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Old 3rd September 2007, 07:35 PM   #1
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Default Leach Superamp questions

I purchased some Leach boards from another member on the forum. After reading the construction notes, I see that Prof. Leach recommends 93V rails. I'm curious if anyone knows off hand if this can be increased a weee bit (130V rails with MJ21193/94 transistors).

Any reason why this can't be done?
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Old 4th September 2007, 01:42 PM   #2
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Was my question that ridiculous that it doesn't merit an answer?

I have a transformer sitting here, looking very sad with no home. I have the amplifier boards doing the same. I was hoping I could make them a happy couple.
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Old 4th September 2007, 02:49 PM   #3
ptah is offline ptah  United States
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No you will not receive a reply. This forum has been hijacked by an elite audio special forces unit. See the reply to my post.

If you have a transformer with higher than required secondaries you should be able to use voltage regulators to trim them back to the recommended rail voltage. Increasing the rail voltage will effect components in all three amplifier stages.
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Old 4th September 2007, 04:05 PM   #4
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Quote:
Originally posted by bushroot
a weee bit
The nominal 130 VDC rails can go up to >150 VDC, should also be mentioned somewhere on the Professori amp page.
During fast transients that makes >300 volts between rails and output, = 150 plus across each barrel.

The OnSemi MJ devices can likely handle something like 1 amp at a Vce of 150 volts.
Eeeh, at 25C temperature, but at operating temperature you better put your money on 1/2 an amp.
Into an 4 Ohms load impedance, the output stage will skyrocket at an output voltage above 4 Volts.
Easier to bridge the thing => 4WD barrel.

PS : 150/160 volts electrolytic caps will cost twice as much as 100 volt specimens.

(but what do i know, i've been abducted by an elite alien special forces unit)
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Old 4th September 2007, 05:47 PM   #5
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I was just curious considering I already have the transformer. Caps aren't a problem either. I have a box of 20 7700uf 200VDC caps under my desk The transistors appear to be rated for 250V. I could always parallel them to get the desired current couldn't I?
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Old 5th September 2007, 01:11 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
what impedance are you intending to drive from these +-130Vdc supply rails?
Once you have that then start "designing" the output stage. Then "design" the driver stage.
Then think about what devices you can use in the voltage amplifier stage.

When you've done all that, reconsider whether starting a design from an available transformer is sensible or not.
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Old 5th September 2007, 02:51 PM   #7
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Thank you AndrewT. It was a simple question of whether it would work well or not.

I do not design amplifiers. I design control systems for automated equipment. I'm very, very inexperienced with all of this. This is why I ask such questions.

I was trying to reduce a bit of my "junk pile". If I have to purchase another tranny, so be it. I simply wanted to use what I have lying around if at all possible. My pack rat nature causes me to accumulate large quantities of parts. The volume of said parts is getting to be a bit of a nuisance lately. Since you're on the other side of the pond, I'm not sure if you'll appreciate the reference, but my work area in the basement is looking a bit too much like "Sanford and Son".
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Old 5th September 2007, 03:27 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
I'll give you a starter for 10.
2sets of cascoded quads can deliver about 400W into 16ohms but cannot drive moderate 8ohm speaker loads.
4sets of quads can deliver about 760W into 8ohms, but cannot drive moderate 4ohm speaker loads.
6sets of quads can deliver about 1400W into 4ohms, but cannot drive moderate 2ohm speaker loads. But will drive a 2r0 test load if you can keep the transistor cases cool enough during the testing.

Yes, a 16transistor output stage is required to survive 8ohm speaker duty on +-130Vdc supply rails. The transformer will need to be at least 1kVA to produce decent performance as a monoblock.
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Old 5th September 2007, 05:29 PM   #9
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And that is entirely more power than I need. It's tempting, but I'm probably going to let the idea die for just that reason. I'm going to be tri-amping. I'll need about 300W/channel for my woofers. I believe in plenty of headroom, but there comes a point when it becomes insanity.

I suppose purchasing the 40lb E-core that Apexjr sells was a bit insane for a 4 channel BPA200 too though

My first amplifier was an ESP P101. It weighs about 65lbs. If you'd like to see what it looked like before it was done...


http://home.comcast.net/~bushroot/Projects.htm

I put it in a flimsy par-metal chassis. It hummed like hell and I couldn't find where it was coming from. After it was completely dismantled, I decided on the "industrial look".

So, I'm no stranger to "overkill". This however, may be even too excessive for me.

Thanks to everyone for their replies!
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