Parentheses Mini - (beware of LM308 type used)

C

CA138

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This thing is absolutely crushing. I used a Motorola LM308N IC from Smallbear and ended up with a matched set of D9B diodes (after testing matched D9B, D9E, D9K, BAT41 sets).

The only issue I have is that when I set the distortion and octave controls both to max, the signal cuts out on heavy palm muting. My pickups are very high output and it doesn't occur with the volume rolled back or coils tapped to reduce output. Is this a feature of the circuit or does this indicate an issue with the build? I have tried swapping diodes and power supplies. The pedal still sounds great with both controls at about 80%.
 

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Last edited:
Nostradoomus said:
Does it cut out completely or just kinda over compress and fart out? If it's the fart kind, it's a feature.
Click to expand...
Hi, it's definitely a complete cut-out for about 200-500ms on heavy pick attack. Not the usual fuzz sputter. It seems to be an issue with the green ringer part of the circuit cutting out on pick attack when dialed up. I'm thinking maybe a bad transistor - sadly I didn't stop to test or socket them.
 
In case this helps anyone else, the 'cutting out' on max gain problem was due to the LM308 I used. It happens with any of the 'Motorola LM308ND K8505A' chips in the recent batch from Smallbear (pictured left side). When I used another type of LM308 (National Semi - pictured on the right) it sounds even better and works fine even when everything is dialed - zero cutting-out issues.

1728897161176.png


Another comparison shot (problem chip on the left):

1728897213700.png

These are the ones that cause the issue: https://smallbear-electronics.mybigcommerce.com/lm308n-op-amp/

They appear to have solder on the legs and the printing is quite rough. Does anyone know if they are still usable in other circuits or a known bad batch at all? I am yet to test them in another circuit.
 
Thanks for that. I was worried that was the case but hadn't heard reports of them selling bad ICs.

I wonder whether I should also be concerned about the OPA2134s they sent me. I can see three different types in the ones they sent:

1728899750712.png
 
Small Bear has this on the LM308 product page:

“We can no longer say with any certainty what a 'genuine' LM308N is, and will not guarantee it unless we have written documentation (provenance) for a particular batch. “

So genuine level prices for what are likely fakes. That is a pretty shitty business model.
 
Zanshin said:
Small Bear has this on the LM308 product page:

“We can no longer say with any certainty what a 'genuine' LM308N is, and will not guarantee it unless we have written documentation (provenance) for a particular batch. “

So genuine level prices for what are likely fakes. That is a pretty shitty business model.
Click to expand...
I mean, I kind of accepted it may be some odd variant/equivalent of the LM308N without a documented history, but didn't expect to receive a batch of chips at that price that literally do not work in an audio circuit:

First half of the clip is the smallbear IC, second half was recorded about a minute later with the replacement LM308N (direct-in - exact same pedal settings):

Dropbox

www.dropbox.com www.dropbox.com
 
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