I have a working unit im looking at and it has a couple of items i am going to look at but havent come across yet and thought i would see if you guys had any ideas before i started.
sound is generaly ok, and not distorted at all, but the levels are lower than what i would expect.
tone controls appear to be ok.
loudness doesnt seem to have any effect.
when volume is turned right down you can still hear the slightest of sound.
when you turn balance left to right and visa versa you still have sound coming out of the opposite one, not fully, but noticible.
There isnt any problem with the phono/aux/tuner switch so thats ok
im thinking it might be something to do with the fact it has mic/source mixing
when you turn that down to source only with the tape/source switch in 'source' it seems ok, but if you turn it to tape and leave the switch as it was, you can still hear it,but at a reduced volume(unless its supposed to be like this)
im just starting to go through the schematic, but the quality isnt brilliant
the amp is pretty dirty inside and i will clean all the switches and pots as this may be having some effect.
could this just be poor/failing caps??
sound is generaly ok, and not distorted at all, but the levels are lower than what i would expect.
tone controls appear to be ok.
loudness doesnt seem to have any effect.
when volume is turned right down you can still hear the slightest of sound.
when you turn balance left to right and visa versa you still have sound coming out of the opposite one, not fully, but noticible.
There isnt any problem with the phono/aux/tuner switch so thats ok
im thinking it might be something to do with the fact it has mic/source mixing
when you turn that down to source only with the tape/source switch in 'source' it seems ok, but if you turn it to tape and leave the switch as it was, you can still hear it,but at a reduced volume(unless its supposed to be like this)
im just starting to go through the schematic, but the quality isnt brilliant
the amp is pretty dirty inside and i will clean all the switches and pots as this may be having some effect.
could this just be poor/failing caps??
More information as to how your system is set up , what is the chain of components that you are using . And the cabling and Speakers and some pictures showing this for us that are a little slow up top and like visual aids, a.k.a.a myself. Lol
I'm a novice but my theory is the caps around the pre or input transistors. The selector is a physical disconnect so the sound must be getting through the ground because they're not being held down to 0v by the caps. Likewise the caps are not strong enough to drive the transistors hence low volume.
This is pretty much an entry level product of 40 years ago and an example of early Japanese builds. I wouldn't expect hi-end sound or stellar isolation between channels because the "offness" of level controls often depends on careful grounding and wiring practice or the signal may be compromised by the effects of noise, signal crosstalk and leakage. Sometimes price constraints prevent using the best methods and you wind up with a compromise arrangement that doesn't impress when pushed to the limits of adjustment but nonetheless may work just fine at normal stereo settings.
I'm not saying that's the problem and answer but if there are no further related faults, it could be a matter of what you have come to expect from newer, higher grade audio products. If it's more obvious than you think is acceptable, the problem will likely be in the grounding which could well be via the chassis and/or just not good enough due perhaps, to the failure of electrolytic caps in the signal path as mentioned by k.
High impedance signals can also crosstalk quite readily over old, open style rotary selector and slider switches, also between bundled, unshielded wiring. If that's the case, by grounding the signal at various points along the path, you may be able to isolate the area and the likely culprit(s).
I'm not saying that's the problem and answer but if there are no further related faults, it could be a matter of what you have come to expect from newer, higher grade audio products. If it's more obvious than you think is acceptable, the problem will likely be in the grounding which could well be via the chassis and/or just not good enough due perhaps, to the failure of electrolytic caps in the signal path as mentioned by k.
High impedance signals can also crosstalk quite readily over old, open style rotary selector and slider switches, also between bundled, unshielded wiring. If that's the case, by grounding the signal at various points along the path, you may be able to isolate the area and the likely culprit(s).
Your description sounds like what is called crosstalk, and it is pretty common in older amplifiers and amplifiers in the lower price ranges. Expensive high end amplifiers use a number of strategies to reduce or illuminate crosstalk.
Crosstalk generally has two sources:
This can be corrected sometimes, but if the common grounds are on the circuit board it may mean cutting and rewiring the tracks on the circuit board. Often hum and ripple noise gets into the audio if any of the supply currents flow in tracks used for signal ground, and can be fixed the same way.
The balance control is a slightly different problem. Each end of the control needs to be a very low resistance to a good clean audio ground. Even a tiny resistance here will stop the panned out channel going to complete attenuation. It's probably possible to fix this too. One thing to try first is just to clean the control with DeOxit. A small amount of contact resistance at the wiper of the balance control will also cause this fault.
Crosstalk generally has two sources:
- Capacitive coupling between two sections of the amplifier, like one input to another input. This is reduced or eliminated by screened cables in wiring and by guard tracks on PCBs (a guard track is a ground track between two signal tracks, to shunt stray capacitive signals to ground).
- Common ground wires or tracks, like between the input connectors of two different inputs to the circuit board or selector switch. Common grounds will have the return currents for all of the signals going through them, and current cannot flow without some voltage drop, so these common grounds introduce a small voltage from one circuit into the other one that shares the ground.
This can be corrected sometimes, but if the common grounds are on the circuit board it may mean cutting and rewiring the tracks on the circuit board. Often hum and ripple noise gets into the audio if any of the supply currents flow in tracks used for signal ground, and can be fixed the same way.
The balance control is a slightly different problem. Each end of the control needs to be a very low resistance to a good clean audio ground. Even a tiny resistance here will stop the panned out channel going to complete attenuation. It's probably possible to fix this too. One thing to try first is just to clean the control with DeOxit. A small amount of contact resistance at the wiper of the balance control will also cause this fault.
I just had a look at the service manual and there are common signal earths everywhere, including to the balance control. Sadly I think the crosstalk in this amplifier is not going to be easily sorted out. The manual quotes "intersource crosstalk" as -55dB, which is really quite a poor specification. I decent figure would be >80dB.
I just had a look inside the amp on the copper side,
I found that the ground pads (trace) form the ground of the two big capacitors to other amp stages not quite ideal, it can not travel in a straight line and have to go a longer way round,
most important, the trace of the pads are very thin. suspect it was the cause.
suggestion
use a star grounding method,
from the joints of the two big caps,
use wires not less than no.19AWG,
to build a ground network to connect all the amp stages' grounding,
in a direct and shorter way,
so to help re-enforce the present grounding.
hope you solve it soon.
I found that the ground pads (trace) form the ground of the two big capacitors to other amp stages not quite ideal, it can not travel in a straight line and have to go a longer way round,
most important, the trace of the pads are very thin. suspect it was the cause.
suggestion
use a star grounding method,
from the joints of the two big caps,
use wires not less than no.19AWG,
to build a ground network to connect all the amp stages' grounding,
in a direct and shorter way,
so to help re-enforce the present grounding.
hope you solve it soon.
not having alot of luck with this, but only just started again today looking at it.
grounding seems good, there is good continuity to the chassis from the board in all the places i have checked
not too sure where to start with this one TBH
Well done. It's hard to describe the exact nature and severity of a problem like you had and the assumptions I made about what you were hearing were obviously wrong. Glad you got it sorted.
all suggestions are helpfull.
im not very experienced yet so every suggestion is a help whether it solves the issues or not,it gives me other senarios look at in future if i get simlar issues.
as always thanks to all who contributed 🙂
im not very experienced yet so every suggestion is a help whether it solves the issues or not,it gives me other senarios look at in future if i get simlar issues.
as always thanks to all who contributed 🙂
Thank you! This saved me a lot of searching. I had the same issue with the amplifier. Replaced R806, all good now.