Maestro Filter Sample and Hold

[leonhendrix]

I thought id mention it cos RG modded the neutron to use a charge pump as you have done with the FSH

leon

[soggybag]

I tried hooking two 9V batteries to the DC jack as the power supply and recorded a could of samples. This seemed get rid of most of the noise I was experiencing.

These samples are a little quiet.
sample and hold mode
http://webdevils.com/stompbox/audio/FSH-1_01.mp3
Filter mode
http://webdevils.com/stompbox/audio/FSH-1_02.mp3

There is some bleed thorugh of the LFO on the sample. it's hard to hear in this sample.

I am still having trouble getting the Up/Down sweep switch working. It works in one direction but I get no audio in the other setting.

[soggybag]

I updated the sample and hold track to better hear the background noise. You definitely here the LFO back there. It's not too bad. On some setting it is not as noticable.

[Fp-www.Tonepad.com]

Soggy,

That sounds pretty good. I can hear the click on the new updated sample. It is possible that a 0.1 or so capacitor added right on the ic's pins 8 and 4 and replacing the jumper to the left of IC3 with a 10 ohm resistor could decouple the power supply if that's the source of the click.

The other place that could be source of problem is the traces to the resonance pot, I wanted to have the pot on the edge of the board and that's why those long traces are there but they could be picking up the lfo click. That's a bit harder to fix, you'd have to cut the traces and drill new pads.

I haven't had a chance to build my own. I wonder why the 1044 is giving so much problems, could it be the current draw surge that LFOs seem to have?

Fp

[Ry]

Soggy,

Does your circuit sound different with the 1044?  It didn't make a difference when I used two batteries.

Yours sounds so much better than mine.  I need to try to reduce the bleedthrough somehow.

[soggybag]

I used two batteries but attached them with aligator clips. I attached them at the DC jack and everything seemed to work. I also tried attaching them to one of the big caps at the PS. It seemed to work there also. Though it did drain the batteries very quickly.



I have been testing with the wallwart, but I did the recording with the batteries.

I'm having problems with the up/down switch.

Right after I tested this morning it stopped working again!

I swear, I moved one wire on the up down switch, only one single wire, and I don't know what happened now when I plug in the wallwart the 1044 gets really hot? This had me so infuriated this morning!

I even put the wire back and it still didn't work again? I think I will have to do some trouble shooting...

[Fp-www.Tonepad.com]

Ry, Soggy,

I have updated the pdf to show the two DPDT switches. Check it out.

Fp

[soggybag]

Thanks for posting the updated diagram. It looks like Ihave everything wired exactly the same. It seems the down sweep is not working and the up sweep is working. I'm checking all of the component values in the imediate area...

[Fp-www.Tonepad.com]

I wish Tonda could post some info on his mods (that I have included in the pdf). I believe he compensates the circuit changes with all those resistors in order to just flick the switch and change the sweep direction, rather than also have to adjust the sensitivity (as it is with the MXR Envelope Filter). Which makes the switching a bit more complex.

Still, I think the mp3s sound very promising, I have to find the time to build this one!

And sort out the MAX1044 issues....

Fp

[Ry]

My direction switch seems to work fine, but I haven't played with it too much.  The filter on this is really kind of a bonus feature, I'm most interested in the sample and hold.

I'm about to start the process of replacing my wire leads to the switches/pots with coax to see if that helps the bleedthrough issues I'm having.

I had to put this thing down for a couple weeks because it gave me a headache to think about, but I'm back at it.

Ry

[soggybag]

I made the LFO and sample and hold sections on a breadboard and have been getting a lot of bleed through of the LFO into the noise signal. I think the LFO and might need to be on a singal opamp to isolate it.

II used a 1458 as the opamp. With the audio probe I can hear the LFO on the out of the noise amplifier. I should only be gettting noise.

The original might have used singal op amps for that reason.

[Fp-www.Tonepad.com]

Interesting. I'll think of a way to try using a single opamp.

Since you breadboarded it and it sounds the same, it's not likely to be a layout issue, but a circuit issue.

More later.

Fp

[soggybag]

I just breadboarded the LFO, noise and the sample and hold sections. I used a single +9v supply and made Vref with two 100k resisters and a 47u cap. Everything worked. I got good white noise. The LFO cycles.

But the sample and hold section didn't seem to be working correctly. I tested the noise at the op-amp output and there I see big spike with each cycle of the LFO.

I'm guessing that the LFO draws a large amount of current when it swings from one rail to the other.

I was able to smooth things out a little by adding some big filter caps. I think I change the 47u to 100u and added 1000u across the power supply.

Here's a drawing of what I built.