you need do something about the wiring on the left ch. don't let the wires run under the PCB like they do. wire insulation can be damaged by the solderjoint/end of component legs and short out the amp. its better to run the wires over the top of the PCB.
Thanks for the advise, but I think I've put that cover on for the last time
It is all sit back and enjoy for now. It is playing great.
my rule of thumb is to do it right the first time
PSU wires running between the PCB and heatsink can do a lot of damage. and there will be no heads up. it can happen tomorrow. in a year. next week. never. you'll never know.
one thing is certain. if it happens, the amp is gone.
In this case, the heatsinks do not get hot enough to hurt wire insulation, much less Teflon insulation that is some of it, it will hold out for good while. But, point considered for next time.
The amp is working perfectly and will continue to do so...
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Curious me, at which Idss value did you match them ?
(Noise figure in the J manual is 100uV, that's -89dB in reference to 2.83V Noise of the J176 is 20dB worse than the Toshiba part. Normally, a noise level of -69dB would be audible on your 100dB/W horns)
It is not a straight one-to-one match to the Toshiba J174, but a "C" level match and it is the only part in stock at Mouser that comes close to a J174. No noise at all, so far it works very well. Here is the Fairchild spec sheet for the J176. Can you tell what the transconductance might be for J176?
IDSS:
J176: -2.0 - 25.0 mA
Toshiba: -2.6 - 20.0 mA
VGS (off)
J176: 1.0 - 4.0 V
Toshiba: .15 - 2.0 V
Transconductance:
J176: ??
Toshiba: 8-22 Ms
Were you getting these numbers from these charts?
Attachments
Manufacture of GR, BL, and V-grade devices are not 3 separate production runs, they all come from a single batch.
Parameter spread in manufacture generally has a symmetrical bell curve.
Typical means that the mean (average) gm value will be 22mS at 3mA Idss.
(same goes for scale factors in the mathematical expressions for JFETs, btw. gm = [ 2 * √(Id* Idss) / Vp ] The scale factor 2 is a typical value, in reality it can range from just over 1 to 2.5)
Parameter spread in manufacture generally has a symmetrical bell curve.
Typical means that the mean (average) gm value will be 22mS at 3mA Idss.
(same goes for scale factors in the mathematical expressions for JFETs, btw. gm = [ 2 * √(Id* Idss) / Vp ] The scale factor 2 is a typical value, in reality it can range from just over 1 to 2.5)
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I have a small problem with the zero adjustment. I adjust R27 to measure 0,45V between R16. When trying to adjust R7 to measure 0V, the values range from -18 / + 18V, and for a short tour of a turn, comes to 0V but is very unstable.
R8 fixed to 1K. The tension between R7 is 4.7V, and between R8 is 8,4V
Any ideas?
R8 fixed to 1K. The tension between R7 is 4.7V, and between R8 is 8,4V
Any ideas?
Hi,
planning this build now and have started collecting parts, boards are on the way and Power fets have arrived from Austria thanx to h_a.
A question about balanced VS unbalanced input:
I want to run unbalanced Rca inputs only,
Can i drop all the Components in the negative input Chain : R3 C1 and possibly C5?
Or do I need to assemble the whole lot and short Gnd and negative ?
Thnx
Per
planning this build now and have started collecting parts, boards are on the way and Power fets have arrived from Austria thanx to h_a.
A question about balanced VS unbalanced input:
I want to run unbalanced Rca inputs only,
Can i drop all the Components in the negative input Chain : R3 C1 and possibly C5?
Or do I need to assemble the whole lot and short Gnd and negative ?
Thnx
Per
