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Old 4th July 2010, 07:00 PM   #21
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Here are the two versions I simulated with, both zipped and make sure they use the Mongrel.txt file with the models I include.

- keantoken
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File Type: zip Mongrel_Ksim.zip (10.5 KB, 164 views)
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Old 4th July 2010, 10:51 PM   #22
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Quote:
by Dr. EM - I certainly don't mind a more complex design if the parts go toward creating better performance
The design is only slightly more complex than my present one. The 2 transistor CCS's can be SMD dual devices (2n5550) or .08 cent ksc/a 1845/992 devices. The only important design criteria parts- wise is the KSC3503/KSA1381 VAS.

I will begin now to Tidy up the schema , use the new LT to generate a BOM , and make my boards.

And thank you , KEAN. When I finish , I might give you the boards in post #8 !
OS
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Old 5th July 2010, 06:20 AM   #23
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Finalized the Schematic and generated a BOM .. very verbose. Board layout is next.

A mongrel ..
Click the image to open in full size.
ThanX again, Keen.. ,your simulations are the teeth that bite..
OS
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File Type: jpg Mongrel_schema.jpg (196.2 KB, 1568 views)
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File Type: zip Mongrel_BOM_Schematic.zip (165.9 KB, 367 views)
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Old 5th July 2010, 08:38 AM   #24
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Quote:
Originally Posted by ostripper View Post
When I finish , I might give you the boards in post #8 !
OS
That would be great!

Look at these two OLG plots. They are of the same Mongrel, but with different plot settings. The one on the left has "unravel branch wrap" clicked. The one on the right is without. So your OLG phase actually comes around a full 360 degrees and lands at 101 in the right place. Interesting. I was simulating with the first graph, which explains why my compensation is always rather extreme... AARGH.

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File Type: png LTOLG_Branch.PNG (15.0 KB, 1440 views)
File Type: png LTOLG.PNG (14.5 KB, 893 views)
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Old 5th July 2010, 09:23 AM   #25
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Wait, that still doesn't make sense. We're looking for -100 degrees, not +100, right?

The thing that's confusing is why the circuit is so stable in transient analysis while the OLG phase margin is way out there.

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Old 5th July 2010, 03:52 PM   #26
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The thing that's confusing is why the circuit is so stable in transient analysis while the OLG phase margin is way out there.
Way out there ? Below (attachment 1)is typical of most amps on the forum (I have simulated them all).

here is a generalized bode plot of loop response ...
Click the image to open in full size.

Another one..
Click the image to open in full size.
90db below the "breakpoint" coincides with unity gain.

Here is a thread you should read.. The Frugalamp by OS ... Post 128 starts the lesson. post 139 and 145 concludes the lesson. Cdom , the LTP degen. resistance and any lead comp. will affect the final Bode plot.

BTW - the bode plot below shows a bit of overcompensation.

OS
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Old 5th July 2010, 04:19 PM   #27
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Silly, silly me. I was entering the wrong trace equation.

Everything's fine now.

Thanks,
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Old 5th July 2010, 08:11 PM   #28
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Have you simulated a +/- 30V version of your amplifier that uses lower noise, higher hfe transistors?

I'm a believer in the Thermal Trak output transistors with packaged thermal sense diodes, especially for class B amps. Have you tried them in your amps?

An amp specifically designed for 30V- 35V could have advantages over an amp designed for 75V but run down at 30V. It might be very popular and easier to obtain parts.

Common low cost, low noise, high hfe transistors
BC550C BC560C 45 volt
BC549 BC559C 30V
BC556B BC546B 65V for cascodes

Lower capacitnce Thermal Trak 180 watts
NJL0281D NJL0302d
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Old 5th July 2010, 10:25 PM   #29
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Quote:
linesource - lower noise, higher hfe transistors
What transistors are they ?? ks-a992/c1845 have 400-800 Hfe (grade E), Cob 2pF - very low noise (uA) , the only Xters I've seen higher are some of the Zetex line. ( Ztx1056- Hfe1200 http://www.diodes.com/zetex/_pdfs/3.0/pdf/ZTX1056A.pdf )

Quote:
I'm a believer in the Thermal Trak output transistors with packaged thermal sense diodes, especially for class B amps. Have you tried them in your amps?
Too expensive , too hard to source. They are a fad , they will be gone soon.

Quote:
An amp specifically designed for 30V- 35V could have advantages over an amp designed for 75V but run down at 30V. It might be very popular and easier to obtain parts.
This amp will run great at +-50 V rails. Most recycled audio equipment have 300-400 VA 40-0-40 trafo's. What is wrong with a little extra headroom (300w peaks) , I am a firm believer in that.
OS
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Old 6th July 2010, 04:34 AM   #30
Bigun is offline Bigun  Canada
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Do I understand right - the outputs don't switch off ? And this thing sounds as good as a pure Class A amp ? - then this is great !

I'd be quite interested to know how well you think the output stage can be operated separately as a power buffer with no nfb ?
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