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Marantz 2230 Unbalanced volume

TellMeWhy

TellMeWhy

Active Member
Hi guys, I recently purchased a very nice 2230, serviced and partially recapped (but with original power and cap coupling caps). The receiver sounds wonderful but I notice that the L channel is quite a lot louder than the R. In fact the balance needs to be turned to the 2 o clock position to become equal. I checked this carefully and it's the same on all inputs, whether in mono or stereo with loudness on or off. I also checked swapping the speaker connections of course. Any ideas?
 
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Thanks ton4eff, I tried directly into the main in and the sound is perfectly balanced. Does that mean it's a question of adjustment in the preamp rather than the amp output itself?
 
This means that the power amp is OK. You have to clean all the switches (check the tape monitor especially) and if the problem persist, there is a problem with the preamp board, may be bad cap or transistor...
 
Thanks ton4eff. The unit has been thoroughly cleaned and many of the caps replaced. The sound in the L channel isn't bad, just quieter. I may just to live with the balance control at 2 o clock until anything worse sets in...
 
It could be an error in cap replacement, it happens, or bad transistor in the preamp... Can you upload a picture of the preamp board?
 
ton4eff said:
It could be an error in cap replacement, it happens, or bad transistor in the preamp... Can you upload a picture of the preamp board?
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Hi ton4eff, some pictures of the restored pre-amp board... Thanks, Jon
DSCF0952.JPG DSCF0956.JPG DSCF0957.JPG DSCF0962.JPG
 

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C405, C406 and C409 have all been replaced and they are correctly oriented. Everything else appears to be original.
I don't see any obvious issues from these pictures.
 
Jon_Bawn said:
R channel is 10.5v, L is 11.9v. With no load (no speakers) attached. Problem there?
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Is that the power supply voltage at the preamp board as asked for, or the voltage measured at the speaker terminals? The 2230 is a capacitor coupled amp circuit so must have speakers or a load attached to measure potential offset correctly. Otherwise, it will have a positive voltage on the speaker terminals. The measurement of DC offset with no load on it is for non-capacitor coupled amps.
 
mech986 said:
Is that the power supply voltage at the preamp board as asked for, or the voltage measured at the speaker terminals? The 2230 is a capacitor coupled amp circuit so must have speakers or a load attached to measure potential offset correctly. Otherwise, it will have a positive voltage on the speaker terminals. The measurement of DC offset with no load on it is for non-capacitor coupled amps.
Click to expand...
Sorry I misunderstood there then. J08 according to the service manual is the speaker outputs. Where would I measure the voltage at the preamp board please?
 
Whenever I see a gain difference between channels the first thing I do is check all the resistor values in-circuit, with the unit off and fully discharged. They should be close to marked, or if shunted by something else, should at least be the same on both channels. If that doesn't do it, measuring the DC voltage at all three pins of each transistor often offers a clue, but you need the right probes so as not to short anything out. It helps to put heat shrink tubing over the probes of a DVM, exposing only a tiny part of the tip, so as not to short anything. I sometimes take a photo of the top of a board, then mirror it in the computer, to give me a better map of where to probe on the trace side, if that's easier. Write those numbers in red on a copy of the schematic to ponder or post.

(edit/addition) I also would do a quick square wave test (400 Hz + scope) to be sure some response problem or tone control misadjustment isn't fooling me.
 
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ConradH said:
Whenever I see a gain difference between channels the first thing I do is check all the resistor values in-circuit, with the unit off and fully discharged. They should be close to marked, or if shunted by something else, should at least be the same on both channels. If that doesn't do it, measuring the DC voltage at all three pins of each transistor often offers a clue, but you need the right probes so as not to short anything out. It helps to put heat shrink tubing over the probes of a DVM, exposing only a tiny part of the tip, so as not to short anything. I sometimes take a photo of the top of a board, then mirror it in the computer, to give me a better map of where to probe on the trace side, if that's easier. Write those numbers in red on a copy of the schematic to ponder or post.

(edit/addition) I also would do a quick square wave test (400 Hz + scope) to be sure some response problem or tone control misadjustment isn't fooling me.
Click to expand...
Thanks Conrad. Actually I was lucky enough to have the seller offer to recap the preamp board and replace the transistors there. But sadly now my 2230 sounds really dull and muted. The receiver previously sounded great, and had been partially recapped, but had a louder, stronger, clearer sound on one channel. Renewing the preamp board has equalised the sound quality in both speakers, but now both channels sound pretty bad- so dull it's almost muffled unless you add extra treble. Is a burn in time of caps and transistors a reality I should get used to? Does it really matter which brand of caps are used on the lower value one? I didn't do the work myself- it was done by a very generous eBay seller... The power and cap coupling caps are original and apparently tested as good. The amp sound great direct to the main in so the problem must be in the preamp. Any advice gratefully received! Thanks, Jon
 
Burn-in, if it's a factor at all, wouldn't account for that dramatic a difference. If you were used to some super bright bass-free sound because the old caps were so bad they weren't passing any bass, that could account for it, but I doubt it. The fastest way to tell is ten minutes on the test bench, looking at a low frequency square wave to see if the response is as expected, then the usual power and THD tests just for good measure. A couple things you might do would be to verify the tone knobs are mounted on center, equal travel to each side. Then maybe make up a tone CD using Audacity or something similar. Play spot frequencies or a sweep and see if there's any unusual roll off as the pitch gets higher. Check your tweeters too! Do you get the same sound quality from both speakers and headphones? You can do response checks with a sound card, but instructions for that are beyond a short post.
 
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