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 15 Oct 2019, 07:37

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 97 posts ]  Go to page Previous  1 ... 3, 4, 5, 6, 7, 8, 9, 10  Next
Author Message
 Post subject: Re: Baxandall circuit
PostPosted: 07 Jul 2015, 00:19 
Offline

Joined: 01 Feb 2015, 13:41
Posts: 144
Location: Athens-Greece
Thanks Matt. I follow exactly the scematics not any difference at all. I think that problem might be the potentiometers types. I have to check them again since they might be linear type. I do not see something else.

Furthermore, bass & tremble are not working well and you can easily understand it by listening the sound. Actually it looks that there is no bass. I will revert with results


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 09 Jul 2015, 06:46 
Offline

Joined: 01 Feb 2015, 13:41
Posts: 144
Location: Athens-Greece
Just a note. I hope that I have connected properly the potentiometers and are not reversed. Thanks for any comment.

Optional pad has already been installed


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: 20 Jul 2015, 18:11 
Offline

Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
I have have recently run into problems with the circuit Baxandall circuit I used with my headphone amplifier. If I turn the bass potentiometer to full boost and rotate the amplifier volume to full the output of my headphone amplifier will oscillate quite loudly. Also if I set the volume to minimum the output of the amplifier will hum loudly. There will also be a loud pop if I turn the volume up to around half way. Its as if there is a D.C voltage present on the volume potentiometer.

Meassuring for any voltage accross the potentiometer revealed 0v.

I managed to eliminate the problem by installing a 100K resistor accross the output of the baxandall circuit. Right after the 0.47uF decoupling capacitor.

Can I leave the fix as is or should I be looking for a different fault that would cause the above symptoms?


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: 20 Jul 2015, 19:16 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1592
Location: US Pacific Northwest
philip davies wrote:
If I turn the bass potentiometer to full boost and rotate the amplifier volume to full the output of my headphone amplifier will oscillate quite loudly.
Insufficient phase margin in the feedback loop. How is the circuit loaded?
philip davies wrote:
Also if I set the volume to minimum the output of the amplifier will hum loudly.
Bad ground on the potentiometer. Look for cold solder joints.
philip davies wrote:
There will also be a loud pop if I turn the volume up to around half way. Its as if there is a D.C voltage present on the volume potentiometer.
You'll need to post the entire schematic so that we can see how you've wired it in. Where is the volume control?

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


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 20 Jul 2015, 20:45 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4030
Location: Arizona, USA
Yes please post the whole schematic. I would add it sounds as if there might not be enough inter stage decoupling in the power supply.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 21 Jul 2015, 18:39 
Offline

Joined: 19 Mar 2012, 19:22
Posts: 168
Location: Wales, UK
The volume control has been placed between the output of the baxandall circuit and the headphone amplifier input. The pot has a value of 50K. I have also checked the ground on the potentiometer and gone over the solder joints.

I have attached a drawing of my amplifier and its psu. If I remove the baxandall circuit completely i.e disconnect it from the psu and remove it from the audio path then the amplifier works fine.


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: 21 Jul 2015, 20:18 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4030
Location: Arizona, USA
Hi Check out Duncan's Web site for Tone Stack Calculator. It will do all the calculations for you and show graphically what happens. Nice thing is that it shows what happens if you alter the components. It does several popular types of tone controls not just the one you were using. It's a free program as well. I'll see if I can post the link.

http://www.duncanamps.com/tsc/download.html

I have used it and the values seem to match my expectations.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 22 Jul 2015, 18:30 
Offline

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

Thanks for showing me the Tone Stack Calculator. It has shown me some interesting things when decreasing the value of the load resistor on the tone stack output. I am quite surprised how much of the low frequency is lost by just decreasing the value a little bit.

I did try my setup again today and I also removed the 100K resistor that I placed accross the the tone control output. Everything seemed to work fine but unfortunetly I couldn't get the amplifier to oscillate like it did before I added the resistor. It seems that there could be an intermittent fault somwhere either in my wiring or a bad tube socket or perhaps tube pins that are not clean.

I will try again tomorrow to see if I can get the amp to missbehave and find a proper fix to the fault.

Phil


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 23 Jul 2015, 07:22 
Offline

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

I have made some more testing today and the problem is back. Also the problem is more persistent so I have managed to use my multimeter to check voltages. Looking at the baxandall circuit that I am using I meassured for any dc offset voltage after the 0.47uf cap that's connected to the cathode of the cathode follower section. There appears to be some voltage present here so in other words a small dc voltage is going through the bass and treble pots. Also there is voltage after the 0.47uf cap on the output of the circuit. I am guessing there is voltage on the output due to the feedback going back to the bass and treble section. So if there is voltage going into the bass and treble section it will go straight to the output.

I am using brand new Mundorf caps so I'm hoping they haven't started to leak dc voltage.


Top
 Profile  
 
 Post subject: Re: Baxandall circuit
PostPosted: 05 Aug 2015, 00:38 
Offline

Joined: 01 Feb 2015, 13:41
Posts: 144
Location: Athens-Greece
I finally made my pre-amp based on the attached drawing but I am not happy with tone control performance,it is not so good for my ears, so at the end I stay with the by-pass function with the optional pad. I used various types of potentiometers as advised with no significant improvements. Hence, I decided to stay with pure sound. The problem is that I have too much gain so, when I connect the pre-amp to my 6SN7-300B SE, using a CD player, I have to turn the potentiometer of the pre-amp almost at zero to 1, since I want to keep the amp's volume control high. Generally, I red that if the potentiometer is at low position then the ration signal/noise is decreased and noise effects increase. Any idea to reduce gain or to look somewhere in my circuit?

Is it better to have two stage pre-amp instead of a simple Universal 4S ? I tried the 4S and got good results, but I though that with two stage (a 12AU7 as follower) would get better results. Any opinion on that?

Thanks Dimitris


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  [ 97 posts ]  Go to page Previous  1 ... 3, 4, 5, 6, 7, 8, 9, 10  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Google [Bot] and 7 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