Salas hotrodded blue DCB1 build

[KatieandDad]

I'm using 60VA 15-0-15 with Salas Shunt Reg and it runs perfectly cool.

30VA 9-0-9 also ran cool with a simple CRC filter into LM317.

My original construction was 15VA 9-0-9 with CRC.

Try them all, you'll be hard pressed to hear the difference.

 

[TheShaman]

Thank you Andrew.
The Selectronic R-Cores are a bit under-rated in terms of VAs but I too doubt they'll handle that much current.
I should have a 50VA toroid around here somewhere but perhaps it's more convenient to just drop the current. Will make heat management easier as well.

 

[oneplustwo]

What other grounding requirements are there? I need to ground the transformer shield and the earth ground from the IEC.

Are the RCAs supposed to be isolated from the chassis or do they get grounded to the chassis as well as go to the volume pot?

And grounded along with the bottom plate of course. Did you get its DC conditions measured yet? Running well?

 

[KatieandDad]

Even at HOT ROD 600mA Plus, the transformer should run cool. If you are running at an insane 600mA the 15-0-15V transformer is only running at 1A (Max) ie 30VA.

There are loads of arguments about the choice of transformer but at 30VA NOTHING should be running even vaguelly warm with a 50VA transformer. .

 

[CR500]

I'm sure this has been covered and recovered, I just can't remember.

I have to choose between a 10k and 50k pot.

Any suggestions?

Currently running a 20k motorized (cheap version of the Alps) but want to try a different one which is only offered in the two other values.

Hopefully, one of these days I'll be building a B2 (as soon as the design is available)!

Thanks!!

 

[KatieandDad]

I found 50K Log B to be the best.

 

[buzzforb]

Jfets have high input capacitance and it might be best to stay lower than 50. I know it is very wideband buffer, but Mr Miller will come knocking if not careful.

 

[KatieandDad]

For the sake of a few dollars, try 10K and 50K. Take your ears for a listening test.
Try cheap pots to prove theory and then buy expensive NOBLE or ALPS pots.

 

[Salas]

I'm sure this has been covered and recovered, I just can't remember.

I have to choose between a 10k and 50k pot.

Any suggestions?

Currently running a 20k motorized (cheap version of the Alps) but want to try a different one which is only offered in the two other values.

Hopefully, one of these days I'll be building a B2 (as soon as the design is available)!

Thanks!!

This circuit has been designed to have optimum bandwidth with up to 20K ish pots. 50K is not recommended both technically and subjectively. In case you insist, substitute the parallel input resistors from 220K to 560K.

 

[Salas]

What other grounding requirements are there? I need to ground the transformer shield and the earth ground from the IEC.

Are the RCAs supposed to be isolated from the chassis or do they get grounded to the chassis as well as go to the volume pot?

The RCAs must be isolated, they have their own ground path to the PCB. Ground the IEC's earth prong near it to chassis with a short cable.

 

[CR500]

Good point about trying the two values with less expensive pots. I'll give it a shot next week when I'm back home.

 

[Siberia]

Hello,

I can't get rid of the feeling that something is wrong with my DCB1. It seems I've been here before: lack of articulation in rhythm, weak slam and bass. It's almost like somebody would play the drums with cotton buds.

I had this some time ago, but then eagle eye Salas has spotted my amateur grounding technique and made me a happy man.

It came back three weeks ago. Then I've spotted rca grounding wire badly soldered and voila back too good again. Then I had to change rca sockets because one was damaged. Everything seemed fine, until two weeks ago something went wrong again and again.

I've been searching for the problem for two weeks to no avail. Looks like checked all connections, solderings, cables...

So i've decided to record straight a sample straight from dcb1 output to computer (audacity software). Source is Rega3 with Goldring 1012gx and Graham slee phono.

Could somebody please listen to it on their own systems or headphones to tell me if overall balance is ok?

Maybe it's not DCB1 related problem at all. Maybe it's amp, speakers or room problem...

I can provide photos and measurements if anybody have a clue where to start looking...

Here's the link to the sample:

http://wtrns.fr/rkUS4DkZ4BJOv4

 

[ClaveFremen]

I can't get rid of the feeling that something is wrong with my DCB1. It seems I've been here before: lack of articulation in rhythm, weak slam and bass. It's almost like somebody would play the drums with cotton buds.

Did you checked transformer primary wiring?

Some time ago I've had a similar problem and it was caused by a bad contact between AC power cord and transformer primary.

 

[Salas]

Is the TT spinning well? Check with strobo.

 

[Siberia]

Primary wirings seem fine. My Tx is in a separate box running quite a long cord to dcb1 one box. Maybe I should try Tx wires direct to buffer..

Salas, I don't have a strobo handy. Is there any indication it's running off speed? The problem persists with all sources, be it a cd or a pc.

 

[Salas]

Heard something like instability but if its on all sources, then it is not the TT. Just because its mechanical it could have periodic issues was my first thought as you said good sonic comes and goes out of the blue over the weeks. Get your AC wiring to DCB1 box drastically shorter first, maybe there is an issue there.

 

[Skywave-Rider]

This circuit has been designed to have optimum bandwidth with up to 20K ish pots. 50K is not recommended both technically and subjectively. In case you insist, substitute the parallel input resistors from 220K to 560K.

Can I run a 10k pot successfully? I will be experimenting with a transformer input that wants a 10kOhm load.

 

[Salas]

10K pot OK. You have a transformer coupled output source that needs see 10K load, yes?

 

[Skywave-Rider]

Salas, I am going to try transformers connected to the DCB1 inputs, and those transformers want to see a 10kOhm load on their output, which is the pot. Yes I think we understand each other. Thank you.

 

[oneplustwo]

Is there an optimized way to route the signal wires? I can either have short wires from the RCA jacks in the rear or to the pot but not both. I guess I can have an extension shaft to go from the front to the rear. Is that necessary or am I being overly anal about this?