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Post subject: Mod'ing Bassman 250 head so that compressor out is "pre"
Posted: Thu Nov 01, 2012 9:11 am
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Hi,

I'd like for the output of the compressor to be the "pre" point of the signal flow.

As designed, the "pre" selection for the line out XLR is after the input buffer, but before the compressor.

I'd like the compressed signal (but not the EQ) to be present at the line out XLR.

Looking at the schematic, it seems like it's do-able - specifically to move the "pre" point to the output of U2-B.

But, I haven't been inside the Bassman 250 to see what it looks like. The diagrams make it seem like it might be some trace cutting and jumper.

Has anyone tried anything like this before?
Thanks much!
CC


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Post subject: Re: Mod'ing Bassman 250 head so that compressor out is "pre"
Posted: Sat Nov 03, 2012 5:56 pm
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Aspiring Musician
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Location: Lititz, PA
I think that could be done. The Fender Bassman 250 is pretty serviceable.

So, you are essentially adding in one more stage (the compressor) before the "PRE" signal feeds the line out circuit. U2-B (TL072) is the next stage and the one you want to include. U10-A (CA3080) provides negative feedback (based upon the signal level) to perform compression.

So, I take it you like the Bassman compressor. I love the Bassman 250 but the compressor is the one source of consternation for me. That feedback IC (CA3080) can insert a "click" when switching in or out. If your cab doesn't have a tweeter, you probably won't hear it. But, if you do have a tweeter, it can be very annoying. It is most noticeable with low notes at certain levels. You'll hear a buzz with the note.

I still use the compressor. I just turn my tweeter down. I like that old school bassy sound anyway. And I set the line out for "Post." I love that Bassman tone. Sometimes I feed it to my Crown XLS 1500 amp for 1500 watts of glorious Bassman tone. :D


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Post subject: Re: Mod'ing Bassman 250 head so that compressor out is "pre"
Posted: Fri Nov 09, 2012 11:50 am
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Rock Star
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Instead of modding it I'd get either an Aphex Punch Factory or a MarkBass Compressore pedal and put it before the amp. Either one outperforms the built in compressor and would be an improvement. Neither one pumps. The Aphex is a tad hissy when you crank the treble and use a horn though, however it is no problem with the high end EQ and horn level set to sane levels. Those are my two favorite bass compressors. I've yet to find a built in compressor I really like.


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Post subject: Re: Mod'ing Bassman 250 head so that compressor out is "pre"
Posted: Mon Nov 12, 2012 1:49 pm
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Thank you both very much for your replies!!

I hadn't purchased the Bassman 250 head yet - there was one for sale near that I was considering.

I do like some high end (tweeter) in my rig, so the artifact that you described warnergt would probably bum me out quite a bit.

Thanks for the compressor recommendations brotherdave - that does sound like a better way to go.

Much appreciated!!


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