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post #1 of 7 Unread 05-04-2017, 09:36 AM - Thread Starter
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Vintage NAD Amp Troubleshooting Help

Hey all,

I recently picked up a vintage NAD Integrated amp (7250pe) on craigslist.



Before agreeing to purchase I brought a long a set of speakers and ran it through its paces, testing all inputs, testing all knobs/pots/switches making sure they are smooth and noiseless and listening to make sure nothing obvious was wrong.

Once I got it home - however - I started having minor problems.

In its stock configuration this amp, while the receiver/integrated portion is in the same cabinet, is configured such that the pre-amp/receiver section has stereo RCA outputs, and the power amp-section has stereo RCA inputs. From the factory these were bridged, but those bridges disappeared at some point in the last 35 years.

At first, I hooked it up by using RCA splitters connected to the pre-amp section output, so I could connect my subwoofer, at the same time as I am feeding my signal back in to the power-amp inputs.

This sounded good, but I had intermittent problems on the right channel, where it would go from sounding good, to starting to distort (even at low volumes) and then the right channel would go down to extremely low volume/go out all together. Powering the amp down checking the connections and bringing it back up again, corrected the problem for a while, until it recurred.

As art of my troubleshooting efforts, I remembered that I have had issues with weird intermittent shorts when using firm RCA adapters/splitters in the past, so I decided to test if these might be the issue. I disconnected the splitters, and instead ran an RCA cable from the pre-amp out to the subwoofers in, and then another cable back from the subwoofers outs, into the power-amp inputs on the NAD amp.

In this configuration I never had the right channel drop out (or at least not yet, I only tried it last night for about an hour)

I have - however - noticed that there is a not insignificant difference in volume output between the right and left channels.

Doing some rudimentary measurements using a ruler to keep the distance equal at 12" and a cheap SPL meter I got on Amazon I have measured that at 12" and normal listening levels (for me, about 70-80db) the right channel is consistently about 3db quieter than the left channel. I can compensate for this using the amps balance knob and it sounds pretty good, but I am still concerned.

How would you guys recommend going about troubleshooting and potentially fixing this issue?

My thoughts are as follows:

1.) All knobs/pots are smooth and there is no noise over the speakers when they are turned, so I don't suspect that pot degradation is the issue, but I'm open to hearing your thoughts.

2.) I remember reading that pots can produce unequal volumes across the channels at low volumes. In my near-field listening setup, the pot is usually in the 20-30% range. Is this considered "low volume"? Could this be the cause?

3.) Could this be due to the 35 year old caps finally giving out? Is it even worth having the caps replaced on an old amp like this? (I have no idea what this would cost me to have this done at a repair shop, and I have tried by hand at board soldering in the past and found that I really don't have steady enough hands for the job)

4.) Would taking it to a shop to have cleaning and "tune up" done make sense? What should I expect this to cost approximately?

5.) Things I plan on trying when I have some time, but haven,t gotten around to yet:

- Switching the speakers left to right to see if the problem persists. (I don't think this is speaker related, as I don't recall having this issue on my Emotiva UPA-2, which I am moving to a different application, but it is worth checking out I guess.)

- Switching the speakers from Speaker A to Speaker B to see if the problem persists.

Other than this, I am at a loss right now. I'd be interested in hearing ANY comments you might have that could be helpful!

Thank you,
Matt

Livingroom: 65" Panasonic Plasma, Denon AVR-x1300w, Fronts: RBH SX-6300 Towers, Center: RBH 441-se, Surrounds: RBH 41-se Sub: Dual SVS PC13-Ultra, Source: Custom Kodi Box

Desk: DAC: Schiit Modi Multibit,
Headphone Amp: Schiit Jotunheim, Heaphones: Sennheiser HD650 and Beyerdynamic DT770 Pro
Speaker Amp: Emotiva UPA-200, Speakers: RBH 41-se, Sub SVS SB12-NSD
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post #2 of 7 Unread 05-04-2017, 02:16 PM
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Originally Posted by mattlach View Post
Hey all,

I recently picked up a vintage NAD Integrated amp (7250pe) on craigslist.



Before agreeing to purchase I brought a long a set of speakers and ran it through its paces, testing all inputs, testing all knobs/pots/switches making sure they are smooth and noiseless and listening to make sure nothing obvious was wrong.

Once I got it home - however - I started having minor problems.

In its stock configuration this amp, while the receiver/integrated portion is in the same cabinet, is configured such that the pre-amp/receiver section has stereo RCA outputs, and the power amp-section has stereo RCA inputs. From the factory these were bridged, but those bridges disappeared at some point in the last 35 years.

At first, I hooked it up by using RCA splitters connected to the pre-amp section output, so I could connect my subwoofer, at the same time as I am feeding my signal back in to the power-amp inputs.

This sounded good, but I had intermittent problems on the right channel, where it would go from sounding good, to starting to distort (even at low volumes) and then the right channel would go down to extremely low volume/go out all together. Powering the amp down checking the connections and bringing it back up again, corrected the problem for a while, until it recurred.

As art of my troubleshooting efforts, I remembered that I have had issues with weird intermittent shorts when using firm RCA adapters/splitters in the past, so I decided to test if these might be the issue. I disconnected the splitters, and instead ran an RCA cable from the pre-amp out to the subwoofers in, and then another cable back from the subwoofers outs, into the power-amp inputs on the NAD amp.

In this configuration I never had the right channel drop out (or at least not yet, I only tried it last night for about an hour)

I have - however - noticed that there is a not insignificant difference in volume output between the right and left channels.

Doing some rudimentary measurements using a ruler to keep the distance equal at 12" and a cheap SPL meter I got on Amazon I have measured that at 12" and normal listening levels (for me, about 70-80db) the right channel is consistently about 3db quieter than the left channel. I can compensate for this using the amps balance knob and it sounds pretty good, but I am still concerned.

How would you guys recommend going about troubleshooting and potentially fixing this issue?

My thoughts are as follows:

1.) All knobs/pots are smooth and there is no noise over the speakers when they are turned, so I don't suspect that pot degradation is the issue, but I'm open to hearing your thoughts.

2.) I remember reading that pots can produce unequal volumes across the channels at low volumes. In my near-field listening setup, the pot is usually in the 20-30% range. Is this considered "low volume"? Could this be the cause?

3.) Could this be due to the 35 year old caps finally giving out? Is it even worth having the caps replaced on an old amp like this? (I have no idea what this would cost me to have this done at a repair shop, and I have tried by hand at board soldering in the past and found that I really don't have steady enough hands for the job)

4.) Would taking it to a shop to have cleaning and "tune up" done make sense? What should I expect this to cost approximately?

5.) Things I plan on trying when I have some time, but haven,t gotten around to yet:

- Switching the speakers left to right to see if the problem persists. (I don't think this is speaker related, as I don't recall having this issue on my Emotiva UPA-2, which I am moving to a different application, but it is worth checking out I guess.)

- Switching the speakers from Speaker A to Speaker B to see if the problem persists.

Other than this, I am at a loss right now. I'd be interested in hearing ANY comments you might have that could be helpful!

Thank you,
Matt
I am currently listening to my 7250PE that I bought brand new back in the day and also have a sub in between the pre out/line ins.

I do find occassional channel dropout issues and they were driving me a bit mad until I discovered on thing.

Pushing in the Tape Monitor button repeatedly to clear the connection seems to be the solution in my case.

It is likely the one important button/knob function that has seen the least use since I've owned it so the one most prone to having an oxidized connection.

I'm not smart enough to be able to disassemble it completely so the rapid button pushing seems to do the trick for me!

It's a great little unit.

Geoff A. J., California
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post #3 of 7 Unread Today, 12:29 PM - Thread Starter
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Quote:
Originally Posted by gajCA View Post
I am currently listening to my 7250PE that I bought brand new back in the day and also have a sub in between the pre out/line ins.

I do find occassional channel dropout issues and they were driving me a bit mad until I discovered on thing.

Pushing in the Tape Monitor button repeatedly to clear the connection seems to be the solution in my case.

It is likely the one important button/knob function that has seen the least use since I've owned it so the one most prone to having an oxidized connection.

I'm not smart enough to be able to disassemble it completely so the rapid button pushing seems to do the trick for me!

It's a great little unit.
Thanks for the heads up. I tried toggling them to no effect.

I think I am going to try some contact cleaner on the pots and switches and see if that helps.

Do you know which to use? Deoxit seems to be the product of choice, but they seem to have an alphabet soup of products, not sure which one is the best for this purpose. D5? There is also an F5 Federlube that gets mentioned?

Other than that, I'm not sure what to do. I talked to a shop, but came to the conclusion it's probably going to cost me about $200 to have it fully serviced. That's getting pretty close to a new Emotiva in cost... Not sure if a 35 year old amp is worth that much in service.

Livingroom: 65" Panasonic Plasma, Denon AVR-x1300w, Fronts: RBH SX-6300 Towers, Center: RBH 441-se, Surrounds: RBH 41-se Sub: Dual SVS PC13-Ultra, Source: Custom Kodi Box

Desk: DAC: Schiit Modi Multibit,
Headphone Amp: Schiit Jotunheim, Heaphones: Sennheiser HD650 and Beyerdynamic DT770 Pro
Speaker Amp: Emotiva UPA-200, Speakers: RBH 41-se, Sub SVS SB12-NSD
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post #4 of 7 Unread Today, 12:31 PM - Thread Starter
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Quote:
Originally Posted by Zorba922
Hmm, can't say I've ever had any of those problems with the NAD gear I've had in the past. However, I think replacing the capacitors is often mentioned/recommended by people who use vintage gear of any kind, not just NAD.

The volume pot issue regarding L/R imbalance is something I experienced with a Trends Audio T-amp, and seems fairly common. Unfortunately I never got around to researching a fix for it, though as I understand it, replacing a volume knob is said to be a pretty simple and cheap DIY solution.

But yeah, if you take it into a shop make sure to ask for an estimate of the repairs before proceeding, keeping in mind that you can get a good 2-channel integrated like the Onkyo 9010 or 9050 for $300-350.
Thank you, I appreciate the input!

Livingroom: 65" Panasonic Plasma, Denon AVR-x1300w, Fronts: RBH SX-6300 Towers, Center: RBH 441-se, Surrounds: RBH 41-se Sub: Dual SVS PC13-Ultra, Source: Custom Kodi Box

Desk: DAC: Schiit Modi Multibit,
Headphone Amp: Schiit Jotunheim, Heaphones: Sennheiser HD650 and Beyerdynamic DT770 Pro
Speaker Amp: Emotiva UPA-200, Speakers: RBH 41-se, Sub SVS SB12-NSD
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Originally Posted by mattlach View Post
Thanks for the heads up. I tried toggling them to no effect.

I think I am going to try some contact cleaner on the pots and switches and see if that helps.

Do you know which to use? Deoxit seems to be the product of choice, but they seem to have an alphabet soup of products, not sure which one is the best for this purpose. D5? There is also an F5 Federlube that gets mentioned?

Other than that, I'm not sure what to do. I talked to a shop, but came to the conclusion it's probably going to cost me about $200 to have it fully serviced. That's getting pretty close to a new Emotiva in cost... Not sure if a 35 year old amp is worth that much in service.
I used CRC contact cleaner to good effect.

Geoff A. J., California
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post #6 of 7 Unread Today, 12:52 PM - Thread Starter
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Hmm.

I re-connected the speaker wire to the binding posts on the amp, and things seem improved (but not perfect)

I'm wondering if maybe one of the binding posts on the right channel has an intermittent connection problem on the inside.

Livingroom: 65" Panasonic Plasma, Denon AVR-x1300w, Fronts: RBH SX-6300 Towers, Center: RBH 441-se, Surrounds: RBH 41-se Sub: Dual SVS PC13-Ultra, Source: Custom Kodi Box

Desk: DAC: Schiit Modi Multibit,
Headphone Amp: Schiit Jotunheim, Heaphones: Sennheiser HD650 and Beyerdynamic DT770 Pro
Speaker Amp: Emotiva UPA-200, Speakers: RBH 41-se, Sub SVS SB12-NSD
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post #7 of 7 Unread Today, 02:01 PM
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Originally Posted by mattlach View Post
Hmm.

I re-connected the speaker wire to the binding posts on the amp, and things seem improved (but not perfect)

I'm wondering if maybe one of the binding posts on the right channel has an intermittent connection problem on the inside.
My 7250PE was in mothballs for over a decade and took a lot of use, button pushing, knob twirling, contact cleaner on the volume control etc. before it settled down.

The more I used it the less the occasional channel dropouts or channel volume differentials went away.

I still have to occasionally do the button pushing/knob twirling thing but much less so since I used contact cleaner on the volume pot.

I did it by cheating.

I put the amp vertically with the knobs facing the ceiling, pulled the volume knob and balance know and created a moat with paper towels around the volume stem and filled it with contact cleaner.

Let it sit like that for a while, turning the knob back and forth, let it dry overnight and it made a big improvement.

I'm sure there's a better way but I'm no electrical genius.

Geoff A. J., California
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