...... maybe he will offer the quantities you all want to a reasonable price,
I would mail him!
Tech DIY Company Store
I would mail him!
Tech DIY Company Store
(56/56,2)x100) -100 = -0.356%
if I paid 40 cents for a .1% resistor I'd be dissatisfied
yep, I always use what I have, Im not sure it really makes that much difference, and quality probably matters more than a few hundred uF. If you get obsessive about it later you can allways start upgrading parts, then again you may move onto a new project.
OK is it just me or are the ZTX450/BC550 opposite pinouts and the ZTX550/BC560 are
also opposite pinouts.
That is, the pinouts are not identical, but if you design for the ZTX parts you can
substitute the BC parts by inserting them turned around 180 degrees. And therefore
vice versa.
Guess what I just noticed....
also opposite pinouts.
That is, the pinouts are not identical, but if you design for the ZTX parts you can
substitute the BC parts by inserting them turned around 180 degrees. And therefore
vice versa.
Guess what I just noticed....
1) Short inputs to ground.
2) With a voltmeter across Vout+ and Vout-, adjust the 25R pot to read 0V (relative offset)
3) Votlmeter between Vout+ (or Vout- if you want) and ground, adjust the 50R pot to read 0V (absolute offset)
4) Let warm up for 1/2 to 1 hour
5) Recheck point 2 & 3
6) You're done
Best
Thanks guys. I did a fair bit of thinking about the circuit yesterday, as I
fired up one amp that I just built. I came to the conclusion that something
was very wrong because all the bias was way off and I couldn't do anything
to get them anywhere near close.
As you can tell from my second post, i found a problem.
I ordered some ZTX parts. I'll just cut off the BJTs that are all
facing the wrong way round right now, clean up the boards, then solder in
the new BJTs.
As bugs used to say, "what a maroon".
fired up one amp that I just built. I came to the conclusion that something
was very wrong because all the bias was way off and I couldn't do anything
to get them anywhere near close.
As you can tell from my second post, i found a problem.
I ordered some ZTX parts. I'll just cut off the BJTs that are all
facing the wrong way round right now, clean up the boards, then solder in
the new BJTs.
As bugs used to say, "what a maroon".
Well the plot thickens.
One of the boards fired right up. THe other one,,,, not so much and I can't
figure out what the problem is. I think the n-ch JFET is dead. I can't see
any shorts or opens on the board and it is not oscillating. The DC levels
just set to values that I can't decide what the issue is. But the voltages
in the lower half of the amp are below ground and the outputs are around
-5V and the inputs therefore near -2.2V or thereabouts (looks like the
JFET gates are still high impdance and input V is voltage divide from
output feedback Rs and the input Rs.). THe Cascode voltage divider is also
dead on - about +/- 10.8V on the bases of the cascodes. Current mirrors
also look sane.
I think this PCB was the one I tested when the BC version BJTs were
stuffed in the boards the wrong way round.
Since I have more PCBs and the parts are cheap, I'm going to just populate
another pair of boards to get hopefully 3 working amps using the best
remaining pairs of JFETS I have. This thing has been taking a couple months
of elapsed time and I want to see what these babies sound like.
THen if that works out maybe I'll cut off the JFETs from the dead PCB and
solder in new JFETS to see if that was the issue.
Another week to wait for parts.....
One of the boards fired right up. THe other one,,,, not so much and I can't
figure out what the problem is. I think the n-ch JFET is dead. I can't see
any shorts or opens on the board and it is not oscillating. The DC levels
just set to values that I can't decide what the issue is. But the voltages
in the lower half of the amp are below ground and the outputs are around
-5V and the inputs therefore near -2.2V or thereabouts (looks like the
JFET gates are still high impdance and input V is voltage divide from
output feedback Rs and the input Rs.). THe Cascode voltage divider is also
dead on - about +/- 10.8V on the bases of the cascodes. Current mirrors
also look sane.
I think this PCB was the one I tested when the BC version BJTs were
stuffed in the boards the wrong way round.
Since I have more PCBs and the parts are cheap, I'm going to just populate
another pair of boards to get hopefully 3 working amps using the best
remaining pairs of JFETS I have. This thing has been taking a couple months
of elapsed time and I want to see what these babies sound like.
THen if that works out maybe I'll cut off the JFETs from the dead PCB and
solder in new JFETS to see if that was the issue.
Another week to wait for parts.....
By "these critters" I take it you mean the JFETs?
I'm afraid of a false negative after removal. That would REALLY mess up my debugging.
But you're right, given no false negative it would be a good indication
before soldering on new parts that I'm replacing the bad part(s). I would
replace in pairs anyhow so it doesn't matter which of the two is dead
if it's one of the JFETs.
What I might try first is applying signal and see what stacks up. I haven't
done that yet.
Do you think they're robust enough to stand up to solder wick and high
temps for the time it takes me to remove them? I don't have any special
tools for desoldering.
Wayne,
Just begin by removing the two Rfb resistors on the bad module (unsolder just one lead on each rfb, that's enough)
Then fire it again and measure the voltages across the Jfets drain resistors (1K47 and 1K5)
You should find about 5.2V (and thus a current of 3.5mA).
If not, measure the voltage across the 22R & 47R source resistors and tell us what you find.
If yes, measure the voltages across the 750R current mirror resistors. You should read the same 5.2V voltage
Measure also the cascode bias voltage (between ground and the base of the cascode trannies). It should be near 10V (absolute value)
Tell us what you find.
Best,
Just begin by removing the two Rfb resistors on the bad module (unsolder just one lead on each rfb, that's enough)
Then fire it again and measure the voltages across the Jfets drain resistors (1K47 and 1K5)
You should find about 5.2V (and thus a current of 3.5mA).
If not, measure the voltage across the 22R & 47R source resistors and tell us what you find.
If yes, measure the voltages across the 750R current mirror resistors. You should read the same 5.2V voltage
Measure also the cascode bias voltage (between ground and the base of the cascode trannies). It should be near 10V (absolute value)
Tell us what you find.
Best,