Memory Toy Trimpots Information

[JRM]

Hi,

I bought a Memory Toy on ebay and opened it for inspection and possible fine tuning (it did'nt oscilate as expected when one max the feedback knob).

There's not much information regarding this particular circuit, so I thought it could help someone if I'd spread some info. By what I saw on the Memory Man schematic, on BL3208 datasheets and making some measurement with my multimeter I've found out that for Revision D of the Memory Toy PCB we have:

4 bias trimpots, one for each BBD chip, trimpots marked with numbers 1, 2, 3 and 5
1 modulation depth control trimpot, marked "MOD DEPTH"
1 Balance adjustment trimpot, marked with number 6, placed at the output of the last BBD
1 feedback loop gain adjustment trim, marked with number 4
1 unity gain adjustment trimpot (Trimpot #7), placed on the main board

Yesterday I've played a little bit with the #4 and found out that finding a sweet spot wasn't easy  I've measured the bastard and found out that a slight turn made a huge change in the resistance value (0-20k). I'll do some more experimentation tonight.

[Mark Hammer]

Yesterday I've played a little bit with the #4 and found out that finding a sweet spot wasn't easy  I've measured the bastard and found out that a slight turn made a huge change in the resistance value (0-20k). I'll do some more experimentation tonight.

This is why 10-turn trimpots exist.  Whether it is possible to retrofit one in there is something I leave up to you.

[GGBB]

Hi,

I bought a Memory Toy on ebay and opened it for inspection and possible fine tuning (it did'nt oscilate as expected when one max the feedback knob).

There's not much information regarding this particular circuit, so I thought it could help someone if I'd spread some info. By what I saw on the Memory Man schematic, on BL3208 datasheets and making some measurement with my multimeter I've found out that for Revision D of the Memory Toy PCB we have:

4 bias trimpots, one for each BBD chip, trimpots marked with numbers 1, 2, 3 and 5
1 modulation depth control trimpot, marked "MOD DEPTH"
1 Balance adjustment trimpot, marked with number 6, placed at the output of the last BBD
1 feedback loop gain adjustment trim, marked with number 4
1 unity gain adjustment trimpot (Trimpot #7), placed on the main board

Yesterday I've played a little bit with the #4 and found out that finding a sweet spot wasn't easy  I've measured the bastard and found out that a slight turn made a huge change in the resistance value (0-20k). I'll do some more experimentation tonight.

I don't know what revision mine is, but I know I don't have #7 since I had to hack it to fix the level issues.  Can you tell what value trimpot is used there?

[JRM]

Yesterday I've played a little bit with the #4 and found out that finding a sweet spot wasn't easy  I've measured the bastard and found out that a slight turn made a huge change in the resistance value (0-20k). I'll do some more experimentation tonight.

This is why 10-turn trimpots exist.  Whether it is possible to retrofit one in there is something I leave up to you.

Retrofiting anything in this crouded smd components PCB is a nightmare. I'll see what I can do before advancing to replace the trimpot as I'm also afraid to damage the board and loose a cool effect.

GGBB: I'll check that tonight and I'll post it with some more details and maybe a picture or two.

[JRM]

Playing a little bit with trimpot #4 allowed me to control the feedback and oscillation quite well. The initial problem was that the trimpot was at the end of scale and any small deviation would make it change from 0 to its full value (20k). Set it first to the middle (10k) and then fine tuned it to taste (oscilation starting when we max feedback knob).
I couldn't find the exact value of the #7 trimpot (the other gain trim): I've measured 3,3k between centre lug and one of the ends and 0 Ohm between the centre and the other; I didn't wanted to further play with the trims as I don't have na osciloscope and I don't want to ruin the pedal (I'm not that electronicaly skilled that I can safely play with everything).

[GGBB]

Thanks JRM.  I'll have to open mine up again as it's been a while, but from what I recall it's a bit different.  I assume trim7 is the one partly hidden between the jacks.  On my unit, there was an empty space for trim7 but it was not close to the jacks.  I think it was like this one:



Interesting that they added that trimpot.  When I got mine, there was a lot of internet bias against it because of unity volume problems.  Of course even if they had included it, with that layout it would have been a pain to make adjustments.  Good thing they fixed that too.

[ode2no1]

i got my memory toy about 4 years ago and noticed that at bedroom levels in my apartment it wouldn't self oscillate even with the feedback knob full up, but when i took it to my rehearsal spot and played at full volume it would do so with the feedback knob around 2 o'clock. how loud are you playing? i did tweak the modulation trim pot and lowered it a bit to sound more like the way i set my deluxe memory man, but yeah, the feedback might be a volume issue? maybe not in your case, but it definitely was for me.

[JRM]

Volume wasn't an issue as I was connecting my strat directly into the memory toy and then to amp. In order to make the fine tuning more easy I've made my TC Flashback delay play a single note loop. Volume can be an issue if you put the pedal in the FX loop of the amp (then you should increase the trimpot resistance that will reduce the feedback loop 4558 opamp gain). I usualy prefer to just setup the amp clean and put all pedals before (thinking of modding the amp to remove that part of the circuit, including two TL071 and a switch that only add noise).

[GGBB]

Volume wasn't an issue as I was connecting my strat directly into the memory toy and then to amp. In order to make the fine tuning more easy I've made my TC Flashback delay play a single note loop. Volume can be an issue if you put the pedal in the FX loop of the amp (then you should increase the trimpot resistance that will reduce the feedback loop 4558 opamp gain). I usualy prefer to just setup the amp clean and put all pedals before (thinking of modding the amp to remove that part of the circuit, including two TL071 and a switch that only add noise).

Yeah - mine is in my effects loop - without the hack it boosts volume a fair bit.  Which 4558 and what role is it playing (I don't know this circuit at all) and which trimpot controls its gain?

[JRM]

Which 4558 and what role is it playing (I don't know this circuit at all) and which trimpot controls its gain?

As far as I know this circuit is pretty similar to the EHX Memory Man one, just without some controls and with 4xBL3208 instead of 2xMN3005. There are 2 gain adjustment trimpots, one between the BBD stages and another after the BBD and before the expandor and the feedback pot. In this http://www.4shared.com/photo/Hi54vmxe/EH_Deluxe_MMan_2_x_MN3005.html schematic is trimpot #5 the one that is equivalent to the one I've adjusted.