This part of the night shift has been looking closely at my own MXW 606 clone boards. I can see several spots where I have to stop and think, check pinouts etc. I first thought this would be an issue with T15,16 which I understood defined virtual ground, because the pinout doesn't match the overlay diagram. Well it seems there are many more possible faults, with the masked ground plane area being a mystery as to whether you solder to all those untinned holes that have no clearance or not. I guess not but why have the foil right up to the holes but no solder pad?
I'll leave you with this charming piece of useless advice from Quad in the SM, re. the offset:
The centre tapped DC line (+55,-55V) is floating and some faults may cause this to shift putting up to 110V on one side - possibly damaging R38 and R39 (2K2 ohm). These components should always be checked during repairs.
Oh wonderful, now just what faults that could cause this did you have in mind, Mr Quad? 😉
I'll leave you with this charming piece of useless advice from Quad in the SM, re. the offset:
The centre tapped DC line (+55,-55V) is floating and some faults may cause this to shift putting up to 110V on one side - possibly damaging R38 and R39 (2K2 ohm). These components should always be checked during repairs.
Oh wonderful, now just what faults that could cause this did you have in mind, Mr Quad? 😉
I've found the error, as suspected it was in the 909 BOM.
The BOM has T2, 4, 5 & 6 all as MPSA 43. (NPN)
T4, 5 and 6 should be MPSA 93. (PNP)
The BOM has T2, 4, 5 & 6 all as MPSA 43. (NPN)
T4, 5 and 6 should be MPSA 93. (PNP)
One amp hasn't been powered up yet so that will have sufferred no ill effect.
I'm hoping that just replacing the NPNs with the correct PNPs will sort out the amp under test ?
I'm hoping that just replacing the NPNs with the correct PNPs will sort out the amp under test ?
While I'm at it I've just found some 11A 4.0uH inductors. They are SMD but I'm sure I'll find a way around that problem.
On my boards a lot of the transistors are shown with the pins 180 degrees from the T092 outline.
If you fit the TR's iaw with the silk screen outline they are correct, even if the (B) middle leg is kicked out to the front as opposed to the rear.
Some of the caps you have to look at the PCB traces as allowance has been made for different pin spacing.
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Is it a 909 clone or a 606 clone ?
I think they are practically identical.
The schematic is the same with a few component changes.
The dropper resistors for the 6v8 zeners have been altered - I can't see that making too much difference.
R3 becomes 5K6 and R12 becomes 3K3
The collector resistors in the virtual earth have been altered.
They have been increased from 2K2 to 3K3.
All the transistors have changed.
TR1 is now a BC560B
TR2 is now a MPSA43
TR3 is now a BC237C
TR4 - 6 will be MPSA93
TR7 & 8 are now BD244C
and the O/Ps are MJ15003
Anyone embarking on this clone, the Quad 909 Service Manual is full of mistakes.
I think they are practically identical.
The schematic is the same with a few component changes.
The dropper resistors for the 6v8 zeners have been altered - I can't see that making too much difference.
R3 becomes 5K6 and R12 becomes 3K3
The collector resistors in the virtual earth have been altered.
They have been increased from 2K2 to 3K3.
All the transistors have changed.
TR1 is now a BC560B
TR2 is now a MPSA43
TR3 is now a BC237C
TR4 - 6 will be MPSA93
TR7 & 8 are now BD244C
and the O/Ps are MJ15003
Anyone embarking on this clone, the Quad 909 Service Manual is full of mistakes.
Interesting, I've removed the offending NPNs from the board, TR4,5 and 6 and all of them are still working.
Good that you found it was components and thanks for passing on the tips about the design errors you found. You'd hope there is a more recent, corrected version issued to service agents. Their customers will be waiting a long time for repairs otherwise. 😡
Was there a problem with the original 1mm wire you used for the 2 uH chokes? Surely you can just replicate the originals rather than go to a ferrite choke, and this can't be a critical component. I wound one on 3/8" fibreglass rod according to your original spec. and it measured on an LCR bridge as 1.82uH. Although uncalibrated, accuracy should be within 0.5%. That agrees with calculators I posted earlier and it seems you needed 22 turns to be within 10% tolerance, if that was needed.
A 4uH, 2-layer coil with 14 turns per layer needs only 3ft of 1mm wire and would fit easily there. 1mm wire is rated for 10A continuous current but perhaps heavier 1.29mm (16 AWG, ~18 SWG.) would offer more safety. I don't think an SMD will get near that.
Was there a problem with the original 1mm wire you used for the 2 uH chokes? Surely you can just replicate the originals rather than go to a ferrite choke, and this can't be a critical component. I wound one on 3/8" fibreglass rod according to your original spec. and it measured on an LCR bridge as 1.82uH. Although uncalibrated, accuracy should be within 0.5%. That agrees with calculators I posted earlier and it seems you needed 22 turns to be within 10% tolerance, if that was needed.
A 4uH, 2-layer coil with 14 turns per layer needs only 3ft of 1mm wire and would fit easily there. 1mm wire is rated for 10A continuous current but perhaps heavier 1.29mm (16 AWG, ~18 SWG.) would offer more safety. I don't think an SMD will get near that.
I'm still playing with the 2 x 2uH. I'm going to see if I can get these to fit.
COILCRAFT, SER1052-402MLB, INDUCTOR, PWR, 4UH, 11.5A, 20 | eBay
COILCRAFT, SER1052-402MLB, INDUCTOR, PWR, 4UH, 11.5A, 20 | eBay
At 16.5 x16.5 x 10mm, that's a big SMD. I would think it needs a mounting bolt.
It's even rated at 28A RMS current, so it must have substantial wire though the image doesn't appear to show it. Composite core or Soft magnetic composite (SMC) material is essentially an iron powder/resin or other insulating binder mix so I assume it doesn't saturate at audio frequencies within the expected range of output currents. Does anyone know of likely limitations for audio?
Coilcraft Power Inductor Finder
It's even rated at 28A RMS current, so it must have substantial wire though the image doesn't appear to show it. Composite core or Soft magnetic composite (SMC) material is essentially an iron powder/resin or other insulating binder mix so I assume it doesn't saturate at audio frequencies within the expected range of output currents. Does anyone know of likely limitations for audio?
Coilcraft Power Inductor Finder
I'm guessing here.
D3 has survived and all the rogue NPNs are OK. It looks as though nothing broke down so it can be treated like TR4 -6 just failed open cct.
D3 has survived and all the rogue NPNs are OK. It looks as though nothing broke down so it can be treated like TR4 -6 just failed open cct.
I've been doing a bit of research on TR7 and TR8.
In the original Quad products these were RCA 40872.
Now I've used BD244C as a substitute.
On paper the 40872 does appear to be the better transistor. I can still get the originals but they are quite expensive - is the extra expense worth the cost ?
In the original Quad products these were RCA 40872.
Now I've used BD244C as a substitute.
On paper the 40872 does appear to be the better transistor. I can still get the originals but they are quite expensive - is the extra expense worth the cost ?
In the World of the great unknown, as I'm not certain that the BD244C's survived the NPN excursion, I've ordered 4 of the 40872s anyway.
They're only £2.00 each so that wont break the bank.
They're only £2.00 each so that wont break the bank.
I wouldn't think they are super critical tbh. The vas/driver triples look to be reasonably heavily slugged.
As I've got to take them out anyway for testing, I'll change them. So far I haven't found any duff components.