Hi Pj,
If I understand correctly how those measurements were made on one end of R49, and R87. Was the common, or black, meter lead at ground and the other end on one of the resistors?? If so, remember that the amplifier output is not a ground reference. It will have some sort of DC offset. The DC offset will be either positive or negative relative to ground. This DC offset voltage may be large compared to the voltage that you should measure across R49 (or R87).
Lets say you have a positive DC offset of 15 mV appearing at one channel's output. Say your bias requirement is 60mA and let's just say your emmiter resistor value is 0.22 ohms. (You'll have to use your own values based on the service manual). So you'll need 60 mA flowing through the transistor with no signal.
I(60mA) * R(0.22ohms) = E(13.2mV). With this 15mV offset, the voltage you'd expect at the top of your resistor is: the 13.2mV(bias) + the 15mV(offset) = +27.2mV measured from ground. OR if the DC offset is negative: 13.2mV(bias)-15mV(offset) = -1.8mV
Since DC offset drifts, it is not good practice to include the offset in any bias calibration. Put your common (or black) lead on the output point of the amp and probe the emmiter resistors with the Red lead. ....or whichever testpoints the manual indicates. Isolate your measurement to just across the resistor. It'll all be good.
so if i understand correctly, my 30mv reading at the top of the resistors r49 or r87 using the red probe on the resistor and black probe on the ground on my right channel is correct, and the reading on my left channel is about 15mv so this is normal due to the negative offset, i thought both board were equal ? 
and that the bridging was done by inverting the phase of the inputs only 
right now i am learning more about this amp that i did in the last few years about just about any nad / adcom / technics crap out there....i wonder if this is a good point or bad
:
and that the bridging was done by inverting the phase of the inputs only right now i am learning more about this amp that i did in the last few years about just about any nad / adcom / technics crap out there....i wonder if this is a good point or bad
:
The reading might be correct, but the method is not the best. Do not measure from ground when making bias measurements. Isolate the measurement to R49 (or R87). You may measure by placing 1 lead at either end of the resistor, or one lead at the output point and one lead at the other side of R49 (or R87)
The bias was mesured the proper way with probes directly on the emiters of that output transistors, as described in the manual, they sre now set a the correct value of 3.4mv and stable, the values i am describing are the ones i found when i misread the manual, and noticed a large difference between both amp boards, but i am now assured with the readings i just did about the negatve offset...did'nt take that into consideration...Thanks, tonight i'll check for the parts needed to replace both gain sections on my boards,
Seriously, you should come and visit us in montreal, i've been to "reputable" service centers to get some parts and most people i've talked to were either ignorant on some of the issues i had here, or even what bias adjustments would do to an amp....so i guess you can understand why i am saying that, but i do know excelent techs that have now retired and if you pronouce the word "new tech" to them they start laughing and tell you the new kids out there know close to nothing, on wich i have to agree, i am from the PC world i build and design pcb's and did my fair share of repairs on "std" electronics tv's vcr's cable boxes and home receivers, service bulletins for the good o'l dynacos and castec amps, but this technology that Mr. Carver did is just out of my league, and quite splendid...
Hi pjaneiro,
I have a very good idea what the average technician is capable of. We had to discontinue the service contract with many of them due to service issues.
Many are too proud and will not admit they could use some help.
An instant kill for me is seeing a tech actually pick up and ECG or NTE replacement catalog. The second is seeing an open ECG or NTE bag in the bench or waste basket.
-Chris
I have a very good idea what the average technician is capable of. We had to discontinue the service contract with many of them due to service issues.
Many are too proud and will not admit they could use some help.
An instant kill for me is seeing a tech actually pick up and ECG or NTE replacement catalog. The second is seeing an open ECG or NTE bag in the bench or waste basket.
-Chris
The state of technicians these days is sad. ....Generally speaking. There's not enough money in it to motivate people to excel. Most good techs move into High tech industrial jobs.
Most bench techs I've worked with from the late 70's through the mid-80's were good. Of course there was some "dead wood" along the way, but most were good.
A few years ago I worked with a guy that worked at the Circuit City Regional service facility. I thought that he should have been pretty good. I asked about how they aligned FM. He said "FM?, ...we just replace the pack". Gross. No component level anything. RIAA? what's that? It's truly sad. It's business, driven by cost. Most people aren't too picky either. Look at the success of MP3. Repair has been left to those who have freinds that have broken stuff and and just love to fix things.
Most bench techs I've worked with from the late 70's through the mid-80's were good. Of course there was some "dead wood" along the way, but most were good.
A few years ago I worked with a guy that worked at the Circuit City Regional service facility. I thought that he should have been pretty good. I asked about how they aligned FM. He said "FM?, ...we just replace the pack". Gross. No component level anything. RIAA? what's that? It's truly sad. It's business, driven by cost. Most people aren't too picky either. Look at the success of MP3. Repair has been left to those who have freinds that have broken stuff and and just love to fix things.
Well i just did the part swaps and same results, so i think i'll just give up, the only other way i know would be to trick the led by changing the scaling resistor values on the right board, just for fun i plugged in my analog needles and indeed my right channel does have a higher value, but just barely so i guess it's enough for the leds to trip !!!, Thanks for all your help on this, i now have two monster carver amps that work flawlessly, now time to go buy those pm 2.0T on ebay i just saw....now let's see if those babies can truly play hifi like they say in those ads...
Hi pjaneiro,
You do realize how much power a PM2.0 packs ........ right? It's lighter and more powerful.
Also, it has a completely different power supply. This unit runs off a 2KHz PWM switcher. The power supply unit is extremely compact. If something goes wrong with this fella, send it in. Don't even open it. The bench soft start procedure is completely different for this guy. It external DC supplies and a variac.
-Chris
You do realize how much power a PM2.0 packs ........ right? It's lighter and more powerful.
Also, it has a completely different power supply. This unit runs off a 2KHz PWM switcher. The power supply unit is extremely compact. If something goes wrong with this fella, send it in. Don't even open it. The bench soft start procedure is completely different for this guy. It external DC supplies and a variac.
-Chris
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.