NSM ES V CD amplifier bias Question

Well, this ones a little out of my comfort zone!
After working on this for 3 years I've got this NSM Performer Grand II working.
Seems too good to be true.
My question is while repairing the amplifier I replaced the driver Transistors and was wondering if there needs to be any adjustments made like adjusting bias on the transistors??
It's playing now but I'd like to keep it that way.
I would love to hear from some NSM guys as I've never worked on a CD juke before this.
Thanks,
Mauro

Any replacement of transistors, resistors, etc. requires checking and setting proper bias - to spec.
Replacement is only half the job.

The reason I ask is that I cannot find any instruction on how to do this adjustment.
If someone who has the procedure could share it with me I can finally complete the repair and I'd be very grateful for the information.
Please share
Thanks,
Mauro

Mauro, this may be a help:

http://arcarc.xmission.com/PDF_Jukebox/ ... Manual.pdf

Quiescent current is item 2 on Pg92.

As a general rule, if the amp does not idle hot and you do not hear crossover distortion it is safe to leave it as-is. In these compact higher powered amps it can be hard to discern what actually is a 'too hot" idle so a measurement is a good idea.

Rob-NYC

Rob,
Thanks for pointing that out.
My manual, which came with the jukebox, is missing this page. There must have been a separate service manual. Mine is more of an operation manual with schematics.
Edit:
I just found the information, 40ma read by removing each fuse I believe, and putting in a ma meter. I'm guessing it is adjustable by R150 and I'm guessing this trimmer is located on the solder side of the board since it's not visible from the parts side.
So I guess one removes the fastening screws, hooks up a meter to the back side of the fuse holder, with volume at 0, and adjust the trimmer R150 for each channel?
If this is correct? I will try it next weekend.
If not please let me know.

"Up' R150 appears to be located between the two 4700mfd caps and is accessible from the top of board. The outlines are on pgs 102 thru 104.

If possible I suggest measuring the actual resistance value w/no power and with a meter connected, vary the resistance and see how the meter responds. This is important in that a dead spot on the pot due to dirt can blow out the finals. If all OK, return to the initial value you read and power up to measure the actual bias.

FWIW: I am not a big fan of the method that NSM suggests here for measuring bias. i would adjust for the lowest reading consistent with good sound at low levels.

FWIW-2: I've never warmed to the idea of fans in commercial amplifiers. They do get filthy -even in seemingly clean locations and must be examined and cleaned occasionally to avoid amp overheating. In the home this won't be a problem.

I remember seeing a lot of NSm product here in NYC during the early-mid nineties. While I had doubts about the design and layout, the sound quality was always excellent.


Rob

Thanks Rob,
Excellent tip, never thought about checking the pot before attempting adjustment.
I tried the NSM method tonight but failed, the amp is running very hot now in just a minute of play. I couldn't get a steady reading on my DMM ? It's probably user error, can't understand what I could possibly be doing wrong.
The suggested ma setting is DC I'm assuming, I tried both AC and DC and couldn't get a reading. I should have left well enough alone.
I'll do some reading over the next couple days and see if I can figure it out.
Thanks for the revised methodology and I'm always open to further suggestions.
Mauro

Uptown wrote:Thanks Rob,
Excellent tip, never thought about checking the pot before attempting adjustment.
I tried the NSM method tonight but failed, the amp is running very hot now in just a minute of play. I couldn't get a steady reading on my DMM ? It's probably user error, can't understand what I could possibly be doing wrong.
The suggested ma setting is DC I'm assuming, I tried both AC and DC and couldn't get a reading. I should have left well enough alone.
I'll do some reading over the next couple days and see if I can figure it out.
Thanks for the revised methodology and I'm always open to further suggestions.
Mauro

My advice is to have that amp serviced by a knowledgeable technician, before you fry it to oblivion.
It's apparent you've no clue as to doing critical bias adjustments / readings.

Uptown wrote:Thanks Rob,
Excellent tip, never thought about checking the pot before attempting adjustment.
I tried the NSM method tonight but failed, the amp is running very hot now in just a minute of play. I couldn't get a steady reading on my DMM ? It's probably user error, can't understand what I could possibly be doing wrong.
The suggested ma setting is DC I'm assuming, I tried both AC and DC and couldn't get a reading. I should have left well enough alone.
I'll do some reading over the next couple days and see if I can figure it out.
Thanks for the revised methodology and I'm always open to further suggestions.
Mauro

The range for the meter is; DC milliamps and the connection is to place the meter's connections in place of the removed fuse...or if more convenient, remove the temp sensor switch and use those two terminals.

Did you measure and note either the original resistance or positions of the bias pots?

If not; set the pots to their midpoint position and check for approximately correct bias and adjust if necessary.

Do not get discouraged about this stuff, bias is one of those minefields that people often screw up if they are inexperienced. It is not nuclear physics -it is just a simple analog amplifier, but transistors are unforgiving of major errors. Proceed carefully and make sure you are connected and reading the right scale on your meter (most DVM;s have two scales and two different connections, one for AMPS and the other for milliamps).

Rob (who has blown his share of transistors).

Rob,
Thank you very much for your well thought out response and perfect instruction. You always have insightful tips and opinions and share them in a very enjoyable and eloquent prose.
It is unfortunate that some who frequent these forums have nothing of value to contribute and rather than take the time to share whatever puny knowledge they posses instead choose to use criticism to fool only themselves in some ill begotten superiority complex.
The problem was that both my fluke meters had open internal fuses. Must have happened the last time I used them for current measurements; that was a few months back, so it didn't dawn on me immediately.
One again I am in your debt,
Mauro