"Color" Tube Pre-amp for Solid State Amps: Final Review
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- Опубликовано: 17 окт 2024
- I promise, this IS the final video :) Final testing and listening impressions, this thing rocks! I honestly don't get why so many people wanna trash talk this, other than it's something different than your boring, everyday version of a pre-amp. Thanks again to Matt for the thought and work he put into this unique design, I was happy to just tweak a few things on it :)
I think this design really hits the mark on what most folks are looking for from a vacuum tube pre-amplifier!
This series is about building a tube pre-amplifier for use with any "overly sterile" sounding solid state amplifier. This device introduces the warmth and second order harmonics people associate with tube gear, in a controllable and consistent manner. The builder can add multiple sources and other options, we are building a basic version to showcase what it can do. At the end of the series we will be doing a complete technical and subjective test of the unit.
Here is Matt's website explaining the design of this amp:
www.cascadetub...
Here he explains the placement of the volume control:
www.cascadetub...
Here is my Patreon, as well as the donation page at my site, if you feel so inclined to help fund some of the future projects for the channel!
www.patreon.co...
www.skunkiedes...
![OhGeesy x Lefty Gunplay - What It Iz [Official Music Video]](http://i.ytimg.com/vi/L0yzW9t2ixk/mqdefault.jpg)
I find myself loving all these builds. Another great one. So interesting as I remember years ago digging through specs in Julian Hirsch’s Stereo Review articles looking for the lowest possible THD. I hope you document your upcoming clone for us to learn and enjoy.
By the way, as I’m always looking for new music suggestions, and after watching several of your episodes, I decided to look up the group you always seem to be showing us, only to discover it was, in fact, some photographic paper. 😂
HAHA and yeah I will do a highlight video of the clone build to show you how I do the next one.
Thanks again for such a detailed and deep dive into this build. I’ve learned so much from it. Those results look excellent, especially with those 6.8uf caps. Regardless of where the volume is set, the frequency response looks fantastic.Seems like an overall amazing design. I can only imagine the beautiful synergy between components it’s able to create.
I learned a lot too!
Brilliant. I've yearned for a higher end sound for years and people like Skunkie are now turning it into an affordable reality. I'll keep exploring your content and channel and i'll have a go at building this. Thanks ever so much.
Thanks Stephe,
Finished your Color preamp last weekend and have been enjoying it ever since! 👍🏻👍🏻
I am very Appreciative of you keeping us SS guys in the mix !
Due to a budget I would like to do a tube amp someday.
Best.....
Great job on this! I learned much from this in depth build and test. NOW, what I would love to see is if you can do a test of how the sound is colored if you use a tube amp hooked up to this preamp vs a solid state amplifier.
Hey Stephe, I was wondering if you played with the load line with this preamp? I guess flatter is better given that the tube circuit was designed to push the tube more, just wondered how a little steeper line would sound without hitting clipping that is. Thanks.
no and the whole point of this pre-amp is adding some 2H distortion.
This is a really nice result Stephe
Hello Stephe,
I’m diving in on the color preamp. I’m very excited! I have a question on the skunkified schematic. I’m not using the 100k input pot because I have a variable out from my DAC. So I will have the one pot on the output. I noticed you changed the cathode voltage to 6.5v on the primary tube. Would I use the same components for the grid and cathode voltages if I wasn’t using the 100k pot? Thanks much!
I would replace the 1M grid leak resistor with a 100K one.
@@SkunkieDesignsElectronics Got it. Thanks!
This really exposes the engineering perfection approach to audio, striving for ultra low harmonic distortion....I wonder why we prefer a little distortion? Is it something to do with what the recording process takes away or doesn't capture, that we are putting back with devices like this?
I think some of it is that the right type of distortion fools our brain into thinking we are in a large venue, like you would be if you were listening to live music. It really seems to work closing your eyes and just listening. And IMHO this effect is found by trial and error.
@@SkunkieDesignsElectronics I just listened to Janos at Real World Audio discussing this issue of measurements in relation to subjective experience and music enjoyment... very pertinent to your work here. Thanks for pushing the bubble of audiophile experimentation....
Hello Stephe - question on the grid stopper resistor for the following stage. Why did you add it to the skunkified schematic when one was not used in the original? Are there high frequencies we need to filter? I will be using the skunkified version without a pot on the input. Thanks much.
It's just there as a precaution, feel free to built it however you would like.
@@SkunkieDesignsElectronics thanks!
Hello. I was following the voltages and paths on the schematic and couldn’t figure out how the cathodes gets their voltages. I see the grounds and B+, but where do the voltages come from for the cathode side of the tube? Thanks.
Through the tubes themselves. Current passes through the tube and the voltage on the cathode is the voltage drop across the resistor to ground. This is how it creates the negative voltage bias on the grid. The bias is measured between the grid and the cathode, if the grid is referenced to ground and the cathode is at a positive voltage, the difference between them is the negative grid voltage the tube need to operate.
@@SkunkieDesignsElectronics ah, that makes sense. Thanks!
This Won looks like a Winner.
Starting my part's list then I got curious, where do you get your parts from??
You have a wonderful channel with great presentation as always.
I like the way you approach things, not so mainstream like a lot of these forums are with a narrow-mindedness You just work it out!
Best....
Mostly from mouser or Parts Connexion.
Stephe, I’m using the 269JX transformer. On the primary the 0 volt top lead is white and the bottom 125 volt lead is black with a grey 115 volt lead in the middle. A bit different than the 6K88VG. Does the white lead go to the switch and the black to the white lead of the power cord or the other way around or do I use the grey 115 volt lead? Thanks.
Use the 125V leads and I honestly don't think it matters which lead of the transformer goes where, it's AC. You do want to "hot" lead from the wall outlet going to the fuse, then the switch, then to the transformer and the neutral connected to the transformer.
@@SkunkieDesignsElectronics Got it. Thanks!
I wonder if you could explain the two stage amplification in this preamp. Is that to get better/more distortion, or is it just better to not tax the tubes. Thanks.
The second stage isn't doing any amplification, it's a cathode follower which gives more "drive" and lowers the output impedance. This allows it to drive a solid state amp.
@@SkunkieDesignsElectronics interesting. Thanks!
Hey Stephe - all my parts are here and I’m looking forward to getting the power supply started! On the schematic there are 2 - 100 ohm resistors on the heater 6.5v leads. Was that to lower the voltage for a different transformer? It doesn’t look like you used them in the build. So I guess I don’t need them right?
If your transformer has a center tap on the heater winding, just connect that center tap to ground and you don't need the two 100 ohm resistors. If it doesn't have a center tap, like mine did not, you use the two resistors across the 6.3V winding and connect the center point of these two resistors to ground creating a virtual center tap. I 100% used them on my build.
@@SkunkieDesignsElectronics Ah ok. Mine does not have a 6.3v center tap. So I guess after I solder the heater leads to the tag strip I would add a 100R resister to each and combine them to the star ground point. Thanks.
Yes, just like that. I try to keep a ground nearby just for this purpose.
Thanks I just Love it Just what I need, one question, when I need a balanced one… do I make 4 chanal like two amp to be able to run balanced ? Bet to Y all Greatings from Denmark DK ,;-)
I don’t think I’ve watched any RUclips series as much as this one! I want to make this!
I’ve watched other videos to increase my understanding of different concepts and on one of these crosstalk was discussed. In that vid the simple recommendation to reduce crosstalk was after the rectifier, to have a split rail voltage supply, so I guess in this case a duplicate set of caps, choke and resistors and thus a dedicated B+ for each valve. Do you think there are any merits to this?
Thank you
I think in this case, the current is so low it's not an issue.
Question - if I were to switch the volume pot to the input with no pot on the output are there any changes to the components on the schematic? Thanks.
It's no longer the same pre-amp, it's just like any other boring solid state sounding preamp and defeats the purpose on building this one.
@@SkunkieDesignsElectronics ok thanks.
Hello - I finished the build and I'm getting 277V for a b+, 142V on the plate for the amplification tube, 6V on the cathode, 47V for the grid, and 78V for the cathode on the follower. Should I change the power supply resistor or leave it alone? Thanks!
It wouldn't hurt to lower it and raise the B+ to 300V
@@SkunkieDesignsElectronics Sounds right. I have a 2K in there now. Would you go 1.8 or 1.6K? I don’t want to solder the hell out of the capacitors to get that B+ up to 300V. I’m not sure what it will take to get that 30V that I need. Thanks.
Measure the voltage drop across the 2K, that will give you the ma across it. You can then calculate what resistor will get you close. ohmslawcalculator.com/ohms-law-calculator
@@SkunkieDesignsElectronics awesome thanks!
This is a great exercise! I’m not sure I get it though… so, the voltage drop is 39 volts (318 to 279) with the 2K reaistor. At 20 mamps. I want an 18 volt drop. Will the current remain the same? In which case, plugging in 18v and 20 mamp I get .8K or there abouts. I’m not sure if I’m getting ohms law right.
Where did you get those black tube accent rings? Thanks.
youdaelectronics.com/
Great conclusion. It would have been great to show the added 2nd harmonic distortion. Determine its percentage relative to THD.
I may do a few more tests before I ship this off. I'm actually going to build another one for my personal use!
I'm super interested in this design and waiting for you to offer one this upcoming year. Quick question..will the pre pair with a solid state that has a super low 10k ohm input impedance?
I have a semi expensive amp that has some great qualities to it...though i also enjoy the sound of tubes with solid state but pairings with that amp havent always been ideal..even with adding larger values to the output caps. I have a Dac that im able to control the output voltage on that i think will work well with this pre in a streaming set up.
10K ohm is SUPER low. not sure how well this would work. That is like 1 of 5 amps ever made that are that low?
@@SkunkieDesignsElectronicsSuper Low indeed. It's not an older amp and is made by a rather mainstream company. Arcam PA240. It was more expensive than I would normally spend but they gave me a trial and $800 off on a demo. I had never experienced such a powerful amp that was so clean and quiet. Something about the higher frequencies stood it apart from other amps at the same price. I didn't even consider the input Z til later on when I tried some tube pre's with it. It really is fine running straight from dac but I strongly feel a tube can add just a little something nice to really clean SS amps. The right amount and right type of distortion sounds more natural than something completely transparent. Obviously this is just my opinion and personal preference. Many people want no distortion whatsoever in their signal chain.
Ty for the response.
stephe,
I got my BOM ordered and I was thinking about the design is around the 12au7 tube but can a 6sn7 be dropped in with the same results.
I have several 6sn7s is what got me thinking.
But I don't know if It will be for better or worse.
I'm just a noob but read where outhers don't like the 12au7, but the design is around a cathode follower+
So I ask your expertise.
Thanks in advance
Have a nice day!
Without building one and trying it, I can't give a green light on that swap.
@@SkunkieDesignsElectronics Thanks again I'll stick with your original layout!
hi skunkie do you know the output impedance of this preamp ,thanks
Stephe, Can we Replace the 10k output pot with a 50k pot?
It depends on what the input impedance is of whatever you are driving. It was designed to be able to drive a SS amp with 50K input impedance. If you are driving a tube amp with 250-500K input impedance, you could.
What's the max output voltage with 2v in?
It's shown on the scope in the video... 9:15
TL;DR 2Vrms in = 20Vrms out at max gain.
Hi, once again thank you very much! Another stupid question: what if use preamp tube not one per channel, but one per cascade?
Cascade?
@@SkunkieDesignsElectronics we’re now using 1 shoulder of the tube for 1st amplification stage, and another for 2nd. Can we use 1st tube for L&R 1st amplification stage, and 2nd tube for next stage?
Sure, just would make the wiring a different
@@SkunkieDesignsElectronics do you think that would make channels a little bit more even?
No, I don't see why it would make any difference other than making the wiring longer and have more of a change to pick up interference.
Skunkie, it will be awesome...if you sell these as a kit!
Probably gonna sell some built amps first, I have to think about doing kits.
@SkunkieDesignsElectronics I'm fine with that! It is probably too early but how much do you think it will cost ?
$800-900 is my guess depending on parts costs.
Okay, thank you! I was wondering how would the output side pot would affect the overall output impedance. Typically, output impedance should be low for any amplifier. Typical power amps have input impedance in the range of 20k to 50k ohms. Will your design match these specifications?
You can read more about how that affects output impedance here: amzn.to/3pdUmQC
Note this page is discussing the effect of an output pot using a 250K pot on a different pre-amp, this color preamp uses a 10K pot so TL;DR, this isn't an issue at all.
Hi stephe on your shematic circuit you have 12au7 and the supply shematic you have 12ax7 which you use cause its not the same amplification factor( the u ) 12au7 has 20 and 12ax7 100 its not the same ,so why put a pot on the ouput to rise impedance ,normally we create a desigh to lower impedance ,i think its not logical.
It's a 12AU7, the "supply" schematic says 12a*7 which was a typo. In the video I explain it's a 12AU7 multiple times. I've explained the volume pot on the output in the video and a dozen times in the comments, I'm not going over that again.
Older video, but I think I build one designed for installing in my tape loop.
I'm still building these. They sound AMAZING! especially the final version with input AND output pots.
@@SkunkieDesignsElectronics do you think it would be worthwhile to instal meters to match output to what the line level should be?
You could if that is important to you. I just use my ears to what sounds good. If you were using this to adjust level for tape recording, probably is a good idea but doesn't the recording deck have level meters?
No, I should have said my tape 2, monitor loop, just line out, and right back in. With color amp in line.
It’s a pity that there’s no motorised 10k potentiometer of >50 mWt on the market. Looks like if one wants to create remote controlled preamp, it’s needed to motorise normal potentiometer or use relay-controlled unit.
Right, this is a unique case use for sure. Honestly I think a 50mw would work if you limit the input signal to keep the output signal send to the pot max of 20mw or so.
I WISH YOU WOULD actually play some kinda music through it and let us hear WOULD BE NICE FRIEND
and yes you sure can can get an idea of it anyways that is very true my friend SKUNKIE anyway have a good night
The couple of times I attempted this, it sounded absolutely horrible. I chatted with a few people who do this and they explained "Well I started with about $4000 worth of professional studio microphones".... and then went on to explain how they setup a very specific home studio designed to record them. Using normal video microphones won't work given they are designed to record human voises.
Until someone is willing to donate $4000 worth of microphones so I can do this right, I am not going to post horrible sounding "demo" videos.