Can someone check these conversions for me?

[SDRed]

I built the Eighteen from ROG and it is getting VERY low volume.  In fact it seems to be attenuating the signal even with the volume and gain cranked.  Also with the volume and gain up I'm getting a lot of hiss/RF.  Since I'm new to this I want to make sure that I have these conversions right

http://www.runoffgroove.com/eighteen.html

4n7 = .0047 uf
10n =.01 uf
2n2 = .0022 uf

If these are right, are there any suggestions for the aforementioned volume and hiss problems?  I also had to use ceramic caps for the 2n2s, I don't know what effect this has on the sound. Thanks!

[96ecss]

I don't know about the problem you're having, but your conversions are right. Can you post some voltages, like in this thread?

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Dave

(Edited for punctuation)

[SDRed]

yeah, I'll post those voltages tomorrow with some pics, I'm about to go to bed.  Thank you

[SDRed]

Okay, I checked my voltages and they are way off what the schematic says they should be, I'm still getting a lot of noise and picking up some RF

http://www.runoffgroove.com/eighteen.html

My substitutions:

Q1 MPF 102 instead of J201
Q2 NTE 326 Instead of J201
Q3 NTE 458 Instead of J201

I also used a 10n cap instead of the 15n cap since I couldn't find one locally
For the 2n2 caps I used ceramic caps since I couldn't find film caps in that value locally
All other values are correct with the schematic and I have checked the pin outs


Here are my voltage readings from a fresh battery:
Q1

D=4.48v
S=2.34v
G=0

Q2
D=7.04v
S=6.31v
G=7.02v

Q3
D=4.55v
S=180.8 mv
G=0

Here are some pics
http://i14.photobucket.com/albums/a332/SDKing/eighteen006.jpg
http://i14.photobucket.com/albums/a332/SDKing/eighteen008.jpg
http://i14.photobucket.com/albums/a332/SDKing/eighteen010.jpg
BTW I'm going to build a chip amp of some type on the other half of the perf which is why it is so long.  Sort of mini amp eighteen

Any help would be much appreciated, Thanks!

[Jered]

  Your using a P channel J-FET for Q2, the schem calls for an N chan J-FET.
  Jered

[MartyMart]

  Your using a P channel J-FET for Q2, the schem calls for an N chan J-FET.
  Jered

Yup that's P channel device, try another MPF 102 in Q2, you'll have lower gain than J201's. aron sells bags of them here in
the store BTW 
MM

[ambulancevoice]

also, check for shorts etc, just to make sure, aspecially around the transistors

[SDRed]

Thanks for the help guys.  I'm new to this so I don't know what the difference is in J-FETs yet.  I'll just hunt down the J201s because it sounds like your opinion is that they will sound the best.  Should any NPN JFET work?

Thanks

[dschwartz]

NPN--> P channel
PNP--> N channel

Any N channel jfet with decent gain will make it work, as long as it has the same pinout as j201 (as mpf1032 has)

anyway..i strongly recommend to use j201, 2n5458 or mpf102 for this type of work...other fets have too little gain

[ambulancevoice]

pnp is n channel???

[PerroGrande]

In my experience building Eighteens, the J201 (at least the batches that I've encountered) seem to produce the best result.

Your Q1 and Q3 voltages look good.  Get yourself a J201 for Q2 and set the bias potentiometer for it to run at around 6.8v. 

[SDRed]

okay,
I've got some new JFETs in and I'm getting great volume. I'm able to get some really nice tones with this now, but the radio frequency is still a problem.  Not as bad as it was, but still a problem.  Any suggestions on where to go from here?

Thanks

[MartyMart]

You can try a couple of things :
First, try to tune out the hiss/hash with the trimmers, so you're settting by "ear" for a decent tone, no gating
and perhaps less hiss, you don't HAVE to aim for the magic 4.5v, can be 4 to 5.5v drains for Q1/Q3
You'll be amazed how just one mm of turn can change the setup .....
Try a small pf value cap to ground at input, perhaps 120pf or so and add a resistor BEFORE the very first 1M resistor
value 10k to 33k or so.
Your RF and hiss will improve

MM.

[alfafalfa]

+ 1

Try a small pf value cap to ground at input, perhaps 120pf or so and add a resistor BEFORE the very first 1M resistor value 10k to 33k or so.
Your RF and hiss will improve

Especially RF problems can be cured with this solution !!

Alf

[GibsonGM]

I'm not sure if you have the board in an enclosure yet, but a properly shielded/grounded enclosure does wonders for blocking RF coming into your effects!  I pick up tons of radio stuff when I have things on breadboard or testing a PCB "in the open".  It goes away back in the box.   And the small pF cap to ground at input would help, too...

[SDRed]

All right, thanks everyone, I know what my next steps are now.

[SDRed]

You can try a couple of things :
First, try to tune out the hiss/hash with the trimmers, so you're settting by "ear" for a decent tone, no gating
and perhaps less hiss, you don't HAVE to aim for the magic 4.5v, can be 4 to 5.5v drains for Q1/Q3
You'll be amazed how just one mm of turn can change the setup .....
Try a small pf value cap to ground at input, perhaps 120pf or so and add a resistor BEFORE the very first 1M resistor
value 10k to 33k or so.
Your RF and hiss will improve

MM.

Marty, your suggestions did the trick.  It's up and working great, Thanks.  And thank you everyone else who gave input as well.

[rackham]

Obviously you've got things sorted now but I thought this might help anyone who (like me) occasionally struggles with converting cap values ...

http://www.translatorscafe.com/cafe/units-converter/electrostatic-capacitance/calculator/picofarad-%5BpF%5D-to-nanofarad-%5BnF%5D/

This one can certainly help sometimes too:

http://www.avishowtech.com/mbhp/res.html

[MartyMart]

Hey that's great - very pleased to help and ..... guess what ? That help came from me being right here
and learning stuff at this forum
Great place isn't it ?
Marty.