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travis 13th July 2003 05:17 AM

how horrible would a guitar sound through a gainclone without any tone control stuff?
i have an extra 1875. i just looked up the bridge pickup in my guitar and it says it puts out 425mV. so i just put a pot for one of the gain resistors and set it up so i can clip my like 18V rails? do these chips clip normally or do they have some kind of weird protection thing that sounds odd? i bet i could use it to play grim and frostbitten black metal at least.

i was planing on making that rod elliot graphic equalizer someday...

what i should really do is make a slave, i think that's the right word, to connect to the line out of my real guitar amp, so that i can power a 1x15 cabinet that i want to build as well. but then i have to find a nice tube guy who will fix the line out cos it doesn't seem to be working.

is it possible to use a guitar as a balanced input? pickups love to hum.

AudioFreak 13th July 2003 06:23 AM

When they clip, they sound terrible and can produce all sorts of nasty sound effects when operating near their limits.

tschrama 13th July 2003 09:00 AM


A LM1875 can be used as a guitar amp indeed. I've never heard a LM-chip amp clipping but I also suspect it would not give a nice overdriven sound. The nice thing is that youy can very easely use a combination of voltage and current drive to increase the output-impedance. See Rod Elliots website for more info on that:

To prevent the chip from clipping you could use a couple of 12V Zeners in series across the feedback resistor. This will give a much nice sound when you overdrive the amp.

For real metal-overdrive you will need something like 40dB of gain beyond linear amplification. A fair bit of bass roll-of is needed before overdrive (6db/oct @ 1KHz) if you don't wan't to sound like a fart. And offcourse a EQ section is needed if you don't want you guitar sound like a funky-jazz instrument. I prefer the Fender type (see GMarts website, from Rod Elliots links)

Best option is indeed to uses the LM1875 as a power amp, feeding it from a preamp, or other power amp.

The Humbucker elemets are allready in a balanced kind of topology, single coil element will allways hum more.

I hope I don't come on to strong, but I love building guitar amps.


travis 13th July 2003 02:48 PM

do you think amplifying the line-out from my sovtek is a better idea? still gonna be kind of bright?

tschrama 13th July 2003 03:54 PM

Yes, I think that would be the a very good option. I didn't know Sovteks had a line-out... it is taken from the preamp? post EQ?, post mastervolume? is it a FX-loop or true line-out? post output-transformer?

I thought the Sovteks do have a traditional presence controll which controll the amount high-frequenxy feedback around the output stage. This can be incorperated with a LM1875 very easy. I don't think it will sound bright, but maybe a little lack of highs: hende the presence controll.


BTW They are excelent amp fot the money!

travis 13th July 2003 06:03 PM

yeah, they are good amps.
i found the schematic

i don't understand what's going on in this crazy tube stuff.

tschrama 13th July 2003 11:09 PM

Hi travis,

Well it looks like the line-out is just a scaled down version of the speakers output, with some strange filtering. The filter is set a bit odd, I don't understand why. Just use it a tell us how it sounds.

Don't forget to use a dummy load if you disconnet the speakers from your tube-amp, and you will need a volume controll because the line-out is pretty hot.


PeteMcK 14th July 2003 12:36 AM

clipping chips
A chip driven to clipping sounds bloody awful (but you might like that sound!!!!)

I suggest a simple 2 stage pre amp using FETs, 1st stage to give a Hi-Z input, & 2nd stage to add some distortion with a bit better character

Pete McK

sangram 26th September 2003 09:11 AM

Sorry to dig up this old thread.

I just find these chipamps great for:

1. Bass amps, if powerful enough. The 1875 doesn't qualify.

2. Small practice amps. Some fender models use the TDA 2030 (!)

AFAIK the 1875 is NOT SPike-protected.

Also if you have a good amp simulator it would be the best.

A lot of the character of guitar amps comes from cone breakup as well. some of the poorer combos fart rather than breakup. Good ditortion is impossible to achieve on SS, unless it is done before amplification.

Maybe a tube/1875 hybrid concept would be very good here. Which would be the point of using the Sovtek line out...

Circlotron 26th September 2003 11:37 AM

Re: how horrible would a guitar sound through a gainclone without any tone control stuff?
Not nearly as horrible as playing a guitar through a hifi speaker instead of a proper musical instrument one. Even the terminally desperate should avoid this. :dead:

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