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Output stage for the Soekris R2R
Output stage for the Soekris R2R
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Old 18th January 2017, 08:20 AM   #101
Firschi is offline Firschi  Germany
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Join Date: Dec 2016
Hi folks,

my dam1021-12 will arrive tomorrow - or so... I want to use the unbuffered se outputs to feed an output stage that offers both, se and bal outputs. Adding gain would be a nice feature. As I cannot make my own boards I would rather like to buy a kit or at least a pcb plus additional information (BOM, schematics, etc.).

Do you guys have solutions that you're willing to share? Btw. I don't like tubes...


Best,
Dominik
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Old 18th January 2017, 08:38 AM   #102
TioFrancotirador is offline TioFrancotirador  Poland
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Join Date: May 2014
Location: Poland
Quote:
Originally Posted by Firschi View Post
Hi folks,

my dam1021-12 will arrive tomorrow - or so... I want to use the unbuffered se outputs to feed an output stage that offers both, se and bal outputs. Adding gain would be a nice feature. As I cannot make my own boards I would rather like to buy a kit or at least a pcb plus additional information (BOM, schematics, etc.).

Do you guys have solutions that you're willing to share? Btw. I don't like tubes...


Best,
Dominik
Hi Dominik,

Why you need more gain, since most of the times you have attenuator in front of amplifier anyway. Do you really need more gain? If you want to use headphones then watch for Salas DCG3 in this forum. He makes spectacular designs. DCG3 is discrete preamp and headphone amp with gain of 3 times.

Last edited by TioFrancotirador; 18th January 2017 at 08:41 AM.
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Old 18th January 2017, 08:46 AM   #103
Dimdim is offline Dimdim  Greece
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Join Date: Sep 2008
Location: Athens
DCG3 seems to be a very good candidate for an output stage for the DAM. With a gain of 2 it would put out ~2V RMS. No balanced-out though.

I'll try to test out such a configuration.
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Old 18th January 2017, 09:42 AM   #104
Firschi is offline Firschi  Germany
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Join Date: Dec 2016
Wow, thanks for the fast replys!

I plan using a "The Wire BAL-BAL" as an amp. So, balanced outs of the buffer stage are needed. I thought it would noisewise be better, to have some gain (2x or maybe 3x) right after the DAC. Am I wrong?

Of course I will be using the volume control auf the dam module only.
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Old 18th January 2017, 10:16 AM   #105
bambadoo is offline bambadoo  Norway
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Location: West Coast of Norway
Quote:
Originally Posted by Dimdim View Post
DCG3 seems to be a very good candidate for an output stage for the DAM. With a gain of 2 it would put out ~2V RMS. No balanced-out though.

I'll try to test out such a configuration.
Thinking of the same..
In a process of building the DCG3
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Old 22nd January 2017, 05:32 PM   #106
Firschi is offline Firschi  Germany
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Join Date: Dec 2016
It seems I found the perfect solution. A friend of mine inspired me to read the book "Small Signal Audio Design (2014)" by Douglas Self. I'll go for the circuit that can be seen on page 545 Figure 19.8 b).
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Old 23rd January 2017, 09:27 AM   #107
GourouLubrik is offline GourouLubrik  France
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Join Date: Mar 2012
Location: Grenoble, France
Quote:
Originally Posted by Firschi View Post
Wow, thanks for the fast replys!

I plan using a "The Wire BAL-BAL" as an amp. So, balanced outs of the buffer stage are needed. I thought it would noisewise be better, to have some gain (2x or maybe 3x) right after the DAC. Am I wrong?

Of course I will be using the volume control auf the dam module only.
I've such a configuration, but I have avoid using the buffered output of the DAM, because the OPA1632 used in the Wire BAL-BAL have the same capabilities of doing BAL out of a SE signal when tying Vin- to the ground (figure 13 of the datasheet : http://www.ti.com/lit/ds/symlink/opa1632.pdf ) .

I've also raised the input impedance to 10k ohms (it's 1k ohm default for the Wire).

Last edited by GourouLubrik; 23rd January 2017 at 09:30 AM.
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Old 23rd January 2017, 02:38 PM   #108
spikestabber is offline spikestabber  Canada
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Join Date: Feb 2015
Quote:
Originally Posted by Firschi View Post
Wow, thanks for the fast replys!

I plan using a "The Wire BAL-BAL" as an amp. So, balanced outs of the buffer stage are needed. I thought it would noisewise be better, to have some gain (2x or maybe 3x) right after the DAC. Am I wrong?

Of course I will be using the volume control auf the dam module only.
See my setup, except I'm using a pair of dam1021 boards for balanced raw output feeding the BAL-BAL rather than the buffered outputs of a single board. I solely use the dam based volume control. It sounds absolutely incredible with hd800's.

I've set the BAL-BAL to 2x gain using 10k resistors on the inputs and 20k resistors for the negative feedback because the stock config of 1k resistors put too much load on the dam1021's raw output (Zout of 625R), although it should be fine using buffered output which is significantly lower at 20R balanced.

EDIT: Indeed GourouLubrik is correct, its way more suitable to use the BAL-BAL's OPA1632 to convert the single ended to balanced in a single board configuration. You'll still need to change the BAL-BAL to 10k input impedance though for the same reasons we did.
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Soekris dam1021-12v2 dual-mono balanced w/D882/B772 transistor mods & BAL-BAL Headamp: https://imgur.com/gallery/RVBQozq
nc400: https://imgur.com/iORCyna | TT2USB: https://imgur.com/a/p6OiS | HD800 | KEF R300

Last edited by spikestabber; 23rd January 2017 at 02:49 PM.
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Old 23rd January 2017, 09:17 PM   #109
Firschi is offline Firschi  Germany
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Join Date: Dec 2016
You guys are absolutely right! As you mentioned the low input impedance of "the wire" is a problem when connected to a dam1021 (using the RAW output). Although SE to BAL conversion is possible within "the wire" I decided to go for a dedicated output stage, that offers many advantages, such as SE and BAL output and a low output impedance of about 10R. Besides "The Wire" can use it's full potential.
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Old 24th January 2017, 11:00 PM   #110
derekr is offline derekr  Barbados
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Join Date: Mar 2009
And/or you could ask Søren nicely whether he has made progress on his output board - mentioned some time back as 'under consideration'.

Last edited by derekr; 24th January 2017 at 11:03 PM.
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