EM5 Echomachine build

[vortex]

Once again I found my EM-5 producing long crazy delays.

I checked the battery and measured 5.25 volts. Interestingly, the control knobs have very little effect on the delay signal at this voltage.

I keep thinking that the EM-5 would be perfect (for me) if it could squeeze out 800-1000ms delay time. The datasheet seemed a bit vague about maximum delay time IIRC. I didn't find any info about stacking two of these ics for longer delay time either.

Just throwing that in the pot for comments, suggestions, exploration...

[Ice-9]

I keep thinking that the EM-5 would be perfect (for me) if it could squeeze out 800-1000ms delay time. The datasheet seemed a bit vague about maximum delay time IIRC. I didn't find any info about stacking two of these ics for longer delay time either.

Just throwing that in the pot for comments, suggestions, exploration...

I ordered a couple of the SOIC version of these delay chips last week with the idea of putting them in series for longer delays but also to allow multitap delays. There coming from china so I will have to wait to see how well they are suited to this idea.

[newperson]

Can someone post an image of a valid M65831 ic?  I see several variations on eBay and trying to pick out a possible real ic from China is a bit of an issue.

[vortex]

Can someone post an image of a valid M65831 ic?  I see several variations on eBay and trying to pick out a possible real ic from China is a bit of an issue.

Check out this excellent site.
https://mirosol.kapsi.fi/2014/04/ibanez-em5-echo-machine/

[Ice-9]

My IC's from China using Ebay just didn't even turn up, although I did get a refund from the seller.

[rankot]

I've built this one (finally), and the sound's good, or maybe not? First tone is OK, but repeats are distorted. What's going on here? Maybe those 1N4148 in a feedback loop of that op amp are causing this???

Now I have compared original schematic to the one I got with this PCB, and I see that they removed 1k/68n low pass filter that is present in original after output of IC2B. Maybe this filter is actually there to reduce distortion? I must try to add it.

[rankot]

Well, low pass filter didn't solve much, but removing those 1N4148 diodes did it. So I presume I will add two switches for diodes and filter.

Anyone tried to add a LFO for some flutter for this baby? It seems that 390k resistor (R42 on original schematic) can be altered for the purpose.

LPF is made from R16, R18||R19 and C19 from original schematic.

[Ben N]

Rankot, what's on your daughterboard? Is that the LFO?

[rankot]

Yes.

[rankot]

I borrowed this to a friend and he returned it dead No signal passing, although LFO works.

So i tried to trace the signal, and it comes only to the first opamp input, nothing after that. I have measured voltages and V+ is OK on the first opamp, but I also noticed that 78L05 has more than 8V on it's output!!! It seems that they're both fried, right? What could cause this? Maybe he used wrong polarity adapter? Pedal is built using Takota PCB, which unfortunately has no polarity or overvoltage protection... 

I removed both M65831AP and 74HCU04 and 78L05 still has the same voltage at output, so I can hope those two are OK.

[rankot]

Finally found out a part of a problem - the guy who sold me the PCB for this (Takota) flipped 78L05 regulator, so it actually didn't regulate. Now I soldered it to other side of PCB and it works. Now to see why to hell first input op amp is fried... Maybe guys I borrowed pedal to put too hot input? I will add two LEDs at the input, to protect it.

EDIT: No, the first opamp wasn't fried, but the Vref filter capacitor was somehow blown up. It was 10uF MLCC, probably bad quality. Damn Aliexpress goods... I replaced it with normal electrolytic 10uF and everything works fine, so now just to assemble everything again and check if everything's working.