DIY Audio Projects Forum

Unless you connected the circuit wrong way, otherwise is the same with or without 6v6.

Because the gain stages are capacitor couppled they are fully isolated from each other in terms of DC biasing.

Good Morning IloveHiFi,
I’m building a 6V6 with a Baxandall Tone Stack Pre-Amp in in one chassis. I’m using an adapted 6V6 Power Supply to run both. See the adapted PSU here in the 6V6 V.2 thread. viewtopic.php?f=9&t=5736&start=220
You and Matt steered me in the right direction. (13th April 2019).
I have the 2k7 resistors but can’t get the 47uF caps to finish the pre-amp/tone stack legs of the PSU as we’re on a four week lockdown here in Spain, so I decided to just fire up the amp with the pre-amp/tone stack hooked onto the B+ of the 6V6. With the ‘scope and signal generator connected I couldn’t find a clean signal anywhere.
Once you had informed that I could test the pre-amp/tone stack stand alone without any load, I tested it and it worked fine. I also tested the 6V6 on it’s own and it worked fine.
I hunted around and managed to find two 68uF 400v caps which I used to finish the modified PSU and connected up again. Everything is now working fine.
Matt did say that I would likely have problems without the extra stage of power supply filtering and he was 100% correct.
I would like to understand about PSU filter isolation if anyone could explain it to me in laymans terms or point me towards a good article on it.
I will change the 68uF caps to 47uF when I can get hold of them. How does using larger caps affect the PSU and/or Amp?

John;

I'd leave the caps alone. The larger ones will provide a little extra filtering for your tone stack B+. No real need to change them out.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog

Larger cathode bypass caps do no harm, this will allow the frequency respoese to be even flatter, but too large of a bypass cap then you get reduced sound quality, or even may cause the amp to do weird things and blow up.

Hint that if the cut off frequency is below 1HZ then you can have serious prolbems and reduced sound quality, pro tip set the stuff up at 5HZ for optimum exprience.

hello!!! is possible use a 6sl7/12sl7 on the second stage of this preamp? in the 4s preamp?? thank you!

Yes; with one caveat.

The grid to plate capacitance of the 6SL7 tube is much larger than the corresponding smaller tubes. As such the miller capacitance will be higher and may affect high end rolloff. However, I have not performed a detailed analysis. My gut check says you should be fine.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog

thankyou for the answer... if i change the second eq stage for two 6sl7 in srpp mode? would work better?
i ask this because when a listen my oddblock straight without preamp,just conecting the notebook interface in the oddblock,i just love it,so i want this sund in the baxandall eq...crazy ? or make sense?
hope your all be safe in home..
thanks.

Not crazy. However, the tonal shaping your hearing in your OddBlock is likely due to the power stage operation and not the SRPP driver. SRPPs as most people use them are very tonally neutral.

Just remember that the second stage in this circuit is there for isolation and gain recovery. Any substitutions must support those objectives.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog

yeah!!! thank you for the answer...im just have one 12au7.wich is now the input valve,catode fowlloer,in the second stage im using a 6n1p voskod,reading the datasheet ths tube is close to 12av7wich can be used on the second stage (4s),just re-wiring the filaments and..niiiice sound!!! just love it!!!

hello people.....baxandall with two 6n1p voshkod...extended bass and highs,less hum... very recomended!!!