Aleph clone ID

[brownie]

Hi Everyone

I recently picked up a used Pass Aleph clone amp. The boards are laid out like the F series - a long thin circuit board an each side and a central power supply board. On the circuit boards the following info is printed : upper left hand side has Aleph clone and on the lower left 327791 Thank you Nelson Pass.

This little guy appears to have been built on a very tight budget. I'm mainly looking for power supply requirements as it's likely the transformer is marginal at best. I would love it if you can direct me to any further info as well. I went through all the Aleph stuff here and on the Pass site. I could not find anything with picture of the boards that looked right.

Any information would be greatly appreciated.

I was going to get in on the group buy for the F3,4,5 series Peter Daniel has going, but as I tinker with this little rascal the more I like it. I'm starting to question whether to get involved with an F series build. (plus I'm amassing parts towards a TubelabSE 300B project so I want to allocate my toy money as wisely as possible.)

Thanks
Kevin Bown

[hifimaker]

Post a picture of the board, maybe someone can ID it. Also list the type of parts any quantity the amp has, such as output fet's. Use a volt meter to determine the rail voltage. Also is the PSU single or dual voltage.

-David

[brownie]

Hi

While I try to figure out how to post a picture I'll give you the following information.

The Voltage coming onto each circuit board is 35VDC.
The power supply has 8 x 2200uF caps and a single bridge rectifier is used ( 35.9VDC @ the rectifier)
The output fets are TO220 style Fairchild 19V20C 200V N mosfet.@ 2 per board.

I'm borderline ingnorant as far as electronics go so I don't want to poke and prod anything more than that without a schematic or advice on what/where to check.

thanks
Kevin

[Zen Mod]

Originally posted by brownie
Hi

While I try to figure out how to post a picture I'll give you the following information.

The Voltage coming onto each circuit board is 35VDC.
The power supply has 8 x 2200uF caps and a single bridge rectifier is used ( 35.9VDC @ the rectifier)
The output fets are TO220 style Fairchild 19V20C 200V N mosfet.@ 2 per board.

I'm borderline ingnorant as far as electronics go so I don't want to poke and prod anything more than that without a schematic or advice on what/where to check.

thanks
Kevin

send pictures to me , and I'll shrink them and post ;

>choky@neobee.net<

[hifimaker]

Are you sure the output devices are TO-220 and not TO-247?

to-220 devices are not up to the job for a power amp, especially with 36vdc rails.

What size are the heat sinks (H-W-D)?

You can upload a digital picture to a thread up to 102K in size. Take a picture in the lowest resolution for your camera. I use 640x480 resolution for attaching pictures here.

-David

[Zen Mod]

1/2

[Zen Mod]

2/2

judging by round holes in bottom plate .... and few other things - possibly Rawson's work

with just two mosfets ( TO247) per channel and aroound 40Vac across graetz- you're in Aleph 30 area ...

put more caps for starters ;

adding one more pair of outputs per channel can be wise , but you must match new ones , and just hope that old ones from one channel can put on other channel , as matched

[Zen Mod]

btw - tidying those pcbs and overall wiring can be good thing

if nothing else - glue some plastic spacers between heatsink and pcb corners

[hifimaker]

Hi Kevin,

I agree with with Choky that it's an Aleph that could have been better built.

If the board was mine, I'd either install more output mosfet's or bring down the voltage and bias. Consider installing 2 sets matched triplets of IRFP9240's for each channel. It also looks like the protection diodes are missing. This is not a big deal but you do run a risk of blowing the input mosfets if the input source cables are plugged in or pull out when the amp or source is turned on.

An Aleph 30 has about 25 volts at the rails and an Aleph 60 has about 35 volts. Those heat sinks don't look like they can dissipate 200 watts, but maybe 100 for the A30.

Nelson has a good DIY heat sink test. After the amp has warmed up, place your hand on the top of the heat sink. If you can keep your hand there for 5-7 seconds without it getting uncomfortable, the heat sinks are dissipating about 150 degrees F. This should be an absolute max for generated heat.

John here on the board sells matched mosfets and a good guy to work with. http://www.tech-diy.com/Store/Hexfets.htm

John can sell you the matched devices.

I also agree with Choky's suggestions regarding construction.

-David

[hifimaker]

One other suggestion, place a large washer with a small hole between the output mosfets and the head of the mounting screw to ensure even pressure of the device to the heat sink. Spreading out the pressure not only helps with heat distribution, but also helps to keep the mosfet from cracking.

-David