Reliable Source for LM308s?

[Philtre]

Give this a read. http://www.davidrolo.com/2014/09/28/giant-hogweed-fuzz-octave-up-octave-down/

He says the 308 does matter. Closest is a tl070.

Right, that's interesting. Thanks for finding that. 

[somnif]

Yeah, while technically speaking the circuit would FUNCTION with some other single op-amp, it would not SOUND the same.

See, the LM308.... sucks. Its old, slow, worn out, obsolete technology. And that is why we love it in the audio world. That slow sluggish get-off-my-lawn response gives it this fantastic growl in distortion circuits.

Newer tech, its too precise. It keeps up with your signal too well, and you get this scratchy, sreechy sorta tone in circuits that were designed around the old bludgeoning curmudgeon of a chip.

If you can't find an authentic LM308, try for an NTE938 (same part re-badged). The next best I've heard of is an "over-compensated" TL070/TL080. So put a ~150-200pF cap between pins 1 and 8 and it will drop the slewrate right down to... close-ish.

BUT the key is what sound you prefer (I personally dislike Rat style distortions). If its not true-to-classic, but you like it, screw the haters and do what you want.

[stringsthings]

I found these over on BG Micro:



The website incorrectly advertised these as UA308's, so I wasn't overjoyed when they arrived.
Oh well, the packaging is nice.  I haven't tried them in a rat, so I can't vouch for their performance. 

The chips in the background are LT1054's.   $1.20 a pop. 

[somnif]

I found these over on BG Micro:



The website incorrectly advertised these as UA308's, so I wasn't overjoyed when they arrived.
Oh well, the packaging is nice.  I haven't tried them in a rat, so I can't vouch for their performance. 

The chips in the background are LT1054's.   $1.20 a pop.

108s are the Mil-spec equivalent of 308s. Same function, but tighter tolerances and wider operating temperature range.

[stringsthings]

I thought so.   When I get around to it, I'll pop one in.


.... so much mojo! 

[alanp]

Just think, if you have to troubleshoot, you get to scream at it, "What is your major malfunction?!?!"

[Philtre]

So I built the Giant Hogweed circuit here - http://tagboardeffects.blogspot.com/2015/10/giant-hogweed.html

The schematic is here - http://www.davidrolo.com/wp-content/uploads/2017/07/GiantHogweedSchematic_zps445f5a36.png

I still haven't found an LM308, so I popped in an OP07. The pedal works, but so far I don't know how it compares to an LM308 or a TLO70. Also, I'm not sure whether the 30pf compensation cap between pins 1 and 8 of the OP07 needs to stay, be removed, or the value changed.

[reddesert]

OP07 datasheet: http://www.analog.com/media/en/technical-documentation/data-sheets/OP07.pdf

The OP07 does not need the 30 pf external compensation capacitor. It uses those pins for offset nulling (which is something that never gets used in pedals AFAIK), and the cap probably won't do anything if you leave it in.

[Philtre]

OP07 datasheet: http://www.analog.com/media/en/technical-documentation/data-sheets/OP07.pdf

The OP07 does not need the 30 pf external compensation capacitor. It uses those pins for offset nulling (which is something that never gets used in pedals AFAIK), and the cap probably won't do anything if you leave it in.

Yep, you're right, thanks. The 30pF cap does nothing if I leave it in. Wonder if it will do any harm leaving it in, just in case I ever slot in a LM308 or TL070?

[Philtre]

I'm intrigued by trying out an actual LM308. There are some on eBay. Anyone have any experience of eBay LM308s? Fake? Unreliable?

https://www.ebay.co.uk/itm/LM308N-DIP-8-Integrated-Circuit-UK-SELLER/273271724172?hash=item3fa043988c:m:mRRRNL-ddJXw4RDEq0XRW7A

[somnif]

I've been burned by Ebay chips too often, but I have gotten lucky occasionally with domestic vendors. Avoid Chinese sellers and throw the dice.

Banzai also has them in stock for about 3 euros a pop:
http://www.banzaimusic.com/LM308N.html

[Philtre]

I've been burned by Ebay chips too often, but I have gotten lucky occasionally with domestic vendors. Avoid Chinese sellers and throw the dice.

Banzai also has them in stock for about 3 euros a pop:
http://www.banzaimusic.com/LM308N.html

Cheers for that.

I've ordered this one from eBay - https://www.ebay.co.uk/itm/LM308N-DIP-8-Integrated-Circuit-UK-SELLER/273271724172?hash=item3fa043988c:m:mRRRNL-ddJXw4RDEq0XRW7A

I'll update soon when I test it.

[chromesphere]

If you ordered one from ebay (or anywhere that's not trustworthy infact) how would you know if its real or not?

[Philtre]

If you ordered one from ebay (or anywhere that's not trustworthy infact) how would you know if its real or not?

I don't know, TBH. What would a fake one do or not do?

I suppose I can compare with an OP07. And check if the 30pF compensation cap between pins 1 and 8 makes any difference in sound.

[somnif]

If you ordered one from ebay (or anywhere that's not trustworthy infact) how would you know if its real or not?

Measure resistance between pins 1 and 5 (the offset null pins). Single op-amps like TL071 or LM741 will have a resistance (around ~2k for the 741, higher for the TL071), the 308 will show no connection.

And if its a dual-opamp re-painted, the pinout won't match and it won't actually work in the circuit.