Salas hotrodded blue DCB1 build

I have now used my DCB1 for about 9 months with the 220R, 220K and 1M prp resistors and I'm still very satisfied with them, but I'm thinking of using trying some different resistors types in my DBC1. Just to see what happens :)

I have some 249R and 249K tt welwyn 0.1% RC series lying around. Is it OK to use these instead of the 220R and 220K ones or would these values do no good to the circuit?
 
Hi Andrew

I tried to use a cheap 10K smd stepped attenuator between my main amp (fetzilla) and DAC 5 and it and sounds good.
I also found out that the dac has OPA2604 and output voltage max 2v p-p (can't find other info about impedance etc).
Is there a way to measure if this dac can drive a 10k pot and my cables adequately? I can have access to an oscilloscope, if needed.
 
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25k to be on the safe side of not stressing any unknown impedance sources now or in the future.

For sources you can measure their AC output on a steady signal and then load them with a trimmer across or with various resistors 2k down and see when the signal halves. That value that halves them is their output resistance. Use pots at least 20x that value.
 
Hello all, I hope this is the right place to ask this...

I've just built a Hypnotize black with 10 Ohm resistors taking it to 200mA as my first project and really enjoyed it. I've just plugged it in for the first time and everything lit up, the readings across the PSU are 9.9v each side so I'm ready to put it in a case.

I'd like to run two sets of outputs, main and subwoofer so how would I wire the pot? Would it be two wires on each relevant leg on the pot - one to each output (i.e. parallel connections)? I read somewhere of someone using a capacitor for the sub outs but can't find it now. The sub is a powered one and the amp is a modded Quad 405-2 with 220kOhm input impedance. Thanks.
 
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diyAudio Chief Moderator
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The pot normally resides at the input side before the DCB1. You can simply wire a second set of RCA outputs after the DCB1, parallel to its main ones. Some use coupling capacitors in series to the secondary set just to have both DC thru and DC blocked coupling capability, others just use 100R in series with the secondary outputs to avoid possible interaction when driving two circuits at the same time, but its still having two DC coupled outputs unless adding a coupling capacitor in series also.
 
Thank you Salas, yes, the other point was that I needed to confirm where the pot was in the setup.

I'm guessing that a DC blocked coupling doesn't give the same sound, otherwise it would be part of the design? Of the other two options it looks like the series resistor (just 100 Ohm resistors spanning the 'hot' RCA connections for left and right?) would be the better designed solution?

And thanks for being an architect of this project, I think I'm hooked now. I just need to read up quite a bit on theory!
 
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diyAudio Chief Moderator
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Best transparency is attained when fully DC coupled. If there is no suspicion of any faulty source component either own or random one with high DC offset and/or the power stages have input capacitors or fault detection & shut down systems then there is no reason to add extra capacitor blocking along the way. You can review your source components' audio outputs with your DMM in DC mV mode to make sure there is no significant offset in any of them before configuring the system anyway. Any fault protection automation in the power stages remains useful for possible failure in the circuits during the lifetime of the system. Thanks for the appreciation and you are welcome to post us some photos of your efforts even.
 
I'll certainly pop some pictures up when I can work out how to do it. I have a funky heatsink arrangement that's worth a look if nothing else!

I don't quite get it, I should make sure there's no DC offset on the RCA outputs of my DAC? I'm guessing that whatever that reveals I need to make sure the power amp has an 'Output Voltage Offset clamp' (as it seems to be described in Quad circles) - it's some sort of speaker protection.

Regarding the DC coupling, would the resistor approach be better than two straight parallel connections to the DCB1 out?

Thanks again.