NAD 1020 Preamp Problems

[sorenj07]

All right! Thanks for your reply on a long-dead thread by the way. In the future if we decide to put back the muting feature we'll do a proper bypass for sure.

 

[DarthBubba]

All right! Thanks for your reply on a long-dead thread by the way.

It popped up as a notification in my email. Imagine my surprise at a three year old thread coming back to life.

In the future if we decide to put back the muting feature we'll do a proper bypass for sure.

I'd also be inclined to replace some of the signal path electrolytics as they are likely on their last legs by now at 30+ years old. Presuming that the part numbers are the same in a 1020 as they are in a 1020B (whose schematic I do have): look at C401 & 402, 421 & 422, 519 & 520, 305 & 306. All the following are not in the signal path but affect frequency rolloffs, etc.: C407-410, 417 & 418, 525 & 526, 529 & 530, 301 & 302. Replacing the power supply electrolytics with new, low ESR caps should quiet down the noise floor.

Just my $0.02, and worth every penny you paid.

 

[anatech]

If you need the muting feature, use a small relay. No distortion and positive muting. You can drive the coil from somewhere in the muting circuit, I would have to figure it out for you if you need assistance.

-Chris

 

[sorenj07]

OK. Recapping might have to wait until I'm next in the States and able to get my hands on the thing. The 1020 is at a friend's place in New York and I'm doing remote troubleshooting

The next problem is - somehow the garbled / cutting off noise phenomenon still comes back in ONE channel every now and then, but can apparently be fixed by jiggling the "Tape" button..? At this point given that the muting transistors have now been bypassed my first guess would be a mechanical issue.

AudiogoN Forums: NAD Model 1020 Preamp and 2150 Amp

But here's the kicker - the Aux input is the one being used, generally with an iPod or computer. So why would the Tape button make any difference at all??? And

An externally hosted image should be here but it was not working when we last tested it.

 

[sorenj07]

Here is the muting transistor fix, before soldering. Pins 1 & 2 of the transistors are connected, bypassing the gate. It seemed to work perfectly.

An externally hosted image should be here but it was not working when we last tested it.

 

[anatech]

Hi sorenj07,
All signals are routed through the tape switch. You have to clean that switch as well.

-Chris

 

[sorenj07]

Well that's tedious. I don't suppose bypassing that switch for now would cause too much of a loss in functionality. I'll have a peek at the schematic. Is the 3020 an OK one to work off of?

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[anatech]

These days? I sincerely doubt it would cause any grief if it was made non-functional. The tape monitor switch is the single biggest cause for audio cutting out or being distorted.

 

[sorenj07]

My thoughts as well. I just had a brainstorm: never mind the schematic, a simple jumper across the traces on the underside of the circuit board should do it right?

 

[anatech]

Yup!

Can't find manual.

 

[sorenj07]

Great. so just to be sure we're soldering it so that it's closed right? i.e always on

 

[sorenj07]

Sorry, I suppose we'll want it off. Going to see if there's a discreet way to cut a trace or disconnect a jumper.

 

[anatech]

You need to short the contacts in the source position. You could cut the tape traces, but there is unlikely going to be a tape deck plugged in. If there is, you'll want to be fixing that switch!

-Chris

 

[kurtvisti]

In my case on the 3020A, the capacitor powering the JFET's gate pin had 80VDC on it but was only a 63VDC cap. The result was predictable. I replaced it with a 100VDC cap and the mute circuit has worked properly since.

Hi DarthBubba
I think I have the same problem with my 3020i.
Can you please tell me which capacitor powering the JFET gate pin on either the 3020A or 3020i?
Thanx in advance.
Regards
Kurt

 

[DarthBubba]

On the 3020i schematic I think it is C603, 22uF at 100VDC. Be warned that this bit of circuitry is slightly different than the 3020A's preamp turn-on muting circuit. As you can see, the cap's voltage rating was already increased to 100VDC from 63VDC. I would also check C601(same value), Q516 and its associated resistors, R536 (47K) and R602 (390R). R605 & 606 are 10Megs and are unlikely to open, but you might as well check them too.

Hope this helps.

-DB