AMZ MOSFET Booster Problems...

[Blues_Boy_4096]

Hi!

I'm having trouble getting this to work.

When I turn it on, I only get a boosted signal in the last quarter of the sweep of the pot, and the circuit is overall noisy.

I used GGG's layout (BTW, am I looking at it the wrong way or GGG's layout has the pot wired backwards?).

Already checked the pinout of the BS170 (and even tried it backwards).
The only change I made was substituting the 62k resistor for a 68k (couldn't find a 62k).

The voltages I get from the MOSFET are:

D - 5.89 V
G - 2.69 V
S - 3.09 V

Any thoughts are welcome.

Thank you all.

[zjokka]

hi,

did you check whether the pots ok? Did you try another one? maybe you need a logarythmic (audio) pot?
noise problem: check grounding before anything else.

hope this short note might help,
zj

[Blues_Boy_4096]

did you check whether the pots ok? Did you try another one? maybe you need a logarythmic (audio) pot?

Yes I did (both). The schematic asks for a linear one...

noise problem: check grounding before anything else.

Everything seems to be well grounded (how do I check this more thoroughly?).

[zjokka]

If you would like more boost earlier on in the taper, you could use a audio pot

noise problem: check grounding before anything else.

Everything seems to be well grounded (how do I check this more thoroughly?).
[/quote]

Resistance between the point to be grounded and actual ground contact should be zero.

[Blues_Boy_4096]

Checked the grounding; seems OK.

About the pot, it's like the first 3/4 of the sweep didn't exist, it only starts working in the last 1/4 of the sweep. Cheked the pot with a multimeter and it's ok (also replaced it, just in case...)

Any more thoughts?

What do you think about my voltage readings?

Thanks

[Blues_Boy_4096]

Sorry about the bump, but does anyone have an opinion about this?

Thanks again.

[Blues_Boy_4096]

I've made all the verifications on the sticky "what to do when it doesn't work" thread...

Sorry again for the bump, but I'm getting pretty disappointed (my last two effects didn't work as supposed, and they are very simple ones: an Orange Compressor and this one...)

[geertjacobs]

Don't give up yet!
It can be frustrating, but you'll find it.
If necessary, go do something else for a while and then return with a clear head.

BTW I just noticed that the AMZ article mentions

The dc voltage measured from point A on the schematic to ground should be 4.5v to 5.5v with the circuit idling and no input. The value of R2 should be tweaked until the point A voltage is correct. If two or more of these circuits are mounted in the same enclosure, only one R1/R2 network is necessary and the R3 from each stage can be connected to the Vr point.

If I'm correct point A is the drain voltage, that is 5.89V in your measurements.

Maybe this can help?