Deluxe Memory Man RI (Big Box) Calibration

[jtrezzo]

I am hoping this is appropriate to post here, since the members have such a wealth of knowledge I am hoping someone can help. I have two 90s RI DMMs. One sounds great, perfect. The other, it sounds good, but the max delay time is literally half of the other. I am hoping someone here can tell me which trimmer needs to be adjusted to increase it. I have been looking at the schematic of it here https://www.scribd.com/document/17686322/A-a-Deluxe-Memory-Man but can't figure out which I would need to adjust. Then again, maybe it's more complicated.

These are the trimmers, but mine has 2x MN3005.

Any help much appreciated.

[Kevin Mitchell]

If the BBDs aren't biased right it takes away some of the audio quality coming out the other end. V6 and V8 according to that schematic set the bias for the mn3005 BBDs. You may also see other trimpots. V7 and V9 are the gain of what's coming out of the BBDs. Turning those up should increase the output volume. Adjust them for the loudest, cleanest delay you can get from it. It might help to put an audio probe to the BBDs outputs to see if the signal is getting squashed somewhere.

That was at a quick glance, killing time at work. Sorry if I missed something! 

[jtrezzo]

Hmm I am also now looking at Madbean's Dirtbag Deluxe at http://www.madbeanpedals.com/projects/Dirtbag/DirtBagDeluxe.pdf. It says clock time is set by the 240pf capacitor. I suppose it could also be related to a bad Delay pot maybe. Wish I could find the full service manual/calibration procedure from EHX for this. I am afraid to start turning with all those trimmers.

[Kevin Mitchell]

The delay pot has nothing to do with the quality/level of the delayed signal....

To really calibrate that thing you'd need a signal generator and a oscilloscope. I suggest you tune them by ear. It's obvious when you hit the point of signal loss, you turn back the other way.

[jtrezzo]

The delay pot has nothing to do with the quality/level of the delayed signal....

To really calibrate that thing you'd need a signal generator and a oscilloscope. I suggest you tune them by ear. It's obvious when you hit the point of signal loss, you turn back the other way.

Well that's the thing. The quality and level of the signal is fine, it's just the delay time is about half of what it should be. Put in other words, they sound identical when the good sounding DMM has it's delay pot set to half, and the short one is set to full.

[Kevin Mitchell]

Oh! So you're saying the speed of the delay is much less! I apologize 

As far as I know, you calibrate the BBDs - not the LFO. If the LFO is the same config/parts value then there shouldn't be a reason for the issue you're having.

[jtrezzo]

It's almost as if the first half of the pot sweep of the good DMM is spread out across the full pot sweep for the short delay. That's the best I'd describe it. Maybe I'll do a little experimenting with the trimmers and just take a picture of them first so I can revert them back.

[Govmnt_Lacky]

Does the DMM in the OP have 3 or 4 MN3008s?

You mention that one of your RI DMMs has (2) MN3005s which equates to 8192-stages.

In the pictured RI DMM above, I only see (3) MN3008s which accounts for 6144-stages.

If it has only (3) MN3008s then this would account for the "lesser" delay time than the unit with the (2) MN3005s

[jtrezzo]

Does the DMM in the OP have 3 or 4 MN3008s?

You mention that one of your RI DMMs has (2) MN3005s which equates to 8192-stages.

In the pictured RI DMM above, I only see (3) MN3008s which accounts for 6144-stages.

If it has only (3) MN3008s then this would account for the "lesser" delay time than the unit with the (2) MN3005s

Both have 2x MN3005s. Sorry for the confusion with the photo - it is that same circuit board but neither have MN3008s. The two middle slots are empty on mine.

[Govmnt_Lacky]

Could be anything from a bias adjustment (trimmer) to a bad MN3005 chip.

If you do not have the proper test equipment (sig gen and oscope) then I would mark the trimmer original positions with a marker and SLOWLY make TINY adjustments to the bias trimmer of the first BBD. If you get no better results, put the trimmer back to its originally marked position and do the same with the other BBD.

Best thing to do is to find someone with the proper test equipment as this will isolate the problem much, much faster.

[Ice-9]

From what I have been led to believe the DMM ver with the MN3008 should have 4 chips each are 2048 stages giving 102.4ms of delay per chip, appx. 409.6ms total delay at the specified clock speed.
The DMM ver with the MN3005 chips has 2 chips in place, these are 4096 stages with 204.8ms each, so the total delay available should also be 409.6ms.

Did you buy these new or second hand, is it possible someone has modified the circuit, I see in the picture that depending on what BBD chips are fitted then a different configuration on the PCB is used to set this, (SP or JP  probs a jumper of some type).

On the other hand maybe the delay pot has been replaced with one of a different value, or possibly one of the components around the clock circuit have been changed ??

The trims have nothing to do with delay time.

[jtrezzo]

From what I have been led to believe the DMM ver with the MN3008 should have 4 chips each are 2048 stages giving 102.4ms of delay per chip, appx. 409.6ms total delay at the specified clock speed.
The DMM ver with the MN3005 chips has 2 chips in place, these are 4096 stages with 204.8ms each, so the total delay available should also be 409.6ms.

Did you buy these new or second hand, is it possible someone has modified the circuit, I see in the picture that depending on what BBD chips are fitted then a different configuration on the PCB is used to set this, (SP or JP  probs a jumper of some type).

On the other hand maybe the delay pot has been replaced with one of a different value, or possibly one of the components around the clock circuit have been changed ??

The trims have nothing to do with delay time.

They are both bought secondhand and I have no clue if they have been modified. They weren't advertised as such, anyway. Now I am wondering if perhaps the one with longer delay was actually modified to do just that. You're right about the jumpers on there being used to set operation for either 4x MN3008 or 2x MN3005 for the same delay amount. I will have to inspect the pot more closely, I suppose it could just be a mechanical issue and that would be really easy to fix. I'll have to test the actual delay time on both when set at maximum and see how many ms they're at - I've never had a brand new DMM to actually test what it is "supposed to" sound like.

[Ice-9]

From what I have been led to believe the DMM ver with the MN3008 should have 4 chips each are 2048 stages giving 102.4ms of delay per chip, appx. 409.6ms total delay at the specified clock speed.
The DMM ver with the MN3005 chips has 2 chips in place, these are 4096 stages with 204.8ms each, so the total delay available should also be 409.6ms.

Did you buy these new or second hand, is it possible someone has modified the circuit, I see in the picture that depending on what BBD chips are fitted then a different configuration on the PCB is used to set this, (SP or JP  probs a jumper of some type).

On the other hand maybe the delay pot has been replaced with one of a different value, or possibly one of the components around the clock circuit have been changed ??

The trims have nothing to do with delay time.

They are both bought secondhand and I have no clue if they have been modified. They weren't advertised as such, anyway. Now I am wondering if perhaps the one with longer delay was actually modified to do just that. You're right about the jumpers on there being used to set operation for either 4x MN3008 or 2x MN3005 for the same delay amount. I will have to inspect the pot more closely, I suppose it could just be a mechanical issue and that would be really easy to fix. I'll have to test the actual delay time on both when set at maximum and see how many ms they're at - I've never had a brand new DMM to actually test what it is "supposed to" sound like.

I would also think it would be an easy enough mod to double the delay time by setting a pedal up to the MN3005 jumper selections and fitting 4 X MN3005 BBD chips to give almost 1 second of delay. You would have to set the trims for each chip for symmetry though.

[jtrezzo]

From what I have been led to believe the DMM ver with the MN3008 should have 4 chips each are 2048 stages giving 102.4ms of delay per chip, appx. 409.6ms total delay at the specified clock speed.
The DMM ver with the MN3005 chips has 2 chips in place, these are 4096 stages with 204.8ms each, so the total delay available should also be 409.6ms.

Did you buy these new or second hand, is it possible someone has modified the circuit, I see in the picture that depending on what BBD chips are fitted then a different configuration on the PCB is used to set this, (SP or JP  probs a jumper of some type).

On the other hand maybe the delay pot has been replaced with one of a different value, or possibly one of the components around the clock circuit have been changed ??

The trims have nothing to do with delay time.

They are both bought secondhand and I have no clue if they have been modified. They weren't advertised as such, anyway. Now I am wondering if perhaps the one with longer delay was actually modified to do just that. You're right about the jumpers on there being used to set operation for either 4x MN3008 or 2x MN3005 for the same delay amount. I will have to inspect the pot more closely, I suppose it could just be a mechanical issue and that would be really easy to fix. I'll have to test the actual delay time on both when set at maximum and see how many ms they're at - I've never had a brand new DMM to actually test what it is "supposed to" sound like.

I would also think it would be an easy enough mod to double the delay time by setting a pedal up to the MN3005 jumper selections and fitting 4 X MN3005 BBD chips to give almost 1 second of delay. You would have to set the trims for each chip for symmetry though.

Now that would be an interesting project to attempt....someone has to have tried that already! Seems too easy though...

[Govmnt_Lacky]

Wait.....

Didn't you say in one of the posts above that BOTH of your DMM units in question have the (2) MN3005 configuration? So... you cannot put any more 3005s in there.

If this is indeed the case, then your problem is that one of the MN3005s is out of bias and/or dead -OR- the delay pot is wrong/bad.

[jtrezzo]

Wait.....

Didn't you say in one of the posts above that BOTH of your DMM units in question have the (2) MN3005 configuration? So... you cannot put any more 3005s in there.

If this is indeed the case, then your problem is that one of the MN3005s is out of bias and/or dead -OR- the delay pot is wrong/bad.

They both do have 2x MN3005 and there is 2 empty sockets for when they use 4x MN3008 for the same delay time. Looks like I'll have to try switching out MN3005s between the two next.

[Kevin Mitchell]

They both do have 2x MN3005 and there is 2 empty sockets for when they use 4x MN3008 for the same delay time. Looks like I'll have to try switching out MN3005s between the two next.

Heads up, assuming the mn3005 BBDs aren't from the same factory run, you'd very likely have to re-set the bias with the trimpots after re-homing the BBDs. But my guess would be they wouldn't be too far off.

[Fender3D]

Please!!!!
Let those bias trimmers in peace!!!!!

When, on earth, a bias setting has to do with delay time?  Never!
Mick said it a few posts above...

Greg, BBDs are in series: if one does not work (be it by bias mis-setting or whatever) you have no delay signal at all.

If delay time (expressed in milliseconds, not in repeats number) is different, you only have to check VCO.
Hook an o-scope or freq. meter to BBD's pins 2 or 6 and check clock frequency for both pedals.
At the same clock freq. you must achieve the same delay time. Period.

Check min and max freqs.

Clock freq depends on C43 (240p), R61 (5k6), VR4 (100K lin.) and voltages applied at D3.

[Ice-9]

They both do have 2x MN3005 and there is 2 empty sockets for when they use 4x MN3008 for the same delay time. Looks like I'll have to try switching out MN3005s between the two next.

Heads up, assuming the mn3005 BBDs aren't from the same factory run, you'd very likely have to re-set the bias with the trimpots after re-homing the BBDs. But my guess would be they wouldn't be too far off.

Yes Kevin that is right, but I did mention that anyway when I suggested that putting the 4x MN3005 chips in the one pedal would need the trims set for symmetry. I expect it would work in a fashion as is, as you say the Bias would not too far off but may take some tweaking.

[Kevin Mitchell]

Please!!!!
Let those bias trimmers in peace!!!!!

When, on earth, a bias setting has to do with delay time?  Never!

I was only saying if he starts swapping the BBDs he's probably going to have to mess with the bias trimpots to get them to work right. And assuming someone has an osciliscope or a suffucient frequency counter is asking for a bit much