Best strategy to convert Aleph 3 to monoblock

Sony · 11:53 PM

The idea is to convert a pair of stereo Aleph 3 into two monoblocks.

I was wondering if I could just isolate one channel's output stage's transistors and wire them in parallel into the other channel, thus getting an output stage of 4+4 transistors instead of 2+2. I think this may be a light mod that just involves rewiring and minor resistor changes. See diagram below.

Do you think this would work or there might be a better solution?
One one hand I would be 'throwing away' most of the components of one channel per amplifier, but perhaps this could provide a cleaner result than possible alternative solutions? (I mean same sonic purity and more power than a single Aleph 3)

What values would you recommend for R1 and R2?

Thanks and regards.

jacco vermeulen · 23rd April 2012, 12:17 AM

For more output power you'd need to swap the transformer and lytic caps for higher voltage ones.

For more output current, just run both channels in parallel.

Nelson Pass · 23rd April 2012, 01:53 AM

Quote:

Originally Posted by jacco vermeulen

For more output current, just run both channels in parallel.

Zen Mod · 23rd April 2012, 05:53 AM

with mono input to paralleled channels , off course

KatieandDad · 23rd April 2012, 07:59 AM

All the IRFPs in the upper half of the circuit need to be matched for Vgs with each other as do the lower ones.

Two halves of two amplifiers (stereo) will not necessarily be matched.

The bias remains the same for each MOS-FET as you increase the number of devices unless you wish to reduce it.

KatieandDad · 23rd April 2012, 09:06 AM

Just paralleling the MOS-FETs wont increase the power with the same rail voltage.

You can bridge the amps of course.

What you can do, after re-matching up the relevant MOS-FETs is convert the Aleph 2 to an Aleph 4. This will need a new mains transformer and higher voltage caps as well as a few minor changes to component values.

Sony · 23rd April 2012, 06:51 PM

Thanks for the answers!

My intention was to keep the chassis and major parts unchanged.
So, if adding more MOSFETs in parallel (with unchanged voltage) won't provide more power I discard my suggestion.

I was a bit reluctant in connecting each amp in parallel (with no further changes), however given the reputed opinions and consensus I will give it a try! If they explode or something I will post back.

Meanwhile I have checked the DC offset and it stays between 10 and 30mV on the four channels, which I suppose to be low/safe values...

Do you think the paralleled version will work well on a 8 ohm load? (which would be equivalent to have a single Aleph running 16 ohm) or a 4 ohm load would be preferable?

23rd April 2012, 12:17 AM	#2
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, Rotterdam or Curaçao	For more output power you'd need to swap the transformer and lytic caps for higher voltage ones. For more output current, just run both channels in parallel. __________________ Not so much,.......if it says "ZM" in the corner.

23rd April 2012, 05:53 AM	#4
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	with mono input to paralleled channels , off course __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; Mighty ZM's Bloggg;I'm dumb

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23rd April 2012, 07:59 AM	#5
KatieandDad diyAudio Member Join Date: Nov 2011 Location: UK	All the IRFPs in the upper half of the circuit need to be matched for Vgs with each other as do the lower ones. Two halves of two amplifiers (stereo) will not necessarily be matched. The bias remains the same for each MOS-FET as you increase the number of devices unless you wish to reduce it.

23rd April 2012, 09:06 AM	#6
KatieandDad diyAudio Member Join Date: Nov 2011 Location: UK	Just paralleling the MOS-FETs wont increase the power with the same rail voltage. You can bridge the amps of course. What you can do, after re-matching up the relevant MOS-FETs is convert the Aleph 2 to an Aleph 4. This will need a new mains transformer and higher voltage caps as well as a few minor changes to component values.

23rd April 2012, 06:51 PM	#7
Sony diyAudio Member Join Date: Sep 2004 Location: Europe	Thanks for the answers! My intention was to keep the chassis and major parts unchanged. So, if adding more MOSFETs in parallel (with unchanged voltage) won't provide more power I discard my suggestion. I was a bit reluctant in connecting each amp in parallel (with no further changes), however given the reputed opinions and consensus I will give it a try! If they explode or something I will post back. Meanwhile I have checked the DC offset and it stays between 10 and 30mV on the four channels, which I suppose to be low/safe values... Do you think the paralleled version will work well on a 8 ohm load? (which would be equivalent to have a single Aleph running 16 ohm) or a 4 ohm load would be preferable?