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Old 16th June 2011, 02:45 PM   #1
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Default Buffer preamp tone issue - advice wanted!

Hi there! I've recently looked into making a buffer/preamp for my Fender Stratocaster - all single coil. My reason for doing this was primarily to maintain a strong signal when running through a passive A/B/A+B switch, as I noticed a clarity drop-off using A+B.

I built this buffer:
Click the image to open in full size.
and it definitely took care of the issue stated above. However, I find now that there are a couple of undesireable effects:

1) too amount of treble in the signal. Am I boosting treble here?

2) though I don't lose treble when bringing down the volume, the volume does drop off too fast.

if there are changes to the circuitry that would address these issues, please point them out to me. i'm learning as i go on all things electronics related!

Also I have not changed tone pot or volume pot values.

I suspect that the volume issue could be adjusted by changing R1 or possible even removing it. ?

And - this preamp is between the pickup and the volume knob, powered by a 9v battery, wired to a TRS input jack to "turn it off" when the cable is out.

Thanks in advance for any help!

Jeff
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Old 16th June 2011, 04:04 PM   #2
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I think you need to use log pots for the volume control. Look for suffix B in the pot. Yours might be an A.
mandu
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Old 16th June 2011, 04:33 PM   #3
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The link isn't working. Please repost your schematic.
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Old 16th June 2011, 04:52 PM   #4
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that shows up as a link? I just selected a gif of it and pasted it into the message body.

its the top schematic at this page:
AMZ - Guitar Effects & JFET Splitter
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Old 17th June 2011, 01:35 AM   #5
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Post part bump, part disclosure

I forgot to mention the jfet is an MPF102.
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Old 17th June 2011, 01:36 AM   #6
Minion is offline Minion  Canada
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Log Pots are A , Linear Pots are B ..... either way that would not effect the trebble ....
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Old 17th June 2011, 03:45 AM   #7
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I would lose R1 and R5. I'm not sure why they're being called "pulldown resistors." Don't remove the capacitors. And at the "original article" link it states, "The values shown here will give good performance but can be tweaked to suit your taste. For example, if it is a bit too bright for your rig, reduce the values of both R2 and R3 to 1M, or even 470k to see if the lower input impedance takes some of the edge off." Hopefully these things will fix the volume control problems too.
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Old 17th June 2011, 04:19 AM   #8
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thanks for the read-over, sofaspud - I'm embarrassed to have missed that, but am not surprised considering how many things I was reading over before choosing which circuit to build.
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Old 17th June 2011, 04:44 AM   #9
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Don't mention it. I'm not much of a guitar tech, so I like to learn a little while helping out. Let us know how things progress.
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Old 18th June 2011, 04:59 PM   #10
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Thumbs up its getting better!

I took your advice, dropped R1 and R5 entirely, and effectively brought R2 and R3 to 687k. Its much better! Not as much emphasis on the treble side for sure, a little beefier tone. I still may try something to "bleed" off a touch of high end response. Do you know - could a capacitor be used across R2 similar to a treble rolloff capacitor on a plate in a tube gain stage? What would be the harm in trying? I've got plenty of 250pf s sitting around. I may give that a whirl at my next string change.
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