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 23 Sep 2019, 06:41

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 97 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6, 7, 8 ... 10  Next
Author Message
 Post subject: Re: Baxandall circuit
PostPosted: 04 Jun 2015, 09:43 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1591
Location: US Pacific Northwest
Ok. That makes more sense.
dimitris1811 wrote:
but should I measure the amplitude in both cases?
Yes. Measure the input and output amplitudes at each frequency. The difference between the two is the amplifier gain at that frequency. Then plot the calculated gain numbers against the frequency and you should get a plot that looks something like this.
Attachment:
Screen Shot 2015-06-04 at 7.41.43 AM.png
Of course your numbers will be different.


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


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


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 07 Jun 2015, 03:42 
Offline

Joined: 01 Feb 2015, 13:41
Posts: 144
Location: Athens-Greece
Matt at your tone control circuit you use two resistors 5K for each channel. I found 5.1 K. Is it still ok orI have to try to find 5K only? Nichikon and AudioNote promote 5.1k in general


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 07 Jun 2015, 08:42 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1591
Location: US Pacific Northwest
dimitris1811 wrote:
I found 5.1 K. Is it still ok orI have to try to find 5K only?
5.1kΩ will work just fine as the CF bias resistor and the 4S grid stopper.

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


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 12 Jun 2015, 07:03 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5136
Location: Australia
Not asking for a design here but for me the preamp with bass\treble controls could be expanded to have a balance control. And add to that a left\right swap-over switch and a few inpit selection switches. Most of my preamps have two selectable inputs but I found I really require three inputs. This is easily achieved with two small DPDT power switches. I would never use a ganged rotary switch here because all I have ever seen are of poor quality and action. Small precision power switches fell better and look quite smart.

A friend of mine builds a "tilt" control into his preamps. On knob is used to turn up the bass as it lowers the treble or as you raise the treble the bass is lowered. This tilts the bass\treble balance of the preamp. If any one is interested I'm sure he would give me a schematic for one.

_________________
Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 22 Jun 2015, 07:18 
Offline

Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
Hi,

I am thinking of adding this circuit into my headphone amplifier. I already have most of the parts required to build this onto test board.

I am planning of inserting the circuit betwean my source (Cd Player) and the headphone amplifier. The headphone amp uses a 12au7 for its gain stage and a 6080 tube configured as a cathode follower. I am concerened that the gain stage of the baxandall circuit and the gain stage of the amp could cause excessive gain.

So my question is could I have problems or should it all work fine?

Phil


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: 22 Jun 2015, 18:27 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1591
Location: US Pacific Northwest
The circuit you posted is a symmetric stack which is gain limited by the feedback from the output to one side of the the signal stack. If you look at the schematic you'll see that the input is from the cathode follower but there is another input on the opposite side of the stack from the inverted output. The input to the last stage comes from the center branch of the stack.

I haven't done the math but I believe that this is unity gain stage that gets its "cut" from the application of negative feedback from the output. With the two controls at the center point, the stack is equally driven from both the input and the output; with the two drives in anti-phase to each other. At this balance condition, I believe that the output is forced to track the input; hence unity gain. This also represents a massive level of negative feedback in the circuit.

As such, I don't think that you'll have excessive gain issues if you put this in line with your headphone amp. But at this stage it's just an educated guess.

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


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 22 Jun 2015, 18:48 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1591
Location: US Pacific Northwest
As I thought, the post over at the "Fun with Tubes" site has this to say about your circuit...
Quote:
Its gain when set to flat is about -1 dB which is close enough to unity to not cause overload problems in a preamp or integrated amplifier.
This 1dBv loss is essentially the loss in the input cathode follower. The entire gain of the backend triode is lost in negative feedback. You shouldn't have a gain problem.

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


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 26 Jun 2015, 05:53 
Offline

Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
Thanks Matt for the confirming that. I have given the circuit a try and it seems to work quite well. I do think though that when I position the bass and treble pots to center the sound is not completely flatt. Although I don't think this will be a problem as I will have a switch to remove the circuit from the audio path.

Could this curcuit work with a 12au7 tube instead of a 12ax7?


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 06 Jul 2015, 02:02 
Offline

Joined: 01 Feb 2015, 13:41
Posts: 144
Location: Athens-Greece
I tried this circuit. Finally, I decided to go with one valve per channel and not two halves per channel. The problem is that I used 12AT7 instead of 12AU7 because I have only one 12AU7 available (others on the way). If the problem is the type of the valve I am thinking to test one channel only with the 12AU7.

Now the problem:
When I activate the tone control , volume is decreased significantly and both bass & tremble do not work properly. I checked the connection of the potentiometers. 500K and 1M are TOCOS and 100K AudioNote.
When I deactivate the tone control , the result is excellent with my 300B SE amp.
Note, that I tried two ways; mounting of components on the potentiometers, and using a board but results remain same.

Any ideas?


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: 06 Jul 2015, 19:43 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1591
Location: US Pacific Northwest
Ok, lets walk through this...
dimitris1811 wrote:
... I used 12AT7 instead of 12AU7...
The cathode follower is a 12AU7 design. Use that tube. Others will have higher output impedances that will affect the bass operation of the stack.
dimitris1811 wrote:
When I activate the tone control , volume is decreased significantly...
Did you use the optional pad or a direct bypass? You need to show us the schematic that YOU built, not just a copy of what I posted. If you didn't use the optional -21dBv pad then the volume will drop by 21dBv when you switch in the tone stack.
dimitris1811 wrote:
... both bass & tremble do not work properly.
What exactly do you mean by "not work properly"? You need to start measuring the response curves for the controls at nominal and extreme positions and posting this data. Then we can see what's going on.

Also, make sure that you have the proper components. The potentiometers need to be audio or "A" taper. Linear taper potentiometers will give improper results. The lower capacitor values are in "nf"; that's "pf"/1000. So the lower capacitors are 4.7nf or 4700pf. Make sure you have the correct values. Check ALL component values again and report back.

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


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 97 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6, 7, 8 ... 10  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Google [Bot] and 12 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