Salas hotrodded blue DCB1 build

very nice rodeo dave!!

The power resistors I used are non-inductive planar 10R 5w thick film resistors (BI Technologies BPC5100J).
I was looking at these as the spec is rather interesting and they look really cool, but for now i'm going with 7r5 mills 5w PCX are taking ages to get their **** together with my order, guess this sale has them run off their feet.
 
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Thanks qusp! These resistors really seem to be quite nice. They sink the heat nicely and look swell. They come across pretty brittle though, being deposited on a ceramics plate and all. I'll be very likely using them in future projects again. I wonder how they'd perform directly in the signal path.

Meanwhile I made a quick PSU for the DCB1. It's simply a metal box housing the transformer, a fuse and a thermistor, plus an X2 cap. The transformer is a traditional E-I type with two secondaries with several taps (0-10-12-15V, twice). It's rated 25VA (0.8A per 15V winding) and, if you believe the stamp on it's bottom, was made on August 23rd 1982.
It's dead quiet, gets slightly warm and I have several of them, which is good since I plan on making several DCB1 buffers.

The problem with the oscillating relay apparently was solved by a 470nF cap between C and B (pin 1 and 2) of the BC547 that I am using instead of the BC517. I can't see the relay doing any funny stuff on my scope anymore, and neither anything audibly strange during power-up happens when the buffer is hooked up to my amp.

And since I'm using the DCB1 purely as a buffer without a volume control I paralleled the 221k resistors with 20k underneath the board to get the input impedance within the desirable range.
The orange blob you can see in the picture of the underside of the pcb is a 100nF cap at the output of the 7812 (and it has been there before the final mods so it's not related to the relay stopping to oscillate).
Oh, and for interconnects I'm using RG316/U if someone wants to know.
 

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The capacitor was the patch before the BC517 was deemed best and made the first BOM. It does the same job on any account. No need to get the Darlington any more if its not easily accessible. Looking like the PSU coming together well in a box. What will be the application? Active crossover?
 
yeah I need to do the same thing with mine WRT the inputZ, as i'm also just using it as buffer as I run digital volume on my dac. i'll probably end up with TX220Z for the 7.5-10R and TX2575 for the 221K/R, but mills and PRP are as far as I go before finding the best current and deciding if I like this in the chain. got some conrad sinks on order for my balanced build
 
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Damn I should have checked that first - I'll email the seller.

I have just asked Spencer for some matched 2SK170BLs for the DCB1. He said he can provide them matched to within 0.2mA idss. Is this tight enough matching for this project?

Thanks,

- John

That's pretty good for a quad I guess. It's not going to kill anything to have DC offset <10mv IMO. Better matched better sonically.