LM308N

xscaramanga

I quite fancy building a Rat clone from a Fuzzdog kit, but they're out of LM308Ns. I know it doesn't make much difference, but I'd I'm going to build a clone I want the classic circuit. There are some cheap ones listed on eBay. Are they OK, or will they be inferior/fake? 

Roland

How about building it as part of our Q4 challenge? http://www.thefretboard.co.uk/discussion/139711/q418-challenge-build-an-item-of-musical-equipment-from-a-kit

Philtre

eBay ones are fake. I know from experience. I used a LM301 in my Rat clone.

xscaramanga

Philtre said:

eBay ones are fake. I know from experience. I used a LM301 in my Rat clone.

Good to know! How about these? Also fake?

https://www.silicon-ark.co.uk/lm308n-op-amp-by-national-semiconductor

Thanks for the heads up, @Roland. Definitely interested in taking part.

Philtre

@jonnyscaramanga I don't know about the Silicon Ark ones but, as they're always out of stock, there's no way to find out.

The "LM308N" I got off ebay turned out to be an OP07. See http://www.madbeanpedals.com/forum/index.php?topic=26581.msg272629#msg272629

marauder

I've got one you can have PM'd.

roberty

Hey I am in exactly the same situation, ordered a kit from fuzzdog but no LM308s

I am after one too and willing to pay

I know the difference is negligible but I am so used to the sound after nearly 20 years

Going to build mine to Turbo/Clean toggle. Clean RAT works so well as a lead boost

xscaramanga

Next q (i've googled this but still don't have an absolutely firm answer): Are LM308N and LM308AN different, or just different packages of the same chip? LM308AN Rat copies are relatively easy to come by, even now.

roberty

Well I've wired mine up and it sounds immense. I'll keep the new style op amp in for now as I'm really pleased with the sound.

@jonnyscaramanga I would just go for it and maybe change the op amp later as it is socketed and easy to do

I tried to make a clean rat mode by jumpering D2 and D3 but that switch position is silent :-( open to suggestions here

Apologies for thread hijack

Sporky

I was going to suggest socketing the op-amp so you can swap later if the chip you want appears.

Different op-amps can sound different, but from the ones I tried it's basically down to whether they're suitable for audio or not. The ones that are sound the same, the ones that aren't don't. Mostly seems to be slew rate that determines it. 

stickyfiddle

+1 on the socketing thing. 

I have to say, I have one kit-built Rat with the "right" chip, and one Rat2 without, and while they do sound a bit different, they both sound great. 

roberty

BTW I've since learnt that the clipping diodes go to ground so jumpering D2 and D3 dumps your whole signal

springhead

roberty said:

Well I've wired mine up and it sounds immense. I'll keep the new style op amp in for now as I'm really pleased with the sound.

@jonnyscaramanga I would just go for it and maybe change the op amp later as it is socketed and easy to do

I tried to make a clean rat mode by jumpering D2 and D3 but that switch position is silent :-( open to suggestions here

Apologies for thread hijack

If you jumper across the diodes then with the switch in that position you're shorting the op-amp output to ground - hence it's silent.

You'd have to lift one end of both diodes off the board and put a switch in there, or replace the switch with one that has a centre off position - on-off-on. 

Edit: Looks like you've just worked that out!

roberty

@springhead thanks all the same! Got the bug now, want to build the warp sound and op amp muff. Mostly so I can swap all the pedals on my board for identical ones with swear words scrawled across them