Nordmende Menuett Stereo follow-up: remaining problems!

[Patrice B]

Hi,

Back in the autumn, I bought a Nordmende Menuett Stereo as documented here:

http://www.audiokarma.org/forums/showthread.php?t=251263

Since day one, there's a difference in tone between left and right (so it was there before the restoration). Left is beefier than right, more bassy and the most important, more distorting. Just to precise, there's also distortion on left...

One would think that a complete restoration should cure the sound (including me) but for the first time in my case, serious problems remaining.

So, after a complete restoration (selenium, filter caps, all caps and almost all resistors, new tubes everywhere, deep cleaning of sockets and controls, double-check of the solder traces on the PCB's, reheating all solder, verifying each connection and value...), it sounds like crap to my point of view: I can't put too much volume or too much bass before it distorts, more on left than right.

A lot of questions:

1- Is it supposed to sound like this (I'm sure the answer is no but...) looking at the weird way it is built, meaning half an EABC80 (6AK8) for left preamp and an EBC81 (6BD7A) for preamp right? The schematic is linked at the end...

2- Do you see something obvious I could had missed during the process?

3- Is it possible the OPT's are saturated (or simply going south)? They're built a strange way: the two OPT's are in one physical part...

I'm not so bad when the time comes to read a schematic and replace parts to original specs... but I don't understand how and why those values or components are chosen instead of others. To resume, I do not understand really well the theory behind the circuitry.

For the record, I suspected first the internal speakers but it sounds like this on a spare set. It is the same, for FM, AM or any band and phono also (I installed a set of RCA plugs going in the tape in, TB on the schematic).

BTW, if it is of some interest, I had to up the value of R200 at 750 ohms to get the correct voltages after the rectifier.

If no solution come to my mind soon, I plan (maybe) going directly from the tape outs (I guess pins 3 and 5 on TB connector) to my Fleetwood little console amp... Finally, putting together a good sounding console amp without a working radio section (the Fleetwood) with another one (the Nordmende) missing a good amp/preamp section but with a good tuner.

This way, I would preserve the beautiful look of the furniture and I could use the original tuner (it seems to work fine on the tuning/sensitivity side) and the original speakers.

Thanks.

Patrice

linked schematic:http://cid-21651cbc33527896.skydrive.live.com/self.aspx/Public/3^_616^_s.tif

 

[Phototone]

Thats a truly bizzare schematic.

 

[Pio1980]

Don't worry about the different driver tubes, they had one triode in the EABC80 and chose another type with essentially the same triode section for the 2nd channel driver. The audio ckt is pretty conventional single-ended EL84 if you ignore the feedback tone features. Short list from an outside perspective follows;
One source of problems could be the transfer switches in the speaker sockets being contaminated/faulty.
Another that I'm having with a different receiver is one of the volume pot sections is defective, open to be precise.
You should know if you have a problematical function selector switch with contaminated contacts.
A faulty transformer is likely if the thing was played hard with the speakers disconnected, otherwise it could be smoked by leaky grid coupling/blocking "capacitor-of-death".
Re R-200. You could have just used a single 1N4007 in halfwave as the rectifier for lower average voltage but you fixed it with R-200. Do the voltages in the amps check with the diagram values and are they the same in both channels?

 

[Patrice B]

One source of problems could be the transfer switches in the speaker sockets being contaminated/faulty.

The auxiliary set of speakers is connected directly inside the receiver...

Another that I'm having with a different receiver is one of the volume pot sections is defective, open to be precise.
You should know if you have a problematical function selector switch with contaminated contacts.

Yes, could be the volume pot (or I guess the balance pot, treble and bass pots also...). As for the function switches: presence, brillant and bass. They look effectively to be dirty. There's also the main selector, looking like a piano keyboard... In the case the volume pot is worn or defective, it won't be easy to find a replacement (1.3m with integrated balance).

A faulty transformer is likely if the thing was played hard with the speakers disconnected, otherwise it could be smoked by leaky grid coupling/blocking "capacitor-of-death".
Re R-200. You could have just used a single 1N4007 in halfwave as the rectifier for lower average voltage but you fixed it with R-200. Do the voltages in the amps check with the diagram values and are they the same in both channels?

I doubt that the original owners played that thing hard without speakers to listen to some prog or heavy rock... but who knows?

The original caps were simply disintegrated (crumbling and completely dried)...

Concerning voltages, I overlooked this obvious diagnostic. This way, if I notice that voltages at the same point do not correspond between left and right, I'll have more clues where to look for.

Thanks.

**No way to look for diagnosis now as this console/receiver is located in our cottage, 1 and a half hour from here... Next weekend!

 

[Pio1980]

"The auxiliary set of speakers is connected directly inside the receiver..."
Yes but unless someone has changed the connections to make direct to the output transformers the high speaker line goes thru a cut-out switch in the speaker socket. See socket terminals #3 and #4, this is a disconnect for the internal speakers when external speakers are used.

 

[Patrice B]

"The auxiliary set of speakers is connected directly inside the receiver..."
Yes but unless someone has changed the connections to make direct to the output transformers the high speaker line goes thru a cut-out switch in the speaker socket. See socket terminals #3 and #4, this is a disconnect for the internal speakers when external speakers are used.

Ok, I understand... No, the high line isn't directly tied to the OPT's. I have to connect a big three pins connector onto a socket right to the amp chassis. Another trail of investigation here for me...

Also, the auxiliary set is always connected (I soldered directly on the back of the aux speakers terminals) and it doesn't cut the mains. In fact, the connectors (proprietary I guess) permit to use two sets of external speakers...

About the pots: you made me think that when I turn the balance full left, it loses more high frequencies on this side. It's not doing it on right. More I think, this three-ganged pot(vol L - vol R - Balance) could be part of the problem too.

Thanks.

Patrice

 

[Patrice B]

Just to add: when it was on the workbench, I used only external speakers (obviously, as it was out of the cabinet!) and it sounded the same. Does it rule out the main cut-out switches?

 

[Pio1980]

Probably yes. Look elsewhere then.

 

[Patrice B]

Hi Pio,

Say I want to bypass the tone control circuitry (for troubleshooting purpose), how would I do it?

I plan to investigate:

1- measure all voltages against the schematic first;

2- look on the tone control circuitry (bass, presence, brillant, alto, treble) and disconnect to look for sound improvement;

3- diagnose and measure the volume/balance pot and replace if needed (I'll probably remove the balance thingy as I don't really need it).

To bypass, is it just a matter of removing by example c170 to c177 and r173 to r175 to get rid of "jazz" and "bass" (on right channel for example purpose)?

Also, there's always two voltages readings indicated (I guess one for 110v and one for 220v maybe?). Which one have I to follow?

Thanks.

Patrice

 

[Pio1980]

To simplify, you can have an operating voltage problem or a signal path problem, or both. We will first look at the operating voltages as proposed earlier. Before doing anything of the sort first place an insulating sheath around the bare probe shaft so that only the tip end bit is exposed to prevent expensive or painful accidents. Even so, take care to only touch one single point at a time to avoid ruinous short-circuits.
To answer you question about the voltages, if your line voltage is between 110 and 130, set the selector to 125V and be sure the fuse is the appropriate value. Since you've changed the rectifier and R-200, the voltages are going to be whatever the R-200 replacement you've selected allows for the current drain of course. The voltage range shown is somewhat approximate, depending primarily on the actual line voltage and condition of the output tubes. The two voltage values shown are dependent on current draw in that portion of the circuit, you are looking for voltages that are way off and not just a bit different as shown. There will be loud noises from the speakers with some of the voltage tests that the controls won't affect, be prepared for that.
Otherwise, forget the controls, audio filters, and tone ckts for now, they are signal path. We'll save those for later.

 

[Patrice B]

To simplify, you can have an operating voltage problem or a signal path problem, or both. We will first look at the operating voltages as proposed earlier. Before doing anything of the sort first place an insulating sheath around the bare probe shaft so that only the tip end bit is exposed to prevent expensive or painful accidents. Even so, take care to only touch one single point at a time to avoid ruinous short-circuits.
To answer you question about the voltages, if your line voltage is between 110 and 130, set the selector to 125V and be sure the fuse is the appropriate value. Since you've changed the rectifier and R-200, the voltages are going to be whatever the R-200 replacement you've selected allows for the current drain of course. The voltage range shown is somewhat approximate, depending primarily on the actual line voltage and condition of the output tubes. The two voltage values shown are dependent on current draw in that portion of the circuit, you are looking for voltages that are way off and not just a bit different as shown. There will be loud noises from the speakers with some of the voltage tests that the controls won't affect, be prepared for that.
Otherwise, forget the controls, audio filters, and tone ckts for now, they are signal path. We'll save those for later.

First, thanks a lot for your help. Sure, I'll report back to you as soon as I have the offending piece of gear (the Nordmende that is) in front of me again (probably next weekend).

Even if the schematic indicate AC adjustment going from 110 to 240v, mine has only 110v and 220v to choose from...

This schematic could be used for several models of Nordmende so I assume there's minor differences or bits missing.

BTW, what "ckts" stands for?

Thanks.

Patrice

 

[Pio1980]

Ckts= circuits, ckt= circuit.
Use the voltage selection range closest to the AC line voltage there, probably 120V. It will affect the measured voltages somewhat but they should have the same relative relationships.
The Diagram is for chassis model 3/616, there are several name models listed using it including Menuette. The voltage range may be destination dependent tho' the economy of making different versions for domestic vs export vs one version for all possible markets seems questionable. I would expect that to be the main difference between versions but one never knows for sure.

 

[Patrice B]

Thanks...

 

[Patrice B]

A little OT but anyway...

Here's what I've found today:

Looking really similar to my Nordmende:

A little look closer on the first one (Fleetwood, a Canadian brand) and I see "Made in West Germany".

I didn't had the time to open it yet (stayed in the car for tonight).

I don't even know if it is stereo 'cause there's no balance knob but 4 speakers however (2 woofers and two twitters).

The TT is a Collaro (beautiful):

The precedent owner said it worked fine and I didn't even tried it yet... I like surprises and I guess that the chassis layout should be similar to the Nordmende.

Patrice

 

[Pio1980]

Could be Grundig, show me pix of the chassis and tube chart. If it was made in Nuremburg/Furth definitely Grundig.

 

[Patrice B]

Could be Grundig, show me pix of the chassis and tube chart. If it was made in Nuremburg/Furth definitely Grundig.

As soon as I get it out of the car... tomorrow 'cause it's a little dark know to unscrew back panel in this small space. Yes, I know I could do it with a flashlight or even the little light in the car but, hey, a little tired now!

Could be Grundig like you said as those German tube receivers all looks the same...

 

[Patrice B]

Good morning,

Yes, you're right Pio1980. It's definitely a Grundig as a web search pointed me toward Fleetwood being one distributor of Grundig gear in the 50's and 60's.

They also made their own consoles, like the (good sounding) 6AQ5 receiver I also own.

Impatient to open the back later today. The pictures posted are from the ad and not mine.

Patrice

 

[Patrice B]

Well, I'm a little deceived...

It's a mono unit finally. I don't know what to do. In the case one of the OPT's of the Nordmende is dead, I can't even use the one on the Grundig as it's a PP.

 

[Pio1980]

The Menuette is stereo audio, mono everything else without the FM Multiplex unit. It'll take a CD player in and produce 2 channels of audio out the speakers. No need to salvage the Grundig as it's complete and deserves it's own resto, there are plenty of junker parts donors out there. Let's not panic and we'll just get thru the diagnostics when you are ready.

 

[Patrice B]

Continued here (Grundig): http://www.audiokarma.org/forums/showthread.php?t=292763