Boss HM-2 Troubleshoot

[Arnoodles]

Hello people,

I'm working on building an HM-2 with the layout done by parasit studio, http://parasitstudio.weebly.com/vero-layouts/archives/06-2014, (it's about 2/3 of the way down the page) but I can't get any sound to come out. The only sound I get is a faint hum if I turn the amp way up, but I don't think that's out of the ordinary for the amp. I followed the veroboard layout as closely as I could but did swap out a few parts when I didn't have the right ones. The swapped parts are as follows:

Main board
Distortion pot is 100k
Q2 for a 2SC2240
Q3 for a 2SA970
C5, C9 and C10 for 100pF
D4 and D5 for 1N60

Daughterboard
C1 for 5.6nF
C7 for 1uF

The rest of the parts, all resistors, IC's, etc. are all correct. I've checked that all electrolytics are oriented correctly, as are the IC's and transistors, including the ones I substituted. I've checked for issues with the offboard wiring but that all seems to be correct with no cold solders, and I've checked the pots with an ohm-meter as well. Went ahead and checked voltages for the transistors and IC's which are as follows:

Main board
Battery: 8.74v
Ground to 9v+: 8.52v
Ground to 9v-: 0v

With Voltmeter - to ground

Q1
g 7.75v
s 8.51v
d 7.75v

Q2
c 4.09v
b 0.58v
e 0.01v

Q3
c 8.03v
b 7.51v
e 0.93v

IC1
1 4.02v
2 4.02v
3 3.99v
4 0.00v
5 0.93v
6 1.41v
7 1.44v
8 8.43v

Daughterboard

IC1
1 3.99v
2 4.00v
3 3.97v
4 0.00v
5 3.95v
6 4.00v
7 4.00v
8 8.41v

IC2
1 4.00v
2 4.00v
3 3.99v
4 0.00v
5 3.95v
6 3.99v
7 3.99v
8 8.38v

Anyone know what the problem might be? Let me know if there's anything else you need to know. Thanks.

[Arnoodles]

Anyone got any ideas?

[ubersam]

I'll give it a shot. But first, a schematic

You're Q1 voltages look off. You should see something like Vdrain = 9, Vgate = 4.5, Vsource = ~5. Check if you have the jfet in correctly. Check the datasheet for the proper pinout. For example, if you have a Fairchild BF245 (datasheet), and you follow the vero-layout as is, Q1 gate will be getting 9V instead of the input signal. The input signal is going to the drain.

[MrStab]

i'm seeing 6 op-amps in the schematic, so no unused halves of dual op-amps, and they all seem to be connected to vbias. Your readings for pins 5, 6 and 7 of IC1 don't seem to reflect vbias, so you should do what Sam said and check the connections on that op-amp, too.

[PRR]

> Q1
> g 7.75v
> s 8.51v
> d 7.75v

Wrong pinout. You actualy have Gate going to +9V, both other terminals hanging 0.6V lower (the gate diode drop).

And I would expect a little more difference between the "7.75V" pins (they have different pull-downs, 1Meg and 10K), unless there is also a short between them.

Re-re-re-check the pinout of the actual JFET you have. Some makers supply different pinouts under the same basic part-number.

TIP: with a *digital* ohm-meter, across S and D will read very low (500 Ohms) either way. The G to either S or D will read higher than that (or infinity) one way, infinity the other way. Once you know S and D, and find G by elimination, you can stick it in. You do not really have to know *which* is S or D; they are essentially interchangeable (in most audio). An S/D swap is fine, but G/D or G/S swap is no good at all.