Hi KatieanDad - nice coils 🙂 wrt output transistors as others have said going plastic is an easier option from a mounting perspective. I chose to use the MJ15003 as I am building 8 channels and the price break made them affordable even with mounting kits and had read elsewhere that some of the higher frequency plastic cased modern ones did lead to unwanted ringing and/or oscillations, so I think they probably are a safer bet.
Good luck with your build
Good luck with your build
Just about every negative side O/P stage with a CFP or collector drive shows instability. ESP (Rod Elliott) makes quite a point of that with his projects too.
I think 2N3773 and MJ15003 are probably not as high Hfe even though Ft is comparable. This may be why in real applications they don't have many oscillation problems.
It might save some time but it won't so much fun...
Cheers
1PC REF.QUAD 606 mail amplifier DIY PCB board | eBay
Cheers
1PC REF.QUAD 606 mail amplifier DIY PCB board | eBay
TBH, seeing the long, grinding efforts of others here to replicate the Quad PCBs, those are a no-brainer - Nice find!
Each to their own but I'd really rather stuff boards and listen to the results than struggle over a doubtful PCB layout, for as long as it takes. 🙂
Something wrong here.
The inductances increases roughly with the square of the Turns.
26^2 and 20^2 give 676 and 400
That is a ratio of 1.69:1, i.e. 1.5uH @ 20T should become ~ 2.5uH @ 26T
Have you measured the impedance of your coils?
I notice that the Quad should be run with 82V RMS secondaries.
Although the power will be slightly reduced, will it run on 70V RMS until I can afford the bigger transformer(s).
Although the power will be slightly reduced, will it run on 70V RMS until I can afford the bigger transformer(s).
OK. I'll try adding the additional windings to the toroidals to build them up to the 82V of the original Quads.
It will run using 70V secondary without any problem. Less power, that's all. If you check schematics for 306,520,606,707,909 you will find out that it's basically the same amp just different number of outputs and supply voltage.
One more thing. You mentioned AD....something. Some expensive op amp. Well tlc271 is used as dc servo. It is not in audio path and there is no use of installing some ''exotic'' component.
Btw. Do you have those J503 constant current diodes? If not PM me. I could miss one pair easily.
Cheers
One more thing. You mentioned AD....something. Some expensive op amp. Well tlc271 is used as dc servo. It is not in audio path and there is no use of installing some ''exotic'' component.
Btw. Do you have those J503 constant current diodes? If not PM me. I could miss one pair easily.
Cheers
I wonder why the "ultimate upgrade" included changing the op-amps ? I've bought the posh upgrade op-amps as a starter but as has been stated already, they are only in the servo loop.
I've got no means of measuring them, I just poked the figures into a calculator and that is what popped out. The length of the coil also plays a part which I think you have missed out.
The length of the 1.5uH coil is 20mm and the length of the 2.0uH coil is 26mm.
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Solenoid Inductance Calculator
Using this, I arrived at inductance figures 4% higher for both coils than KatieandDad but the assumptions made about actual
pitch, length and varnish thickness are probably a little different.
The documentation gives explanatory details of a number of interesting corrections to the simple formulae often used for small
solenoid coils, as these would be termed. As expected, even lacquer thickness and hand winding pitch errors affect inductance.
The main point is that 4% higher inductance was consistent for both 20 and 26T coils.
Using this, I arrived at inductance figures 4% higher for both coils than KatieandDad but the assumptions made about actual
pitch, length and varnish thickness are probably a little different.
The documentation gives explanatory details of a number of interesting corrections to the simple formulae often used for small
solenoid coils, as these would be termed. As expected, even lacquer thickness and hand winding pitch errors affect inductance.
The main point is that 4% higher inductance was consistent for both 20 and 26T coils.
Wheelers Formula is:-
L (uH) = (r^2 x N^2) / (9r + 10l)
Therefore for coil 1 r = 0.2", l = 0.79", N=20
L = 1.64uH
For coil 2 r = 0.2", l = 1.02", N=26
L = 2.25uH
Very slightly high but I used the diameter of the former 9.5mm instead of the outside diameter of the winding when I made them.
L (uH) = (r^2 x N^2) / (9r + 10l)
Therefore for coil 1 r = 0.2", l = 0.79", N=20
L = 1.64uH
For coil 2 r = 0.2", l = 1.02", N=26
L = 2.25uH
Very slightly high but I used the diameter of the former 9.5mm instead of the outside diameter of the winding when I made them.