collection of boards not be implemented using a DSP processor and EPROM containing the firmware and a Dual channel ADC and dual channel DAC.
Judging by the way the keyboard changes the frequency of the notes at 15:25, there’s a lot more wrong with that 😉😉
Mangle Wurzled is what's happening.
Marcusfuller did a repair series on a similar Maplin synth a few years ago with an entirely different set of problems. ruclips.net/video/7Wy5X4IGozc/видео.html
yeah cool vids. enough problems for everyone
Yeah that was the top-of-the-range Maplin 5600S - an awesome synth indeed :)