Z.Vex SHO (souper douper) BS170 troubleshooting

[Gebrey]

Hallo everyone,
Here Gebrey
Im an expert of diy and electronic diy and Ive succesfully made more than 30 effects and some amps.

Whats going on with SHO??
Maybe my chinese supplier gave me fake BS170? Maybe almost all SHO schemes are wrong?

The problem is... volume. It seems that voltage supplied is too less even at 15V.
I barely hear something ONLY if I push 2 Tubescreamer is series into SHO (forced FET by large input voltage signal)

Ive made 5 times this circuit and every time this happens:
- no volume (until I push some OD in it)
- real volume came only for a fraction od time when I rotate pot (B5K)

If I made the 2N7000 version (1M instead of 10M resistors) it works perfectly.

Im aware that there are 2 pinout for BS170: CLASSIC DGS and NEW DSG

Voltages @15V are
CLASSIC DGS
POT 0%
D 0.63
G 0.20
S 0

POT 100%
D 8.12
G 7.90
S 7.52

NEW DSG
POT 0%
D 10.00
G 9.40
S 0.0

POT 100%
D 12.66
G 12.06
S 2.67


It is a nightmare guys. Ive made effects that are way more complicated.
I think my chinese BS170 are defective.
Or maybe 10M are working only with selected trannies and so I should lower it to 1M?

Help please

[mauman]

I've made many variations of the SHO and never had any trouble with the available schematics. I think your suspicion about bad BS170s may be correct. You should be able to substitute different values for the 10M and just about every resistor and cap, and it should still work.

[Gebrey]

The 2N7000 version works very well and has @15V
CLASSIC DGS
POT 0%
D 4.05
G 5.46
S 0.0

POT 70% (@100% saturates amp)
D 0.94
G 2.78
S 5.64

[Gebrey]

I've made many variations of the SHO and never had any trouble with the available schematics. I think your suspicion about bad BS170s may be correct. You should be able to substitute different values for the 10M and just about every resistor and cap, and it should still work.

wGPlbB4AqI1cQAAAABJRU5ErkJggg==.png (7.46 KiB) Viewed 702 times

Ive tried both configuration and I think mine are old Pinout and defective since when I use new pinout sound pass since I put signal in source and it come out from drain but obv no amplification occurs (sounds is a bit broken).

I will order premium BS170 soon and I will update this sad experience.

I never use gloves when I work with trannies and maybe I fried a set of 20 just putting my fingers in to pick a tranny... possible? Ive hears that Mosfet are very sensitive but 2N7000 I treated equal and every one work properly.

Thanks for support

[mauman]

I never use gloves when I work with trannies and maybe I fried a set of 20 just putting my fingers in to pick a tranny... possible? Ive hears that Mosfet are very sensitive but 2N7000 I treated equal and every one work properly.

There's a thread about that here: https://www.diystompboxes.com/smfforum/ ... c=110109.0

I use a static mat, wrist strap and static bag storage for all IC's and FETS. I don't worry about BJTs.

[Gebrey]

You rock. Ive made a static wrist with simple taking earth from a socket and wrapping copper round my wrist. But since Ive never had issues Ive never used it.

Thanks for support and infos.

Have a nice day

[mauman]

Ive made a static wrist with simple taking earth from a socket and wrapping copper round my wrist. But since Ive never had issues Ive never used it.

With a DIY static wrist strap, PLEASE put a 1 meg resistor in series between your body and ground! That's how the commercial ones are made. Without a resistor, if you touch live DC or (even worse) AC, you're giving it an excellent path, through you, to ground.

[george giblet]

As you mentioned, there's two types of pinout for the BS170. Who knows what pinout the Chinese units use.
The odd one is the Zetex pinout, which matches the 2N7000 pinout, the technicality is this
part is marked with a P suffix.

mosfet pinouts.png (4.56 KiB) Viewed 516 times

Having a closer look at your numbers. The "CLASSIC DGS" configuration looks like it is working but the voltages imply the MOSFET's Vgs_on voltage is very low like 0.3V to 0.4V instead of being about 2V; ignoring any leakage. It might be worth trying 2x1M gate resistors to see if it does anything to the voltages.

A work around would be to leave the feedback resistor at 10M and reduce the gate to ground resistor. Another workaround is adding a resistor across the gate and source. See which method is closer to the 2N7000 for min/max pot setting.

Some SHO builds oscillate. There's some fixes around for this. Cap across the gate to ground, small value resistor in series with the source (located at the source end of the wire). Your problem is more fundamental.

FWIW, since your 2N7000 is marked as "CLASSIC DGS" I can only assume your Chinese BS170's follow the same - so it's the Zetex BS170P pinout

[george giblet]

The 2N7000 version works very well and has @15V
CLASSIC DGS
POT 0%
D 4.05
G 5.46
S 0.0

POT 70% (@100% saturates amp)
D 0.94
G 2.78
S 5.64

There's something wrong with your "good" voltages.
POT 0%: gate 5V is very high and unlikely.
POT100%: drain voltage is less than the source voltage - that can't happen if everything is working normally.

Also I'm not sure if you used 2x1M on the good 2N7000 version or 1x1M and 1x10M.

[Gebrey]

Thanks for support.
Ive used both 1M/1M and 10M/10M circuit for BS170 and 1M/1M for 2N7000.

2n7000 works very well, especially if you connect it to a clean high headroom amp. It will distort just after 3/4 of the B5K pot (rev is comin).

My 2N7000 is standard pinout (180° rotated compared to CLASSIC DGS BS170).

As you stated, the BS170 pinout seems the classic but voltages are odd. That could be caused by defective MOSFETs, am I right? I'll try to put a BS170 on 2N7000 config.

Thanks for 1M on wrist advice. I just thought that if I touch sink metal the resistance would be almost 0 ohm so I made a similar circuit. Now that you say that, I will put 1M ASAP. Again, thanks.

[Gebrey]

Ive made a static wrist with simple taking earth from a socket and wrapping copper round my wrist. But since Ive never had issues Ive never used it.

With a DIY static wrist strap, PLEASE put a 1 meg resistor in series between your body and ground! That's how the commercial ones are made. Without a resistor, if you touch live DC or (even worse) AC, you're giving it an excellent path, through you, to ground.

Also, Ive grounded my bench frame to EARTH from a 230VAC socket. Should I put also here a 1M resistor?

[mauman]

Also, Ive grounded my bench frame to EARTH from a 230VAC socket. Should I put also here a 1M resistor?

Yes, for your safety, that's how the commercial ones are made.