Dear Steph, as predicted this little guy is amazing. Once again you have proved that "less is more" and "keep it simple, stupid". Now that you have measurements I will be building one of this. Thanks for the great effort. Keep the great work!!!

I've only recently found your excellent channel stephe . Im coming at this from a guitar valve amp(yes im English) perspective. And i must say you go into great detail about the nitty gritty parts,that most others gloss over. Which is super helpful and very cool of you. So much so I'm going to build this little preamp. I've been looking for a compact design like this. That sounds great. Nice one 👍

i love your work

Great. Very informative. This preamp seems to be a tube rollers dream. The simple circuit design should in theory be more faithful to the source without a ton of color added which interest me.

Interesting observation on bypass caps. I have a similar experience with my Audio Research SP9 preamp years ago when I replaced its 0.22 uF Wonder coupling caps with Vcaps. Originally the Wonder caps were bypassed with 0.1 uF Wonders. With VCaps, I found it sounded better without the bypass caps and attributed that to the bypass being of lower quality than that of the Vcaps. With your experiment usingAudionote bypass caps, it now appears there may be another possible reason. I have no idea what that it.

I think the word you’re looking for is Synergy. I’m going to build the little pre amp. Im just looking for something I can hook my iPhone to, an run my tube amps at full volume in my garage. Thanks Skunkie nice job !!

This is an awesome learning experience. The lower system distortion with the high distortion preamp is due to distortion cancellation between the preamp and output stage. You have two single ended amplifiers that distort the signal in much the same way. But the power amp is being fed an inverted signal after it passes through the preamp, so the distortions are in opposition and partly cancel. This is very cool to see, as I often see it in simulation and had always wondered how well it works in practice. I made the mistake of making a very low distortion driver stage in my zero feedback amp and it unfortunately has resulted in very high overall distortion. It would be fun to test your spud amp with a SS preamp of practically zero distortion to see if the overall distortion increases even further.

I am about to start testing the 4S I built. I already tested the power supply and it is working fine, a little high on the voltage but now that I can try it with the tubes in and wired so there is a load I'm hoping the B+ will come down. I would love to share pictures. I installed the ground lift switch but I also installed a 3.5MM input along with the rca input jacks. The 3.5mm socket mounted on the chassis is grounding the speaker ground to the chassis so unless I insulate that input the grnd lift switch is useless. I just might change it to switching in and out the bypass cap. The plan is to use the pre-amp to drive a couple of those 6V6 mono blocks Push Pull amp. I believe the plans for that one are on the same site as the 4S. I'm hoping to put it in for a tv sound system. Another great video and a nice looking little pre-amp. Mine is not so neat looking.

The DIY that I have, really is fairly quiet. I do have a bad ass gaming pc (noisy)to which I connect my dac on. So i am slowly getting it quieter and it really sounds good. I hooked up a ground wire internaly which was easy. The bld is overall pretty good. In the audiophile world this has been a cheap upgrade. I am sure There are better ones out there but I have no buyers remorse.

Hi Stephe, That simple preamp turned out great! I'll need to build one. 😃 I'm looking at transformers for the (56)-27-47 amplifier, and Edcor has some that is like to get: For outputs, the XSE25-7.6K, and for power the XPWR118. These fit the budget well. The 7.6K is a *bit* high, but should be lower in distortion with an 8 ohm load at slightly less wattage. It has an UL tap. The XPWR118 is 600V CT, but I was thinking about using a higher DCR choke, maybe even LCLC or different topology to get the B+ down. This xfmr has two 2.5V taps, perfect to run the 47 outputs, a 5V for the 80 rectifier and 6.3 which should power the 27s in series with a resistor. If you have time, let me know what you think.

Yay! I knew my ears didn’t deceive me! 😂 Thanks for building one and testing it out! Will you be putting up a BOM for the 6BQ5 amp? That may be my first try at a from-scratch power amp.

Interesting observation about distortion at output of preamp compared to that at output of the speaker load end. Have you tried a comparison of the spectrum at preamp output vs the power amp output. I suspect you may find a clue there.Let us know.

Excellent, loving these videos. Just wanted to ask your opinion on burning in tubes do you think they sound better after say 100 hours burn in, as I read mixed opinions on this subject

Really interesting regarding the distortion. Could it possibly be that they have a very similar distortion profile whereby the act in a way in which they kinda cancel eachother out?🤔 I've thought about it trying to run different scenarios and it seems the most likely somehow. There is another thing that could maybe be a factor, to my limited knowledge at least, but could having the volume after the output potentially be a part of the reason, maybe it's causing a slight impedance/phase shift at a small level which is cancelling some distortion.🤔 Regardless, you may have accidentally discovered a really neat trick by accident, would be awesome to find cause and see if it can be replicated.

Maybe there is distortion cancellation going on from preamp to spud amp?.. The simpler preamp reminds me of an Arthur Loesch design (5687) variant with the volume control at the output.

Your revisit of Nobsound 6P1 Tube Amplifier Modifications. Are you done with it or do you intend to 'finish up' any more mods for this amp? You stopped half way through the revisit!

Have enough gain to fully drive the amp but not much more. Fewer stages = less pain.

You dun good!!! (BTW, I'm an electrical engineer and I know precisely why you don't have ground loops and other such issues using your grounding approach. Since you have told others repeatedly how to avoid such issues, I see no reason to repeat what you have said using technical jargon :) keep up the great work!) -bobcat

Thank you. Can I split the the Y cable for signal generator for L and R channels so I can compare both channels for the scope?

The reason you saw more distortion on the 100K load was because the load is static. The load of the spud amp is dynamic. In reality, impedance is a dynamic with frequency.

How do u measure just the preamp with the analog discovery audio suite? Mine wants you to choose 4 or 8 ohm so wouldnt that affect measurements? Thanks

Hello! The black pre amp in the middle, this is a phono pre amp? Mm? Im Looking for this size that's both mm/mc with volume control. Is this unit for sale? If so, will the seller install a sut for mc? I'm very interested. Iv tried to find a original ear 834p- can't seem to find one. There are fakes I. Worried about buying. Thanks.

hi the preamp with a single triode can drive a input transistor amp!.It would be nice to speakl how to measure an input output impedance of amp .

I like tube rectifiers. Tube amp, tube rectifier.

Can anyone tell me the fuse size for the 4S Uni Preamp? I've looked and looked and cannot find this info.

Regarding ground loops, a cheater plug is probably the easiest ground lift anyway?

Hello I have a question about the fact that you put in less then 1V rms. I have a dac that does 2V rms and I simulated this circuit with some free tool online and saw alot of harmonics. Do you have a suggestion on how to fix this? I have jet to build it. My idea was a bit of feedback to also fix the phase shift with the original design of just to increase the 10K input resistor. I am very new to building amps and the theory is hard for me to follow😅 Any help would be great

Instead of a 12AX7, can you try a 12AT7?

But when you did the 3 preamp tests you where using the CV181 tubes but now you have done your listening tests with the rubbish Chinese 6SN7's