Aleph 4 PCB Bulk Purchase

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#123
Transformers/Heat sinks/Transisitors

Hey Guys,

Does anyone want to get together on the transformers or heat sinks?

I was thinking of getting some Plitrons (750VA/31-0-31), but with the electrostatic shield. What about magnetic shield as well?

The minimum order for the shielding is ten units. I could be talked into the 625VA model as well.

What about those nasty heat sinks? Anyone want to get together and avoid all paying for setup charges.

And of course, matched transistors. The mirrors and outputs should be matched. Easier when you buy a bunch? Any group purchases of these?

Let me know!

By the way, I am creating a full parts list.

Dale Herman
dherman@ksaria.com
 
#125
Dale,
1. I was going to use the heat sinks that Wayne uses but if you know where to get heatsinks that are bigger and looks even better for the same price, I'll definitely be interested.
2. I'm getting the matched transistors from Brian.
 
#126
I bought a pair of 1kVA toroids with shielding from:

Victoria Magnetics

They are quite heavy and the guy who makes them, John Snowden rates them quite conservatively. I paid $105 each, and weight 15lbs. He can make any size/voltage transformer that you want.

I also had him make me a custom transformer for the BOSOZ, which was $25. This gets rid of the need for two transformers.

As for heatsinks, I already have mine, but I would recommend checking out the place that Wayne Sankey used for his Aleph 2. Check the posts on his amplifier for more details. It is the cheapest place I have seen yet for new heatsinks. I managed to find used surplus heatsinks for myself from a company in Atlanta, GA called Austin Electronics.

Here is a picture of the transformers:

transformers... more then meets the eye

As for the mosfets, the quality of the matching results increase with the amount that you buy. I bought 124, and have matched 93 so far and the best set of 6 (groups of 6 needed for aleph 2) is withing 0.00259 of the Vgs values. I would recommend someone taking this task. All of mine are already claimed by people. I charged $100 for 24 matched.

--
Brian
gte619j@prism.gatech.edu
 
#128
yeah, as far as capacitors go, I was lucky enough to find new mallory computer grade 5,000uF capacitors for $0.75 each from a local electronics store, Austin Electronics near Atlanta. I actually bought 2 boxes of them (42 per box, still sealed from mallory). I am planning on using about 30 per channel. I seem to have room in the case design that I currently have. The wiring should not be that bad if I use big copper strips (maybe too thick to call strips).

I was looking to get some Nichicon Super Through capacitors, which would have around $160 per channel.

If I find another good deal on some caps, I might ditch the large array of caps, but for now, I will see how it works.

--
Brian
gte619j@prism.gatech.edu
 
#129
Not a cheap DIY amp

Hi fcel,

Yes, they are very costly. Maybe there are some surplus ones around. Unfortunately, electros have a shelf life.

I realized that I used IRFP244 instead of IRFP240. I have changed it. I use 63V caps for 45V rails, but you can get away with 50V versions. You will be able to find some 22000 for a little cheaper. This is not a cheap project!

I also forgot some heatsinks for the current source fets.
 
#131
I asked Nelson Pass and he said that it makes no difference in sound quality if you use 4 caps, or 20 smaller caps. I think that ESR is not really a major concern for amplifiers. 100,000uF is already quite a bit of overkill for one channel anyway. I am using the small caps just for the issue of cost.

I figured that the transformers were one of the most important aspects of the amplifier, so I went the extra distance to get them 1kVA and shielded. I spent probably $40 more then I would if I just got the basic pair of Plitron transformers, but I know the ones I got are very high quality.

I purchased a toroid from Victoria Magnetics for my Leach Amp, and it is rock solid. It never gets hot, and there is absolutely no hum. I had a friend that picked up a cheap surplus toroid for his leach amp, and he is having ac hum problems. I am not saying that Plitron does not make good quality transformers, but they charge an arm and leg for anything custom that you want.

--
Brian
gte619j@prism.gatech.edu
 
#132
I'm not sure if this has been discussed before or not ......
For each channel of Aleph 2, is each of the six transistors from the current source getting the same current as the ones on the output ...... so that every transistor (12 of them) will dissipate the same amount of heat? I don't want to be alarmed after I built it - and think that I did not built it correctly - if I found that one side of the heat sink is hotter than the other side! Just checking first.
 
#133
fcel,

Here is my understanding (correct me guys if I'm in error).

The current through the CS FETs and the output FET's, on the average, are the same. So you should not have "hot spots" in your heatsinks. The output signal (between the 2 FET banks) is modulated between the + and - rail voltages (minus the drops across the resistors). The difference between the output signal voltage and ground divided by the speaker impedance is the value of the current flow through the speaker. The only time both FET banks are flowing the same current is at idle.

I think that's right.

Rodd Yamashita
 
#135
Capacitors????

Thanks H.H. for the link....

Here's my question...

When looking at purchasing surplus stock such as this, what criteria should be looked at to determine the best choice?

For example, why the 36D over the 602D besides cost?

Voltage is obvious; I've also already emailed them inquiring about the age of the units and available quantities; but what else? ESR? Is there a rule of thumb regarding ESR for example the larger values leak more or less than the smaller ones? Any other info on selection criteria would be much appreciated!

I ran a search on the web on a couple of the part numbers and was unable to find anything... Does anyone know where to find info on the old Sprague cans?

Thanks,

Steve
 
#136
Sprague and surplus

I mention Sprague 36D series because it is a favorite of high end manufacters such as C-J and Counterpoint. Also the Sprauges are fairly easy to find when surplus shopping. I think caps up to 10 years old work fine. Look at the section on forming older electrolytics in: http://www.capacitors.com/pickcap/pickcap.htm
Hugh has some cap recomendations at:
http://www.printedelectronics.com/pe/faq/aksa_FAQ2.htm#PSup2
I wouldn't waste a lot of time on finding specs. They won't tell you what the caps sound like. Also the Panasonic FC series are great for local bypassing. Put a 100uF to 300 uF close as you can to the circuit you are filtering.

H.H.
 
#138
Aleph boards

This is a plea to BrianGT, I have sent an email, this is in case it gets bounced again.
I would like a set of boards but I live in the U.K., however I
have a friend who lives in Toledo and will receive the boards
for me and then send them on to me in the U.K.,
If you give me the go ahead, I'll get a money order off to you
right away.
I would hate to miss out on this, I have two huge Avel 40 0 40
Transformers( encapsulated weighing 20lbs each)and a smaller Avel for the input stage , and more large heatsinks than you can shake a stick at, just waiting to be used
Thanks, Jules
 
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