Buffalo II & transformers - Page 30 - diyAudio
Go Back   Home > Forums > Commercial Sector > Manufacturers > Twisted Pear

Twisted Pear Superior quality electronic kits

Reply
 
Thread Tools Search this Thread
Old 29th January 2012, 06:01 AM   #291
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Send a message via MSN to Joe Rasmussen
Quote:
Originally Posted by Terry Demol View Post
Just put a 6 ohm resistor across the Sabres OP.
I don't think you need the ground reference.

T
Hi Terry

Yes, see above, the point I've made as well. But both should be tried if the opportunity presents itself.

Cheers, Joe R.
__________________
The "Elsinore Project" DIY Speaker System
Custom Analogue Audio - we also support and promote non-profit DIY
  Reply With Quote
Old 11th February 2012, 08:18 PM   #292
diyAudio Member
 
nullspace's Avatar
 
Join Date: Oct 2004
Location: Phila., PA
Quote:
Originally Posted by Joe Rasmussen View Post
The context was a DAC with voltage offset, usually near 2.5V but also in some cases 1.65V - you can't just bring it to ground without potential damage (know somebody who did and poof!!).

DACs like PCM1792/1794/1796 (also DSD prefix) all have zero offset voltage (they do have offset current, but that hardly matters) and hence no danger to bring it to ground or even short it.
Thanks Joe. I've been mulling this over, and now get the difference between DC current offset & DC voltage offset DACs in this context. Can hardly believe I'm this dense/ took so long to get it...

I have a COD module in transit. Once I get a chance to mess with it, I'll start a new thread.

Thanks again for your help.

Regards,
John
  Reply With Quote
Old 12th February 2012, 01:25 AM   #293
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Send a message via MSN to Joe Rasmussen
Quote:
Originally Posted by nullspace View Post
...now get the difference between DC current offset & DC voltage offset DACs in this context.
I now avoid current DACs with offset voltage - so that I can do direct-coupled (no caps in signal path) zero feedback I/V post DAC circuit. The other point is that, in this case, offset current is not a problem, but oh boy, offset voltage makes offset current a real problem. But once you get it, as you say, it helps a lot.

My thanks to Terry who I used as a sounding board on this, some time back.

Cheers, Joe R.
__________________
The "Elsinore Project" DIY Speaker System
Custom Analogue Audio - we also support and promote non-profit DIY
  Reply With Quote
Old 14th February 2012, 12:12 PM   #294
hkminn is offline hkminn  South Korea
diyAudio Member
 
Join Date: Feb 2007
Location: seoul
Quote:
Originally Posted by Joe Rasmussen View Post
I still think somebody should try this with a Sabre DAC using Tubes.

Click the image to open in full size.

Normally Tubes are only good for voltage DACs, but use a transformer like this and you will have a Tube I/V stage - and it is the Sabre DAC that makes it possible - offset current = 8mA (I wouldn't do this with any other DAC I could think of). It can be pulled all the way to ground on the Primary and the Secondary grounded - and just input to the grid of your favourite Tube - and away you go.

Somebody should try it - requires gain about 50.

Cheers, Joe R.
Hello Joe,

I have tried this with a Buffalo24 board, using Sowter 8347(1:17) followed by SRPP stage using 6111 subminiature tubes.

First I tried 3R registers. The result was amazingl!! Lots of air and more details without losing too much dynamics comparing to a Buffalo32 with opamp I/V stage.

One problem was too much gain and I could not use more than a quarter of volume control. So, I replaced 3R registers with 1R, and the sound seems to be as good as with 3R (supposed to be better?) and I now can use the volume control in comfortable range.

One concern though. Isn't 1R register too low for the DAC? I asume it is safe since I don't see smoke, but I would like to have your confirmation.

Thank youl.
  Reply With Quote
Old 14th February 2012, 03:58 PM   #295
diyAudio Member
 
Join Date: Sep 2006
How much gain does the stage have?

Thanks

JD

Quote:
Originally Posted by hkminn View Post
Hello Joe,

I have tried this with a Buffalo24 board, using Sowter 8347(1:17) followed by SRPP stage using 6111 subminiature tubes.

First I tried 3R registers. The result was amazingl!! Lots of air and more details without losing too much dynamics comparing to a Buffalo32 with opamp I/V stage.

One problem was too much gain and I could not use more than a quarter of volume control. So, I replaced 3R registers with 1R, and the sound seems to be as good as with 3R (supposed to be better?) and I now can use the volume control in comfortable range.

One concern though. Isn't 1R register too low for the DAC? I asume it is safe since I don't see smoke, but I would like to have your confirmation.

Thank youl.
  Reply With Quote
Old 14th February 2012, 05:31 PM   #296
diyAudio Member
 
Join Date: Feb 2006
Location: In the basement.
Quote:
Originally Posted by hkminn View Post
Hello Joe,

I have tried this with a Buffalo24 board, using Sowter 8347(1:17) followed by SRPP stage using 6111 subminiature tubes.

One problem was too much gain and I could not use more than a quarter of volume control.

Isn't 1R register too low for the DAC? I asume it is safe since I don't see smoke, but I would like to have your confirmation.

Thank youl.
Not surprising. The figure shows a 1:1 transformer, and since you're using a 1:17, I think you must be getting more than 20db gain before going into your SRPP stage. The 6111 is medium mu, so depending on how you have it set up- you may have a lot of unnecessary gain (overall).

Last edited by blackeye*_0; 14th February 2012 at 05:35 PM.
  Reply With Quote
Old 14th February 2012, 06:11 PM   #297
diyAudio Member
 
Join Date: Sep 2006
Just ran my numbers..... as I mentioned in an earlier post I'm using a dual mono setup.
With a 1:1 traffo, using 10R on each primary leg to ground (assuming 97.5 R on the B2 DAC in mono) for each channel, that should net around .2v at the output of each transfomer. With a single gain stage of a 6N6P with a gain of about 20db, output voltage should be close to 2v. per channel. Right at my desired target.

JD
  Reply With Quote
Old 15th February 2012, 12:52 AM   #298
hkminn is offline hkminn  South Korea
diyAudio Member
 
Join Date: Feb 2007
Location: seoul
In the datasheet, the gain of 6111 tube is 20. But I do not sure when it is used in SRPP.
  Reply With Quote
Old 15th February 2012, 09:27 AM   #299
diyAudio Member
 
Join Date: Jan 2011
Location: Germany
1R is no problems as the ESS9018 chip can be used down to 0 Ohms into virtual ground. That is what the IVY uses.



Quote:
Originally Posted by hkminn View Post
Hello Joe,


One concern though. Isn't 1R register too low for the DAC? I asume it is safe since I don't see smoke, but I would like to have your confirmation.

Thank youl.
  Reply With Quote
Old 15th February 2012, 01:27 PM   #300
diyAudio Member
 
pietjers's Avatar
 
Join Date: Oct 2006
Hi hkminn,

Interesting approach!
The Sowter datasheet suggests that the IV resistor may also be used across the secondary winding of the transformer (taking into account that the value of the resistor is reflected on the primaries by the ratio of the transformer (18.7) squared: 18.7 x 18.7= 350). Did you try that also?

What are the drawbacks of the high transform ratio? Or is there something like a free lunch?
Datasheet for Sowter 8347 and 9055:
Sowter Type 8347 DAC INTERFACE TRANSFORMER

Peter
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Buffalo II Russ White Twisted Pear 1841 13th September 2014 12:28 PM
Volumite for Buffalo II? markusA Digital Line Level 15 8th April 2010 02:51 AM
Need help selecting an I2S/DSD/SPDIF connector for my impending Buffalo II orpheus Digital Source 0 9th February 2010 08:03 PM
FS- Twisted Pear Buffalo 32S Board & System New & Unused secretriches Swap Meet 1 10th August 2009 02:17 PM
Citation II output transformers dshortt9 Tubes / Valves 10 12th December 2003 03:45 PM


New To Site? Need Help?

All times are GMT. The time now is 09:05 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2