Switchable Hi-Z input impedance, how ? - Page 30 - diyAudio
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Old 17th September 2012, 10:53 PM   #291
tinitus is offline tinitus  Europe
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hi Kevin
isnt a Fender preamp is supposed to drive a tube power amp, and works better without the buffer

Im driving solid state power amp, and need output buffer

but Im not really after tube sound as such
thats not my reason

anyway, I have made the box and layout like this to make it easier to make curcuit changes
I might start like this, maybe
hope to order a few more parts soon
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Old 17th September 2012, 11:04 PM   #292
Struth is offline Struth  Canada
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Hi Guys

The basic Fender circuit can drive the PA input. If you add an output control as suggested it will still drive the PA from the pot wiper, or a bit better if you add a buffer.

Why add a tube if you do not want tube sound?

Maybe you should do some reading about tube guitar amps to see how they function and how to change things to get alternate sounds. "The Ultimate Tone" series covers this very well. Check out TUT3 for a practical construction-oriented guide including five bass amp. See my site for detailed descriptions of the books.

You seem to be working with only hifi information and that is very limiting when it comes to amp design for musical instruments.

Have fun
Kevin O'Connor
londonpower.com
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Old 17th September 2012, 11:22 PM   #293
tinitus is offline tinitus  Europe
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ohh, I have tons and tons of info on instrument curcuits
and have spent way too much time searching and reading
why tubes ?
dont know, to try it I guess
its DIY
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Old 18th September 2012, 04:11 PM   #294
tinitus is offline tinitus  Europe
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ok, I found a few bits and pieces here and there
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Old 18th September 2012, 04:14 PM   #295
tinitus is offline tinitus  Europe
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and managed to cut this little board off some old amp
I will replace diodes and cap
fuse holder is not connected to anything, and will be used seperately for trafo primary mains connect
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Old 18th September 2012, 05:31 PM   #296
tinitus is offline tinitus  Europe
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everything went in nicely
and I decided to leave the fuse be for trafo secondary
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Old 18th September 2012, 07:33 PM   #297
shanx is offline shanx  Canada
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Tinitus, I think you really want the tube sound(!) And I like the layout potential of 2 jfets going in to 2 tube stages that you show on previous schem. You have enough room and switching possibility to really play around with the staging and tone stack position. Just suggest be careful with the tone stack impedance and previous stage or you are going to get a lot of overall signal loss at the tone controls. That is a potential spot for a j-fet buffer/driver circuit to handle
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Old 18th September 2012, 10:51 PM   #298
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by shanx View Post

You have enough room and switching possibility to really play around with the staging and tone stack position. Just suggest be careful with the tone stack impedance ......
thanks, shanx

yeah, Im trying to keep the att/pot away

but there are two resistors I have doubts about
one is the the tone out grounding resistor
I have marked it with a red dot
the other is tube input grounding resistor

not sure I need both
looks to me like they do the same thing
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Old 19th September 2012, 05:01 AM   #299
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by tinitus View Post
<snip>

not sure I need both
looks to me like they do the same thing
You're right, you don't..
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Old 19th September 2012, 01:58 PM   #300
shanx is offline shanx  Canada
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I am not sure how much gain you are looking for on the first stage fet, but could consider adding bypass cap across the source resistor. And yes 1 grounding resistor will do for the grid.
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