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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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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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Old 21st June 2018, 08:09 PM   #55
blackdod is offline blackdod  Europe
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New PCBs with EUVL and fernanwaka mods.

Click the image to open in full size.

Now the amplifier is very stable. The offset remains stable in a range of 0 to 3mVdc.

I need to finish it and do some more tests but in principle it works perfectly.

Last edited by blackdod; 21st June 2018 at 08:27 PM.
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Old 21st June 2018, 08:15 PM   #56
blackdod is offline blackdod  Europe
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Click the image to open in full size.
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Old 22nd June 2018, 05:44 AM   #57
EUVL is offline EUVL  Europe
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How did you solve your power supply problem ?
Or are you just using 317/337 regulators ?


Patrick
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Old 22nd June 2018, 06:12 AM   #58
blackdod is offline blackdod  Europe
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Iīm using a simple PSU with 317/337 regulators but I didnīt use capacitance multiplier.

Itīs not a "exotic" solution but it works so Iīm happy. However it is a part of the amplifier that I still have to finish.
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Old 22nd June 2018, 08:49 AM   #59
EUVL is offline EUVL  Europe
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Default Lateral FET Output Follower

The basic M2 topology is essentially a JFET input buffer, followed by an audio transformer, and then a MOSFET power follower to drive the load.

As already mentioned in post #26, the loading on the input JFETs is quite heavy because they see R6 and R7 in parallel via the transformer. To alleviate this, one can replace R6, R7 through two constant current sources, which have higher dynamic impedance. But in order to avoid unbalanced current leading to DC offset, they need to be equal and to track each other at all times. In the Pioneer SL headphone amplifier, we have proven the stability of a current-mirror based, self-tracking CCS pair. This would be ideal to replace R6 and R7. If one is not worried about voltage headroom, once can improve this even further by using a 4-transistor full Wilson current mirror.

The capacitance of the output MOSFETs appears as additional dynamic load to the JFETs. Thus it is always advantageous to use devices with low (and constant) capacitances to reduce distortion. In that respect, lateral MOSFETs are superior. In the UTHAiM, as well as a recent (not yet published) shootout between the Borbely EB602/200 and a vertical MOSFET equivalent, multiple testers have observed noticeably smoother mids and highs. (No real surprise as Charles Hansen had been telling us all the time.) Also, as we have already discussed at the UTHAiM thread, the lateral MOSFETs have negative tempco at over 100mA bias, and is therefore self-stabilising. This will allow simply using resistors for bias, as in the UTHAiM.

So for me personally, the circuit below would be a good alternative to the output stage of post #26. But then you should not call this M2 anymore.

The 2SK1058/2SJ162 are already NRND, though not yet quite EOL. But the Exicon equivalents are still available and arguably better.


Patrick
Attached Files
File Type: asc Lateral Follower V1 THD.asc (5.3 KB, 47 views)
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Old 22nd June 2018, 09:43 AM   #60
EUVL is offline EUVL  Europe
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Forgotten to mention that although the simulation was done with 2SC2240/2SA970, we actually used their SMD equivalent in the SL HPA.

They are still active and available at e.g. Mouser.
2SC3324-BLTE85LF Toshiba | Mouser Europe
2SA1312-BLTE85LF Toshiba | Mouser Europe


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