Help With Vintage Receiver

C

cpd

Full Audioholic
My wonderful wife gave me a beautifully reconditioned Marantz 2240 receiver. I'd like to use it as my phono stage. I have my turntable plugged into the phono in. Instead of the jumpers between the "pre outs" and "main in", I am running a Y cable from each preout. One pair from there goes to a line level input on my AVR. The other pair from there goes back to the "main in" on the Marantz (to amplify the headphone output).

Here is the problem. The left channel when on phono input is barely audible, whether using headphones or through the AVR. Switching the red and white RCA's on the phono inputs on the Marantz does not affect it -- the left channel stays quiet. If I press the mono button on the Marantz both channels play at equal levels, but obviously not in stereo. The tuner works fine in stereo and plays both channels.

Not sure what's up. Any ideas?
 
M

markw

Audioholic Overlord
ultimately, it sounds like either the phono stage or the preamp is funky. You'll have to isolate them.

To use that receiver as a phono stage ONLY, you should be using one of the "tape out" jacks to feed your other amp. By tapping the signal after the preamp stage, you are running the signal through two preamp stages.

Naturally, you would probably want to reinstate the original pre out/main in jumpers.

You might get lucky, as it were, to find out that the phono stage is intact and the preamp stage is faulty. My $$ is that it's the phono stage since the tuner works.
 
c.coyle

c.coyle

Audioholic Intern
I'm only on my second cup of coffee this morning. Have you simply run the turntable straight into the Marantz phono inputs and listened? How's that working?

You have also introduced some added complexity with the "Y" cables. Have you checked them and all conections?
 
wiredsol

wiredsol

Audiophyte
I agree with using the tape monitor outputs to feed your AVR.
 
C

cpd

Full Audioholic
Mark, ideally I'd like to be able to use the tuner as well and potentially other inputs. Regardless, I absolutely want to be able to use the headphone jack on the Marantz. The goal is to be able to (1) listen to music on the Marantz with headphones while others may be watching TV through the other amp and (2) still route my vinyl to the other amp to play through the speakers. That's why I thought of the Y cable route. Are there issues with that approach? Are you suggesting to run the signal from the record player into the Tape In and then run the Tape Out to the phono in on the other amp? I tried that and the headphones on the Marantz played in stereo but very quietly. Also, the cable run between the two amps is 50' through the the wall so I'm not sure about sending a low level signal that far. At least I guess that means we know it's the phono stage, right?

c.coyle I have run it just into the Marantz inputs and the issue is still there.

The person she bought it from has been very responsive and said he already ordered a new phono board. He will pay for the repair here or shipping back to him or full refund. So that's a relief.
 
highfigh

highfigh

Seriously, I have no life.
My wonderful wife gave me a beautifully reconditioned Marantz 2240 receiver. I'd like to use it as my phono stage. I have my turntable plugged into the phono in. Instead of the jumpers between the "pre outs" and "main in", I am running a Y cable from each preout. One pair from there goes to a line level input on my AVR. The other pair from there goes back to the "main in" on the Marantz (to amplify the headphone output).

Here is the problem. The left channel when on phono input is barely audible, whether using headphones or through the AVR. Switching the red and white RCA's on the phono inputs on the Marantz does not affect it -- the left channel stays quiet. If I press the mono button on the Marantz both channels play at equal levels, but obviously not in stereo. The tuner works fine in stereo and plays both channels.

Not sure what's up. Any ideas?
When you write 'reconditioned', does that mean it was cleaned and serviced, or cleaned and listened to? As electronic devices age, the controls and switches oxidize and one of the most common symptoms is losing one channel, or both in one or more inputs.

While the problem is only exhibited using the Phono preamp now, the rest of what's below pertains to any/all inputs. If the Marantz has a switch that separates the preamp and power amp, move that a few times to see if the problem stops.

Rotate the source selector quickly through its range while you play an album and see if it A) crackles or B) comes back to normal. If nothing changes, rotate all of the other controls and listen for a scratching sound that comes and goes with movement. If that doesn't change anything, start pressing all of the switches and listen for the same sound. Be careful with the volume control- the sound may come back when the level is high and that could damage speakers.

If you have a 3.5mm-stereo RCA cable & a smart phone or any other device that plays music and has a volume control, use that as your source and lower the volume so it won't be too loud even at maximum on the Marantz volume control. When you connect it to the Phono input, turn the bass down fully- the phono preamp boosts the bass immensely and this can damage speakers if you leave it above minimum and increase the volume level. Use soft music without heavy bass for these tests.

If this does help, you or someone else will need to clean the controls and switches. Caig is the brand many use and it does work well. Radio Shack sells it but if you don't have one of their stores near you, Parts Express sells it, too.
 
M

markw

Audioholic Overlord
Mark, ideally I'd like to be able to use the tuner as well and potentially other inputs. Regardless, I absolutely want to be able to use the headphone jack on the Marantz. The goal is to be able to (1) listen to music on the Marantz with headphones while others may be watching TV through the other amp and (2) still route my vinyl to the other amp to play through the speakers. That's why I thought of the Y cable route. Are there issues with that approach? Are you suggesting to run the signal from the record player into the Tape In and then run the Tape Out to the phono in on the other amp? I tried that and the headphones on the Marantz played in stereo but very quietly. Also, the cable run between the two amps is 50' through the the wall so I'm not sure about sending a low level signal that far. At least I guess that means we know it's the phono stage, right?
In the Marantz, the phono stage (and tuner and whatever is plugged into it) is before the selector and preamp.

Connect the turntable to the phono inputs on Marantz. Connect the "tape out" to any line level (aux) input on the other receiver. It will be treated as any other line level input.

Select that chosen input. Whatever input you select on the Marantz will be sent to the other receiver without going through the Marantz's preamp stage.

If you reinstate the pre out/main in jumpers, nothing on the Marantz will ne altered. It will operate just as it does now. By using the "tape out", it's operation is not altered.

The only difference is that you won't be feeding the output of one preamp into the input of another preamp. Aside from the potential distortion, you won't have to worry about two volume controls.

50 feet is an issue but, in reality, the signal from the preamp out is actually lower than that of the "tape out". Despite it's name, a preamp* actually serves to attenuate the input signal. Try feeding a CD player directly into the "main in" stage of the Marantz if you want to prove that to yourself. ...but wear hearing protection

* in the old days they were called "control amps" for just this reason.
 
Last edited:
C

cpd

Full Audioholic
Highfigh, I'm not sure the extent of servicing but I know he replaced some transistors.

I did rotate the selector knob a bunch and pressed all of the buttons. There was no crackling, and it did not fix the issue. I am going to do some research on stereo repair guys in my area (Milwaukee -- if anyone knows any).

Mark, thanks again. I hooked it up as you suggested, and it works great other than the phono input issue. Tape out basically a works as a direct passthrough. So that solves the y cable issue and use of the headphones.

I appreciate everyone's everyone advice.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Highfigh, I'm not sure the extent of servicing but I know he replaced some transistors.

I did rotate the selector knob a bunch and pressed all of the buttons. There was no crackling, and it did not fix the issue. I am going to do some research on stereo repair guys in my area (Milwaukee -- if anyone knows any).

Mark, thanks again. I hooked it up as you suggested, and it works great other than the phono input issue. Tape out basically a works as a direct passthrough. So that solves the y cable issue and use of the headphones.

I appreciate everyone's everyone advice.
I have downloaded the circuits and service manual.

The phono stage has trim pots R 408 and 409 for the left and right phone amps respectively.

Unfortunately these trim pots are in the low voltage signal pathway before voltage amplification and RIAA equalization. I have to say straight up, this was an awful design choice and asking for trouble.

I would bet that R408 is far more likely than not the source of your trouble.

I would open the unit. Find R 408 and give it a good squirt of tuner cleaner. Now listen to the phono through headphones. With a small screwdriver advance R 408 and see if you can balance the channels.

If you can not then the problem is likely a failing coupling/DC blocking cap, or transistor.

This unit is pretty simple and should be pretty easy to sort out with the basic equipment like a signal generator and scope. The service manual only devotes a small paragraph to testing and analysis of the phono preamp. There are no ICs, so this unit should be readily serviceable.

I don't think there should be much time in this.
 
C

cpd

Full Audioholic
Rather than start a new thread I thought I would mention a new issue that has arisen. Again, I have a TT hooked up to the phono input. I also have a bluetooth receiver hooed up to the aux in. I have the Tape 1 line out hooked up to my Denon AVR 2805 for playing over my speakers. Everythign sounds fine when I play it through the Denon.

But when I listen with headphones connected directly to the Marantz, after a few minutes the right channel begins to crackle and cut in and out. My assumption is that something is wrong with a solder joint or component in the amp section, but I thought I'd ask here before taking it back to the shop.

For what it's worth, the guy my wife purchased it from claims to have refurbished the unit and advertised it with a picture of a bunch of the components he replaced (caps etc.)
 
TLS Guy

TLS Guy

Seriously, I have no life.
Rather than start a new thread I thought I would mention a new issue that has arisen. Again, I have a TT hooked up to the phono input. I also have a bluetooth receiver hooed up to the aux in. I have the Tape 1 line out hooked up to my Denon AVR 2805 for playing over my speakers. Everythign sounds fine when I play it through the Denon.

But when I listen with headphones connected directly to the Marantz, after a few minutes the right channel begins to crackle and cut in and out. My assumption is that something is wrong with a solder joint or component in the amp section, but I thought I'd ask here before taking it back to the shop.

For what it's worth, the guy my wife purchased it from claims to have refurbished the unit and advertised it with a picture of a bunch of the components he replaced (caps etc.)
The problem is almost certainly the volume control. The volume control is after the tape out.

Try cleaning the volume control with tuner cleaner.

These old ganged volume pots are giving trouble now and are almost impossible to find. So the restorer probably could not find one.

I have had variable success building them from single pots. The problem is there is not much accuracy between the pots, and so channel balance can vary quite a bit as you change the volume.

I know it sounds silly, but this has become the most difficult part of restoring this old analog equipment.

If the pot cursor is broken and you can't find a replacement, then the only option is to try and mount two mono pots and change the volume of the channels independently. This would be difficult to do neatly.

The other option is to design and insert a dual IC op amp with a design where both channels are controlled at the same time by one mono pot. This would be by far the best long term fix. I have not seen it done, but that is what I would do if confronted with this again.
 
C

cpd

Full Audioholic
Thanks TLS Guy. I am sure with some instruction I could try and clean the volume control, but the rest of that is pretty foreign to me.

First question, could the volume control cause the crackling/cutting out in one channel when i am not adjusting the volume?

Second, can you recommend a resource to show me how to clean the volume control?
 
C

cpd

Full Audioholic
I guess there is a third question. What do you recommend tuner cleaner?
 
TLS Guy

TLS Guy

Seriously, I have no life.
I guess there is a third question. What do you recommend tuner cleaner?
Yes, the volume control can cause a crackle when the volume knob is not being turned. However it should crackle when you turn it if that is the problem. Either way I would try cleaning the volume control first.

You need to open the unit up and inspect the control. See if there are any openings. If there are not you are probably SOL. Usually there is at least an opening where the contact come out. You put the spray pipe in any opening Turn the control as you do this. Use lots!

Since Radio Shack is now defunct, Amazon.com is your friend.
 
highfigh

highfigh

Seriously, I have no life.
Yes, the volume control can cause a crackle when the volume knob is not being turned. However it should crackle when you turn it if that is the problem. Either way I would try cleaning the volume control first.

You need to open the unit up and inspect the control. See if there are any openings. If there are not you are probably SOL. Usually there is at least an opening where the contact come out. You put the spray pipe in any opening Turn the control as you do this. Use lots!

Since Radio Shack is now defunct, Amazon.com is your friend.
Radio shack isn't totally defunct, they're rebooting. They still have about 1400 stores and they have a store locator on the site. Of course, they don't stock a lot of electronic components, but they have some.
 
C

cpd

Full Audioholic
Does THIS work? They have it in stock at my local radio shack.

Also, I assume when you say volume control we are talking about whatever is on the interior of the unit connected to the volume knob?

I cannot remember whether I heard the crackling when I turn the volume knob but I will check when I get home. I did notice crackling when I moved the balance slider. Could that be a culprit too?
 
C

cpd

Full Audioholic
Update. I got the detoxit and cleaned the volume control pot. I also used it with a q-tip to clean the headphone jack contacts. I did not clean the treble/bass/mid pots or the balance slider. There was no apparent access point and since the tone controls are not continuous (they click when u turn them) and the balance is a slider (with a rectangular control) I wasn't sure I could use the same product/process and i didn't have time to remove the faceplate and look for an access point.

The good news is that what I did do solved 90% of the issue. Before, once the crackling started it would not go away. I listened to two albums and now, it is largely gone except for a few intermittent times.

I am going to try and clean them again tonight, but I wonder if I should try cleaning the balance and tone controls too? Can I even use that stuff on those type of controls?
 

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