Salas DCG3 preamp (line & headphone)

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Salas

Salas

diyAudio Chief Moderator
Joined 2002
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Jim50hertz said:
Salas, just read of the BC327-40 mod. How many should I buy to sort through? Datasheet suggests an average hfe of 400, max 630, making a need for around 500 hfe on the upper end of specs.

Also, I’ve searched and can’t find the answer but, if I drop the gain to 2, how do I do it (r6?) and will it compromise the sound of my unit, which I’ve been very happy with.

I’m building the Pass DIY VFet amp and will be running 99db drivers in a TQWT so the gain in the DCG3 may be too much.
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You do it with choosing R6=499R. Or 2x1k in piggyback parallel if handier.

I know two people with 2X setting personally. One has 102dB horn speakers the other one has 82dB ribbon speakers. First one says 3X was a tad better although he had to cut on preamp gain. Second one says 2X is a tad better although he had to increase his power amp gain. Go figure.

Trust your own ears in the context of your own system. Tech answer is 2X uses 3.5dB more negative feedback than the 3X setting. Also, system noise is 3.5dB lower for 2X.

About BC327-40 get 20 pieces to choose from maybe. Not crucial to pick them absolutely same hfe. +/- 20 is fine. 400+ hfe level is still very good. Not mandatory to hit 500 or something.
 
R

r_jik45

Member
Joined 2005
66deg said:
Thanks, I had a read over the guide earlier today and spotted the very same mistake, appreciate you mentioning it though as I have on occasion missed things just like that.:)
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Guides are well done. Thanks again for that.

Also had to read them several times to stickly follow the procedure, because builds are/were done over several days, weeks and even more.
 
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r_jik45

Member
Joined 2005
Salas said:
Use two coaxial cables. Common their screens at the Select board's output GND pad only. Connect their other screen ends separately to each GND pad near to each DCG3 channel's signal input pad.
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I suppose that the same has to be done for the headphone-jack (R+L+GND, 3 wires): common the screens at the headphone-jack only and connect the other screen ends separately to each GND pad near to each DCG3 channel's signal output (HP) pad :eek:
 
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r_jik45

Member
Joined 2005
Populated and tested DCSTB+DCG3.
After about 15mn heatsinks become a bit warm for both DCSTB and DCG3. The voltages across R10s (7.5R) are 1.056 and 1.060V, indicating around 140mA.
amp1.jpg
Don't ask why the wires are so long. Just to test.
 
337alant

337alant

Member
Joined 2008
Thanks everyone I like the Neutrik Socket so I have ordered one of these
NJ3FP6C | Neutrik

Stixx said:
I've used this one successfully in the past.

BKL Electronic Kreimendahl | Klinkeneinbaubuchse 6,3mm Stereo, Einlochmontage, langes Gewinde

Question is... will you find it in your area?
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Thanks , also looks good, Switchcraft do something very similar so I have ordered one of them as well
152B | Switchcraft 6.35 mm Panel Mount Stereo Jack Jack Socket, 3Pole | RS Components
Alan
 
337alant

337alant

Member
Joined 2008
OK so here are the options for the front panel !
large push button On / Off switch or small ?
Large Neutric Headphone Jack or small Switchcraft one ?
My preference is for the large for both :cool:

The on / off switch and Headpnone socket will be mounted to the right and left of the selector switch and Vol control.
The small hole in the centre of the front panel will have a single red LED from the Pre amp board.
Either side of that there will be 3 green LEDs which will show which source is selected from the switch

IMG_3012 by Alan Towell, on Flickr
Alan
 
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