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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 14th February 2018, 03:55 AM   #2531
Keremito is offline Keremito  United States
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I am happy to report that bass is back. I think that the volume attenuator was the culprit, it measures well through all the rotation tracking was very good, perhaps I had it miswired, who knows it's out now. I am waiting for a new high-grade pot. I will report what becomes of the DCG3 with a high grade attenuator. Thanks to all for the help! I am smiling again!
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Old 14th February 2018, 04:01 AM   #2532
alexkosha is offline alexkosha  United States
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Salas DCG3 preamp (line & headphone)
Quote:
Originally Posted by Keremito View Post
I am happy to report that bass is back. I think that the volume attenuator was the culprit, it measures well through all the rotation tracking was very good, perhaps I had it miswired, who knows it's out now. I am waiting for a new high-grade pot. I will report what becomes of the DCG3 with a high grade attenuator. Thanks to all for the help! I am smiling again!


Congratulations!!!
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Old 14th February 2018, 04:11 AM   #2533
Keremito is offline Keremito  United States
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Thank you Alex!
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Old 14th February 2018, 08:25 AM   #2534
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Tarnished switch pot contacts most probably. The 25k Goldpoint you expect has no harsh or thin traits. It also opens up volume in slower fashion than most 21-24 step switchers. Even if you will need more output impedance from it so to round off your sound further we can always up R1. No worries.
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Old 14th February 2018, 09:23 AM   #2535
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
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Originally Posted by rhythmsandy View Post
can DCb3 be powered with salas bib? if so will the sound signature like bass slam will be same as DCSTB? I believe it might be better with even lower psu impedance? or will it be same?
I had listened to the first beta tester's two realizations with a mono BiB for both channels and they were generally fine. For subjective details between using those PSUs its precarious to say much because I had listened with them in different builds. It takes to have two double mono DCG3 preamps with BiB/DCSTB using exactly the same parts everywhere from trafos, diodes, reservoir capacitors types, down to same volume pots, resistors, and wiring/grounding scheme, to truly can sit down and compare in strict A/B fashion.

Just because its a revealing hard driving preamp with gain and much line output current capability, I designed and tested the fixed parts and fixed voltage DCSTB along with it to secure an author tested easy solution that plays well together. For you guys to can start confidently by avoiding speculation, too much heat build up, more external sinking, or potential for setup and stability errors with general duty variable PSU tryouts depending on type. If already in hand from previous projects its painless to try them. But sometimes they can be costly enough new experiments to risk subjective disappointment especially when investing in double mono.

From there on you may experiment according to your curiosity. The preamp's electrical needs are not weird demanding only one certain PSU. Beardman for instance applied three different PSUs already during his saga to fit the sound hand in glove for a particular system. Two highly respected third party ones from the kits/modules market and the DCSTB.

Most valuable subjective finding in this thread is have patience. If your build does not mix and match perfectly well within an existing setup on first shot don't despair. Leave it powered on for some hours, play again to make sure of your goals, and start trying things. Its worth the effort as it proved again and again. New bold gear can be upsetting an existing system's balance sometimes or there is an influential internal part to better manipulate or fix.
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Old 14th February 2018, 07:43 PM   #2536
rhythmsandy is offline rhythmsandy
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ok is it really required to run it at +/-17V or even lower V is also fine like +/-13 or 14V?
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Old 14th February 2018, 10:00 PM   #2537
Salas is offline Salas  Greece
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Keep it at +/-17V. There is a three Leds drop to the relay calculated for giving it 12V on nominal rails (that can be changed to less Leds if the preamp MUST be used with lower voltages if the HP output max power does not matter to you). But the capacitive parasitics of the Mosfets are better on the higher voltage rails so the THD and the speed aspects fare better.
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Old 15th February 2018, 10:02 AM   #2538
Salas is offline Salas  Greece
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Quote:
Originally Posted by Keremito View Post
Thank you Salas. Here are the measurements:
Resistor values while on the board: Left/Right
R12: 1mohms/1mohms
R13: 0.585 mohms/0.585 mohms
R14: 10 kohms/10 kohms
R15: 50 ohnms/50 ohnms
Q1 collector: 12.66/12.74 Volts
Q2 collector: 16.58/16.61 Volts
J3 drain: 400 mV/275 mV
J3 Vgs: 1.014/1.003 Volts
Those are healthy results and you also stated that after changing a dubious volume pot the bass feels normal again. This build behaves and reacts well then.
There is no basic assembly error indication. But I forgot to ask you the DC mV across R3 also. Let me know those R3 voltage drops when its handy to measure.

Thanks
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Old 15th February 2018, 10:13 AM   #2539
Salas is offline Salas  Greece
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Originally Posted by arnd13 View Post
Most all items are delivered now (except the final heatsink).

I was so impatient that I bought heatsink (not really the right one) in a local store because I wanted to test my build.

Everything works, offset is fine and the DCG3 sounds good. I just have to test a little bit more and decide wether I should increase the gain about 6db. Could be a little bit more of power for my DT1990 Pro.
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Originally Posted by Salas View Post
Things working good. The gain decision also goes hand in hand with your audio source's output level of course.
Quote:
Originally Posted by arnd13 View Post
My source is a soekris dam1021 using the raw output, controlled by audiozen OLED Kit. Due to the kit output ist limited to 0db. When using the soekris normal pot +10 db are possible.

I‘ll try 1.5k for R6 to get 4x gain or is 2.2k possible to get 5x gain without clipping in frontend of DCG3?
Quote:
Originally Posted by Dimdim View Post
Regarding the Soekris' analog output, you'd better plan your gain structure assuming that it outputs 1V RMS, since a bunch of the better custom filters include some volume reduction to protect against inter-sample peaks that might result in clipping.

Also, that +10db output option is practically useless since we're talking about digital gain. The resistor ladder is limited to outputting 1.4V RMS max (~1V RMS with the better filters).
Quote:
Originally Posted by Salas View Post
Your DT1990Pro will be at 120dB SPL with 3.97Vrms by the way. I just checked using 102dB/mW sensitivity and 250 Ohm impedance as claimed by Beyer. Translates to 63mW power draw by the headphone.
Quote:
Originally Posted by Salas View Post
So use gain X4 for Soekris as a source. Thus R6=1.5K.
Quote:
Originally Posted by arnd13 View Post
Changed R6 to 1.5k. Now it's perfect, there's enough headroom upwards now.
How is it going in the meantime? Did you let it rest waiting to be boxed or you clocked some further music replay time with it?
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Old 15th February 2018, 02:04 PM   #2540
Keremito is offline Keremito  United States
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Quote:
Originally Posted by Salas View Post
Those are healthy results and you also stated that after changing a dubious volume pot the bass feels normal again. This build behaves and reacts well then.
There is no basic assembly error indication. But I forgot to ask you the DC mV across R3 also. Let me know those R3 voltage drops when its handy to measure.
Hello Salas, thank you forr all the advice, the pre is sounding excellent. Goldpoint pot arrives today. We'll see how that works out.
The voltages across R3 are 1.014/1.003 Volts.
Thank you again.
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