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Old 13th September 2008, 02:38 PM   #1
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Default realistic schematics...

I'm looking for schematics for a realistic solid state amp model# 31-1982B

mostly I just want to figure out how to wire the stereo volume controls cause there was two broken pots.

on the left channel you have 2 points that say "L CH" and two that say "VR1"

same with the right only they say "R CH" and "VR 2"

I have a stereo pot to put it becasue I don't see the point in having two for what I'm doing with it. it's got 2 in put lefts and rights "+" and two input lefts and rights "-"

so what goes where? I've never heard of VR1. if anyone has could you let me know.
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Old 13th September 2008, 11:28 PM   #2
lineup is offline lineup  Sweden
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VR1 and VR2
could probably be
where the wiper of your stereo potentiometer should connect

wiper is the output of one pot
the variable point
between lowest and highest value of resistance
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Old 14th September 2008, 12:19 AM   #3
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VR1 and VR2 are the schematic locations of Variable Resistor 1 and 2.

you could replace the two pots with a dual pot, but if i remember some of that radio shack stuff, especially if it's as old i'm thinking it is, they had separate volume pots, because it saved the price of a second dual pot- the balance control, and two single pots were cheaper than 1 dual pot.
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Old 14th September 2008, 04:07 PM   #4
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yeah, i got it working, probably not they way it's supposed to be wired, but I just found a couple of guitar pots and just wired both VRs to the right lead on the left channel and the two CH points to the left lead and vr 1 to lead 2 and vr 2 to lead 3.

it makes no sense but the unit turns on and I can control the volume. I just have to turn the left pot to the left to turn it up and to the right to turn it down. I do know from experimenting that you can't wire them the same way. that seems strange to me.

maybe I'll just throw a penny and giles RF15 on my radio shack amp in a cardboard box enclosure. and here's the story behind that...

I took out all the outer screws and the unit would not slide out. so I checked behind one of the knobs to get the nuts off the pots, but the but was on the inside not clamping itself to the enclosure... I got frustrated and just ripped it apart with a needle nose pliers. Later I realized that the knob I looked at was just a factory mistake or something and all the other knobs were hugging the enclosure... oops.
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Old 15th September 2008, 01:05 AM   #5
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assuming the CH1 and CH2 wires sre the signal coming into the volume control, and the VR1 and VR2 lines are the output lines, here's how they should be wired:
Attached Images
File Type: jpg pot wiring.jpg (40.1 KB, 319 views)
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Old 16th September 2008, 03:00 PM   #6
orbanp is offline orbanp  Canada
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Hi,

Just came across this site:

<http://www.rocketroberts.com/techart/sa10.htm>

This is on the Realistic SA-10 amplifier, that is the 31-1982A. It is not the B version, but should be close enough.

Good luck, Peter
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Old 16th September 2008, 08:41 PM   #7
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Quote:
Originally posted by unclejed613
assuming the CH1 and CH2 wires sre the signal coming into the volume control, and the VR1 and VR2 lines are the output lines, here's how they should be wired:

Quote:
Originally posted by orbanp
Hi,

Just came across this site:

<http://www.rocketroberts.com/techart/sa10.htm>

This is on the Realistic SA-10 amplifier, that is the 31-1982A. It is not the B version, but should be close enough.

Good luck, Peter
oh man, thanks for all the help guys! I really appreciate it. I think I'm going to order up some parts and get this thing cooking. I was thinking I may as well give it an upgrade. anyone ever upgrade a cheap amp like this? I was thinking just replace the caps with metal film and the opamps with higher end TI or that chips.
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Old 17th September 2008, 12:50 AM   #8
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a recap would be a good start. i notice there are 4 in the signal path and 1 in the feedback path (C102,C106, C109, and C112, also C110 in the neg feedback path). these are the most critical. next on the list is the bootstrap C111, which if it' marginal will decrease the output swing, and cause distortion. C105,C108, and C114 are essential for keeping AC ripple out of the output (comp-symms like this one and Dynaco amps never get rid of ALL the hum without regulated supplies). you could replace C114 with a 2200uf, but don't go much higher than that. in the process, change D102 and D103 to 3 amp diodes. if you're feeling particularly brave, you could replace D101 and R118 with a real bias transistor (but know what you're getting into first, since a mistake can cost a pair of output transistors).

the (B) taper on the volume control is a log taper, and the control has a loudness tap, which boosts the highs and lows at low levels to keep the amp sound spectrally balanced.
the other pot is a linear (A) taper, it is the balance control.

i see what you're getting at with op amps. you could replace all of the circuitry except for the ouput transistors with an op amp. the power transformer has a center tap, so modifying the power supply into a bipolar supply would be easy. this is only a 1watt amp, but a bridge should give you +/- 12V rails, so you might actually be able to squeeze a few more hundred milliwatts out of it, and ditch the output cap too. but don't try changing the power supply around while keeping the existing amp circuits
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