Many years ago I had both the QUAD 405 and a pair of QUAD ESL’s. The combination was incredible! I still have the 405 in a box in the basement. Now I have a new project! Glad I found your channel by pressing “new to you!”
After spending many years replacing TTL chips, I used a different method to remove IC's which reduces the amount of time you have heat on the board for de-soldering and gives less chance of damaging the tracks in the removal process. As you are not going to re-use the chip, the quickest way to remove it is to chop the legs at the shoulders where it enters the chip body with a pair of side cutters. To remove the pins you add a little solder to the pin from above the board, the meniscus effect of the solder sticks the pin to the iron tip and you lift it out. You can the clear the holes and the pads on the other side for the board with solder wick or a sucker, without having to mess about trying to get the chip out. It is so quick and reduces the risk of damaging the board. Great work though on the refurb.
A small flat blade screwdriver leaving under the chip did it for me after a go with the solder sucker. You can get the chip out in working condition that way.
Thanks great video. Clear discription and confident work. I have a 405 2 as my Amp now running for 15 years since "refurbishment as described" I love it, pure as it comes.
Fantastic - yeah, that's the great thing about good quality vintage (and new) gear, you can use it for decades and decades. I may be be biased, but I think this is much more sensible than buying something new every few years.
I couldn't have wished for a better guide to refurbing a Quad 405-2 ... i shall be embarking on mine as winter arrives here in the UK, using your patient and methodical process as a guide. Thank you!
What a quality bit of kit. I worked on mod products in the UK in the 1990s . This is very near this standard. And still easily repairable and good quality audio
I worked for many years in a Professional Audio Shop Repairs - Service & Sales, I sold Quad, Sugden, Armstrong, Kenwood, Pioneer etc 5.5 years prior to that worked on a Saturday Job, 405 BTW Stands for 40V 5A & 303 Stands for 30V 3A 👍 I had a 405 & 44 but last year someone decided lift it up & put it in their car, I was gutted, not only was it kept in mint condition it was purchased by myself from the Audio shop I worked for, I was saving up on a Saturday's job for that & my late parents contributed as a gift with one of my auntie, although I have other units that are superior it's not the point, It was marked as 405, but updated PCBs to Quad 405 Mk2 44 Control unit was first Generation, so if anybody is offered those units then I be very pleased to get them back 👍🙏
55:10 that's a great point. on some designs the heat sink and/or mounting screw connects electrically to the transistor's collector when the leg is not used (like the shown transistors were missing the middle legs), so a silicone pad or insulator plug wouldn't work... something to keep in mind..
Again, correct me if I'm wrong but is that a halogen bulb on the dim bulb tester? That is less likely to burn out than a standard incandescent bulb, thus lowering its function as a protection feature.
I know someone who hooked a modified 405 up to Lowther speakers, even though a risky thing to do the sound was interesting, mids were like a decent valve amp, bass was very good but typical for Quad transistor amps the treble sounded like it was traveling through broken glass. Still an interesting experiment.
I cannot thank you enough for this video I can finally get started on my amp rebuild I have been waiting for this video and parts list so exited :) TY i was donated mine known dead and have another to repair after I get this one working.
Hi, I've just done a recap on one of these thanks to this video 👍 . My question is , is their an upgrade i can do to stop the loud pop when you first turn the amp on ? Thanks
I would recommend an external speaker protection circuit - as the protection in these is rudimentary, and quite frankly I wouldn't trust it to save my speakers. Most external protection circuits will also provide a start-up delay, which will deal with the pop.
I'm sure power devices such as those OP transisters need a higher base current to test - they will read low gain if you don't drive them properly under test. I stand to be corrected on this......
I would imagine this would be taken into account in the design of the transistor tester. I accept I was using a cheap eBay one, but it is still a good way to compare different transistors, and to see if some have lower gain than others. The tester did show me that the gain on the cheaper transistors was much less than the OnSemi ones I ended up putting in, and I have no reason not to believe that those results were valid. I don't think I would go as far as claiming that transistor testers are not a valid way of qualifying transistors because they don't "drive them properly under test". Sometimes it can be possible to over think things. Transistor testers exist for a reason.
I wasn't sure what the op-amp is in it is it a LT 071 H maybe What does yours have? Is there a free schematic online service manual? What's so special about the nichicon muse then? What op amps did you use to replace them with them? Is it a TL051A?
Thanks so much for watching. Schematics and service manual is available online. Nichicon muse is generally regarded as being a very good high quality cap for audio applications. Op amps are TL071. I replaced with TLE2071, which is a substantial improvement on the original. Yes, there are much higher specced op amps available, and some people like to experiment with different op amps in these. Personally I think you are going to run into other deficiencies in the design first. These were an interesting concept in their day, and do have a cult following, but if you were looking for a high end power amp I think personally I'd go for something a bit more conventional in design. Of course its the unusual design that makes these what they are.
@@audionautica6843 got any sites that might have schematics, googled it couldn't find anything! Yeah that op amp is a good option it's got much better properties than the original, I would have thought it would work very well, I'm not sure which is better than that tho! I wonder if it's worth putting MOSFETs in replacing the original power transistors probably make it sound good. have you done anything with local feedback making it less?? Maybe you could try different power filter capacitors split film DMN 4ttn are good. I've noticed a couple of those amplifiers seem to have half bridge rectification people have done it like that, I'm not sure if there's any benefit in doing that tho. What do you class as a good amplifier? it sounds like you haven't got them anymore.
In that keys made barrels from copper and shield that electrolyte capacitors (big ones) like barrel in barrel with holes on bottom sheet between, to cooling capacitors.
excellent vid a lot of valuable info...but could do a vid on the Quad 303 Amp...and explain why Quad were ashamed of it's performance what in it's design let it down ?
My first amp was a 405-2 . Sold it when the transformer started to hum. But it didn't go out to the speakers. But no one could figure it out was what wrong. So sold it for a Vincent SP-311.
I have a early 405 MK1 it has twice blown up it has some device across the output terminal which fails and has damage my speaker and the output transistor which is obselete. It is been scraped .
Copyrite only lasts 99 years - you could have tried some classical music after such a long video l was really looking 4ward to hearing something more entertaining than a hum at the end mate! Nice work really good explaining everthing keen to buy a knackered old quad amp now see if they beat my Quad VA1.
Because the ESR meter will measure the ESR of whatever it happens to see in between its test leads. If there are other things in circuit, then these can affect the reading. A classic example was if you had two capacitors in parallel, then the ESR meter would be reading the ESR of the two capacitors, not one, and it will read back the total capacitance. So if you know that there is nothing else in the circuit, you can get away with reading in circuit, or sometimes you might want to just get an indication that there isn't a dead short, but the best way to be sure is to take the device under test out of circuit, hence unsoldering the wires on one side.
Thank you for doing this video- learnt a lot. I have a 405-2 of a very similar vintage as my daily driver, scared to turn it on now with all those cap failures you found ! Another RUclipsr I saw was testing some copy boards he had made up and was quite dismissive of the performance especially using square waves as an input. Previously I’d only seen testing done using sine waves like you did . Would square waves tell you more or not ? I love my 405-2 and have no intension of ever changing. The chassis and wiring seem to be built to a industrial standard rather than down to a price.
Glad to hear you're in the 405 die-hards club! As your 405 is your daily driver, I would recommend getting it looked at. You will have peace of mind and know it's good for another 30 years or so. I haven't really looked at the clone scene for precisely the reason you mentioned, the results seem to be consistently underwhelming. Also, the power transformer is a big part of the sound as well, and this cannot be cloned. In terms of square wave response, if we consider a perfect square wave (which of course is never what comes out of a function generator), it is a periodic step between the + and - voltages. Each step has a theoretical rise/fall time of 0 seconds. A perfect step has an infinite number of frequencies in it. As such, a square wave will tell you more about your amp's broadband response than a sine wave. How much more is a very good question. I want to make a video on this but currently do not own a function generator and I am waiting for an old Tek one to come up with a shipping price less than that of the FG!
@@audionautica6843 Thank you for your long reply. I will at least have a look at the boards over the week end as I think those brown caps have been replaced but even if they have the replacements may also be on their way out. There is a good local ( to me in the UK at least) vintage amp specialist in Worcester which I’ve promised myself to get both 405 and it 34 preamp mate a service when funds permit.
By replacing soldered components with socketed ICs don't you run the risk of thermal creep stopping your amp working one day? It's common to find socketed components lying on the bottom of the enclosure where they've fallen after being forced out of their sockets by constant heating and cooling of the apparatus during operation.
Lots of mid priced pro audio gear uses this sockets without troubles. Connectors for ribbon flat cables carrying audio signals are more of a problem, amps as 405 can easily have this connections soldered.
@@BrianSmith-ow9gy As I said, I have never ever encountered this in my entire professional career. I wonder if it might have been more of an issue with the older style sockets. I've always used Machine Pin sockets as they are much more reliable.
39 years old amp and replacing the main caps of the power bank is not a first option? Why? Even if they work so-so now...how long they will keep on working?
There is a common myth out there that electrolytic capacitors have a self destruct timer in them that once they reach a certain age they will explode. This just isn't the case. And it usually isn't the main power caps that fail first. That's why I tested all of the capacitors and only replaced the ones that actually needed replacing because they had or were on the way to failure. Willy nilly replacing components is not the best approach to servicing electronics. Quite bizarre that I had people criticising me for replacing the main caps on the first 405 I did, and now people want to criticise for not replacing them - weird. I'm beginning to think it just isn't possible to keep every single person on RUclips happy - GASP.
Big electrolytics in a linear power supply have a fairly easy life and can last a very long time. If it was a switching supply, then yes, they'd very likely be needing replacement.
@@audionautica6843 I agree! Another RUclipsr, who I won't name, even replaces transistors in vintage gear as a matter of course. I just can't get my head around that, it's just not necessary unless the replacements are going to improve performance. He has it in his head that they're old so they must be worn out!
@@ProdigalPorcupine The only other reason I can think of is that certain transistors gained reputation for being failure prone/leaky/noisy ie. A726, 733, C1313, 1400 to name but few.
Thanks for the video. In addition to ESR, I have taken to testing any electrolytic capacitor I intend to leave in place for dc current leakage at the full rated voltage. If you cannot find the original datasheet, compare the leakage current with a modern equivalent.
Good point , I recently repaired an exposure amp with major silicon failure. The main caps had normal capacitor value and esr but leakage was way out .I think people confuse esr with dc parallel resistance. Quad is still finest sound for me though .
I'm not sure it is a good idea to use a bipolar electrolytic in place of a polar, i.e. where it will have a permanent DC bias in one direction. As they are I think effectively made of two back-to-back polar caps, one part will be permanently reverse biased.
@@audionautica6843 Fair enough - I won't argue with Liquid Audio :-) My comment was based on the Muse ES series data sheet, which says something to the effect of the specifications are met after so much time at the rated voltage with the polarity reversed every 250 hours. Which just made me think if the polarity is never reversed, can that cause an issue?
Yeah, I saw that - don't know for sure, but I think they are just outlining a test procedure. While the data sheet is a little light on, I would have thought that if there was an issue with DC offset surely it would say so???? They have a maximum DC voltage rating, but doesn't say anything else....
@@audionautica6843 Yes indeed, the data sheet does leave us wanting a bit more. But in the mean time if they are working and sound great - why not! Excellent work on this lovely amp and thanks for sharing the video.
Placing electrolytics next to wire-wound resistors and power transistors is so dumb. The trouble is the Hi-Fi journalists of the time were as if they were on drugs. This amp was allegedly the holy grail. Carbon film resistors are bad for audio as well, all for the saving of a few pence eh?
@@esci8978 Metal film are better. They are low noise and accurate to 1%. If money is no object there are specialist resistor manufacturers for audio. There's a Japanese firm for example that sells very high quality ones for about 75p each. A bad resistor will also add distortion through vibration as well.
Many years ago I had both the QUAD 405 and a pair of QUAD ESL’s. The combination was incredible! I still have the 405 in a box in the basement. Now I have a new project! Glad I found your channel by pressing “new to you!”
I'm so glad you found my channel. Make sure you check out my other videos.
After spending many years replacing TTL chips, I used a different method to remove IC's which reduces the amount of time you have heat on the board for de-soldering and gives less chance of damaging the tracks in the removal process. As you are not going to re-use the chip, the quickest way to remove it is to chop the legs at the shoulders where it enters the chip body with a pair of side cutters. To remove the pins you add a little solder to the pin from above the board, the meniscus effect of the solder sticks the pin to the iron tip and you lift it out. You can the clear the holes and the pads on the other side for the board with solder wick or a sucker, without having to mess about trying to get the chip out. It is so quick and reduces the risk of damaging the board.
Great work though on the refurb.
Entirely agree @stripey1960
A small flat blade screwdriver leaving under the chip did it for me after a go with the solder sucker. You can get the chip out in working condition that way.
So nice to see a proper craftsman taking his time, being respectful with the gear and quiet confidence. Chapeau.
Thanks so much for watching!
Thanks great video. Clear discription and confident work. I have a 405 2 as my Amp now running for 15 years since "refurbishment as described" I love it, pure as it comes.
Fantastic - yeah, that's the great thing about good quality vintage (and new) gear, you can use it for decades and decades. I may be be biased, but I think this is much more sensible than buying something new every few years.
I couldn't have wished for a better guide to refurbing a Quad 405-2 ... i shall be embarking on mine as winter arrives here in the UK, using your patient and methodical process as a guide. Thank you!
Thanks so much - good luck
What a quality bit of kit. I worked on mod products in the UK in the 1990s . This is very near this standard. And still easily repairable and good quality audio
Yep - designed for use in the back of a broadcast van. Thanks for watching!
I worked for many years in a Professional Audio Shop Repairs - Service & Sales, I sold Quad, Sugden, Armstrong, Kenwood, Pioneer etc 5.5 years prior to that worked on a Saturday Job, 405 BTW Stands for 40V 5A & 303 Stands for 30V 3A 👍 I had a 405 & 44 but last year someone decided lift it up & put it in their car, I was gutted, not only was it kept in mint condition it was purchased by myself from the Audio shop I worked for, I was saving up on a Saturday's job for that & my late parents contributed as a gift with one of my auntie, although I have other units that are superior it's not the point,
It was marked as 405, but updated PCBs to Quad 405 Mk2 44 Control unit was first Generation, so if anybody is offered those units then I be very pleased to get them back 👍🙏
Thanks for sharing your memories!
Had this amp many years ago ,started distorting in left channel and i ended up selling it to a friend for 50$ . one of my many regrets in life !
wrong decision It seems very easy to repair Old british school It sound nice Caps are usual suspect expecially after seeing this video
55:10 that's a great point.
on some designs the heat sink and/or mounting screw connects electrically to the transistor's collector when the leg is not used (like the shown transistors were missing the middle legs), so a silicone pad or insulator plug wouldn't work... something to keep in mind..
Again, correct me if I'm wrong but is that a halogen bulb on the dim bulb tester? That is less likely to burn out than a standard incandescent bulb, thus lowering its function as a protection feature.
Beautiful circuit on these amplifiers. I admire the design. Reminds me of well engineered amps like Dynaco or McIntosh.
I know someone who hooked a modified 405 up to Lowther speakers, even though a risky thing to do the sound was interesting, mids were like a decent valve amp, bass was very good but typical for Quad transistor amps the treble sounded like it was traveling through broken glass. Still an interesting experiment.
Cool - thanks for that!
I cannot thank you enough for this video I can finally get started on my amp rebuild I have been waiting for this video and parts list so exited :) TY i was donated mine known dead and have another to repair after I get this one working.
You're welcome. I hope I included everything you need.
Wonderful video, I learned so much. Thank you.
Quad used Beryllium Oxide as their Heatsink compound in the 70's/80's.......
Hi, I've just done a recap on one of these thanks to this video 👍 . My question is , is their an upgrade i can do to stop the loud pop when you first turn the amp on ?
Thanks
I would recommend an external speaker protection circuit - as the protection in these is rudimentary, and quite frankly I wouldn't trust it to save my speakers. Most external protection circuits will also provide a start-up delay, which will deal with the pop.
I'm sure power devices such as those OP transisters need a higher base current to test - they will read low gain if you don't drive them properly under test. I stand to be corrected on this......
I would imagine this would be taken into account in the design of the transistor tester. I accept I was using a cheap eBay one, but it is still a good way to compare different transistors, and to see if some have lower gain than others. The tester did show me that the gain on the cheaper transistors was much less than the OnSemi ones I ended up putting in, and I have no reason not to believe that those results were valid. I don't think I would go as far as claiming that transistor testers are not a valid way of qualifying transistors because they don't "drive them properly under test". Sometimes it can be possible to over think things. Transistor testers exist for a reason.
Great vid just wondering if you have worked on the bbc modded version? I have one that keeps tripping the mains,any ideas?
No I haven't - assuming it's an earth leakage problem.
I wasn't sure what the op-amp is in it is it a LT 071 H maybe
What does yours have?
Is there a free schematic online service manual?
What's so special about the nichicon muse then?
What op amps did you use to replace them with them? Is it a TL051A?
Thanks so much for watching. Schematics and service manual is available online. Nichicon muse is generally regarded as being a very good high quality cap for audio applications. Op amps are TL071. I replaced with TLE2071, which is a substantial improvement on the original. Yes, there are much higher specced op amps available, and some people like to experiment with different op amps in these. Personally I think you are going to run into other deficiencies in the design first. These were an interesting concept in their day, and do have a cult following, but if you were looking for a high end power amp I think personally I'd go for something a bit more conventional in design. Of course its the unusual design that makes these what they are.
@@audionautica6843 got any sites that might have schematics, googled it couldn't find anything! Yeah that op amp is a good option it's got much better properties than the original, I would have thought it would work very well, I'm not sure which is better than that tho! I wonder if it's worth putting MOSFETs in replacing the original power transistors probably make it sound good. have you done anything with local feedback making it less?? Maybe you could try different power filter capacitors split film DMN 4ttn are good. I've noticed a couple of those amplifiers seem to have half bridge rectification people have done it like that, I'm not sure if there's any benefit in doing that tho.
What do you class as a good amplifier? it sounds like you haven't got them anymore.
In that keys made barrels from copper and shield that electrolyte capacitors (big ones) like barrel in barrel with holes on bottom sheet between, to cooling capacitors.
have you tried testing the big cps for leakage? only reading capacitance and esr dont show if they are leaky
Yes
excellent vid a lot of valuable info...but could do a vid on the Quad 303 Amp...and explain why Quad were ashamed of it's performance what in it's design let it down ?
Sorry, I'm not familiar with the 303.
My first amp was a 405-2 . Sold it when the transformer started to hum. But it didn't go out to the speakers. But no one could figure it out was what wrong. So sold it for a Vincent SP-311.
Thanks for watching. I believe the hum is caused by the deterioration of the laminate adhesive in the transformer core.
1:18:43 You have installed a TLE2072CP, don't you think a NE5534 or an OPA 604 or 627, would be a good upgrade for a small expense ? 😉
The NE5534 has a much higher input current and will cause a high ofset. The TLE is a FET input opamp with very low current.
Hello, have you ever used the nichicon super through kg Capacitors on the power supply, as the smoothing caps, as an upgrade?
No I haven't. Thanks for watching!
I have a early 405 MK1 it has twice blown up it has some device across the output terminal which fails and has damage my speaker and the output transistor which is obselete.
It is been scraped .
Sorry to hear that - thanks for watching!
Copyrite only lasts 99 years - you could have tried some classical music after such a long video l was really looking 4ward to hearing something more entertaining than a hum at the end mate! Nice work really good explaining everthing keen to buy a knackered old quad amp now see if they beat my Quad VA1.
A noob question...At around 17:28 why was it necessary to unsolder the wires on the big cap to test ESR using the Peak ESR70?
Because the ESR meter will measure the ESR of whatever it happens to see in between its test leads. If there are other things in circuit, then these can affect the reading. A classic example was if you had two capacitors in parallel, then the ESR meter would be reading the ESR of the two capacitors, not one, and it will read back the total capacitance. So if you know that there is nothing else in the circuit, you can get away with reading in circuit, or sometimes you might want to just get an indication that there isn't a dead short, but the best way to be sure is to take the device under test out of circuit, hence unsoldering the wires on one side.
Thanks so much AN6843 👍👍
Learning more in your channel.
Cheers 🤙
Thank you for doing this video- learnt a lot. I have a 405-2 of a very similar vintage as my daily driver, scared to turn it on now with all those cap failures you found ! Another RUclipsr I saw was testing some copy boards he had made up and was quite dismissive of the performance especially using square waves as an input. Previously I’d only seen testing done using sine waves like you did . Would square waves tell you more or not ? I love my 405-2 and have no intension of ever changing. The chassis and wiring seem to be built to a industrial standard rather than down to a price.
Glad to hear you're in the 405 die-hards club! As your 405 is your daily driver, I would recommend getting it looked at. You will have peace of mind and know it's good for another 30 years or so. I haven't really looked at the clone scene for precisely the reason you mentioned, the results seem to be consistently underwhelming. Also, the power transformer is a big part of the sound as well, and this cannot be cloned. In terms of square wave response, if we consider a perfect square wave (which of course is never what comes out of a function generator), it is a periodic step between the + and - voltages. Each step has a theoretical rise/fall time of 0 seconds. A perfect step has an infinite number of frequencies in it. As such, a square wave will tell you more about your amp's broadband response than a sine wave. How much more is a very good question. I want to make a video on this but currently do not own a function generator and I am waiting for an old Tek one to come up with a shipping price less than that of the FG!
@@audionautica6843 Thank you for your long reply. I will at least have a look at the boards over the week end as I think those brown caps have been replaced but even if they have the replacements may also be on their way out. There is a good local ( to me in the UK at least) vintage amp specialist in Worcester which I’ve promised myself to get both 405 and it 34 preamp mate a service when funds permit.
Thanks for this interesting video, great work! 👍
By replacing soldered components with socketed ICs don't you run the risk of thermal creep stopping your amp working one day? It's common to find socketed components lying on the bottom of the enclosure where they've fallen after being forced out of their sockets by constant heating and cooling of the apparatus during operation.
No I don't - I ran a factory making military and medical grade electronics and I've never heard of such a thing. Thanks for watching.
Lots of mid priced pro audio gear uses this sockets without troubles. Connectors for ribbon flat cables carrying audio signals are more of a problem, amps as 405 can easily have this connections soldered.
@@audionautica6843 en.wikipedia.org/wiki/Chip_creep#:~:text=Chip%20creep%20refers%20to%20the,also%20occur%20due%20to%20vibration.
@@BrianSmith-ow9gy As I said, I have never ever encountered this in my entire professional career. I wonder if it might have been more of an issue with the older style sockets. I've always used Machine Pin sockets as they are much more reliable.
39 years old amp and replacing the main caps of the power bank is not a first option? Why? Even if they work so-so now...how long they will keep on working?
There is a common myth out there that electrolytic capacitors have a self destruct timer in them that once they reach a certain age they will explode. This just isn't the case. And it usually isn't the main power caps that fail first. That's why I tested all of the capacitors and only replaced the ones that actually needed replacing because they had or were on the way to failure. Willy nilly replacing components is not the best approach to servicing electronics. Quite bizarre that I had people criticising me for replacing the main caps on the first 405 I did, and now people want to criticise for not replacing them - weird. I'm beginning to think it just isn't possible to keep every single person on RUclips happy - GASP.
Big electrolytics in a linear power supply have a fairly easy life and can last a very long time. If it was a switching supply, then yes, they'd very likely be needing replacement.
@@audionautica6843 I agree! Another RUclipsr, who I won't name, even replaces transistors in vintage gear as a matter of course. I just can't get my head around that, it's just not necessary unless the replacements are going to improve performance. He has it in his head that they're old so they must be worn out!
@@ProdigalPorcupine The only other reason I can think of is that certain transistors gained reputation for being failure prone/leaky/noisy ie. A726, 733, C1313, 1400 to name but few.
@@paulb4661 Yes, I agree - there are certainly times when transistors should be upgraded for those reasons.
I would suspect the filter caps of DC leakage if they showed a higher capacitance like yours.
That's why the capacitor tester tests DC leakage.
I wouldn't. Electrolytics have a ridiculously loose tolerance, especially over the stated value. They'll be absolutely fine.
whats the difference between the 405 and 405-2?
liquidaudio.com.au/quad-405-power-amplifier-review/
Leaky capacitors can have very low ESR, but often much higher capacitance (even double). The readings seem good, but leaky caps are never good.
Absolutely, need to check DC leakage .
The tester does that.
Hi .no tester I have measures DC leakage, but can easily be measured using a bench power supply and micro amp meter
Thanks for the video. In addition to ESR, I have taken to testing any electrolytic capacitor I intend to leave in place for dc current leakage at the full rated voltage. If you cannot find the original datasheet, compare the leakage current with a modern equivalent.
Good point , I recently repaired an exposure amp with major silicon failure. The main caps had normal capacitor value and esr but leakage was way out .I think people confuse esr with dc parallel resistance. Quad is still finest sound for me though .
Great post . Out of interest I checked THD of iPad sine wave ..1.4%thd
Ex bbc oscillator 0.04% (40 years old )
Cool!
I'm not sure it is a good idea to use a bipolar electrolytic in place of a polar, i.e. where it will have a permanent DC bias in one direction. As they are I think effectively made of two back-to-back polar caps, one part will be permanently reverse biased.
The professionals disagree - liquidaudio.com.au/quad-405-2-power-amplifier-restoration/
@@audionautica6843 Fair enough - I won't argue with Liquid Audio :-) My comment was based on the Muse ES series data sheet, which says something to the effect of the specifications are met after so much time at the rated voltage with the polarity reversed every 250 hours. Which just made me think if the polarity is never reversed, can that cause an issue?
Yeah, I saw that - don't know for sure, but I think they are just outlining a test procedure. While the data sheet is a little light on, I would have thought that if there was an issue with DC offset surely it would say so???? They have a maximum DC voltage rating, but doesn't say anything else....
@@audionautica6843 Yes indeed, the data sheet does leave us wanting a bit more. But in the mean time if they are working and sound great - why not! Excellent work on this lovely amp and thanks for sharing the video.
Thank you for these great videos 👍
You're welcome. Thanks for coming by.
@@audionautica6843 btw what's meant by "current dumping" on these amps?
I have a pair of simple 405
Very beautiful work!👍👍👍🤝🤝🤝
Placing electrolytics next to wire-wound resistors and power transistors is so dumb. The trouble is the Hi-Fi journalists of the time were as if they were on drugs. This amp was allegedly the holy grail. Carbon film resistors are bad for audio as well, all for the saving of a few pence eh?
Hello…. Curious to know what the ideal resistor for audio is..?
@@esci8978 Metal film are better. They are low noise and accurate to 1%. If money is no object there are specialist resistor manufacturers for audio. There's a Japanese firm for example that sells very high quality ones for about 75p each. A bad resistor will also add distortion through vibration as well.
Would've been nice if you showed us the schematics!
I did - right here:
ruclips.net/video/2Tt5jwwvEx4/видео.html
Great amps 👌
Love the work, just the unskippable adds are annoying