Marantz SR4500 no treble in 1 channel

[srinath]

I got this sr4500 which has no treble in 1 channel. I am yet to open it up so its a very vague question for now even by my standards.

What component in an amp controls treble - and I know its a general vague question but something like "a capacitor in the power amplifier circuit" or a resistor before the power amplifier section" or whatever will suffice for now.

I would use the replies I get to open it, search for the component more intelligently (yea right that'll be a first) and then post back an even more obtuse Q.

Thanks much.
Srinath.

[jaycee]

It really depends how the amp is built. This is a reciever, so all bass/treble processing would be done at the preamp stage. If a power amp channel itself has lost it's treble then the usual culprit is a coupling capacitor, but these tend to result in loss of bass response.

[srinath]

OK I will open it and check. If its the preamp wont it affect all channels 5 channels ? Its of course ready for 5.1 input presumably it decodes dolby first and delivers 5 channels into the pre amp, so it may have that issue there. Thanks so much.
Cool.
Srinath.

[srinath]

Well, I played a whole cd, plenty of high notes in it, on both left and right only connected. No difference really,
I am calling this thing automagically fixed till it starts acting up.
Thanks.
Srinath.

[Fast Eddie D]

Originally Posted by srinath

No difference really,
I am calling this thing automagically fixed till it starts acting up.
Thanks.
Srinath.

You have a bad switch or intermittent component. Sometimes a bad electrolytic works fine in a device that sees regular use, but let it sit and it acts up when you power up again. Turn the device on and let it "warm up" for a while and it starts working fine again. I have seen this in a couple of old amps and recievers. Coupling caps make the worst sounds when they are intermittent; distortion, clicking, and popping.

Switches in the signal path are very troublesome in older units. I got a Nakamichi reciever for free because it was acting up. It did not take me long fiddling with it to determine that the tone defeat switch was the culprit. I removed the switch and hard wired the circuit so you couldn't defeat the tone controls. That old reciever now rocks my auto shop. It sounds great, and I fixed it for free.

[srinath]

Ooooo fast eddie you're making my day ... not for this 4500 marantz, that is a 2003 amp, and it worked fine from the startup yesterday, no warm up time, it sounded fine all the way across. Anyway I'll take your advice ad remmeber it if the thing acts up.
However I have a old fisher ca 2110 integrated amp that has 1 channel out, but flipping the tone defeat switch makes it pop in both channels. I have swapped the output modules from one side to other, made no diff, still the same channel is bad.
I thought it may be in the preamp stage, but you give me food for thought. maybe its the tone defeat switch after all.
I have a marantz 2226 that has a tape monitor switch that can eat 1 channel. Its got some crap in there, usually pumping it takes care of it. Maybe I should clean and deox - but well ... You'd think these things are going to eat both channels ... but no.
Cool
Srinath.

[Fast Eddie D]

Originally Posted by srinath

I thought it may be in the preamp stage, but you give me food for thought. maybe its the tone defeat switch after all.

If a problem is not immediately obvious, one of the first things you do is evaluate the preamp/ power amp separately in order to start isolating the problem. Even in an amp without pre amp out and power amp in jacks, you can find a place to separate the circuits usually pretty easily.

You'd think these things are going to eat both channels ... but no.
Cool
Srinath

It's never that way in practice.

Many repairs to older recievers and amplifiers are quite simple to track down and with some imagination you can repair them with available or salvage parts. Sometimes it's even better if they're not worth repairing because then you have lots of parts to DIY or repair another vintage unit. Old power transformers make a nice starting point for a new amplifier. Ditto the heat sinks, etc.

I have used whole circuits out of old units as a building block for a new device. Recently I built a whole "mid-fi" integrated amp out of circuits from several different units, and it sounds pretty good, with lots of punch and sparkle. I even cut down an old chassis and rebent part of it to make a smaller chassis. I used a "50 + 50W" chip amp circuit out of a big tabletop stereo, beefed up the power supply a little and it plays loud with lots of punch. I used a whole preamp/ tone control board (replaced the caps is all I did to it) out of a Mitsubishi reciever that went up in smoke and took my speaker with it. This is an old circuit with passive tone controls and variable loudness control (about 8 different settings). The amp sounds real clean and punchy without a lick of harshness. It exceeds my expectations; I really assembled it just as an exercise and to use up some of my junk.

[srinath]

I have been trying, rather sporadically on that ca2110. But let me redouble my efforts asap.

The Marantz sr 4500, I have heard it for 2 hours today, nothing seems amiss in it. I have a theory though. When listening to somehting, you suddenly have a tweeter die in 1 channel. We know that can and does happen, but to the average user of audio, that will sound an awful lot like the most complicated piece in the room - the thing with the most lights and buttons gave up the ghost. My theory ... and I am sticking to it.

Cool.
Srinath.