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Post subject: Preamp questions
Posted: Mon Feb 10, 2014 7:09 pm
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Hey guys, I've got a 1973 SF Bassman 100 that needed a complete rebuild and that part is done, but since I'm going to keep this (for now) I want to make some modifications.

I worked on the tube series amps a long time ago and just started back into it, but I never thought about why different models use different pre-amp layouts. I get the difference in components for different sounds, but there are other differences I'd like to get straight in my head.

For example: a '65 SR has the first half of V1, then the tone controls, then the volume control, then the second half of V1. A Twin (5F8) has the first half of V1, then volume controls, then a full V2, then tone controls.

Why a different placement of volume and tone controls? What's the benefit of each? The reason I'm asking is I am making a second pre-amp board to use that has a better tone than the stock circuit since I'm going to use my standard electric through it instead of my bass and I want it to have a far better sound. That also means re-vamping the power section too but that's a bit easier to fiddle with. No pun intended.

Any ideas?

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Post subject: Re: Preamp questions
Posted: Mon Feb 10, 2014 8:59 pm
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Tone stacks precedences were shuffled around between the tweeds, the brownfaces, and the blackfaces during Leo's relentless quest for ever-cleaner tone. As well, many of the brownface models utilized center-tapped tone pots to provide actual "boost" and "cut" functions. The variable negative feedback loop with its attendant presence control was another of his experiments that yielded a mix bag of tonal choices. The resultant sonic differences between these three periods of "Fender-ology" were both distinct and unique.

Arjay

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Post subject: Re: Preamp questions
Posted: Tue Feb 11, 2014 6:50 am
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So what you're saying is about all I can do is experiment and see which one I like better with my current setup. :wink:

I have no interest in keeping this a stock bass amp, I have an Ampeg SVTIII that I gig with. I am going to retain the replacement board I made (with all the parts) so it can be a quick job to return it to stock if I decide to part with it.

I know there are several other "custom" circuits that people have developed but I don't want to just copy someone else's, I want to see what I can come up with. I don't need all that power for guitar but it'll still be fun to see what I end up with.

Thanks!

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Post subject: Re: Preamp questions
Posted: Tue Feb 11, 2014 6:49 pm
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jimolson1963,

You can download the Duncan Tone Stack calculator and play with some parameters. See the resultant shape of the tone.


http://www.duncanamps.com/tsc/download.html


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