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It is currently 28 Mar 2020, 10:33

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 Post subject: Re: Baxandall circuit
PostPosted: 23 Mar 2020, 18:45 
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Joined: 23 Feb 2017, 02:02
Posts: 614
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.


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 Post subject: Re: Baxandall circuit
PostPosted: 24 Mar 2020, 03:11 
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Joined: 13 May 2016, 02:02
Posts: 137
Location: Javea, Spain
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?


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 Post subject: Re: Baxandall circuit
PostPosted: 24 Mar 2020, 17:49 
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Joined: 06 Apr 2009, 10:08
Posts: 1620
Location: US Pacific Northwest
john55 wrote:
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.

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


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 Post subject: Re: Baxandall circuit
PostPosted: 25 Mar 2020, 00:45 
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Joined: 23 Feb 2017, 02:02
Posts: 614
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.


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