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Old 24th January 2013, 04:29 AM   #131
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Quote:
Originally Posted by danielwritesbac View Post
The idea of lower HFE drivers looks good but doesn't help in practice. Outputs with higher HFE and still linear, would help. But those you've selected look pretty good. The actual problem is 150W to 4R with a single set of output devices. Simple answer: The LTP soft clipper accessory can be set for rapid recovery, to prevent the amplifier from getting stuck in a non-linear condition.

Here is a new adjustable version (attached). The 500R potentiometer allows you to synchronize the soft clipper to fit your amplifier for instant recovery. The 500R variable resistor allows you to choose the force of the clip for softer or harder as needed. The dials do "when" and "how much." If you need it more aggressive, you can put a 470 ohm resistor in parallel with one of the diodes. All of the diodes are BAT86 or whatever sort you have used for D7. Low capacitance types are preferred. This accessory is easy to install and use.
I get the feeling that reducing my expectations would be a better idea than trying to keep it stable at the very limit of what it can do. If I reduce the expected output power to say 125W into 4R, would it work gracefully in it's original design state? Or maybe 100W into 4R?
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Old 24th January 2013, 08:42 AM   #132
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Originally Posted by ImmortalZ View Post
I get the feeling that reducing my expectations would be a better idea than trying to keep it stable at the very limit of what it can do. If I reduce the expected output power to say 125W into 4R, would it work gracefully in it's original design state? Or maybe 100W into 4R?
I think you can use a 25+25vac transformer. This looks like it might do 130W but given the 4 ohm loads, I believe transformer pulldown will make the amplifier go down to about 115W. And, considering the big bass slam of Class Aa, it will probably meet or exceed your expectations despite a few less watts.
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Old 18th February 2013, 07:36 AM   #133
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So the donor has a 2x34VAC transformer, giving 45V rails. It seems to be a lean Class AB design, so the rail voltages are too high for 2SD424/BD183 ? Or I am OK? Please comment on any changes needed to accomodate this rail voltage.

Donor Photo for reference. It is a 1U chassis,
Click the image to open in full size.

Thanks!
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Old 18th February 2013, 08:18 AM   #134
Elvee is offline Elvee  Belgium
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Originally Posted by costis_n View Post
So the donor has a 2x34VAC transformer, giving 45V rails. It seems to be a lean Class AB design, so the rail voltages are too high for 2SD424/BD183 ? Or I am OK?
Too high for the BD183, but the 2SD424 is rated at 180V and is suitable.
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Old 18th February 2013, 08:28 AM   #135
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Sorry, I meant BD317 _facepalm_

Driver ecommendations at this rail voltage?

Last edited by costis_n; 18th February 2013 at 08:34 AM.
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Old 18th February 2013, 04:19 PM   #136
Elvee is offline Elvee  Belgium
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Originally Posted by costis_n View Post
Sorry, I meant BD317 _facepalm_
BD317 is fine too. Mind the SOA however.

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Driver ecommendations at this rail voltage?
There are many recommendations in this thread and the main one, try to pick one that is easily available for you.
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Old 19th February 2013, 02:38 AM   #137
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Originally Posted by costis_n View Post
Driver ecommendations at this rail voltage?
See Post#1
Many of the options there have high voltage tolerance. Do you have availability of any KSA1220, 2SA1930, 2SA1837, 2SA1358, 2SA968, 2SB649?
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Old 19th February 2013, 02:33 PM   #138
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Yes, I just got Toshiba 2SA1837 from the shop. The rest of the circuit stays the same, right?
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Old 19th February 2013, 07:06 PM   #139
Elvee is offline Elvee  Belgium
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Originally Posted by costis_n View Post
Yes, I just got Toshiba 2SA1837 from the shop. The rest of the circuit stays the same, right?
Yes, R21 and the zeners have to match the voltage: 56 or 68K and 24V zeners
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Old 20th February 2013, 07:04 AM   #140
abetir is offline abetir  Philippines
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Sir Elvee,
Can a TO-3 darlington transistor also be used on the Circlophone?
A friend of mine had MJ2500 (TO-3), I was thinking of using them on this amp.

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