Parentheses Mini - (beware of LM308 type used)

[CA138]

Build Rating

5.00 star(s)

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%.

 

[Nostradoomus]

Does it cut out completely or just kinda over compress and fart out? If it's the fart kind, it's a feature.

 

[CA138]

Does it cut out completely or just kinda over compress and fart out? If it's the fart kind, it's a feature.

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.

 

[BuddytheReow]

Rats tend to do that. I have the same issue with high output pickups with the gain dimed.

 

[CA138]

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.




Another comparison shot (problem chip on the left):



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.

 

[Nostradoomus]

Those are fakes. Email smallbear and say they're fake, you should get a refund. Them shit's ain't cheap!

 

[Zanshin]

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.

 

[CA138]

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.

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

 

[Small Bear Electronics]

With respect to all here, what we have listed on our webpage includes more language than excerpted above. In particular the LM308ND variant is an interesting one because it's been tested by trusted customers and used in their products...

"These have become the stuff of myth and legends. We do our best to find, test and offer genuine chips. We do test chips ourselves and also ask a few trusted customers to try them out from time to time in their own distortion circuits. The two tests we do internally are :

1) Do they sound right in a distortion circuit?

2) What's the impedance between pins 1-5? (The datasheet says that impedance should be zero. However many chips labelled LM308N measure 2.4K-2.8Kohm impedance and sound genuine in the circuit.)

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.

What we CAN say is that these ICs are tested using the two tests we noted above. We consider them 'real' LM308N for purposes of this listing and your circuits.

SKU ICTHLM308ND: Motorola logo - This batch is from a trusted supplier. These chips measure zero impedance between pins 2-5 and sound genuine in our test circuit. Date code is K8505A. The 'ND' suffix is unusual.

SKU ICTHLM308NJM36RB: Natl Semi logo- From another trusted supplier. These test well in the test circuit and measure impedance at 2.4kohm to 2.8kohm between pins 2-5.

SKU ICTHLM308NJM21RB: Natl Semi logo- Part of Small BEar acquired NOS. These test well in the test circuit and measure impedance at 2.4kohm to 2.8kohm between pins 2-5. "

We've been selling trusted chips for many years and stand behind them; any and every customer who claims we've sent fakes has been taken care of. As will this customer. We're down to the point of saying "if you don't like the sound of your LM308 in your specific build of a clone circuit then send it back to us for a refund".. and sometimes what we get back is even different than what we shipped out!

 

[Zanshin]

With respect to all here, what we have listed on our webpage includes more language than excerpted above. In particular the LM308ND variant is an interesting one because it's been tested by trusted customers and used in their products...

I believe I quoted the most relevant information regarding the topic at hand.

"if you don't like the sound of your LM308 in your specific build of a clone circuit then send it back to us for a refund"

I am being pedantic but the product page doesn't say this anywhere, nor is it implied anywhere on the product page, nor do I find it by a cursory look around the website. I am not trying to light SynthCube on fire, it is good you are standing behind what you sell, but the language on the product page implies otherwise.

 

[CA138]

They may be genuine of some sort, I can't confirm either way, but they definitely return very different resistance readings when compared to the LM308N (and clearly don't work as an LM308N in this particular circuit). I have posted the readings below (several of the LM308ND vs an LM308N on the right) in case someone with more expertise is able to shed more light. I double checked the readings and there is a fair bit of variance between the LM308ND samples.



After some research, the only other source I could for LM308ND was this Chinese eBay account which appear visually identical: NOS LM308ND LM308N Amplifier for 80's ProCo RAT2 very rare x 1pc They seem to have some positive reviews so I have reached out to see whether they know more about them.

I appreciate the opportunity to return them. I'll keep one to get tested properly and report back if we find out more. I'm hoping to track down the original datasheet for these as I have a feeling they were taken from old boards of some kind and may have had a specific use. Thanks to everyone for the insight.

 

[szukalski]

Pedal part vendors are few and far between, with a challenging business model (lots of suppliers, large inventories, consumers who make building errors). Maybe worth chatting to them before shit-slinging.

 

[CA138]

Pedal part vendors are few and far between, with a challenging business model (lots of suppliers, large inventories, consumers who make building errors). Maybe worth chatting to them before shit-slinging.

From my perspective, this was a purely diagnostic approach to working out what the issue was. Once identified, I felt responsible to share this with others who may benefit or provide insight (hence 'In case this helps anyone else..' in reporting back afterwards - post no. 5).

I don't feel right about your suggestion of overlooking info on problematic ICs for these circuits that is likely to be useful to others. For example, in another recent thread I helped someone else identify fake OPA2134s. The member thanked me afterwards for saving him grief and money. Note, Tayda actually reached out to me to let me know about the issue as I had purchased a decent amount of them - I hadn't even had a chance to test them at that point. They slipped through the cracks in their testing/disposal process and were working with clients to resolve. They also issued an instant refund.

Taking your point though, I completely agree that bad components are absolutely part of the game and a risk for all involved. I do also believe in sharing of info however - as long as it aims to be factual and unbiased.

 

[szukalski]

I don't feel right about your suggestion of overlooking info on problematic ICs for these circuits that is likely to be useful to others.

I didn't say anything about that. My comment was a general one about talking to vendors before besmirching their name.

 

[mdc]

To the OP's credit, they didn't say anything about the ICs being "fake" or even seem particularly fussed about it.