[Jaypee]

Last part of M³ Initial setup step 4.

You mean "4.Install the ground channel opamp OPAMPG into its socket. Be sure the orientation is correct."? No OPAMPG here?

I cant get any voltage readings from R9R+ - or R9L + - .. no matter if I turn BIASL or BIASR..

 

[amb]

Sorry, I meant step 6.

These trimpots are are 15 to 25 turn devices (depending on your choice of part), so you will have to turn it a bunch of times in order to register any voltage across the R9s.

 

[Jaypee]

I'm getting 16,8kohms between V+ and V- whenever connected to the sigma, is this ok?

Tried turning the BIASR several turns (6-8) and nothing happens, I get a reading of zero volts across R9R..

 

[amb]

Quote:

Originally Posted by Jaypee /img/forum/go_quote.gif I'm getting 16,8kohms between V+ and V- whenever connected to the sigma, is this ok?

Close... It should read the series value of σ11's R8 and R10, which, for a 36V config should be ~15K ohms.

Quote:

Tried turning the BIASR several turns (6-8) and nothing happens, I get a reading of zero volts across R9R..

Does step 6-9 pass completely? If so, keep turning the BIAS trimpot clockwise. Note that the voltage across R9 will remain low until a certain point, and it will begin to rise rapidly. Use the mini-grabber probe attachments on the resistor so you could watch the voltage as you turn the trimpot. Don't let it shoot too high.

 

[ShinyFalcon]

Is the resistance reading across V+ and V- stable? I recall that I was able to get a number, and it concerned me, but I think you're fine.

Check the voltage on an unoccupied opamp slot across pins 4 and 7 and make sure it reads 24V/30V/36V, whichever your σ11 is set at.

And make sure you're measuring millivolts instead of volts. How about heat?

 

[amb]

Quote:

Originally Posted by ShinyFalcon /img/forum/go_quote.gif Check the voltage on an unoccupied opamp slot across pins 3 and 7 and make sure it reads 24V/30V/36V, whichever your σ11 is set at.

That should be across pins 4 and 7. Also, the voltage will be a couple of volts less than the σ11 voltage, due to drops across D1 and Q5+/Q5-.

 

[Jaypee]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Does step 6-9 pass completely?

well..
step 1 - check
step 2 (no opamps on at this point)-
- got >2000kohms or 234kohms between V+ and V- depending on which probe of the multimeter is touching which terminal (nagative to V- and positive to V+ = >2000kohms <--> positive to V- and negative to V+ = ~234kohms)?
- same thing with pins 7 and 4 in the opamp socket, negative to 7 and positive to 4= -611kohms , the other way around >2000kohm ...
- next between pin 7 to IG, and this time the reading started to ascend from ~ - 237kohms (pos to 7 and neg to IG) or from ~ 599kohms (neg to 7 and pos to IG)
- same thing again with pin 4 and IG

what do you make of these readings?

 

[Jaypee]

Could bad/wrong volume pot's cause this? they're the only part in which I didn't use recommendations, but trusted the local electronics shop guy who said "these are cheap and will work. I've used them dozens of times"...
Theyre something from this catalog

 

[Beefy]

I doubt that would cause problems, but that probably isn't anywhere near as good as the venerable/default Alps.

 

[amb]

Quote:

Originally Posted by Jaypee /img/forum/go_quote.gif - got >2000kohms or 234kohms between V+ and V- depending on which probe of the multimeter is touching which terminal (nagative to V- and positive to V+ = >2000kohms <--> positive to V- and negative to V+ = ~234kohms)? - same thing with pins 7 and 4 in the opamp socket, negative to 7 and positive to 4= -611kohms , the other way around >2000kohm ... - next between pin 7 to IG, and this time the reading started to ascend from ~ - 237kohms (pos to 7 and neg to IG) or from ~ 599kohms (neg to 7 and pos to IG) - same thing again with pin 4 and IG what do you make of these readings?

These are all fine... the resistance measurements will vary because the DMM is charging the bank of rail capacitors.

The volume pot choice should not impact the bias adjustments.

 

[Jaypee]

okay, onwards then.. had the chance to try a more reliable multimeter to verify my measurements..
step 3 - check
step 4 - check (although it was OPAMPR, because no ground channel)
step 5 - check
step 6 - check
step 7 - check (set the voltage over R5R to 0,45VDC)
step 8 :
- Measured voltage between IG and OR and got 10,1VDC instead of something less than 100mV ???
NOTE : turned off power, let the caps drain, inserted OPAMPL to it's socket (both OPAMPS now on the board), measured voltage between IG and OR again and got 6,8mV ???
step 9 :
-Measured voltage across R9R+ and got exactly 0,000mV. Turning BIASR doesn't affect the voltage over R9R+ at all (verified, tried turning it enough)

There's where I am so far.. stuff I've checked:
-BIASR and BIASL are fully functional
-R9R+- and R9L+- are of right value
-All the right FET's are on the right places
-Soldering looks good overall (can see any coldjoints or anything)
-The extra resistor Rx is of right value and correctly between the OL trace and pin 2 of OPAMPR
-PSU is good

Regarding bass boost, which I left off this amp, is there anything more to do than to jump wire SBBR pins and SBBL pins?

Right now, I'm out of bullets.. can't figure this one out. help needed.

EDIT: I get EXACTLY similar values off the second MMM board, so it can't be individual solders or stuff like that, these boards are not connected to each other in any other way, than they both share the same ground (IG connected to chassis)

 

[Beefy]

Are the MOSFETs getting warm?

 

[amb]

In your config (bridge operation with unbalanced inputs), you need to install both opamps while measuring the DC offset. So your observed behavior is correct.

Make sure you didn't install the wrong value trimpots. All the BIASOP trimpots should be 1K ohm (probably marked as "102") and the BIAS trimpots should be 5K ("502").

How many turns clockwise did you adjust the BIAS trimpot before "giving up"?

Measure the voltage across the C2 capacitor as you turn the BIAS trimpot. What do you get, and does it increase as you turn the BIAS trimpot clockwise?

If no bassboose is desired, simply install jumpers at SbbL and SbbR.

Oh, and one more thing, make sure your Q2 and Q5+ are not Fairchild's 2N3904 with the C-suffix (i.e., 2N3904CTA or 2N3904CBU). Those have the wrong pin-out.

 

[Jaypee]

Quote:

Are the MOSFETs getting warm?

No.
Quote:

Make sure you didn't install the wrong value trimpots. All the BIASOP trimpots should be 1K ohm (probably marked as "102") and the BIAS trimpots should be 5K ("502").

I have this as BIASL/-R and this as BIASOPL/-R so all cleared there..?
Quote:

How many turns clockwise did you adjust the BIAS trimpot before "giving up"?

started from zero, then +10 turns initially, and +10 more while powered and measuring, still no sign of life across R9.
Quote:

Measure the voltage across the C2 capacitor as you turn the BIAS trimpot. What do you get, and does it increase as you turn the BIAS trimpot clockwise?

The voltage across C2 (after the initial 10 turns) is 1.65VDC and increases as BIAS is turned clockwise.
Quote:

Oh, and one more thing, make sure your Q2 and Q5+ are not Fairchild's 2N3904 with the C-suffix (i.e., 2N3904CTA or 2N3904CBU). Those have the wrong pin-out.

I've got this as Q5+ and Q2 so all cleared there..?

 

[ShinyFalcon]

Are we troubleshooting the ground channel? Have you tried working with one of the other channels?

Edit: This is a balanced amp?