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Old 1st March 2011, 11:44 PM   #1
ontoaba is offline ontoaba  Indonesia
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Default My VAS performance "NEVER LET ME DOWN"

I am redraw the schematic from the PCB and hand writes. Its coming from this discussion (when not redraw yet): solid state amplifier obsolete ??
This one is very good and stable, I am using it for long time with various output stages and usually results in great sounds.
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Old 2nd March 2011, 12:07 AM   #2
ontoaba is offline ontoaba  Indonesia
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OOps. At the pcb V+ is V+5 and E is V+. Also for V-, its V-5 and W is V-.
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Old 2nd March 2011, 05:16 AM   #3
MiiB is offline MiiB  Denmark
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around the input pair you have a second set of transistors...What to they do...and could they work around a set of jfets...
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Old 2nd March 2011, 09:04 AM   #4
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Originally Posted by ontoaba View Post
results in great sounds.
yes
because it is designed according to low memory distortion rules
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Old 2nd March 2011, 11:15 AM   #5
ontoaba is offline ontoaba  Indonesia
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@MIIB.
The second 2sc3355 is used to boost its gain. When look at BC557, they has almost constant Vbe at low current, then it is good to keep BC557 in very low current operation, it also will draw less input current. Not as low as JFET.

@Pidamiecki
Umm, what is low memory distortion rules? Yes it does has low distortion. Here is some comparison. But I am not following very low distortion is best, output stages has major effect too.
other VAS coming from there: (Iam also post my new output stage there)
A different CAS typology with very low THD
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File Type: png otherVA THD+N.PNG (31.7 KB, 595 views)
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Old 2nd March 2011, 11:33 AM   #6
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Originally Posted by ontoaba View Post
@Pidamiecki
Umm, what is low memory distortion rules? [/url]
Please read whole links
at this thread
Aleph (Single Ended) + Larvadin (no Memory Distortion) = Ultimate Aleph?
and this Memory Distortion Philosophies - Part 8 : More tests
general:
cfp input + cascoded VAS = low memory distortion
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Old 2nd March 2011, 12:09 PM   #7
ontoaba is offline ontoaba  Indonesia
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Quote:
Originally Posted by MiiB View Post
around the input pair you have a second set of transistors...What to they do...and could they work around a set of jfets...
I am simulating it with j117 replacing BC557, and distortion become 0.00006%@1kHz, 0.0017%@20kHz and still very stable when clip.

Thanks padamiecki,
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Old 2nd March 2011, 02:32 PM   #8
ontoaba is offline ontoaba  Indonesia
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Quote:
Originally Posted by padamiecki View Post
Please read whole links
at this thread
Aleph (Single Ended) + Larvadin (no Memory Distortion) = Ultimate Aleph?
and this Memory Distortion Philosophies - Part 8 : More tests
general:
cfp input + cascoded VAS = low memory distortion
I have read them, may be too fast, but it really makes me think that may be memory distortion is true. When I, first placing cfp input, I am hoping it will have constant Vbe and higher gain, because using darlington will also add second Vbe.
I am also going to investigate my output stage with memory distortion philosophy, Thanks alot for that infos .
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Old 2nd March 2011, 06:27 PM   #9
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It would be interesting to hear your thoughts on how you find different input stages and VAS sound. How does CFP and cascode change the sound? I guess you have compared this to a standard configuration.

I also find this complex input stage with CFP and cascode to sound very good. I'm not so sure about cascoded VAS. I've posted my findings here Cascoding the folded cascode
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Old 2nd March 2011, 11:49 PM   #10
ontoaba is offline ontoaba  Indonesia
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Quote:
Originally Posted by nelsonvandal View Post
It would be interesting to hear your thoughts on how you find different input stages and VAS sound. How does CFP and cascode change the sound? I guess you have compared this to a standard configuration.

I also find this complex input stage with CFP and cascode to sound very good. I'm not so sure about cascoded VAS. I've posted my findings here Cascoding the folded cascode
Nice to hear that, nelson ,you also comparing quality by its sounds .
It is long story. I am using some different input stages and VAS in the past.
My first version is simple differential pair with 100mA bias VA to drive single EF directly. This one is my first good sounding amplifier. Then some people very interested in my amps. But the later version is worse with the same EF, this is first time I realize that VAS has the differences too, not just same function to amplify the voltages.
Until I have this VAS, and 2SC3355 or SS9018H/I really help in stability and its performance. Before using them, I have many compensator circuitry to prevent oscillation, and that 150pf is 470pf that time.

I have using cascoded VAS before it because my amps need high voltages, and also using video CRT transistors, some people says that video transistor not good for audio, but I found it nothing wrong.

I am using cfp input when start my V+I amplifiers. That I think it need more linear input stages. I cascoding it to get constant Vce at around 7V, and I see some amplifier using this too. I am impressed in first test, and improving it until now.

If that my VAS really that good (as low memory distortion is true), may be my new VAS will not better than this.

Here is my example if anyone want to hear it. Beware may be it is lttle exciting.

EDIT:
I forgot it, any changes from A872E to BC557B/C or C3355 to S9018H need some different TO-92 legs arrangement in PCB. 2SA/2SC has ECB and BC/SS CBE, see the datasheet for detail. IC hole matrix PCB is usable.
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Last edited by ontoaba; 3rd March 2011 at 12:10 AM.
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