Amp Camp Pre+Headphone Amp - ACP+

[pinkfloyd4ever]

A couple more questions: I've put Vishay-Dale CMF resistors in my Mouser cart for all the 1/2w resistors, except R12 and R13. It seems those values (2.2R and 6.8R) aren't available in the CMF series, nor in the RN series.

Any suggestions as a replacement? I see some Panasonic ERX series are available in 2.2R and 6.8R, but they're 1W and probably won't fit the board lying flat. They would match the ERXs I have picked out for the 3W resistors though. Rrrr, sometimes I wish I wasn't so OCD

Any reason not to parallel a couple of CMF50s to get close to 2.2R and 6.8R ?

Next, does the brand/variation of the Optocoupler matter? I'm seeing variance between the different options in If(Forward Current) Isolation Voltage (3550V, 5000V, 7500V - probably doesn't matter?) and Power Dissipation (70, 150, 250 & 350mW).

If it makes any difference, I'm planning on building with the thru-hole PCB as sold in the DIYAudio store.

Thanks,
Kevin

 

[pinkfloyd4ever]

Ok, another: I assume C5 is a ceramic cap, right? Does the dielectric type or any other specs matter? Anyone have a favorite brand/series of this type of cap to help me narrow down my options? Preferably one that's available on Mouser.

 

[pfarrell]

I have the same question. I've seen it asked a couple times on this thread, but haven't seen an answer yet.

During our project we followed the matching instructions here for the J113s:
JFET matching information – diyAudio Store

And picked up a matched quad of LSJ74s from the store.

Wasn't really prepared for the J113 matching and only ordered 2! They were a match . All said, we still used 125R R4s per Nelson's guide. Wasn't simple (to me) to verify the 10mA noted on the schematic

Right or wrong with any of it, we ended up with a build that measured correctly, based on NP's paper and instructions, at points DC1.

(And thanks to you fine peeps that enjoyed the father daughter time build and commented as such!)

It's a great sounding pre. We recently used it outside, naked style, for outdoor movies in front of Mark's Cordell gainclone. Super good! And LOUD!

 

[codyt]

Ok, another: I assume C5 is a ceramic cap, right? Does the dielectric type or any other specs matter? Anyone have a favorite brand/series of this type of cap to help me narrow down my options? Preferably one that's available on Mouser.

I think Murata or TDK would be fine. Probably anything really. Might be able to find polypropylene.

As for the alternate resistors, I’d look for Vishay/Beyschlag 0207 types.

Edit: Check out Wima FKP2O100331D00KSSD for the 33pf cap

 

[pinkfloyd4ever]

Does anyone have the lead spacing data for the caps on the standard version of the ACP+ board (the one sold in the DIY Audio store)?

 

[ipolyakov]

All capacitors have 5 mm except C1. C1 has ~3.5 mm.

 

[pfarrell]

We weren't able to find the "gold" caps in the right spacing—out of stock most places at the time—picked up some that were 7mm and bent the legs under and in. They sit flush to the PCB due to the insulation pad on the bottom. FWIW. Worked great.

Also—here's a PN for a PC mount power switch (Mouser: 612-100-A1421):
https://www.mouser.com/ProductDetai...bEwqjve6twN2uKtQlAFlb9yVBMH77SOq3/zpvKuZcEg==

 

[nr12]

Wasn't really prepared for the J113 matching and only ordered 2! They were a match . All said, we still used 125R R4s per Nelson's guide. Wasn't simple (to me) to verify the 10mA noted on the schematic

How did you verify those 10 mA? I have a bunch of J113 and want to do the same.

 

[pfarrell]

Couldn't "verify" the 10mA, my understanding is that to actually take that measurement you need to lift an R4 leg while in circuit. Based on the link above I posted with instructions for testing Jfets—it indicates that 1V = 10mA, while that might be accurate, I understand it's different in circuit—maybe someone who knows more can weigh in with details. Our J113s measured 1.68 and 1.66VDC under the test conditions in the instructions.

 

[Dennis Hui]

You can verify the current in circuit by measuring the voltage drop across the 125 ohm
resistor R4.

 

[nr12]

Thank you. Got it.


Next question: Is it possible to measure it before inserting into the circuit?
The range of J113 Idss is quite wide..


Building this little circuit on a breadboard, will this be ok when I measure 10 ma here? Here I can choose the FET or resistor as i like without damaging the PCB...


Thanks,


Ulf

 

[nicoch58]

the simple

 

[nr12]

Ok, thanks, I know that circuit.
I don't want to measure Idss, but the current that I can expect from that current source, when inserted into the ACP+ circuit.


Ulf

 

[Dennis Hui]

Ulf,

The circuit you drew in #491 will work. Just stick V+ at 12V and
select a pair of j113 where the voltages across the 125 ohm resistor
are close to 1.25V and you're done.

 

[pinkfloyd4ever]

If, like me, you still don't have a breadboard or lab PS, is there anything wrong with dialing in 10mA thru R4 by temporarily using a trimpot in place of the R4 resistor, then replacing the trimpot with a standard fixed resistor once the ideal value of R4 is determined?

 

[nr12]

Thanks for your answers.

This works out fine for me. I have a lab power supply, 5.5 digit multimeter and breadboards.
And I had a nice time matching J113 to resistors.

All the best,

Ulf

 

[2 picoDumbs]

If, like me, you still don't have a breadboard or lab PS, is there anything wrong with dialing in 10mA thru R4 by temporarily using a trimpot in place of the R4 resistor, then replacing the trimpot with a standard fixed resistor once the ideal value of R4 is determined?

That is a very appropriate thing to do.

 

[WKCox]

Any downside or compromise in using a 50K ohm pot instead of a 20K? The 20K that I ordered seems to be lost in transit, while I have a good 50K sitting here on my bench.

 

[6L6]

No problem at all.

 

[WKCox]

Thanks Jim! Just testing and sorting J113s so should have this up and running shortly.