FSH-1 Tonepad some problems solved

[soggybag]

I built this a while back and have come back trying to solve some problems. Here are a couple observations. Should be good info for the novices and a good laugh for the pros.

I had some trouble with noise in the sample and hold mode. Today I was playing around and realized that I was still hearing the Sample and Hold effet even when the noise transistor was removed. After looking at the schematic for a while I realized the noise transistor is tied through a 100k resistor to the +9v unfiltered supply! Of course I'm using a cheap wallwart from RS as my power source...

This thing has a wicked saw tooth. I measured it once with the scope.

So I hook up a battery and all of a sudden the noise drops considerably. I'm also getting much better randomness from the noise section.

So the whole time I was not getting noise from the transistor. Instead the sample and hold is reading the saw tooth coming off the power supply and sampling it.

With the battery I still get a little tick but it's not as bad as before.

I'm not sure what to do. Either build a filter and regulator on another board. Or build a regulated PS?

I'm still having problems with the sweep direction. It works going high to low, down mode. But I get no sound in the other mode.

I'd also like to make the trigger on the filter mode a little more sensitive. As it is I need to hit notes pretty hard to trigger the filter. Any suggestions?

[stobiepole]

I had a similar experience. The S&H was weak, until I realised had the noise transistor backwards. The other symptoms sound like build problems. And boxing should get rid of all of the ticking...but maybe it's time for a better power supply.

Chris

[Fp-www.Tonepad.com]

You realize you need a better power supply when you run into these issues.

[soggybag]

A friend gave me an an old bench testing power supply. But it doesn't that have the little jack on the end and I was too lazy to get out the alligator clips. The wall wart seems to work with other stuff though I'll hear a hum at times. The idea that the sample and hold was sampling the wave form from the PS caught me off guard! Of course it made a lot sense after I figured it. It also answered the question of why the randomness of the sample and hold didn't seem as varied as I thought it should sound. The real clincher was when I removed the noise transistor and still heard the sample and hold! I thought, whoa, there's something funny going on here.

[Paul Perry (Frostwave)]

That 100K resistor, you could try a 10K between the 100K and the + rail and put say 100 microfarad electro from the junction of the 10K & 100K to the - rail.
Worth a shot, possibly.
I might add, this is a classic case where trying a circuit on a couple of batteries might have given an earlier indication of the problem.. yeah, easy for me to say.. I usually reach for the batteries FAR too late myself

[MissionBrown]

I've got the ticking problem too.
But I've got a solution.
Make sure the Output socket and the resonance pot are far away from the speed pot and the diode next to it.
Of course you could make a sub board up with the LFO section and move that away from the board, but thats a bit more painful.
Sadly I've now got one nice enclosure with lots of holes in it...
Ahh well I'll pop some krazy bit of crap in it I guess.
Nothing like recycling eh?

P.S. Hi Mr Perry.
My modded resonator is the business!
Cheers
A

[gigimarga]

Hello,

Please help me: post the voltages of Tonepad's FSH-1...i've built one and it don't work anyway!

Thx a lot!

[gigimarga]

 

[MissionBrown]

Hello,

Please help me: post the voltages of Tonepad's FSH-1...i've built one and it don't work anyway!

Thx a lot!

Run's on 9v for me.
Make sure you're using a regulated power supply as the MAX1044 will burn out if over 10v.
Also make sure your pot values/taper are the same as the board as well as double check your switch wiring.
One point I had trouble with was the diodes I used had a very low forward conducting value.
It also wont wah if the diodes are in backward.