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Old 29th October 2005, 09:25 PM   #1
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Default Aleph 30 questions

I think I am going to take the plunge and try to build an Aleph 30 (which will be my first scratch amp build in quite some time) IF I can find a set of Aleph-mini PCBs. If anyone reading this thread has a spare set of the Aleph-mini PCBs, PLEASE send me an email. Also, to get this out of the way early, does anyone have a spare matched set of the IRF9610's and IRFP240's? I am on a tight budget and cannot afford to buy tens or hundreds of transistors to match them.

I am trying to deal with Mouser Electronics only, as I have had great luck with them in the past. I will have to order some parts from other places, but I am trying to avoid Digikey.

1. Are the power supply caps values really important? I think I am going to attempt mono-blocks with six 12,000uF caps instead of the six 10,000uF caps listed in the parts list. Is this ok?

2. What transformer voltage and VA rating should I be looking for? I was thinking about using a 250VA 18V+18V transformer for each mono-block. Is this too much? Not enough? Will the 18V provide enough voltage for the Aleph 30?

3. I am having some difficulty locating .47-ohm 3W metal film resistors at Mouser. Are silicon-coated wirewounds ok?

4. I am guessing it is a good idea to put a fuse on the power input... what current rating should I get if using mono-blocks?

5. Is a heatsink measuring 5 3/8" wide by 12" long by 1 3/8" high with 21 fins and 3/8" base weighing in at about 4.5 pounds ample? I plan on using two of these heatsinks per amp (three output devices on each sink). The thermal resistance is marked as .375 degrees C/W. Is this ok?

6. Is the amp fairly straight-forward to build and troubleshoot (if necessary)? My biggest fear (and the reason I stick to low-power amps) is putting a lot of money into a project that will ultimately fail or cost me tons of time, stress, and grief. Things like this have happened in the past, which has severely lowered by build-rate.

In total I think parts will come in at around $400. Is this a normal price? Too low? Too high? Thanks in advance for any advice, comments, and encouragement (all much needed).
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Old 29th October 2005, 10:17 PM   #2
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OK, I'll have a crack at it. Guys please step in if I give bad advice.

Quote:
1. Are the power supply caps values really important? I think I am going to attempt mono-blocks with six 12,000uF caps instead of the six 10,000uF caps listed in the parts list. Is this ok?
That sounds like overkill IMHO for 1 channel, but some say the more the better. You can't really have too much, you just have to worry about inrush. Make sure they can take the voltage,..say..use a 20% margin rule.


Quote:
2. What transformer voltage and VA rating should I be looking for? I was thinking about using a 250VA 18V+18V transformer for each mono-block. Is this too much? Not enough? Will the 18V provide enough voltage for the Aleph 30?
The VA 'may' be enough but the voltage is low. I would use at least a 300VA at 20 or 21v. Maybe a bit higher and use a CRC filter. You would be surprised the drop you see after giving it a continuous load.

Quote:
3. I am having some difficulty locating .47-ohm 3W metal film resistors at Mouser. Are silicon-coated wirewounds ok?
They will work fine. Some people worry that the inductance will 'darken' the sound. I havn't experienced that but I can't be an authority on that.

Quote:
4. I am guessing it is a good idea to put a fuse on the power input... what current rating should I get if using mono-blocks?
Hmm, that is a good idea! perhaps the lowest value that doesn't blow when the amp runs normally. Your inrush will have a big part in it.

Quote:
5. Is a heatsink measuring 5 3/8" wide by 12" long by 1 3/8" high with 21 fins and 3/8" base weighing in at about 4.5 pounds ample? I plan on using two of these heatsinks per amp (three output devices on each sink). The thermal resistance is marked as .375 degrees C/W. Is this ok?
Better ask someone else on that one. I have simply used a bunch and it worked fine.

Quote:
6. Is the amp fairly straight-forward to build and troubleshoot (if necessary)? My biggest fear (and the reason I stick to low-power amps) is putting a lot of money into a project that will ultimately fail or cost me tons of time, stress, and grief. Things like this have happened in the past, which has severely lowered by build-rate.
The support here is unparalleled. The fact that Nelson helps answers that question.

Mouser doesn't have IR but they have Fairchild. I have heard they are similar enough but I have only used IR. Maybe it would be a good idea to use the spec'd parts on a first build to take that difficulty out of potential troubleshooting. Keep an eye on this board for people selling matched fets...they come up sometimes. I may be able to acquire a bunch of IRFP140 and plan on sellin them cheap..I hope.

BrianGT may have another run of his boards with enough interest. Dig that thread out and express it. They are nice, small, flexible and affordable.

It's a great project.
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Old 30th October 2005, 05:18 AM   #3
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Default Aleph 30 comments

quote:
5. Is a heatsink measuring 5 3/8" wide by 12" long by 1 3/8" high with 21 fins and 3/8" base weighing in at about 4.5 pounds ample? I plan on using two of these heatsinks per amp (three output devices on each sink). The thermal resistance is marked as .375 degrees C/W. Is this ok?

Yeah the manual says the stereo amp dissipates 200 watts at all times, so your monos with only 100watts per channel will do fine on .375 sinks. They will each see 50 watts so your rise above ambient will be in the ball park of .375 * 50 = 18.75 or 45 degrees C that's just how it should be! That is a little extra sinking incase you want to push the bias up a bit, or if you end up with a couple extra volts on your supply.

Service manual says slow blow 4 amp fuse for stereo amp, so start with 2 amps and go from there. Be sure to stick a thermistor on there too, just to be nice.

One last comment regarding the power supply: I would probably use that 250VA transformer. That sounds about right. Especially if you use disreet schottky diodes and a decent CRC the 2 amp draw won't drop your voltage too much. Plus it'll be cheaper than the big boys. The caps are kinda overkill but in the schematic in the service manual the "common to both" channels dotted line is not around the caps. I think this means that Nelson is using six caps per channel, so 6x 12,000 should be great. 30v caps right, not 25v?
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Old 30th October 2005, 11:51 AM   #4
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Eclipse is correct in that the transformer you want to use will work. The voltage will most likely end up at ~22v under load IMHO and from my experience. My point is that it's no longer an A30 but a lower power variant of same, not that that's a problem. (I built an a30 with 2 225VA 21v trannys once, and ended up with +-23v no CRC, after taking the bias up a bit)

I recall nelson saying to multiply your secondary voltages by say x 1.2 (total) instead of x 1.414-.5v. as the constant load does a number on it (unless your tranny is really stout, and 250VA is not). I didn't believe him. That was my mistake as it was exactly true. Cranking the bias up dropped it even more but it still sounded good. The 'R' in a CRC will lose more volts.

If you alreadY have the transformers, yeah use them, but leave room for an upgrade. I was under the impression you were still shopping.

my 2 pennies...

Regards,
Marc
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Old 30th October 2005, 02:39 PM   #5
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I am still shopping... and having a difficult time finding a suitable transformer that doesn't cost a fortune. Parts Express has Avel's, which is where I was looking. The only problem with them is that they have 160VA 18V and 22V transformers and 250VA 18V, 25V, etc. But, they don't have a 250VA 22V transformer. So, I'll be stuck with 25V, which will put me almost in Aleph 5 voltage range. I guess if the heatsinks provide a little headroom, it'll be put to use here.

I am not very familiar with thermistors... what exactly will it do for me in this case?

Also, what about inrush? I noticed in one of the owner's manuals for an Aleph (can't remember which one) it said the amp will peak at 50A at 120V during a half-cycle (or something to that effect) on startup. I have an old house with old wiring... Will I run into problems here?

Thanks for the help so far... it has really, um, helped.
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Old 30th October 2005, 02:49 PM   #6
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I have no experience from this seller ... but have heard the toroids are pretty good. here

They would definitely deliver the goods...
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Old 30th October 2005, 03:30 PM   #7
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Thanks for the link... I forgot about that guy. $43 for a 400VA transformer isn't bad- that is what I was going to pay for the 250VA ones from PE.

I was wondering, though, do you think it would be advisable to get two of the loudspeaker DC protection kits to tack on the outputs in case something went terribly wrong? I'd hate for anything to happen to my speakers because of something I did...
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Old 30th October 2005, 04:27 PM   #8
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Quote:
Originally posted by needtubes
Thanks for the link... I forgot about that guy. $43 for a 400VA transformer isn't bad- that is what I was going to pay for the 250VA ones from PE.

I was wondering, though, do you think it would be advisable to get two of the loudspeaker DC protection kits to tack on the outputs in case something went terribly wrong? I'd hate for anything to happen to my speakers because of something I did...

I can recomend Antek. I have bought several transformers from him and they work well. Send him an email and ask for a deal on a pair.

Blessings, Terry
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Old 30th October 2005, 05:32 PM   #9
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needtubes,
Add your name and your needs to this wiki http://www.diyaudio.com/wiki/index.p...+PCB+Group+Buy
By the time your chassis is done and all the parts have arrived, the boards might be here too.
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Old 30th October 2005, 08:38 PM   #10
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AH! Great to see a re-order is taking place! I will add my name on there ASAP... Thank you for bringing that to my attention!
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