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Old 13th December 2012, 06:39 PM   #1521
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Thanks for your reply Andrew. About the ripple, I don't worry too much as I don't seem to be able to get a flat line with my scope. Maybe I don't use properly or there's some interference screwing its trace. Even when input in GND'ed the "flat" line is rippled.

When I change the MJE15032 VAS, do I need to change the MJE15033 CCS as well??

Do you have any suggestion that I could use instead?

EDIT: Found a list: http://users.tpg.com.au/gerskine/gre...ransistors.htm

Regards,
Martin.

Last edited by canonnica; 13th December 2012 at 06:42 PM.
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Old 13th December 2012, 06:59 PM   #1522
AndrewT is online now AndrewT  Scotland
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The ripple is almost certainly rail ripple due to the very high current passing through the amplifier when it clips into the test load.
Quote:
that might be rail ripple coming straight through the wide open output stage.
I suspect that if you increased the load resistance you would find that the clipping ripple will decrease and when you clip into a 10k load the ripple will be gone.
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Old 13th December 2012, 07:07 PM   #1523
Vostro is offline Vostro  South Africa
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I have the same problem, finding nice VAS transistors,

Some I've used
http://www.datasheetcatalog.org/data..._e/2SC3788.pdf
and
http://www.cordellaudio.com/book/datasheets/KSC3503.pdf

I have used MJE 340/350 but they not the best for this function.
Always check for pins compatibility.

Change CCS also.

Regards
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Old 13th December 2012, 09:12 PM   #1524
a.wayne is offline a.wayne  United States
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what about 2sc4793,2sa1837 ...?
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Old 14th December 2012, 12:29 AM   #1525
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Well, I returned to simulation and guess what?!? The problem is there also, it's less obvious than in real life but it's there.

In fact two problems are shown... the sticky negetive rail and a kind of glitch on the positive side when starting to go down.

I've implemented the clamping diode as suggested by Vostro in simulation and it definitely solves the sticky rail. Gotta wait until I get the real ones now.

Anyone has a clue concerning the dent on the downward cycle?

Images:
Attached Images
File Type: jpg ChanB-10KHZ_beyond_clip_6R-load.JPG (77.9 KB, 237 views)
File Type: jpg Simulation-noclamp-10KHZ_beyond_clip_6R.jpg (42.1 KB, 231 views)
File Type: jpg Simulation-clamped-10KHZ_beyond_clip_6R.jpg (40.2 KB, 220 views)
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Old 14th December 2012, 10:08 AM   #1526
Vostro is offline Vostro  South Africa
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After you get hold of the diode, and install it.
I think that would stop the amplifier from "crazy oscillation".

The slight ringing will still be there, but should not take over and cause oscillation.

My suggestion is to be satisfied with that outcome, but only if it can go into and out of severe clipping without loosing stability while loaded and unloaded at all reasonable frequencies.

If you not satisfied, then try to add C9 as in my drawing,
I think the ringing comes from the LTP when coming out of saturation.
This capacitor should not affect high frequency distortion negatively, but you might have to tweek the value, I would use 1nF as starting point.

I don't think this will be a popular mod, and I don't know if it will work, I've never tried it.

Regards
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Old 14th December 2012, 10:50 AM   #1527
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Quote:
Originally Posted by Vostro View Post
My suggestion is to be satisfied with that outcome, but only if it can go into and out of severe clipping without loosing stability while loaded and unloaded at all reasonable frequencies.
... you demonstrates wisdom, it's a good suggestion Will try the cap in simulation as well...

Thanks!
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Old 14th December 2012, 10:19 PM   #1528
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Default Put it to play loud with these songs provided in the attached video

There are free software available to extract the MP3 from Youtube's video...but i can provide you if you write to me, i have the master here.

Well..there's no more master in digital media..all the same..all master.

These songs have no copyrigth....sound is interesting..not awesome but has different instruments, some high frequencies, some drums, hit hats and all we need to "feel" an amplifier.

Girls in the video are my daugthers.

Maybe you gonna like it:

Dx Corporation pictures - YouTube

regards,

Carlos
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Old 19th December 2012, 01:52 AM   #1529
bonfis is offline bonfis  United States
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Quote:
Originally Posted by canonnica View Post
Well, I returned to simulation and guess what?!? The problem is there also, it's less obvious than in real life but it's there.

In fact two problems are shown... the sticky negetive rail and a kind of glitch on the positive side when starting to go down.

I've implemented the clamping diode as suggested by Vostro in simulation and it definitely solves the sticky rail. Gotta wait until I get the real ones now.

Anyone has a clue concerning the dent on the downward cycle?

Images:
Hi Mart
I took a look back at my post 1294 that shows my amp at clipping. I have a much less severe degree of rail sticking and a smaller glitch on the negative going slope just after the positive clip. Our amps differ in the value of the stopper resistors 56 vs 100 ohms and mine has been modified for lower gain. I don't know if this suggests any clues about dealing with your situation but thought it was worth noting.
Steve
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Old 19th December 2012, 12:03 PM   #1530
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Thanks Steve,

I didn't get my clamping diode yet so I don't have anything new. Got to mention that I also decreased Cdom to 100pF, but in simulation the value of that cap doesn't seems to modify the resulting trace at all.

As soon as it clips, the headroom I have from clipping to rail sticking to oscillations is very very thin. The amp doesn't cope well with clipping situation, I can't consider it "healthy". Expectedly the clamping diode will permit going into and out of clipping without any problem.
As far as the musical experience is concerned, I don't drive that amp into clipping. Real-world listening is not impaired by its unhealthy clipping behavior. Up to clipping, the scope trace is nice and smooth... and the amp sounds good

Will post more when Cdom is clamped.

Mart.
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