Roender's FC-100 prototype and builder's thread - Page 39 - diyAudio
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Old 4th April 2012, 05:05 PM   #381
zsaudio is offline zsaudio  Europe
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Have you guys ever made a comparison test on different power stage's power supply arrangement. I mean is it worth to go for dual mono or pseudo- dual mono?

I call this one pseudo dual:
PSU_2.jpg

If so what kind of differents did you recognise?
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Old 4th April 2012, 06:22 PM   #382
AndrewT is offline AndrewT  Scotland
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Zs,
I think you will find this even more difficult to get rid of the hum.
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Old 4th April 2012, 06:58 PM   #383
zsaudio is offline zsaudio  Europe
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This is from Mihai from the orig rmi-fc100 thread:
Quote:
In a dual mono amplifier, I used to connect every main starground to the case through 1...2uF foil capacitor.
When I said to connect the ground to the heatsink I mean to connect it at AC, not DC! Therefore, [B]both amplifiers will have a common signal DC ground connected together at the signal source, once the signal source is connected
So when we have one trafo is it better to use the center tap?

I use the pseudo psu (as shown on the attached picture) for testing at the moment and can not hear any hum. I've seen a psu by Mr Nelson Pass and if my memory serves he connected the ground after the rectifiers and not at the center tap(he used two trafos).

Ok let's leave alone this way to hook up the psu. What's your finding between one shared trafo and dual mono config? (according to ground issues and channel separation)
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Old 6th April 2012, 10:07 AM   #384
zsaudio is offline zsaudio  Europe
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Smile Rmi-fc100 games

I was playing with the LTP. I compared 2SK369BL and 2SK170BL

Idss of 2sk170BL 9,31mA/9,31mA other pair 9,34mA/9,34mA
Idss of 2sk369BL 9,40mA/9,43mA other pair 9,45mA/9,49mA

Result of Right channel about 30Wrms 6R resistive load.
Please do not take the high order harmonics into account since those are comming from my sinus generator.

THD1 LTP 2SK170BL:
30Wrms_right_6R_2sk170.jpg

THD1 LTP 2SK369BL:
30Wrms_right_6R_2sk369.jpg

Using 2SK369 in the LTP i can feel more air the vocals are much more defined i can hear the smallest breath.
Hmm... the 2sk369 has more Ciss but more Yfs, maybe the transconductance rules here
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Old 6th April 2012, 10:10 AM   #385
zsaudio is offline zsaudio  Europe
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Another nice candidate would be BF862 but it's a real PITA to match them.
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Old 6th April 2012, 10:24 AM   #386
roender is offline roender  Romania
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Quote:
Originally Posted by zsaudio View Post
I was playing with the LTP. I compared 2SK369BL and 2SK170BL

Idss of 2sk170BL 9,31mA/9,31mA other pair 9,34mA/9,34mA
Idss of 2sk369BL 9,40mA/9,43mA other pair 9,45mA/9,49mA

Result of Right channel about 30Wrms 6R resistive load.
Please do not take the high order harmonics into account since those are comming from my sinus generator.

THD1 LTP 2SK170BL:
Attachment 275684

THD1 LTP 2SK369BL:
Attachment 275685

Using 2SK369 in the LTP i can feel more air the vocals are much more defined i can hear the smallest breath.
Hmm... the 2sk369 has more Ciss but more Yfs, maybe the transconductance rules here
I think k369 pairs are much better matched than k170, not only at Idss :-)
This is the reason behind reduced H2 distortion and much more defined sound (grainy perhaps?)
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Old 6th April 2012, 10:33 AM   #387
zsaudio is offline zsaudio  Europe
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Idss and Vgs matching is worse. The Yfs matching i do not know.
I do not hear more granier than with 170s but i need more listening tests.
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Old 6th April 2012, 10:42 AM   #388
AndrewT is offline AndrewT  Scotland
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389 is the pair of 170s
369 is much the same as a very high current 170.
Yes, the specified transconductance looks higher. I interpreted the datasheet as showing that a similar Idss 170 & 369 perform much the same.

How well are the 369pair matched?
How well are the 170pair matched?

I am guessing that what you are hearing is a difference in pair matching.
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Old 6th April 2012, 11:34 AM   #389
zsaudio is offline zsaudio  Europe
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The Idss matching is shown in my previous post.
The Vgs matching of the 2SK369 pairs is not as good as for the 2SK170 pairs.

I have three times bigger DC offset with the 369's.

I do not know the GM match of any of the pairs.

Here is the gm plot for the 2SK170.
GM_2SK170.jpg

For the 2SK369
GM_2SK369.jpg

I perhaps misunderstood the plots but as i see if the part has the same Idss and running at the same Id the 2SK369 has higher GM. Maybe this for nothing in this case. I'm asking your POV.
It would be better to simulate the amp with 2sk369 too and compare.

What Mihai says is logical for me. Better GM matched devices give me lower
2nd harmonic that's why i hear the vocals cleaner.

But maybe i'm wrong. I'd like to hear your opinions too guys.

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Old 6th April 2012, 12:04 PM   #390
AndrewT is offline AndrewT  Scotland
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You have stated the selection of Idss. That is no where near matching devices.
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