2325 mystery problem

[klamsoss]

@Steven Tate the slider does reduce left side output as it should. I fiddled with it thinking maybe there was some local patches of increased resistance for the right channel, but that doesn't appear to be the issue. Basically I'm calling that a rule-out.

I could theoretically just have the slider always a little off center. That's kind of a band-aid, though, ya know? I would like to actually fix the problem. Especially since this is a nice unit belonging to a friend, and not a garage-system beater-amp.

 

[Steven Tate]

Maybe check the output of the preamp/tone board with a sine wave input and see if your amplitudes are the same. Looks like pins 13 and 14 on the long connector on PE01, with pins 11 and 12 being ground.

 

[klamsoss]

Maybe check the output of the preamp/tone board with a sine wave input and see if your amplitudes are the same. Looks like pins 13 and 14 on the long connector on PE01, with pins 11 and 12 being ground.

Same thing happening at those pins. I can't say for sure if the output was perfectly matched before I started my work, but it wasn't noticeably different that I can recall. I didn't take measurements.

I can't figure anything I would have done during the rebuild that would shift the output. I normally measure all the capacitors I install to make sure they are at spec (although I don't test for leakage because I don't have equipment to make that easy, and I use new, fresh components from digikey, anyway.) and I didn't do anything with any resistors on the preamp board. I didn't try to match the few transistors i replaced... but is that realistically the culprit? I only replaced HE03/05 with KSC1845 and HE04/06 with KSA992.

@67dylan I think you had a similar problem on a different model?

Just to review, I have done a full 2 stage cleaning PLUS lube (cleaner with silicone) on all the controls, have isolated the issue to the preamp (not the source, not the power modules, although I do intend to run a signal in to the "main in" and compare the outputs at the speaker jacks to make sure there isn't an issue there, stacking on top of the preamp issue). I have the tone controls set to "off". Nothing changes when I switch to mono or reverse stereo. The output is always low on the same side. I even got 2 extra sets of meters and switched those around to make sure it wasn't an instrumentation problem. The issue doesn't vary meaningfully as you turn the volume up and down. Seems to happen with all inputs, but I have only done measurements on AUX. My impression with FM going is that it's the same, though, and my instruments aren't lying.

 

[Steven Tate]

OK, I am really spitballing here, but if L/R output is different on the PE01 board, I would try to find some measure points at the front end of the board to compare. The schematic gets a little crazy, but the BA312's might be a place to check for voltages that differ significantly. It looks to me like signal from the volume control goes into pin 2 on each BA312 and out at pin 6. The schematic has some DC voltages listed. I guess measure to see if those are in spec. It would seem to me an AC signal would be at these pins. Could you measure AC in to the board at the BA312? I don't know, but you could look with a scope to see if your signal is present at those pins and measure the voltage. Maybe someone better equipped than me will give you better guidance. But this is probably what I would be looking at next. You need to find out where your signal is losing amplitude. Right before the BA312's is the volume control. Could you be getting different output voltages from the volume control front and back segments? Or, is the balance pot outputting different amplitudes when centered? These are areas that might be worth checking out with your sine wave and a scope.

 

[klamsoss]

@Steven Tate I am basically thinking the same thing. Was going to make sure wherever the signal comes IN to the board is even, then try and find a spot mid way though the signal path. and take the "divide and conquer" approach. I'm not the best at reading these schematics (not quite as simple as the 60s tube gear I've worked on) so I'm very grateful for all the help!

I'll see if I can measure AC at BA312 and check the DC voltages against what is in the schematic.

I didn't think it was related to the volume control since the % difference seems to be relatively consistent across the volume range, but I guess if the issue isn't on the wiper mechanism itself, it wouldn't vary with the volume level. I haven't checked the balance pot jsut because it's probably the most difficult control to get to on these things.

 

[Magnus Back]

I had a similar issue, the volume reduced 25% when the amp (2235B) had been used for about 2h.
Turned out to be HE06 or HE05 on PE01. When cold they test "fine" with a DCA55, decent hfe etc.
Cold spraying them produced crackling.
Could be you have a permanently bad transistor?

 

[klamsoss]

I finished up the ESS AMT1 speakers last week and they turned out pretty nice. I think they are going to match up EXTREMELY WELL with this 2325.

@Steven Tate , many thanks for the guidance throughout this process. Also, to @hirscwi for his cheat sheet.

I don't know what the issue was with the output from the preamp. I took it all apart, cleaned everything again, and started tracing... half way through tracing, the problem resolved itself. One of my 'scope probes gave me problems for about 5 minutes but sorted itself out when I swapped inputs on the 465B (not the first occurrence of the issue). When I had it sorted, I started poking around again for signal and all of the sudden, everything was nice and balanced! I can't, for the life of me, figure out what I did that would have fixed the imbalance issue. I cleaned the volume pot again, but based on the prior symptoms, I really don't think it was a dirty pot.

Over 2 hours of run time later, it hasn't gone out of whack again. It was interesting, though, that the bias and offset were off even though I hadn't really done anything other than the spec adjustments to the phono preamp. It doesn't make sense to me that those adjustments would affect the bias or DC offset.

Whatever it was, I'm not going to complain. As they say, this restoration has been real, and this has been fun, but I wouldn't say it has been real fun. I am happy to be done with it and have my bench open again for my own projects. (LOL just kidding. I have a stack of stuff to get to. Funny how everyone has something that needs a look once they hear you can fix this stuff..... )

Anyway, this this 2325 sounds really, REALLY good.
Right away.
That hasn't been my experience with past marantz restorations (2330B, 1060) which took a little while to "break in" before they sounded their best. It has a warm sound but has as much rhythm, pace, and timing as you could want. It's rich without being syrupy. Mellow, but not boring or lazy. My personal opinion has always been that the marantz sound is towards the "sleepy" side of things. Not so, this! But neither is it fatigue inducing (like the Musical Fidelity A300 [seen below the marantz] can be with certain speaker/source combos). The phono stage is a little rolled off with this AT LP-120 I have in for a repair and some upgrades, but that could be the deck, or the cables, which are crap (part of the repair/upgrade) and probably fairly high capacitance. We'll see how it sounds hooked up to my Thorens over the next few days. My understanding is that the Marantz phono stage in here is nearly identical to the phono stage in the 2330B and the 1060, as well, so I wouldn't expect there to be a significant difference in overall sound/tone character. Someone correct me if I'm wrong...

The FM reception and sound is pretty impressive, though it can't hold a candle to my Fisher FM-100-B. It's as good as 99.9% of people would ever want, and I wouldn't notice the different between it an my tube unit if I didn't do a LOT of radio listening. FM muting works perfectly. It'll find stereo for probably 75% of the stations that the Fisher finds, which is saying something, because that pulls in CRAZY distant signals really well. Haven't tried the AM side of things because there's really no AM that I care to listen to around these parts. AUX seems to work perfectly with the Oppo player I have, and I haven't yet tried the tape loops, which is something I DO need to do.

Yes, I realize it doesn't hurt that it's pushing some gussied-up KLH sixes... they tend to make everything sound good. But regardless, it sounds great, and with the ESS AMT1 speakers leaning slightly towards the brighter side, and this 2325 having boat loads of power to push them, I think my buddy is going to really like the combo.

Anyway, many many thanks to, well, really ALL of the AK community for help, inspiration, and encouragement. To those who have helped, I am in your debt and should you ever find yourself in Cincinnati, don't hesitate to message me. I'll buy ya a beer.

 

[Magnus Back]

I had a similar issue, turned out the new probes I bought had a half broken lead inside. %#$%^&*(~!
You measure, it's good, Measure again, it's bad.