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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Salas DCG3 preamp (line & headphone)
Salas DCG3 preamp (line & headphone)
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Old 29th June 2020, 07:12 AM   #4781
guneyt is offline guneyt
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Quote:
Originally Posted by Salas View Post
Hi, DCSTB is clean, even, and efficient with DCG3, if you want to keep it that neutral use a good switcher pot, if going after a more organic result put a TKD 2CP-2511 20K Log. Also use BC327-40 for Q1 Q2. By the way, DCSTB is already dual mono as it comes.

If you go dual mono shunts its a much more heated solution demanding good sinking and chassis floor real estate too, usually brings even more impressive bass and upper bass resolve in this but it also may come across heavy in some systems. If so happens it may push you to resort in passive parts tonal offset tuning experiments on the shunts. Electrolytics mainly.

All in all a much more involved and bit experimental down to taste affair.
Hello Salas,
is this TKD pot you're suggesting?
seems like a shunt type.
TKD 2CP-2500 Series Potentiometer | Hifi Collective

There is also a new one 2CP-601S. I think this type is directly solderable to your I-select board?
TKD 2CP-601/S Potentiometer | Hifi Collective

Last edited by guneyt; 29th June 2020 at 07:22 AM.
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Old 29th June 2020, 07:16 AM   #4782
le´flu is offline le´flu  Germany
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Hi Salas,
thanks allot for guidance - sounds terrific. Will you expect tonal changees when
using a 50klog pot? And how is the difference soundwise compared to your tube
linepreamp?
As i understand the DCSTB is dual Mono, as is the DCG3 PCB. So GND is connected
at the input-board? Wouldn´t is be better to go dual-mono at the input-board too?

Greetings
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Old 29th June 2020, 08:08 AM   #4783
Salas is online now Salas  Greece
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Salas DCG3 preamp (line & headphone)
@guneyt

Yes that's the one. The other the 601 is mini sized and relatively economic, not as good as the 2511 but still subjectively better than ALPS Blue. Maybe solderable to pads but it won't go sit to the I-Select as an ALPS. Its a different form factor.
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Old 29th June 2020, 08:12 AM   #4784
Salas is online now Salas  Greece
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Salas DCG3 preamp (line & headphone)
@le 'flu

With 50K pot it sounds bit slower and sweeter. Its a matter of going for synergy with sources and mainly loudspeakers. VS the 6V6 line preamp its more revealing and open wide, has more drive in the bass also, less noise, but not tonally aggressive like some older typical solid state. Does not have the triode tinge of course but it meets higher neutrality criteria. Its generally ample sounding, no manifestations of a small hyper organized cold caricature sound. There is naturally expanded midrange and bass slam not boom.

Yes GND will be connected to the relays input board. You could go dual mono switch boards but its a complex enough thing to do. Nobody had problems with normal switch boards though. Using a classic good quality rotary switch with extension rod isn't out of the question also.
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Old 2nd July 2020, 02:14 PM   #4785
66deg is offline 66deg  United Kingdom
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Hi Salas,
I have completed all the tests, results as follows.
Right R10 1.2V.
Left R10 1.1V, both with 10-ohm resistors.
Rails.
Left negative 17.45, positive 17.41.
Right negative 17.29, positive17.32.

Mosfets 40/42°
Sink below mosfets 38/39°.

Inner PSU sinks 49/51°.
Outer PSU sinks 45/46° and 47/48°.

Without the opamp + or- 5MV.
With the opamp one side stayed pretty much around 0 whilst the other side had occasional trips up and down to around + or - 2/3mv.

I have ground continuity to all metal parts, at the moment I do not have ground connected to the DCG3 boards and would like to know if it is OK to use the HP G as I am not using them for anything, should I bridged one to the other and then go to the mains earth or one to mains and one to the pot earth?

This is my first time wiring up a pot and would appreciate a quick check over.
Line out to pin 1, pin 2 to RCA and both grounds are to pin C.
As you can see in the photos I'm just using one input but may add the I select at a later date if required.

I have bridged across for my 2 outputs.

If you could have a general visual check over that would be great and if all is well I'll connect up the PCB earth and give it a whirl.
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Old 2nd July 2020, 02:21 PM   #4786
66deg is offline 66deg  United Kingdom
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A few more pics.
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File Type: jpg IMG_1542.jpg (742.6 KB, 71 views)
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Old 2nd July 2020, 02:33 PM   #4787
r_jik45 is offline r_jik45  France
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Clean built.
How big is the heatsink? Is it also going under the dcg3 board?
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Old 2nd July 2020, 03:40 PM   #4788
66deg is offline 66deg  United Kingdom
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Thanks.
It stops just at the edge of the PCB, was struggling to find one solid piece of ally bar so it's 4 pieces of 35mm x 3mm X160mm all bolted together with heatsink gloop in-between, I wasn't sure how it was going to fit with the support tray but it went in very nicely and is over the vents for cooling.
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Old 2nd July 2020, 08:29 PM   #4789
Salas is online now Salas  Greece
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Salas DCG3 preamp (line & headphone)
Why you wired the volume pot at the output? Volume pot should go between Line in RCA and Line in PCB.
You should move the blue coaxial cables to the correct PCB places for exchanging their now in/out routes.
RCA in hot-->cable-->pot pin 1, pin 2-->cable--> line in PCB. Cable shield RCA cold to C to PCB line in G.

For PCB to chassis ground reference wire see post #4761.

Mechanically its a very good tight build, congratulations.

What was the room ambient temperature when you measured the Mosfets and sinks?
How you did that? With a non contact infrared meter or with a thermocouple probe?
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Old 3rd July 2020, 07:05 AM   #4790
66deg is offline 66deg  United Kingdom
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I don't know the exact room temperature but it will have been quite high as my workshop is outside and Provence has started to get quite hot.
I used a non-contact infrared meter for all the temperature testing.
I'll make the wiring changes and get back ASAP.
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