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

lykkedk 4th October 2016 05:50 PM

2 Attachment(s)
Hey (Salas)

I have one quistion, about the pcb layout.
Actually this is (i think) the only point, where i am in little doubt :

If i look at the schematic, there is connection between top of VR1 -> Q2 -> R9 -> C6 and M1.
I got those connections, when i am making the pcb.

But if i look at youre pcb, i can't directly see connection between those 4 parts, unless as i assume, that the toplayer (red?) and buttonlayer (blue) is connected at left side of R9 !

Am i right ? (Think i am :D)

Rgds; Jesper.

Btw. : Sry. that i "copycat" the layout :cool::violin:

Theodosis O. 4th October 2016 07:43 PM

Hi Salas,

Do both channels share the same gnd?

Wouldn't better to have separated?

Salas 4th October 2016 07:58 PM

1 Attachment(s)
Quote:

Originally Posted by lykkedk (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4847643.html#post4847643)
Hey (Salas)

Am i right ? (Think i am :D)

Rgds; Jesper.

That's the positive rail parts connections going along the +Rail blue line in other words. But VR1 & Q2 get it from the plated canal at the components side R9 left pad. Its soldered leg makes a strong bridge in the end. Don't be afraid following your layout ideas suiting better for your box floor plan or favorite parts and their sizes, no worries.

Salas 4th October 2016 08:15 PM

1 Attachment(s)
Quote:

Originally Posted by Theodosis O. (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4847721.html#post4847721)
Hi Salas,

Do both channels share the same gnd?

Wouldn't better to have separated?

I had them separate on the proto to check that out and did tests with and without a cable jumper bridging the extra outer blue pads at the bottom. I saw no difference in hum for common and double PSU (when all was connected up and chassis grounded through the input's returns at the pot) so I closed the gap for the common op-amp's ground reference to be as close to both channels.

Salas 4th October 2016 08:44 PM

Quote:

Originally Posted by ammel68 (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4847556.html#post4847556)
Is the relay closing time set to a specific time or is it adjustable?

Every 10K about 1 sec. I have 68K Ra now just in case some turn on DC bumps are slower to cycle. I heard nothing different "plop" (which was pretty much nothing anyway) during power up than before (51K) when testing cranked up on headphones, but again, just in case. Nobody should be powering up or down any preamp when the power amp is on as a general good practice nonetheless.

ammel68 4th October 2016 11:02 PM

Quote:

Originally Posted by Salas (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4847770.html#post4847770)
Nobody should be powering up or down any preamp when the power amp is on as a general good practice nonetheless.

Yeah, I know that but others may not.
I never apply power to a preamp/buffer after the power amp is on.

I can live happily ever after without muting circuits(except on power amps) or switched inputs.
But since you incorporated it onto the board, I thought I would ask. I'm quite surprised how simple the muting circuit is.

Any word on pricing for the preamp boards? I asked several posts back, but I guess tea bag, or whoever is doing the boards, didn't reply.

Thanks.

Salas 4th October 2016 11:49 PM

I asked him many days ago if it will be at less than the Hypno which is somewhat bigger but I would like it in matte black also and he said possibly if there are enough pcs but it takes a week more for that color. Which means around $20 for the dcg3 pcb if I did not it blow it with the little changes I sent him for both the preamp and psu which also means retooling. I.e. additional costs and time.

ammel68 5th October 2016 04:21 AM

Quote:

Originally Posted by Salas (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4847867.html#post4847867)
I would like it in matte black also and he said possibly if there are enough pcs but it takes a week more for that color.

Black, red, blue, etc. boards are usually more expensive with most board houses that I've dealt with, but the turnaround time is usually the same.
He must be dealing with some non-Asian board house.

Nonetheless, I'll pay $20 for a single board to try when they're available.

Thanks for your reply Salas.

AndrewT 5th October 2016 08:06 AM

Quote:

Originally Posted by ammel68 (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4847556.html#post4847556)
Is the relay closing time set to a specific time or is it adjustable?

A small relay will open, or close, in around 1ms to 5ms. That's without a reverse current diode across the coil.
A big relay could be around ten times slower.

If you add on a reverse current diode, then those that have measured it seem to indicate that the opening/closing time very roughly doubles.

Adding in the resistor and/or Zener reduces that ~doubling, but never gets back to the no diode times.

Salas 6th October 2016 12:59 AM

5 Attachment(s)
My DCG3 is boxed and back in my hands now. Thanks to the mechanical skills of my friend Michael who turned a cheap aluminum box of almost industrial looks to a nice housing with a perspex front and fitted the PCBs orderly inside. We listened to it in his system for long too. It can be seen sitting in the middle under his vintage and highly modified Walker CJ55 TT which is running on DC motor. The Jelco arm that he transformed with a carbon wand and DIY counterweight looks and tracks super with the Benz Ace cart. There is also a USB enabled Mambo ES9023 DAC sitting bellow the preamp. A Valve Itch phono stage and a Juma's Cubie2 amp in open frame style are situated to the right. Eminent Technology LFT-8 speakers are flanking the equipment rack. They look like the 8b model because they went through laborious modifications that included placing the HF unit lower.


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