Salas hotrodded blue DCB1 build

Hi
I bought a complete Hypnotize kit. Can’t find a build thread on that so hopefully its ok to ask here?
The shunt resistors in the kit is 4pcs 10ohm/3,75W and 2pcs 2,7ohm/3,75W. My transformer is going to be 60VA and diodes are MUR860.
I want to hotrod to 600mA which seems to be a good option (or)?!

How should I combine these resistors? Someone who made to parts kit must have had an idea. The board print suggests 10/5W.

Thanks
 
Asked in wrong thread and got this answer from Salas:

Hypnotize is there: Salas hotrodded blue DCB1 build

Those set resistors are probably for three scales*
Ask any further questions about it in that thread


*Single 10R, double paralleled 10R, single 2R7 for ~150-300-500mA



Is 3,75W really enough for all options?
/Thanks
 
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They should cope well. Keep them bit proud on their legs, not touching the board with their body. Watch the bridge diodes temperature also if you will decide highest running current. They are located on board edge to can be sinked if need arises. Middle scale constant current setting around 300mA is a good compromise between dissipation and subjectivity by the way.
 
Thanks for your answer!
I’ll go for parallel 10ohm which should give a lot of power margin for those resistors.

Next issue is the diode pads and print picture which differs. In another thread I found that the picture symbol (round/flat) was correct, not the pad (square/round). Can someone please clarify?
 
Got one board up and running. Sound is crystal clear and has a nice punch and dynamics!
For my second board there were no diodes. So looking for 16pcs of red ones on Mouser.

One BOM:s I found show "LED" 593-VAOL-3HCE4 (Mouser) which is yellow!
The other BOM says "Green LED" and still directs the same Mouser part no!

As I understand the red ones initially used had very tight forward voltage tolerance. Can someone please recommend which red leds that is most suitable?
Nice to have the same glow in both buffers:)
 
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Thanks for the suggestion.
Will the 2V compared to recommended 1,8V cause any issues?

They are 1.8V at 5mA. But the JFETs at their tail can vary per sample for IDSS current they will force through. No issues if they will give 1.9V each with stronger JFETs. Will be producing bit stronger rails overall. But still within the design's target range.
 

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I'd like to build stereo to mono for my subwoofer using dcb1, is there any special arrangement required? basic summing design just using 2 resistor doesn't seem elegant for me

my requirement will be : dcb1 : regular stereo + mono just like 2.1 output

i have no issue with multiple buffer, alot of jfet in my drawer available
 
Hi Salas,

I have a question regarding the signal Jfet followers. I understand the concept of using two matched 2SK170Jfets with the lower self biased to produce a near zero DC offset. However, I have seen similar configurations that include equal value source resistors for each Jfet as high as 1k. When should one use source resistors and when not in a follower circuit? Puzzled.

Thank you.
nash
 
For degeneration purposes to bring down IDSS either for lowering dissipation and/or matching Id easier for a wider range of JFET samples. To tune THD also, at least when with a specific load value in mind.


Just to further my understanding suppose in the case of the DCB1 I add two 500r resistors one at each Jfet source, I still get near zero DC offset, the Id is lowered so the Jfets run cooler, so whats the advantage here of running them at Idss?
Also, if I do not have closely matched Jfets, say Idss7ma for the follower and 7.5ma for the source I could degenerate the 7.5 to still get zero DC offset. Will this create a different THD profile as opposed to using two 7ma matched? Or is this an acceptable approach?
Thanks. nash
 
diyAudio Chief Moderator
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Running them at IDSS ensures max available current drive to the load and max transconductance. When you got the matched pair why compromise. See an example not with 0R vs 500R, which would be extreme, but with 0R vs 100R on 8mA IDSS K170s. Resulting to 18dB worse 2ndH at 2.5kHz 0dBFS CD output level on a 20kΩ input amp and some cable capacitance for the 100R degenerated version.

You could use small equalizing resistors for offset with a small hit in performance. Natural IDSS matching is best.
 

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Salas,
I went ahead and actually tested them with and without source degeneration and I was surprised by how much higher the distortion was with vs without. Just as you said it would be.

Since these serve as followers only, should the two Jfet pairs for L and R channels also be matched, meaning if one pair is say 10ma idss is it OK for the other pair to be 6ma?
Thanks. nash
 
diyAudio Chief Moderator
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Its not crucial to have exactly same idss pairs in channels. They can be say 9mA in L and 8mA in R. But if much different, THD measurements will noticeably change between channels. Especially at high signal levels.

There is yfs vs id chart in the Jfet datasheets. You want id pairs at a range where yfs is still comparable for use in the channels.