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-   -   Salas DCG3 preamp (line & headphone) (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone.html)

Salas 9th September 2016 11:48 AM

1 Attachment(s)
Yay! George called and says he is planing to come around next week carrying those along. The ones to the left are mine. More soundz to savor for more universal tunings :)

vgeorge 9th September 2016 12:13 PM

I will also bring my old and trusty Sony MDRV6 for a headphone gathering!
Should do some run in on them now......

MagicBus 9th September 2016 02:26 PM

Hi, nice work Salas!
I'm not headphones fun but gain and driving ability in line stage attracts me. My system needs balanced input/balanced output though. Possible?

Salas 9th September 2016 03:23 PM

Its an SE preamp. Possible though. Must simply build two boards for balanced stereo, i.e. four channels, one channel for each signal phase. ;)

The first p2p beta tester (Michael) has American magnetic panel speakers of low sensitivity and got attracted to the same aspects as you do. He never connected headphones ever, has not even a jack for that. Nonetheless it became his line preamp of choice. He uses gain of four. He even made one copy for his best friend.

nashbap 9th September 2016 03:27 PM

Very nice work Salas. Thanks. Will be following keenly.
nash

MagicBus 9th September 2016 03:41 PM

Quote:

Originally Posted by Salas (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4825556.html#post4825556)
Its an SE preamp. Possible though. Must simply build two boards for balanced stereo, i.e. four channels, one channel for each signal phase. ;)

The first p2p beta tester (Michael) has American magnetic panel speakers of low sensitivity and got attracted to the same aspects as you do. He never connected headphones ever, has not even a jack for that. Nonetheless it became his line preamp of choice. He uses gain of four. He even made one copy for his best friend.

Thanks! I' ll be following...

Salas 9th September 2016 03:48 PM

Quote:

Originally Posted by nashbap (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4825560.html#post4825560)
Very nice work Salas. Thanks. Will be following keenly.
nash

Hey Nash, what's up? You are welcome.

Marra 11th September 2016 10:32 AM

Watching with interest. Not that I need another preamp ;)

Salas 12th September 2016 11:35 AM

Few words about power
 
3 Attachment(s)
Lets talk two examples. One is wanting to drive 2.2VRMS into a 32 Ohm headphone*. The other is wanting to drive 2.2VRMS into a 600 Ohm line. Say at the standard 100mA output stage DC bias choice.

The two graphs show output voltage, M3 drain pin current, M1/M2 drain pin current (identical) and M1 source pin current. Its the same PSU drawn current amount just shown reversed phase at source pin. The output stage will only pull steady DC bias from the negative rail because its current source M3 resides alone there while it can pull double that pk-pk from the positive rail before progressively squashing the below zero going part of a waveform. Will drive 200mA pk-pk on 32 Ohm but only 15mA pk-pk is demanded on 600 Ohm for that same output voltage. 33V pk-pk (11.7VRMS) with 55mA pk-pk can be done on 600 Ohm. A 10K amplifier will be driven to 33V pk-pk with just 3.3mA pk-pk.

So the about +/-17.5V PSU should be capable of at least 200mA on the positive and 100mA on the negative to cover the demanding load example. There is little more to add for the input stage and the servo.
If using double mono BIB shunt regulators a 250mA CCS limit for the positives and 150mA CCS limit for the negatives would be the economic choice heatwise. Double that when with common between channels mono regulators. If using the double mono DC stabilizer there is nothing to set. Its just a low noise non amplified voltage reference with a compound current pass transistor (Sziklai) of high enough amperage.

When not planning to use headphones, or at least not below 70 Ohm impedance ones, then 150mA CCS per rail limit for double mono regulators will suffice. When panning to use much insensitive low impedance headphones then more DC current bias and higher super shunt PSU CCS limits can be calculated.


*That is 120 dBSPL on a Grado. Will blow your head :D

Tea-Bag 15th September 2016 04:21 PM

Listened to Peter Gabriel's Scratch My Back version of Heroes over the DCG-3 the other night.
It's a slowly sung song, seems close mic and it ramps up to a kind of chilling end with strings if you let it.
The lower mids of his voice never sounded so strong. The presence of him in the room was both strong, almost uninvited after a certain point. You may get this emotional reaction when you realize the sound can really have a visceral affect on you like that. This is one of the reasons I like audio - to get this experience from music. Sometimes you can only get that when the equipment is crisp and spot on. Like the low-noise of the folded, this pre allows you to squeeze a little more information out of your gear, and push it at you. It's not even a spectacular recording, but it's well delivered.

I felt like sharing this part of it. That the circuit may kick your butt if you let it.

I am very interested in what VGeorge and Salas have to say with their headphone shoot out.


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