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Doug Self Preamp from Linear Audio #5
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Old 11th July 2019, 07:21 AM   #1391
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Hicoco View Post
With no load i am able to adjust the output at +-17V or more.
With 200mA load at the positive rail and 154 mA at the negative rail the output drop from +-17V to +-15V and i am not able anymore to adjust the voltage at a value higher than 15 Vdc when i turn the adjustable Pot.
So what psu is that? Do you have a schematic you can post?

BTW SK129 is mechanically equivalent to SK104 as to PCB holes and TO220 holes, but is a bit wider. IF it fits the PCB it gives you a bit lower temperature.

Jan
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Old 11th July 2019, 07:27 AM   #1392
Hicoco is offline Hicoco  France
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Doug Self Preamp from Linear Audio #5
Quote:
Originally Posted by jan.didden View Post
So what psu is that? Do you have a schematic you can post?

BTW SK129 is mechanically equivalent to SK104 as to PCB holes and TO220 holes, but is a bit wider. IF it fits the PCB it gives you a bit lower temperature.

Jan
That is the PSU board that Carl sent with the Doug's PCB preamp
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Old 11th July 2019, 07:57 AM   #1393
jan.didden is offline jan.didden  Europe
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I think you are hitting the max output level of the NE5534. The opamp output must be about 1.2V above the supply output. With the opamp max output 2V below its own supply you are getting close to 15V + 1.2 + 2 = 18.2V needed input voltage.
R5 aggravates the issue due to several 100mV drop. You can try to change R5 to 50 ohms or so, and make R9 1k.

If you change the output voltage to 14V, does it work as expected? Or find an opamp with RR output.

Jan

Edit: I think there may be as much as 3V or more across R5, which makes the opamp supply needing to be more than 6V above the output.
That's one of the great advantages of the diyaudio Superreg, where the opamp is supplied from the output, needing less headroom (and better PSRR).
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Last edited by jan.didden; 11th July 2019 at 08:11 AM.
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Old 11th July 2019, 08:09 AM   #1394
Hicoco is offline Hicoco  France
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Doug Self Preamp from Linear Audio #5
Quote:
Originally Posted by jan.didden View Post
I think you are hitting the max output level of the NE5534. The opamp output must be about 1.2V above the supply output. With the opamp max output 2V below its own supply you are getting close to 15V + 1.2 + 2 = 18.2V needed input voltage.
R5 aggravates the issue due to several 100mV drop. You can try to change R5 to 50 ohms or so, and make R9 1k.

If you change the output voltage to 14V, does it work as expected? Or find an opamp with RR output.

Jan
Yes i can drop the output under 15V, it work as expected,
I have more than 18,2V at the input..I have 21.8V with load..this is why i don't understand.. if i follow your math i should be able to get more than 17V at the output


Edit: just saw your edit..I will do the test for R5 and R9, Thanks Jan

Last edited by Hicoco; 11th July 2019 at 08:14 AM.
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Old 11th July 2019, 08:17 AM   #1395
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Hicoco View Post

Edit: just saw your edit..
I'm slow this morning, sorry .... ;-)

Jan
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Old 11th July 2019, 05:32 PM   #1396
Hicoco is offline Hicoco  France
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Quote:
Originally Posted by jan.didden View Post
R5 aggravates the issue due to several 100mV drop. You can try to change R5 to 50 ohms or so, and make R9 1k.

Jan

Edit: I think there may be as much as 3V or more across R5, which makes the opamp supply needing to be more than 6V above the output.
That's one of the great advantages of the diyaudio Superreg, where the opamp is supplied from the output, needing less headroom (and better PSRR).
Yes i had 4,27v across R5..
I did the test with R5 50R and R9 1k with 100R and 5kTrimmer Resistors with my breadboard and i am able now to adjust 17v output with load test resistors, i have 0,77V across R5, 17,4Vac secondary, +/-21V after rectifiers.

After 15 minutes with 60R load and 276 mA the BD139/140 was fine, no over heat. i will try longer with a final resistors in the board.
Do you thing i can use 47R instead of 50R.
Thanks again for your help Jan, i really appreciate.
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Old 11th July 2019, 06:16 PM   #1397
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Hicoco View Post
Yes i had 4,27v across R5..
I did the test with R5 50R and R9 1k with 100R and 5kTrimmer Resistors with my breadboard and i am able now to adjust 17v output with load test resistors, i have 0,77V across R5, 17,4Vac secondary, +/-21V after rectifiers.

After 15 minutes with 60R load and 276 mA the BD139/140 was fine, no over heat. i will try longer with a final resistors in the board.
Do you thing i can use 47R instead of 50R.
Thanks again for your help Jan, i really appreciate.
Well done, yes use 47 ohms, or higher, up to 100 ohms should be OK. With 1.2V across the 1k, even 100 ohms only eats 0.12V from your overhead. 100 ohms may be better for stability.

Jan
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Old 12th July 2019, 03:44 AM   #1398
bk856er is offline bk856er  United States
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Doug Self Preamp from Linear Audio #5
Hicoco, glad you got it sorted out.

I just received my 15W power resistors and tested my PS with 100R on each rail.

No load = +/-17.0V set.

After 30min with 170mA load = +/-17.0V (no trimmer adjustment required).
Ambient = 31C
Diodes = 39C
Regulators = 49C at the bolt

All seems well with mine using the schematic values, 115V line input and 18V 7.5VA transformer.

BK
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Old 12th July 2019, 04:20 AM   #1399
Hicoco is offline Hicoco  France
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Doug Self Preamp from Linear Audio #5
Quote:
Originally Posted by bk856er View Post
Hicoco, glad you got it sorted out.

I just received my 15W power resistors and tested my PS with 100R on each rail.

No load = +/-17.0V set.

After 30min with 170mA load = +/-17.0V (no trimmer adjustment required).
Ambient = 31C
Diodes = 39C
Regulators = 49C at the bolt

All seems well with mine using the schematic values, 115V line input and 18V 7.5VA transformer.

BK
Great, what is the value after rectifiers ? and if you can across R5/R6 and R9/R10 ? Thanks

Last edited by Hicoco; 12th July 2019 at 04:22 AM. Reason: forgot something
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Old 12th July 2019, 05:44 AM   #1400
bk856er is offline bk856er  United States
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Doug Self Preamp from Linear Audio #5
Quote:
Originally Posted by Hicoco View Post
Great, what is the value after rectifiers ? and if you can across R5/R6 and R9/R10 ? Thanks
24.5V after the rectifiers, 4.1V across R5/6, 1.4V across R9/10.

BK
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