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Old 9th February 2005, 06:24 PM   #1
zeegeit is offline zeegeit  Netherlands
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Default using a fuzz effect as a preamp

Hey everybody

I was thinking about building a simple guitaramp, using a fuzz effect (http://www.runoffgroove.com/multiface.html that one) as a preamp. My question is, will this effect generate enough output to drive a gainclone (http://www.decdun.fsnet.co.uk/gainclone.html) ?

Another question. The chip suggested isn't available from the source i get my parts from. They do however stock the LM1876TF. Would I have to make any changes to accomodate for this chip? (and if so, which? I couldn't really figure it out myself).

I hope you can answer my questions.
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Old 9th February 2005, 07:47 PM   #2
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Default Re: using a fuzz effect as a preamp

Quote:
Originally posted by zeegeit
My question is, will this effect generate enough output to drive a gainclone?
Yes.

Quote:
Originally posted by zeegeit
They do however stock the LM1876TF. Would I have to make any changes to accomodate for this chip? (and if so, which? I couldn't really figure it out myself).
The datasheet for this chip is here:

http://cache.national.com/ds/LM/LM1876.pdf

The LM1876 is 2 by 20W, you could make 2 channels, or bridge 2 channels if your speaker is 8 ohms, or even just ignore the 2nd channel if you have no use for it.

This is the pinout from that datasheet:
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File Type: jpg lm1876.jpg (12.2 KB, 86 views)
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Old 9th February 2005, 11:42 PM   #3
zeegeit is offline zeegeit  Netherlands
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allright then..I understand. Thanks I found an informative website where someone has published the resistor and capacitator values for a gainclone with a LM1875 as well, here it is http://www.platenspeler.com/gainclone.html

So that should be quite easy to figure out..maybe I can order some samples from National (do they charge you with any shipping? ) . But anyways, I think I can figure out the things I need for the amp itself.

Next problem : the PSU. I'm a bit confused about the transformer I should use(the only thing I do know, is that it's probably going to be the most expensive part of the entire amp). Some people say you should have at least 80 VAC , others say at least 160. Is there a formula to calculate this, so for instance if I would want to make an amp with an output power of , say 20 watts(based on a LM1875) @ 8 ohm , what kind of transformer would I have to use?
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Old 10th February 2005, 12:46 AM   #4
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Quote:
Originally posted by zeegeit
Next problem : the PSU. I'm a bit confused about the transformer I should use(the only thing I do know, is that it's probably going to be the most expensive part of the entire amp). Some people say you should have at least 80 VAC , others say at least 160. Is there a formula to calculate this, so for instance if I would want to make an amp with an output power of , say 20 watts(based on a LM1875) @ 8 ohm , what kind of transformer would I have to use?
If you want to figure out the minimum transformer you need to buy, then read the datasheet, it walks you through the design process.
I would advise you that if you are *buying* a transformer, not recycling one or buying an outstanding deal or surplus, to buy something 150-160 VA per chip. I just see so many people skimping like that and I think "what is the point?"
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