This is from Mihai from the orig rmi-fc100 thread:
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)
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)
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:
THD1 LTP 2SK369BL:
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 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:
THD1 LTP 2SK369BL:
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 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:
View attachment 275684
THD1 LTP 2SK369BL:
View 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?)
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.
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.
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.
For the 2SK369
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.
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.
For the 2SK369
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.
I only can match for Idss and Vgs at a given Id. This gives me 0,1-0,3mV offset in case of 2sk170. The 2sk369 was matced even worse accordind to Idss and Vgs. I do not have a curve tracer to go for gm.
I was curious about my finding that when i swap for the 2SK369 i can hear cleaner vocals. I measured the thd (with my limited tools) and found lower thd with 2SK369.
My question was that i can have the lower thd because of the higher gm or because of the better gm matched (accidentally) of the 2sk369s.
I only can match for Idss and Vgs at a given Id. This gives me 0,1-0,3mV offset in case of 2sk170. The 2sk369 was matced even worse accordind to Idss and Vgs. I do not have a curve tracer to go for gm.
I was curious about my finding that when i swap for the 2SK369 i can hear cleaner vocals. I measured the thd (with my limited tools) and found lower thd with 2SK369.
My question was that i can have the lower thd because of the higher gm or because of the better gm matched (accidentally) of the 2sk369s.
Better GM matched.
H3 sound more "resolute" than H2
... If you like it it's all that it counts
Thanks Mihai.
Just curious did you test jfet/cfp ltp when you developed the amp?
No, I didn't
What is your reason behind this mod?
Some people say cfp in ltp has nice sound character.
If my memory serves AndyC did a nice work on it over Diy Audio Engineering but i did not save that to my computer and the forum is down. AFAIK he examined bjt/bjt cfp ltp.
My reason should be to drop a nice cfp ltp into the rmi-fc100 and compare to the single jfet ltp (sound).
I just was curious that you ever tried jfet/cfp ltp.
I do not plan to ruin your amp Mihai but you know i'm a diyer and always think about mods, new things (for me).
I do not plan to ruin your amp Mihai but you know i'm a diyer and always think about mods, new things (for me).
Just play with what you consider sounding better for your ears and be happy. That's the spirit of DIY
Yes that's true.
May i ask you about your gronding scheme for a dual mono arangement?
You wrote this in your thread:
You mean that your left and right channels are only connected together through the external source? How do you connect the amp's ground to safety earth? Is your chassis earthed?
Sorry if i misunderstood something and i have an already answered question.
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