DCB1 Build

[reubensm]

Sachin, that cab looks very nice. Does FM Raghu do the faceplate printing as well?

 

[sachu888]

Sachin, that cab looks very nice. Does FM Raghu do the faceplate printing as well?

I think he has done it for his DIY ST-70 amp.

Regards
Sachin

 

[omishra]

Next just take care - if we are going to use max voltage something like 12V-14V output then 12-0-12 transformer will suffice.

 

[anilva]

Actually it should be create problem. I analysed this. When we do cold start of preamp, all caps start charging and PS output voltage increase. It stabilizes at regulated level. During this time, JFETs pairs in each channel see increasing dual voltage across it but conduct similarly. So not output offset change at DCB1 unless input influences anything.

But delayed relay like switch could be good idea.

I have seen a small hand drawn circuit by Salas in his Hot Rodded DCB1 for the output delay circuit using a small relay. Om would you have a proper circuit for this?

Cheers.

 

[anilva]

Found this:

 

[mbhangui]

Experts a question for you. Is it feasible to put a fuse in series with the speaker to protect against dc?

power = V x I = IR x I = I x I x R (can't figure out how to put I raised to the power of 2). Hence I = sqrt(wattage/impedance)

e.g. for 100 W 8 ohms speaker
max current = sqrt(100/8) = 3.53 amps

So a fuse of 3 A could protect against a potential DIY mishap?

 

[omishra]

Do you think fuse will blow instantly before voice coil? I don't think so. I suggest - Either do proper cutoff circuit using relay or keep as is.

 

[jls001]

A resistor will limit current rush but can't prevent DC voltage from passing through it. So it's not a feasible plan.

 

[sunilj]

Joshua suggested the idea of the DPDT toggle switch for source switching. Just wondering if there would be a 'pop' when switching sources. Does the wiring need to ' make-before-break ' to avoid that ? How is that done ?

Also does a 3PDT work the same way, but with three sources ?

 

[jls001]

Joshua suggested the idea of the DPDT toggle switch for source switching. Just wondering if there would be a 'pop' when switching sources. Does the wiring need to ' make-before-break ' to avoid that ? How is that done ?

Also does a 3PDT work the same way, but with three sources ?

The DPDT switch which I use does not pop when toggling between the two sources, even on the rare occasions when I forgot to keep volume knob to zero before operating the switch.

Not sure if 3PDT will work in switching three sources. I think it is better to use relay based input selector circuitry when one needs more sources. Check out theaudiocrafts website. They have nice ready made kits for not much outlay.

 

[omishra]

It won't pop because you are not detaching ground level, only switching live wires.

 

[Hari Iyer]

Better to use a relay based switching if click & pop is an issue. Its very easy to implement too.

 

[sunilj]

Thanks for all the replies. I have a relay kit but want to avoid the additional PS for the relays, and, the real estate it will require in the cabinet.

So with the DPDT, can we implement some sort of LED indicator on the front panel ?

 

[sachu888]

Relay based input selector designed by FM Quad works very well. Many of us using it without any issue. DPDT is perfect for two inputs.

Regards
Sachin

 

[Hari Iyer]

Thanks for all the replies. I have a relay kit but want to avoid the additional PS for the relays, and, the real estate it will require in the cabinet.

So with the DPDT, can we implement some sort of LED indicator on the front panel ?

with the relay based switching you can incorporate the LEDs for indication too.

 

[jls001]

with the relay based switching you can incorporate the LEDs for indication too.

That's right!

DPDT is a barebones (and purist) way of doing things but hardly the best. I do miss having a third and fourth input on the DCB1 so sometime soon I will fit the relay based input selector.

 

[omishra]

Also relays are vacuum sealed silver contacts, contamination free low resistance contact. Open switches may clog or get contacts dirty. There after oxidized switch contact can produce undesired sound artifacts. That is why I prefer low voltage operated relays.

 

[Hari Iyer]

That's right!

DPDT is a barebones (and purist) way of doing things but hardly the best. I do miss having a third and fourth input on the DCB1 so sometime soon I will fit the relay based input selector.

I had a ckt drawn in one of my notes book some years ago for time pass. Let me see if i can find the sketch and post it here later.

 

[anilva]

I have posted a circuit in one of my posts in this thread. It is in lower left of the diagram. Please check.

 

[sunilj]

Hari, is your circuit for implementing the LED with the DPDT switch ?

Anil, are you referring to the 'Time delay ' muting circuit ? The image does not enlarge for me and is too small to read as-is. Could you please post a bigger pic ?