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Old 3rd December 2011, 05:01 PM   #341
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Quote:
Originally Posted by terranigma View Post
Hello powerflux,

I etched and drilled one pcb yet. When I try to fit 2sc5200 (to-264) and some similar transistors (including mt-200) as output, but i saw that layout's leg distance was wider to fit. I checked original TIP3055's leg space dimensions in datasheet and I see that it is match to those I had to try. My measured two leg distance on pcb is about 7mm.TIP3055 in datasheet and other devices i tried are about 5.5mm.
I realized later that I have printed first file with wrong aspect. I'm sorry for false report.
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Old 4th December 2011, 08:45 AM   #342
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I realized later that I have printed first file with wrong aspect. I'm sorry for false report.
no problem, hope it works
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Old 7th December 2011, 03:34 AM   #343
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Yes, it worked

I build this time with similar parts in actual schematic.

Philips BC547/BC557 (BC556 for Q13)
Philips BD140 (with small heatsinks)
Motorola 2N3773
2N3020 as servo
30V rails, 190 mA quiescent current. 27mV DC-offset
But: 1.2nF for C6 and without C11

It sounds well with crappy test speaker by now. North side BD140 much hotter than other. And I can't touch 2N3020's even just a second. Dc-offset seemed to me unfair even hfe matched input pairs. Any comment?

Last edited by terranigma; 7th December 2011 at 03:48 AM.
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Old 7th December 2011, 04:30 AM   #344
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Originally Posted by terranigma View Post
And I can't touch 2N3020's even just a second.
It seems just one of them much hotter. That one is Q6. Q5 is gentle.
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Old 7th December 2011, 04:35 PM   #345
Elvee is online now Elvee  Belgium
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Quote:
Originally Posted by terranigma View Post
Philips BC547/BC557 (BC556 for Q13)
Philips BD140 (with small heatsinks)
Motorola 2N3773
2N3020 as servo
30V rails, 190 mA quiescent current. 27mV DC-offset
But: 1.2nF for C6 and without C11
190mA is OK.
27mV is marginal, but still possible if you are particularly unlucky with the input pair. It is within the limits of the datasheet anyway.
But in general, transistors from the same batch rarely show extremes, specially when they are sorted, since there is some correlation between the Vbe and the Hfe.
I just made a quick test on a dozen of unsorted (no suffix) BC557's. The maximum spread was 10mV. Add 10mV for the offset current if the Hfe is also widely different, and you're at 20mV.

You could swap the transistors to see if the offset polarity is reversed. If it is, then the transistors are the cause, otherwise, it is worth investigating further.


Quote:
It sounds well with crappy test speaker by now. North side BD140 much hotter than other. And I can't touch 2N3020's even just a second. Dc-offset seemed to me unfair even hfe matched input pairs. Any comment?
That is fishy: the BD140's dissipate very similar quiescent power, and if there is a difference, it is necessary to find the cause.
Are R13 and R10 OK? Sometimes the color code is ambiguous. Is the track to R13 OK?

Quote:
It seems just one of them much hotter. That one is Q6. Q5 is gentle.
There can be a small difference in dissipation, because the voltage of the zeners will never equal exactly the supply voltage.
But the difference should be minor, unless the zeners are shorted or have the incorrect voltage.
You can check the collector voltages wrt the negative rail: they should be broadly similar.
Normally, they dissipate 350mW each, which is sufficient to raise the case temperature ~75°C above ambient.
You can thus expect 100°C case, that's perfectly safe and normal.

If there is a large difference between Q5 and Q6, and it is not caused by a difference in voltage, you should try to find why the collector currents are dissimilar.
It probably has a relation with the other anomaly, perhaps a solder bridge in the driver or output region, an incorrect resistor value, a wrongly inserted transistor or something similar.
All the symptoms put together look very, very suspect.
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Last edited by Elvee; 7th December 2011 at 04:38 PM.
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Old 8th December 2011, 10:06 PM   #346
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I'm just arrived.

Quote:
Originally Posted by Elvee View Post
That is fishy: the BD140's dissipate very similar quiescent power, and if there is a difference, it is necessary to find the cause.
Are R13 and R10 OK? Sometimes the color code is ambiguous. Is the track to R13 OK?
Yes, they are ok.

Quote:
There can be a small difference in dissipation, because the voltage of the zeners will never equal exactly the supply voltage.
But the difference should be minor, unless the zeners are shorted or have the incorrect voltage.
My supply voltage is 30V. I measured 31.5V one zener to other.

Quote:
You can check the collector voltages wrt the negative rail: they should be broadly similar.
Q6 is -0.60V Q5 is around -7V (yes, seven).

Quote:
If there is a large difference between Q5 and Q6, and it is not caused by a difference in voltage, you should try to find why the collector currents are dissimilar.
It probably has a relation with the other anomaly, perhaps a solder bridge in the driver or output region, an incorrect resistor value, a wrongly inserted transistor or something similar.
All the symptoms put together look very, very suspect.
Replacing input pairs doesn't help. Also, dc-offset is same even shortcut to ground or not. I'm investigating.
Thank you for great support.
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Old 9th December 2011, 03:02 AM   #347
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Yes, they are ok.
No! You hit the target on first shot Elvee..After tracking more carefully, I saw that R13 and R12 are reversed . I just replaced them,and it seems Bd140s ok now.

Still investigating.

Last edited by terranigma; 9th December 2011 at 03:30 AM.
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Old 9th December 2011, 05:23 AM   #348
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DC-offset dropped to 15mV. I will work on this later. But collector voltages on Q6 and Q5 didn't get closed. Q6 is -0.6V, Q5 is dancing around -6.8 -7.3V, not stable. I made two pcbs and both of them have same issue. Q6 is not hot as like previously mentioned but still hotter than Q5.

@powerflux:
15R and 56R on bottom are reversed on silkscreen. Also, you can push them a bit front side due to opening room for driver heatsinks. You can flip 1R and 0.5R in safe. There is enough room.

Bottom side decoupling capacitor's pads different. Upper ones seem good.

You can avoid first bypass cap each side (most left ones) and you can use their pin as supply pad. If you go with this, current will flow through these caps in optimal way. I have modified pdf in this manner. I will post some pics soon.
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Old 9th December 2011, 07:27 AM   #349
Elvee is online now Elvee  Belgium
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Quote:
Originally Posted by terranigma View Post
DC-offset dropped to 15mV. I will work on this later. But collector voltages on Q6 and Q5 didn't get closed. Q6 is -0.6V, Q5 is dancing around -6.8 -7.3V, not stable. I made two pcbs and both of them have same issue. Q6 is not hot as like previously mentioned but still hotter than Q5.
That is not a problem, and anyway the supply is not regulated, meaning that at high output powers, the difference will change (increase further).
The zener's only role is to decrease the dissipation in Q5 and equalize crudely Q5/Q6, but reasonable differences like yours are perfectly acceptable, and have no impact whatsoever on the sonic qualities.
The output offset is also normal, if you want better (not required), you have to match the input transistors. You can also choose suffix -C to minimize offset/bias currents.
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Old 9th December 2011, 08:23 AM   #350
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Thank you Elvee.. I soldered female pin headers in place of input pairs for easy try out.

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@powerflux:
You can avoid first bypass cap each side (most left ones) ...
I meant decoupling caps of course..
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