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Old 6th April 2012, 12:31 PM   #391
zsaudio is offline zsaudio  Europe
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Quote:
You have stated the selection of Idss. That is no where near matching devices.
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.

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Old 6th April 2012, 12:41 PM   #392
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Quote:
Originally Posted by zsaudio View Post
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
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Old 6th April 2012, 12:54 PM   #393
zsaudio is offline zsaudio  Europe
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Thanks Mihai.
I really like the sound of your amp.

Just curious did you test jfet/cfp ltp when you developed the amp?

I was playing with it in LTspice. I got a little bit higher thd because i had to degenerate the ltp to keep the same stability.

rmi-fc100_cfp_loopgain_sch.jpg

rmi-fc100_cfp_loopgain.jpg
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Old 6th April 2012, 01:01 PM   #394
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Some LTspice files

cfp_ltp_loopgain.zip
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Old 6th April 2012, 01:15 PM   #395
roender is offline roender  Romania
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Quote:
Originally Posted by zsaudio View Post
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?
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Old 6th April 2012, 01:30 PM   #396
zsaudio is offline zsaudio  Europe
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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).

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Old 6th April 2012, 01:36 PM   #397
roender is offline roender  Romania
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Originally Posted by zsaudio View Post
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
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Old 6th April 2012, 01:50 PM   #398
zsaudio is offline zsaudio  Europe
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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:
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, both amplifiers will have a common signal DC ground connected together at the signal source, once the signal source is connected
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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Old 6th April 2012, 02:02 PM   #399
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The individual amplifier grounds connects together at the DAC. The amplifier case is not grounded, it is just AC coupled through 2x1uF to each amp ground and all transformer shields are connected together and grounded.

Last edited by roender; 6th April 2012 at 02:16 PM.
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Old 6th April 2012, 02:14 PM   #400
zsaudio is offline zsaudio  Europe
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Thanks Mihai.

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