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Amp Camp Amp - ACA
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Old 14th November 2019, 04:06 AM   #8091
Stanislav is offline Stanislav  Australia
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Quote:
Originally Posted by TonyTecson View Post
mulling an ACA on 48 volts B+ what do you think?
wasting a lot of energy for not much gain.
will need much bigger hardware - heatsinks, PSU.
you might double the output, maybe 10W but at what cost?
unless you double the current you still won't be able to drive low Z reliably.
but if you double the current you don't need 48VDC to achieve that goal.
and then of course the heat dissipation will be enormous.

just look at a Zen Lite @48VDC, 2A to get an idea what to expect.
not exactly but close enough.

better build a different FW amp.
did i mention Zen Lite?

all my opinion off course, you are free to experiment.
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Old 14th November 2019, 04:40 AM   #8092
TonyTecson is offline TonyTecson  Philippines
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thanks, it is just a thought....

perhaps this one...

Click the image to open in full size.
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Old 14th November 2019, 05:38 AM   #8093
TungstenAudio is offline TungstenAudio  United States
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It is very worthwhile to read N. Pass’ original articles on the Zen series of amplifiers; in particular Zen I through Zen IV. The ACA is descended from this circuit. The elegance of the ACA is in the way it uses a simple JFET buffer in front of a Zen/Aleph current source and single ended output stage.
I suspect the practical limit for the ACA power supply is about 32 Volts, and this requires some modification of the circuit to avoid burning the JFET and allow the current source to operate correctly. I have approached this higher voltage with one of my builds, using IRFP140 Mosfets, and was happy with the results. Check out the ACA-220 v2 in the ACA With Premium Parts thread.
More recently I’ve been looking at the FQH44N10 for its higher transconductance with higher Vds. This part appears to be an improvement over the IRFP150, which is often used for higher power builds.
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Old 14th November 2019, 07:18 AM   #8094
PMA is offline PMA  Europe
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This was my option, 18 years ago.

Project 83 - MOSFET Power Follower

It has lower distortion and lower output impedance, however without the preamp stage the gain is just close to 1, as it is a power follower only.
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Old 14th November 2019, 09:36 AM   #8095
Stanislav is offline Stanislav  Australia
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Quote:
Originally Posted by TonyTecson View Post
thanks, it is just a thought....
The beauty of ZenLite is it will dissipate 1/2 the heat through the lamp, therefore the heatsink can be smaller, to accommodate the dissipation of the FET alone.

A ZenLite with a buffer ala Zen V4 is very close as an idea and performance to the ACA, it needs higher B+ to generate wattage and is very transparent.
It is the simplest class A amp and very inefficient, that's why you need high B+.
And it sounds wonderful.

I have both, ACA as a main one, and ZenLite as a headamp (but was my main amp for a long time before the ACA).
Both produce about the same output over my 95 dB series x-over 3-ways.
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Old 14th November 2019, 09:47 AM   #8096
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by PMA View Post
This was my option, 18 years ago.

Project 83 - MOSFET Power Follower

It has lower distortion and lower output impedance, however without the preamp stage the gain is just close to 1, as it is a power follower only.
Gain of 1 is probably enough for most people most of the time using a modern high output source.
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Old 14th November 2019, 09:55 AM   #8097
TonyTecson is offline TonyTecson  Philippines
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Quote:
Originally Posted by TungstenAudio View Post
It is very worthwhile to read N. Pass’ original articles on the Zen series of amplifiers; in particular Zen I through Zen IV. The ACA is descended from this circuit. The elegance of the ACA is in the way it uses a simple JFET buffer in front of a Zen/Aleph current source and single ended output stage.
I suspect the practical limit for the ACA power supply is about 32 Volts, and this requires some modification of the circuit to avoid burning the JFET and allow the current source to operate correctly. I have approached this higher voltage with one of my builds, using IRFP140 Mosfets, and was happy with the results. Check out the ACA-220 v2 in the ACA With Premium Parts thread.
More recently I’ve been looking at the FQH44N10 for its higher transconductance with higher Vds. This part appears to be an improvement over the IRFP150, which is often used for higher power builds.
yes, anyone familiar with circuits would know what Nelson was up to...
p-type mosfet instead of n-type in the ACA....

i think that for the higher voltage ACA, the thing to look at will be the SOA of the mosfet device under consideration...as far as transconductance goes, mosfets are found to be not lacking...
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Old 14th November 2019, 09:57 AM   #8098
TonyTecson is offline TonyTecson  Philippines
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Quote:
Originally Posted by PMA View Post
This was my option, 18 years ago.

Project 83 - MOSFET Power Follower

It has lower distortion and lower output impedance, however without the preamp stage the gain is just close to 1, as it is a power follower only.
yes, i saw this and i was wondering how the bipolars did, i guess again SOA is to be looked at closely, i have some hockey puck trannies on hand sto use here....on by bucket list of things to do...
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Old 14th November 2019, 09:59 AM   #8099
TonyTecson is offline TonyTecson  Philippines
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Quote:
Originally Posted by Stanislav View Post
The beauty of ZenLite is it will dissipate 1/2 the heat through the lamp, therefore the heatsink can be smaller, to accommodate the dissipation of the FET alone.

A ZenLite with a buffer ala Zen V4 is very close as an idea and performance to the ACA, it needs higher B+ to generate wattage and is very transparent.
It is the simplest class A amp and very inefficient, that's why you need high B+.
And it sounds wonderful.

I have both, ACA as a main one, and ZenLite as a headamp (but was my main amp for a long time before the ACA).
Both produce about the same output over my 95 dB series x-over 3-ways.

i would like to try things differently, i clone amps but seldom do a lock stack and barrel clones...
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Old 14th November 2019, 10:03 AM   #8100
Stanislav is offline Stanislav  Australia
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Originally Posted by TonyTecson View Post
i would like to try things differently, i clone amps but seldom do a lock stack and barrel clones...
same here...
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