thanks mooly. it's all good in headphones but on the speaker posts nearer the heat sink the output is quiet. it's there but much lower than the other side. would a higher bias one side to the other sccount for the volume difference?
I'm going to chemically clean the main switch , I'm pulling it now
I'm going to chemically clean the main switch , I'm pulling it now
Bias (as far as we are concerned here) has zero effect on the gain. The only difference it makes is to increase distortion slightly at low levels if it is set to low.
I would start by switching the amp off and then with no headphones connected see if you can trace the continuity back from the speaker sockets to the headphone switch/socket (I'm not sure how this version switches between speaker and headphone) and from there back to the main amplifier outputs. Do that for good and bad channel and see if anything shows up.
I would start by switching the amp off and then with no headphones connected see if you can trace the continuity back from the speaker sockets to the headphone switch/socket (I'm not sure how this version switches between speaker and headphone) and from there back to the main amplifier outputs. Do that for good and bad channel and see if anything shows up.
the headphones don't disconnect the speakers on the cyrus amps, odd but true.
The balance is out on speakers when using the phono stage but not when using the line inputs.
Listening with headphones ALL inputs sound good including both the MM & MC phono stages!
I dismantled and cleaned main switch last night but it didn't help.
Really weird tp have a problem with phono selected using speakers,
but not when using headphones,
and all inputs fine through phones
The balance is out on speakers when using the phono stage but not when using the line inputs.
Listening with headphones ALL inputs sound good including both the MM & MC phono stages!
I dismantled and cleaned main switch last night but it didn't help.
Really weird tp have a problem with phono selected using speakers,
but not when using headphones,
and all inputs fine through phones
is it possible to test continuity from phono stages to speakers ? would the headphone outpust use the same circuits as the speaker outputs or two separate paths. I'm thinking there might be a fault on the signal path between phono and speakers but that's not passed through to get to the headphone output ?
The headphone output almost certainly uses the same main amplifier as the speakers. Typically a series resistor is put into the signal path from amp output to headphone to reduce the available power. That is the most common and simplest arrangement.
The only difference between driving speakers and driving headphones is going to be the current drawn from the amplifier output. So at this point I wouldn't suspect a gain issue on the phono stage... its going to be something much more obscure such as a poor ground that is allowing the gain of the phono stage to be changed due to some superimposed signal voltage. A bit like increasing the feedback, it lowers the gain.
A scope would confirm (or otherwise) all of this.
It would be worth checking the ground return of each speaker socket and making sure its good.
Just seen your new post... again scope checks to confirm. It leaves no doubt.
If you haven't a scope then you can attempt AC voltage measurements using a test tone (test CDR or MP3 file) and comparing levels but its very much second best to a scope.
A dummy load is good as it would allow you to see if the signal dropped when the load was applied.
The only difference between driving speakers and driving headphones is going to be the current drawn from the amplifier output. So at this point I wouldn't suspect a gain issue on the phono stage... its going to be something much more obscure such as a poor ground that is allowing the gain of the phono stage to be changed due to some superimposed signal voltage. A bit like increasing the feedback, it lowers the gain.
A scope would confirm (or otherwise) all of this.
It would be worth checking the ground return of each speaker socket and making sure its good.
Just seen your new post... again scope checks to confirm. It leaves no doubt.
If you haven't a scope then you can attempt AC voltage measurements using a test tone (test CDR or MP3 file) and comparing levels but its very much second best to a scope.
A dummy load is good as it would allow you to see if the signal dropped when the load was applied.
Subjectively 50% would be a massive difference in voltage across the speaker. That would show on a simple AC voltage test with a 400 to 1kHz tone and a suitable meter capable of resolving low AC voltages.
Apply the signal and check the AC output voltage across each speaker feed. Note the readings and then apply dummy load resistors in place of the speakers (4.7 ohm 5 or 10 watt resistor) is a good test value. If the level drops more than a fraction then there is a problem. You would then look to see if the input signal to the power amp was affected or not.
It wouldn't be first on the list. Measuring signals on the pot would confirm in seconds (scope again
)
Its a start. If you try this with a meter then I would recommend not having speakers connected.
Try measuring the amp output by setting the volume control so that the AC voltage is around 3 volts. That would be the equivalent of just over 1 watt into 8 ohms which would be unpleasantly loud on a test tone.
Also note the voltage applied to the input of the volume control and also on its wiper.
See if both channels are the same. If they are then add a load and see if the reading falls on the bad channel. If it does then see if the input voltage has fallen as well.
Got to go
Try measuring the amp output by setting the volume control so that the AC voltage is around 3 volts. That would be the equivalent of just over 1 watt into 8 ohms which would be unpleasantly loud on a test tone.
Also note the voltage applied to the input of the volume control and also on its wiper.
See if both channels are the same. If they are then add a load and see if the reading falls on the bad channel. If it does then see if the input voltage has fallen as well.
Got to go
Yes, you can still apply a low level input tone and check the output of the phono stages. The level required at the input will be just a few millivolts and so a resistive divider is needed to get an accurate and noise free input signal from your MP3 test file.
Work on that later, check the amp and line stages first.
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