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Attenuate guitar signal on 3V
Attenuate guitar signal on 3V
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Old 22nd May 2019, 01:52 PM   #1
vasko is offline vasko  Czech Republic
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Default Attenuate guitar signal on 3V

I have a few old walkmans that I'd like to use with guitar as headphone amps which are practical to use because of 3V supply but guitar signal level is to high and IC's input impedance is low and unsuited for guitar so I want to put some buffer circuit made of bipolar or fet transistors in between. It has to be on 3V also. Does any one has suggestion of such circuit?
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Old 25th May 2019, 04:27 AM   #2
PRR is offline PRR  United States
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Old 25th May 2019, 06:02 PM   #3
vasko is offline vasko  Czech Republic
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Thank you, I will try that.
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Old 25th May 2019, 10:27 PM   #4
vasko is offline vasko  Czech Republic
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I made the circuit, the thing is walkman's amplifier input ground isn't supply ground. How should I solve that?
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Old 26th May 2019, 12:18 AM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by vasko View Post
I made the circuit, the thing is walkman's amplifier input ground isn't supply ground.
How should I solve that?
Does the walkman circuit have a negative ground (battery minus connected to the input common)?
Or does it have a positive ground (battery plus connected to the input common)?

Last edited by rayma; 26th May 2019 at 12:20 AM.
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Old 26th May 2019, 01:41 AM   #6
PRR is offline PRR  United States
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> Does the walkman circuit have

It turns out there were MANY WalkMan circuits, from the original basic to some much more complicated designs. I never knew that the later ones (MEGAbass) had the headphone shell at +1.3V from power common, and a third power amp to drive it. This one's schematic is mind-blowingly complex-- so much that -I- would forget about it and just whomp-up one of the now-common 3V headphone chips with a buffer in front.
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Old 26th May 2019, 01:47 AM   #7
rayma is offline rayma  United States
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Originally Posted by PRR View Post
the later ones (MEGAbass) had the headphone shell at +1.3V from power common,
Does that mean it has +/- 1.5V balanced supplies, so no output coupling capacitor is used?
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Old 26th May 2019, 01:54 AM   #8
PRR is offline PRR  United States
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No.

It's pretty wacky ("Sony-clever"), and I burned-out reading bad scans last night. Since I bet Sony changed the scheme every few models, let Vasco say what specific model.
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Old 26th May 2019, 02:24 AM   #9
rayma is offline rayma  United States
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Quote:
Originally Posted by vasko View Post
I have a few old walkmans that I'd like to use with guitar as headphone amps
Try a series 100k-1M resistor between the guitar and the walkman (maybe a 1M pot).
Adjust the resistor value for just enough gain at the full volume walkman setting.
This assumes that the walkman's input impedance is on the order of 10k or so.

Last edited by rayma; 26th May 2019 at 02:30 AM.
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Old 26th May 2019, 06:01 AM   #10
vasko is offline vasko  Czech Republic
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The chip is LA4570 and signal ground is on the 1.5V.
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