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Old 10th February 2018, 10:11 PM   #51
blackdod is offline blackdod  Europe
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Thanks Patrick

Quote:
Originally Posted by EUVL View Post
You can also adjust the output voltage under load by adjusting the values of R2 and R7 in the power supply schematics.

Connect the PSU to the amp (without headphones).
Use a 5k trimmer, preset to ~2.7k in place of R2 and R7.
Adjust the trimmers until you get exactly 15.0V at the regulator output.
Then measure the values and replace with fixed resistors.
Ok, Done. 2.7K in r2 and r7. 15 Volt on regulators output. (13,6 volt both rails in the Psu output).

Why measure on the regulator output and not on the PSU output? And why Fer has 15volt on the output if he uses the same PSU?

I understand that my problem has been trying to reach 15 volts on the PSU's output. For some reason, I didnīt get it on the negative rail and it caused a mismatch in the offset.

Quote:
Originally Posted by EUVL View Post
When this is done, then measure the output voltage of the amp with the input shorted to Gnd and C2 bypassed.
Adjust the trimmer as you have before.
Let it run for an hour and see if it is stable over time.

Easiest is still to use a DC servo.


Patrick
Done. Now offset is very very stable. Around 0~2mVolt all time with a soft drift (I used all parts matched)

I need to check with headphones but now it looks good.
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Old 10th February 2018, 11:55 PM   #52
EUVL is offline EUVL  Europe
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> Why measure on the regulator output and not on the PSU output?

I meant PSU output, sorry for the misunderstanding.

> And why Fer has 15volt on the output if he uses the same PSU?

I have no idea.
Did you measure (match) the hfe of the transistors in the regulators ?


Patrick
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Last edited by EUVL; 10th February 2018 at 11:58 PM.
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Old 13th February 2018, 05:12 PM   #53
blackdod is offline blackdod  Europe
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Join Date: Jun 2011
Location: Spain
I canīt find the issue of this PSU.

I use 2SC4793 (Q2), BC550 (Q1) and 2SA1837 (Q4), BC560 (Q3) like F5ha PSU too.

I need use arround 17 volt on the output regulator for measure 14volt on the out put and trafo work a bit hot (15Vac@2Amp) Itīs not normal.

I think I'm going to forget about these plates and use a simpler PSU like the cheap PSU I used to test the amps.
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Old 13th February 2018, 05:58 PM   #54
EUVL is offline EUVL  Europe
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> I need use arround 17 volt on the output regulator for measure 14volt on the output
That is certainly not normal.

> and trafo work a bit hot (15Vac@2Amp) Itīs not normal.
Why would it draw 2A when the bias is only 160mA ?
Also not normal.

But as I can tell they are not my PCBs, so not much I can do for you.
The regulator circuit is certainly not the cause of your problems.

> I think I'm going to forget about these plates and use a simpler PSU.
Both followers have good PSRR.
So I would just use a standard 317/337 for now if I were you.

And it is always wise to test the PSUs on their own before putting them to an amp.
You can check all the DC voltages to start with.

Your previous post :
" 15 Volt on regulators output. (13,6 volt both rails in the Psu output)."
is normal. I expect a difference of ~1.3V between regulator out and PSU out.


Patrick
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