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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 13th February 2018, 02:19 PM   #2521
beardman is offline beardman  Denmark
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Hi
just mounted the Salas supply to the preamp

it give me hum...tried my other supply no hum


voltage is ok around 17.3vdc

music is fine

i can measure more ac volt on the output of the pre,,than i have on my other supply (mv ac)

grounding same as with my other supply
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Old 13th February 2018, 02:32 PM   #2522
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Different supplies may have different PCB zero paths needing another grounding scheme. Post a picture of the build to see about wiring and grounding.
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Old 13th February 2018, 02:59 PM   #2523
beardman is offline beardman  Denmark
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problem to take picture,,no working camera

have tried different grounding,,

ground from pre to rca output

no ground from Salas supply

in same boks are supply to dac and to waveio board

tried with an without ground from supplyes no different

hum is same on both channel

is nearly the same with low and high volume
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Old 13th February 2018, 03:08 PM   #2524
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Maybe try with a mobile phone? A picture would really help. Same buzz with low and high volume hints to a ground loop has been created within the various systems in the combo box. Also measure AC mV on the PSU rails to make sure its not an oscillation either.

I also have an idea about separating the ground lane on the preamp board between channels. But it will need a cut with a hobby knife. So we better see the build and catch something incompatible with the wiring first if it exists.
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Old 13th February 2018, 03:28 PM   #2525
beardman is offline beardman  Denmark
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Hi Salas

you have right with taking a picture ---but your idea to thing in other grounding solve the problem..totally noise free

it was my Sowter trafo from output of my dac,,they were grounded to the start point..i tried to remove the wire and that help..i think the problem with them was .they are not isolated from the kabinet

thanks Salas to help me on the right track

now i am waiting for my to trafoes from Poland. so i can mount the hole thing in a fine way
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Old 13th February 2018, 03:45 PM   #2526
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Great! Problem solved just by an answer triggering a correct thinking path

Let it run with music or not for some hours just for the new capacitors to come up. Then let me know if a change happened in some meaningful way to your system between the σ22 and this?
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Old 13th February 2018, 04:11 PM   #2527
beardman is offline beardman  Denmark
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yes Salas always great with good idea

i can already now hear a difference to my AMB supply,,little to early to tell what i hear..must first give the supply some hours to play..

Keremito:::you can have right what you say about the bass from the pre with the Salas supply
it is early in the start of the supply and pre for you but i can hear that the bass (compared to my AMB supply) is so strong and not so round ,,it can sound like the bass is not there
but,,,this is some of the best bass heard in my system,,fast dry dynamik

i think you will discover that the sound settle a little down in the top when you have play some more hours on this pre
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Old 13th February 2018, 04:49 PM   #2528
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
If there is no practical error involved in Keremito's and its only down to quality of bass maybe repositioning his speakers could be also considered as a test. A standard DCG3+DCSTB build presents bass through speakers more like planar headphones do. No bloat is there in the phrasing and suddenly it can slam like a garage door startling you. I would still recommend to him good quality short coaxial wiring though because its 1MHz capable preamp and RFI could go into it when simply using CAT-5 thinning its tone out.
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Old 14th February 2018, 01:43 AM   #2529
rhythmsandy is offline rhythmsandy
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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?
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Old 14th February 2018, 03:23 AM   #2530
Keremito is offline Keremito  United States
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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
I think all is good, I removed the CAT6 wires used 18 ga shielded for the inputs, changed the volume pot to regular fit now while the Goldpoint arrives. With new cheapo pot get loud with less rotation. Old was 20k, the one in use is 50k. I ordered 25k, hopefully it will be ok.
I also put the preamp on the scope, all good consistent gain of 3 20-100 Hz.
The system is very resolving, I have 2 sources, one being a Sony HAP-Z1ES, with it some recordings are on the bright side. Plenty of detail, good sound stage. Not so good recordings just sound like that.
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