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Old 7th August 2012, 04:52 PM   #101
FdW is offline FdW  Netherlands
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Originally Posted by Joachim Gerhard View Post
Yes Frans, that is true for an EF follower ( Self give somewhat over 100mA, depending on the emitter resistors, that has to do with that famous 24,5mV ) but this is a CFP ( Szikley ) with 100% feedback so optimum bias is much lower if you do not bias high into Class A.
Yes that is true (it's different for the CFP as compared for the EF), but still I think 50mA (or even lower) is a bit too low for my expectation. This (it being an expectation) is good ground for experimenting. Currently (in my amp project) I am using BIGBT's (Laze Cat style) output compound devices and I am biasing them as EF's (that is 100mA for each output device).
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Old 7th August 2012, 04:56 PM   #102
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I ran the amps on 120mA so far and it sounded fine. This is of academic interest anyway.
I am really looking forward how your amp sounds when it is ready.
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Old 7th August 2012, 09:20 PM   #103
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Originally Posted by Joachim Gerhard View Post
I am really looking forward how your amp ...
Yes, me too Last saterday the board was compleated, sunday during the day it was mounted, and sunday evening I destroyed it

After first power up I could not set idle current, so I took the meter and the nearest probing pin (it was a (to) large one), and started metering some points. The next thing is, I shorted 70 Volts against the Vas-cascode, this destroyed the cascode and put lots of volts on the opamps... you can guess it from there.

Next weekend there will be time, and the fight goes on ... will be continued ...
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Old 7th August 2012, 09:32 PM   #104
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I am sorry to hear that. It is a massive and complex project. You will make it work at the end, i am sure about that.
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Old 8th August 2012, 06:23 PM   #105
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Puh, one channel of the SBP bridge is ready. That was more work then i thought. I use bigger heat sinks now and put the amp modules vertically for chimney effect. After a lot of head scratching i decided on 125mA idle. I the spirit of DIY i decided on the simplest option : Non inverting amps and Elliot bridging. The bridge puts out plus-minus 17V P-P into 6.6 Ohm. That is around 30W RMS depending on load. I think that is useful. The other two amps are prepared too so maybe i get it complete until the weekend.
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File Type: jpg SBP bridge.jpg (499.7 KB, 427 views)
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Old 10th August 2012, 11:07 PM   #106
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I am still working on the other channel of the bridge. It should be ready saturday night.
I supply the modules with a PSU but it can be driven by a plus-minus 12V battery.
The PSU is a mix of a MosFet cap multiplier and a Zener stabilization.
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File Type: jpg SBP 2nd.jpg (860.2 KB, 392 views)
File Type: jpg SBA 2nd 2.jpg (829.4 KB, 377 views)
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Old 11th August 2012, 11:57 PM   #107
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Very cool. Got my par of 75Ah gel batteries waiting fully charged for your results.
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Old 12th August 2012, 12:08 AM   #108
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The two other channels are ready ! Besides an exploding 4700uF 35V Low ESR Elcap i inserted the wrong way as it is traditional at Maison Gerhard it went smooth.
This explosion was kind of interesting. Modern Elcaps have slots in the top. This cracked open and and some gas came out with a load "ZZZZZZSSSSHHH". It did not smell so this was kind of a surprise. At closer look there is some yellow fiber that came out. That may have sucked up the electrolyte. Good safety measure. 30 years ago this whould have being a real disaster with teribly smelling electrolyte all over the place, and they are very small now. A 4700uF 35V was as big as a glass back then.
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Old 12th August 2012, 04:40 PM   #109
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The second bridge is working. I measured it and also put it in my system and played some music. I can not say much about the sound because i am still tuning in my system but it is very obvious that more power is on tab.
I tell you more soon.
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Old 12th August 2012, 05:32 PM   #110
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Here are pictures.
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File Type: jpg SBP ready 1.jpg (446.3 KB, 319 views)
File Type: jpg SBP ready 2.jpg (537.9 KB, 298 views)
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