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Old 27th August 2012, 03:39 PM   #1201
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Quote:
Originally Posted by Antoinel View Post
Does the underlined mean metalized polypropylene? Are you still working with your schematic in post#1023.
MP is here a catch-all for capacitors; MP has good dynamics. Just a contrast to the electrolytic.
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Old 27th August 2012, 04:48 PM   #1202
generg is offline generg  Germany
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Quote:
Originally Posted by Zen Mod View Post
G.- did you received repeaters?
Oh yes ZM, I am now a Repeater.....

I hope it is something like a Terminator....!
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Old 27th August 2012, 05:19 PM   #1203
lhquam is offline lhquam  United States
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Quote:
Originally Posted by triode_al View Post
lhquam,
  • imho the real reason for the effect might be that
  • you use a bootstrap for the top bias
  • the bias of the top is C4, 44μF connected to the output (and I just note that value differs from C15).
  • sonically this is an electrolytic in the signal path!!
  • an alternate method would be to connect the bias to the output and insert a big bootstrap in the middle of the R20 (1k4+1k4) (and treat it similar with SAME cap in a split up R21).
Q:
if you disconnect the transformer from one of the outputs does it still oscillate/motorboat?
- just for instance the top one gets no modulation, it will be a BA-1 output stage.

I like a method of bias with just a MP cap!
I think I understand the problem with low frequency oscillation. As the frequency gets very low the bypass caps on the input jfet drains become ineffective. What is the impedance of the transformer primary winding as frequencies get very low (<< 1Hz)? The Spice simulation shows the impedance (reactance) of 18 ohms at .7Hz. This means that the jfet input stage will clip at very low frequencies and relatively low signal levels. Of course, with an input cap/resistor RC>.02 secs, such low frequencies will be greatly attenuated before getting to the input stage.

I suggest using 1 watt 15V Zeners to drop the rail voltages to the input JFET drains rather than resistors.
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Old 27th August 2012, 05:50 PM   #1204
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Is'nt your motor boating due to PSU?
Haven't you tried a classical one?
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Old 27th August 2012, 06:16 PM   #1205
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by triode_al View Post
MP is here a catch-all for capacitors; MP has good dynamics. Just a contrast to the electrolytic.

moi witnessed that Pa is one clever chap , using Elna Simics .... all I can do to better it is to put MKC bypass , but same bypass is needed for any other non-audiophool solid cap

Quote:
Originally Posted by generg View Post
Oh yes ZM, I am now a Repeater.....

I hope it is something like a Terminator....!
Generg ....... GET ..... Golden Eared Terminator


Quote:
Originally Posted by lhquam View Post
I think I understand ......... resistors.
in real life you'll have that problem ........ never .
if amp doesn't have motorboating with regular signal , what is possibility to ever have 0.5Hz on input ?
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Old 27th August 2012, 06:18 PM   #1206
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by generg View Post
Oh yes ZM, I am now a Repeater.....

I hope it is something like a Terminator....!
I hope you didn't throw packung in trash....... along with small plastic tube.....

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Old 27th August 2012, 06:47 PM   #1207
lhquam is offline lhquam  United States
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Quote:
Originally Posted by bobodioulasso View Post
Is'nt your motor boating due to PSU?
Haven't you tried a classical one?
I haven't tried a classical (aka. linear) PSU yet. I want current limiting while debugging.

No, I think the problem is transformer impedance related.

I just performed measurements using a signal generator at .2V p-p output and the schematic shown here. Here are the resulting measurements:

Freq(Hz) Y(V) dB Primary Impedance (Ohms)
1000 .19 -.4 9400
100 .175 -1.2 3760
10 .115 -4.8 1106
1 .03 -16.5 552


Note that the primary impedance calculated includes the DC coil resistance.

Compare the tabulated dB numbers to the Spice Bode plot.


Compare these with
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Last edited by lhquam; 27th August 2012 at 06:52 PM.
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Old 27th August 2012, 06:49 PM   #1208
generg is offline generg  Germany
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Quote:
Originally Posted by Zen Mod View Post
I hope you didn't throw packung in trash....... along with small plastic tube.....


Oh man, I nearly did......

thank you very much much much for the known parts!

and for the unknown I must look what they are...rest in PM
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Old 27th August 2012, 06:56 PM   #1209
lhquam is offline lhquam  United States
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Quote:
Originally Posted by Zen Mod View Post
...

in real life you'll have that problem ........ never .
if amp doesn't have motorboating with regular signal , what is possibility to ever have 0.5Hz on input ?
Is it possible on power-on, if there is a power fluctuation, or if the input is unplugged or replugged?
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Old 27th August 2012, 07:17 PM   #1210
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by lhquam View Post
Is it possible on power-on, if there is a power fluctuation, or if the input is unplugged or replugged?
with those RC constants in bias nets , not possible in powering on

for plugging-unplugging - it's not easy to make fool-proof amp , and it's certainly impossible to make it idiot-proof ;
I was repairing one channel/section of radio mixing console - live , during airing,I was frequently plugging/unplugging XLR's ......... but only when I was in idiot-mode , I made the same with RCA's ........

but I think it's not problem even with that
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