DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 27 Oct 2020, 13:49

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 110 posts ]  Go to page Previous  1 ... 7, 8, 9, 10, 11
Author Message
 Post subject: Re: Baxandall circuit
PostPosted: 23 Mar 2020, 18:45 
Offline

Joined: 23 Feb 2017, 02:02
Posts: 677
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.


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 24 Mar 2020, 03:11 
Offline

Joined: 13 May 2016, 02:02
Posts: 152
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?


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 24 Mar 2020, 17:49 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1698
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.

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


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 25 Mar 2020, 00:45 
Offline

Joined: 23 Feb 2017, 02:02
Posts: 677
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.


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 04 Apr 2020, 18:08 
Offline

Joined: 02 Oct 2014, 20:36
Posts: 48
Suncalc wrote:
GOT IT! :D

It was the position of the volume control which was making things too variable. By moving the volume control to the front of the chain everything works out properly and the pad for the defeat line becomes simple. Now using a single 4PDT switch, the tone stack can be shifted in and out without a gain shift in the preamp. First, here is the circuit.
Attachment:
Schematic BEST (CF Input - 4S output) small.jpg

Now here are the embedded response plots with lines for 12AU7, 12AT7, and 12AX7. The 12AV7 and 12AZ7 fall within these three. These are plots with the bass and treble controls at extreme cut and boost compared to the nominal setting. The only deviation is about a 1dB shift in the peak treble boost between the 12AU7 and the 12AX7. Frankly no one would even know this was there from just listening to the unit. :up:
Attachment:
Response Curves 1.png

Attachment:
Response Curves 2.png

And with the tone stack defeat switch in the "Defeat" position, the interstage response looks like this.
Attachment:
-21dBv Pad Response.png

So now the whole thing should work just as intended without weird tone shifts when switching between tubes or flipping the "Tone Stack Defeat" switch.

As always, questions and comments are more than welcome.

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


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 05 Apr 2020, 15:28 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1698
Location: US Pacific Northwest
gonzalo guerrero wrote:
is possible use a 6sl7/12sl7 on the second stage of this preamp? in the 4s preamp?
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


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 06 Apr 2020, 21:31 
Offline

Joined: 02 Oct 2014, 20:36
Posts: 48
Suncalc wrote:
gonzalo guerrero wrote:
is possible use a 6sl7/12sl7 on the second stage of this preamp? in the 4s preamp?
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.

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.


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 07 Apr 2020, 12:16 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1698
Location: US Pacific Northwest
gonzalo guerrero wrote:
crazy ? or make sense?
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


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 09 Apr 2020, 14:34 
Offline

Joined: 02 Oct 2014, 20:36
Posts: 48
Suncalc wrote:
gonzalo guerrero wrote:
crazy ? or make sense?
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.

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!!!


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.



Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 16 Apr 2020, 16:26 
Offline

Joined: 02 Oct 2014, 20:36
Posts: 48
hello people.....baxandall with two 6n1p voshkod...extended bass and highs,less hum... very recomended!!!


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.



Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 110 posts ]  Go to page Previous  1 ... 7, 8, 9, 10, 11

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Google [Bot] and 21 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy