• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Imbalance output

DomPal

DomPal

New Member
Hello good people!

I recently installed new diodes, caps transistors, thermistors.. on my Marantz 2270. Now my mistake is that I didn’t recird the output before I started so there’s no way of knowing i mf the problem was present before. I started on the Right channel board first and I checked every component from the resistors to the caps to see if everything is still within spec and some caps did not but the resistors are all within 2% so I am pretty sure nothing is wrong with that board.

So now I have a new Right channel board and old Left channel board. I tested the output and saw that the left channel was outputing more. About 25mV on idle volume and the Right at about 7mv . As I go up to 10V output with 8ohm dummy load, both channels seem to equalize but when I go at rated output (about 17-18V) the left is out puting by 0.4V more. I thought maybe it’s just because it’s an old board so I «recapped» the SAME components on the left too and I tested again. Same results. I cleaned the balance and Volume pots with deoxit and still the same. is it possible that the imbalance lies on the preamp?
 
Register to hide this ad
Measure R401/R402 and make sure they are matched. Some people go so far as installing very expensive high quality resistors at that place. I replaced them a couple of times with normal film 390R.
 
It's possible it is the volume pot and then if so, it's possible that the volume control is in spec. I believe it only tracks to about to 2 or 3dB. The way to tell is to use a signal generator at low level and turn the volume pot all the way up and see what the output levels are then. That way it's not affecting the levels. Or simply unplug the preamp to main jumper plugs and drive the main inputs with the low level signal applied to both inputs via a "Y" cable. The first methos has the preamp and main amps involved and the second is only the main amp modules.
 
ocdecio said:
Measure R401/R402 and make sure they are matched. Some people go so far as installing very expensive high quality resistors at that place. I replaced them a couple of times with normal film 390R.
Click to expand...
Thanks for the tip :D i checked the R401/R402 resistors and R402 = 392.9 ohm while R401 is 391.1 ohm. Is that close enough to not cause a problem?
 
rBuckner said:
It's possible it is the volume pot and then if so, it's possible that the volume control is in spec. I believe it only tracks to about to 2 or 3dB. The way to tell is to use a signal generator at low level and turn the volume pot all the way up and see what the output levels are then. That way it's not affecting the levels. Or simply unplug the preamp to main jumper plugs and drive the main inputs with the low level signal applied to both inputs via a "Y" cable. The first methos has the preamp and main amps involved and the second is only the main amp modules.
Click to expand...

Thanks I will try this! very good idea. Do you have a link for a new volume pot if ever that needs replacing? Is the left and right channel seperate on the volume knob?
 
Last edited:
I have tested further and can confirm that the problem does not lie on both amp boards. I connected a signal generator directly to the amp boards through Main In and the result are L = 1.12V and R = 1.13V, just a 10mV difference which is fine right? but then I tried inputing a low signal through the preamp and setting the volume to max and I got L = 234mV to R = 226mV which is pretty equal. Does this mean that the volume pot is defective?
 
DomPal said:
Thanks I will try this! very good idea. Do you have a link for a new volume pot if ever that needs replacing? Is the left and right channel seperate on the volume knob?
Click to expand...
No source but can tell you to stay away from the crap $90 ones from "Vintage Hifi Audio" seller on eBay. Yes, they are separate sections.
 
DomPal said:
I have tested further and can confirm that the problem does not lie on both amp boards. I connected a signal generator directly to the amp boards through Main In and the result are L = 1.12V and R = 1.13V, just a 10mV difference which is fine right? but then I tried inputing a low signal through the preamp and setting the volume to max and I got L = 234mV to R = 226mV which is pretty equal. Does this mean that the volume pot is defective?
Click to expand...
Well, it means the volume pot is the reason for the difference. It is not defective if it's off 0.4 volts at 17 volts output which is well under a dB difference.
 
How do you calculate dB? When you save it tracks to about 2 or 3 dB, you mean the difference between the left and right output through the volume pot right?
 
Voltage A / Voltage B, then LOG, then * 20. In formula Log(Voltage A/VoltageB) * 20

Yes to the second question.
 
Thank you so much for the help. I checked and across the volume pot the highest difference it tracks is 0.7dB about 1V of difference. I think I read somewhere that a person cannot tell the difference below 1dB so I think this is ok :D
 
You must log in or register to reply here.
Back
Top Bottom