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 04 Jul 2020, 19:28

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 741 posts ]  Go to page Previous  1 ... 48, 49, 50, 51, 52, 53, 54 ... 75  Next
Author Message
PostPosted: 12 Mar 2017, 06:27 
Offline
User avatar

Joined: 16 Feb 2016, 19:45
Posts: 47
Location: Boston, USA
Here's a simple web page with some layout files for my turret boards, etc:

http://ohm.bu.edu/~hazen/TubeAmp/

One odd thing... the output feedback is currently not connected, but it sounds great. When I connect (as in photo) it I get nasty feedback on both channels. In my photo you can see the feedback wires, they're the orange s-shaped ones up in the air on top of everything. I'm thinking that I should run a twisted pair from the speaker terminals back to the amp turret board section, which is otherwise grounded only to the inputs via a piece of coax.

I'll do some more experimenting today and report.

_________________
----------------
Eric Hazen


Top
 Profile  
 
PostPosted: 12 Mar 2017, 16:51 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4189
Location: Arizona, USA
Hi, Your symptoms indicate that the phase of the output transformer is not correct. A common problem. Manufacturers mark the leads for a non-inverting phase condition. The Poddwatt design uses them to invert the phase. The net result is an amplifier with one less stage (simple is good) that does not invert the signal. It also makes it easy to implement a small amount of negative feedback. Depending on which output transformer you used you can swap the leads on either the primary or secondary side. If you have a single secondary (like with the G series transformers from Edcor the easiest way to fix it is just swap the hot and ground on the output side. Then there should be no problem. If you are using one with multiple secondaries this will not work as well. The reason being that the middle impedance secondaries will not be usable. If you want to know why I suggest looking on the web about transformer windings. It would take a bit of time to explain here. In such a case though you will need to swap both the screen and anode wires for both output tubes. Another possibility depending on the build is to swap which of the output tubes gets the signal from the driver stage.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 12 Mar 2017, 17:02 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4189
Location: Arizona, USA
Hi, An update...it seems that over time the color codes on the wires are not consistent. I can not verify that but I get reports that the brown and blue sets are swapped on occasion. What I have been recommendinf for some time is that during the build that those wires be losely tacked in place to test the amp and swap them if needed. This is also the case for other brands that may not use the same color codes.

A revies of the commercial kits and all newer builds indicates that the brown set of wires go to the tube that gets the signal.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 12 Mar 2017, 17:12 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4189
Location: Arizona, USA
You have me wondering where the schematic came from as it is not part of the posted project. I wonder as it shows the color codes on the transformers reversed from where they should be. If the schematic can be fixed it would probably avoid some problems. It is not any of the current ones and didn't show up in a quick search.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 12 Mar 2017, 18:14 
Offline
User avatar

Joined: 16 Feb 2016, 19:45
Posts: 47
Location: Boston, USA
Bruce, I'm using your schematic posted somewhere on this forum. Link below.

http://ohm.bu.edu/~hazen/TubeAmp/PoddWatt_2C%20Consolidated%20FIX%20December%2015%202014.jpg

It has the wiring colors for the Edcor transformer which I followed. It seems to me
that the in your schematic output tube with the signal (the upper one) has the blue wires, not the
brown one. The output colors are not shown but got them from the Edcor
data sheet:

Image

Looking on the scope with a function gen sine wave input, I see inversion in the
input stage as I would expect but then the "8 ohm" lead (yellow) is the same phase
as the driver grid, so I guess the transformer is the reverse of what you intend?
Presumably the feedback should have the same phase as the input, since it
goes into an inverting node (cathode of the input triode).

Image

Top - amp input
Middle - pin 2 (grid) of upper triode
Bottom - speaker out (output trans. yellow wire)

I'll reverse the wiring on my output transformer and hook up the feedback.
It sounds very nice without any feedback, and I'd like to compare.

_________________
----------------
Eric Hazen


Top
 Profile  
 
PostPosted: 12 Mar 2017, 18:45 
Offline
User avatar

Joined: 16 Feb 2016, 19:45
Posts: 47
Location: Boston, USA
All good now! What a great amp!
I think it sounds a little cleaner with the NFB connected.
I really need to find some better speakers... maybe a set of Pensils or something
like that is my next project!

_________________
----------------
Eric Hazen


Top
 Profile  
 
PostPosted: 12 Mar 2017, 21:23 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4189
Location: Arizona, USA
Hi, I believe that was one for someone that wanted to build the amp and not one of the main projects that were posted...anyhow it is incorrect based on all others I have and have schematics for. There were at least two individuals that indicated the colors were wrong on their transformers at about that time and it might be the source of the drawing. Also more likely the individuals got the drive to the wrong tube and the schematic was showing how to fix it. My memory fails me on the details. That was numerous updates ago and all now show as best I can tell no colors on the wiring. The quite long thread on the amp (and the ones on the other bigger ones) have talked about the phase relations and usual color codes several times. It is kind of amusing that when I built the very first one back in 2008 I must have been lucky as it was correct and I really at the time didn't know what phase the transformers actually were built to.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 12 Mar 2017, 21:38 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4189
Location: Arizona, USA
Hi, I believe either the web has gone nuts or I am. When I first went to this thread to answer a question it vanished..... :confused: But since I did read it I will answer it anyhow.

The amplifier is tolerant of a small amount of dc on the input. 30mv ought to be fine, 2.5 volts no. You can put a capacitor in front of the volume control if needed. I would probably use about a 1uf /100 volt poly. That will insure that the amps low frequency response will not compromised and minimize phase shift.

The input sensitivity of the power section is roughly +/- 10 volts for full output. The impedance there is essentially the 220K grid resistors. You could drive it directly as you seemed to indicate.

Another possibility exists as well. You can replace the 5751 with a 12AU7 and make a few small changes to the cathode resistors and NFB loop. The gain will be lower that way but the sonic qualities essentially identical. I did that with an early version. If you want the info on it let me know and I'll hunt up the data.

If I missed anything please re-post it. If the questions were not here ( :eek: ) then I'll chalk it up to senility.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 13 Mar 2017, 06:25 
Offline

Joined: 19 Jun 2013, 02:39
Posts: 21
gofar99 wrote:
if you use a single powered sub and tie the two channels on the amp outputs together it does affect the cross talk between the main channels. The higher the resistors are the more cross-talk you will have.

Yes I'm going to use a single mono subwoofer. I think not to use a mere "Y" cable and use the method shown here:
http://www.rane.com/note109.html
But is really needed after the voltage divider inside the amp?
Doesn't the VD already isolate the two channels enough?
Thanks in advance


Top
 Profile  
 
PostPosted: 13 Mar 2017, 21:06 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4189
Location: Arizona, USA
Hi, Yes you can sum them that way without causing much crosstalk. You will probably not even notice it.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 741 posts ]  Go to page Previous  1 ... 48, 49, 50, 51, 52, 53, 54 ... 75  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Google [Bot] and 16 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