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Old 11th September 2012, 01:24 PM   #1671
lhquam is offline lhquam  United States
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I am now using the pic A for AC and pic B for DC. Rs=0R12. Bias is perfectly stable and it sounds good. See schematic in post #1647 F6 Amplifier.

Quote:
Originally Posted by Zen Mod View Post
make diff between bias and modulation path

biasing pot is situated between gate and bottom of Rs

modulation path is situated between gate and source

both schmtcs posted by me , same as lhquam's , are as your case A
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Old 11th September 2012, 01:36 PM   #1672
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by lhquam View Post
I am now using the pic A for AC and pic B for DC. Rs=0R12. Bias is perfectly stable and it sounds good. See schematic in post #1647 F6 Amplifier.
you mean other way around (bobo's pics in #1668 ; A for DC (bias) , B for AC (modulation) ?

no need for more confusion , your schm (linked above ) is crystal clear
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Old 11th September 2012, 01:39 PM   #1673
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Quote:
Originally Posted by Zen Mod View Post
.....

both schmtcs posted by me , same as lhquam's , are as your case A
of course , I meant - regarding bias
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Old 11th September 2012, 01:40 PM   #1674
lhquam is offline lhquam  United States
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My bad. Too early in the morning here.

Quote:
Originally Posted by Zen Mod View Post
you mean other way around (bobo's pics in #1668 ; A for DC (bias) , B for AC (modulation) ?

no need for more confusion , your schm (linked above ) is crystal clear
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Old 11th September 2012, 01:51 PM   #1675
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Sorry for making confusion. I am so thick.

ZM, i see you keep a big cap across biasing diodes. I remember Papa said to take them off when Ihquam was troubleshooting his motorboating.

Ihquam, where this motorboating came from at the end, you did'nt tell really, i think?

Last edited by bobodioulasso; 11th September 2012 at 01:57 PM.
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Old 11th September 2012, 02:05 PM   #1676
Zen Mod is offline Zen Mod  Serbia
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I have a drawer full of 470uF/35V/125C industrial Elna's

for my ears , they're same as BG well broken in , both bypassed with 10n-1uF MKC

so , stubborn or what , I'm seeding them and green LED's wherever I can .......

there will not be breathing , when fed with CCS
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Old 11th September 2012, 02:12 PM   #1677
lhquam is offline lhquam  United States
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The moterboating problem went away when I increased the size of the bias caps from around 22uf up to 470uf. I am not 100% convinced that there isn't the possibility for oscillation, but the frequency now will be below about .05 Hz. Also, the motorboating was seen in a somewhat different circuit shown in post #941 F6 Amplifier. In principle, that circuit should perform similarly to the current one. Looking at the Spice AC analysis, there were very low frequencies where the phase margin was questionable.


Quote:
Originally Posted by bobodioulasso View Post
Sorry for making confusion. I am so thick.

ZM, i see you keep a big cap across biasing diodes. I remember Papa said to take them off when Ihquam was troubleshooting his motorboating.

Ihquam, where this motorboating came from at the end, you did'nt tell really, i think?
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Old 11th September 2012, 02:19 PM   #1678
lhquam is offline lhquam  United States
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"there will not be breathing , when fed with CCS"

So you have experienced a similar low frequency oscillation. How much modulation of the bias voltage (or current) have you seen? Do you fully understand the feedback mechanism?

Quote:
Originally Posted by Zen Mod View Post
I have a drawer full of 470uF/35V/125C industrial Elna's

for my ears , they're same as BG well broken in , both bypassed with 10n-1uF MKC

so , stubborn or what , I'm seeding them and green LED's wherever I can .......

there will not be breathing , when fed with CCS
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Old 11th September 2012, 02:23 PM   #1679
x-pro is offline x-pro  United Kingdom
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Quote:
Originally Posted by Nelson Pass View Post
The transformer secondaries are set up to drive the Fets in a matched
fashion, if that is what you're asking.

The Fets can be a wide variety of devices. In this case, R100's.

I no longer apply for patents.

I haven't seen this feedback mechanism as such, but you can be
sure it's been done one way or another, probably a long time ago.

I've played with a very similar idea about 7 years ago and exchanged some emails about it with Ben Dunkan. Here is the basic circuit. At the time I couldn't find a similar feedback circuit - at least not in LF applications, however I also thought that something like this has been done a long time ago.

Cheers

Alex
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Old 11th September 2012, 02:30 PM   #1680
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Preliminary results make me think less feedback, not more. I currently have .47Rs, bias of 1.3A per fet, 8dB of gain. I have some 330R mills, so Iam gong to try that. BTW, Bypass cap is necessary. I have 1K Nichicon Muse and they add their electro sound to the amp. Don't stone me please. I have some 470uF Silmic II's to try. I will be byassing with fancy Film more than likely. Although i cant grasp why you would want to do so considering the balanced nature of the circuit, I have considered putting two resistors in series to form the Rs Total. Put pot across top one and pull modulation point from their. Wouldnt lose all you DF and would allow for Zen adj.
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