Aleph 2

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I have previously built BoSoZ preamp and paralleled Return of Zen biamped monoblocks with outboard power supplies. (These projects are posted on Pass Lab’s DIY Gallery .) Browsing this forum (and the purchase of 24, 1 degC/W sinks from MECI for $3.95 each) has given me the bug again to build a set of Aleph 2 monoblocks. I am not a EE and hope to borrow some insight from this forum. I have some ideas, and I solicit feedback on them:
· Each monoblock’s chassis is composed of 12, 5"x7.25" heatsinks (with 21, 1" fins) connected by 1/8" thick aluminum strips and angle. These sinks will form the 4 sides, with 2 sides being 2 sinks wide by 2 sinks high and the other 2 sides being 1 sink wide by 2 sinks high. The exterior size of each chassis is 16.8"x9.8" (including fins) by 10" tall, before base. The interior size of each chassis is14.4"x7.25"x10". (This is the only stage completed at this time.)
· The top and bottom of each monoblock’s chassis is composed of 7 pieces of 7"x2" by 1/8" thick aluminum strips attached to a shelf for by 1/8" thick aluminum angle attached to the heatsinks. The bottom of the chassis will sit on a walnut base of 2-3" high by 1" thick attached to and below the perimeter heatsinks.
· Power supplies for both channels are outboard in single aluminum box attached to the amps via an umbilicals composed of four 12-gauge solid copper conductors with a Neutrik 3-connection Powercon connector (+45V, +45V, & signal ground) and a conductor for the chassis ground. The aluminum box is constructed of 1/8" thick aluminum sheet and 1/8" thick aluminum angle.
· The current source IRFP240’s will be attached to the bottom rung of heatsinks, while the output IRFP240’s will be attached to the top rung of heatsinks. The IRFP240’s will be centrally located on the heatsinks, one per sink. Small sections of aluminum angles (3/4"x1/2"x1/16") are cut and three screw holes are drilled to sandwich the MOSFETs to the heatsinks. This should allow for more pressure on the MOSFET resulting in more efficient heat transfer.
· Signal boards are 1/16" teflon with all connections point-to-point wiring, NO PCBs, using component leads when ever possible.
· All signal path wiring are solid core fine silver wire, dead-soft annealed from Hoover & Strong, hand stuffed into teflon tubes, with 18ga for higher current paths and 24ga for smaller current signal paths.
· The signal board will be centrally located in the chassis at a vertical level about at the bottom of the top rung of heatsinks. The resistors associated with each IRFP240 will be on the perimeter of the board. Wiring for the current source IRFP240’s will go from the bottom of the board to MOSFETs, and wiring for the output IRFP240’s will go from the top of the board to MOSFETs.
· The NPN transistors Q4-5 are ZTX-450 (like most of the newer Aleph designs) instead of MPSA18.
· The 220uF capacitors are low-impedance Nichicon PWs. These are by-passed with 1uF, 100V, metalized polyester capacitors.
· The 0.001 uF C6-7 capacitors are 600V, Polypro Vishay 715P Orange Drops.
· The 10pF C8 capacitors are 500V, Silver Micas.
· All the resistors except the power resistors are Vishay/Dale RN60Ds 1% metal film resistors.
· The power resistors are Panasonic 3BK, 3W, 5% metal film resistors.
· The input jacks, binding posts, and DC power inputs will be on the amps top to minimize the length of the wiring to the signal board.
· Solder is 4% silver from Welborne Labs.
· RCA input jacks are Cardas GRFA silver/rhodium-plated with teflon dielectric.
· XLR jacks are Neutrik gold plated.
· Chassis IEC connector to the power supply is a single Hubbell 20amp IEC chassis connector.
· Power supply transformers are Plitron 1000VA, 33+33V transformers (one per channel).
· Signal ground is separate from chassis ground by using a thermistor, as shown in schematic.
· Capacitors C1-4 are 24,000uF, 50V computer grade capacitors bought from MECI.
· Capacitors C1-4 are by-passed with GE 41L2151 5%, 250V, 1.5 uF metalized polypropylene capacitor.
· 2mH air-core inductors are placed on the power rails between C1-C2 and C3-4 to form a Pi filter.
· Resistor R1 and LED are eliminated.

I have some specific questions:
· What type of power resistors should be used? Nelson emailed me that he uses 3W Panasonic MF resistors from DigiKey, which I assumed are Panasonic 3BK metal film resistors. I assume that metal film would be preferable to wirewound (lower inductance?), but wirewound Vishay/Dale RS are 1% tolerance while the Panasonic 3BKs are 5%. Would 1% tolerance wirewounds be preferable to 5% metal film resistors? Are there better resistor choices?
· Are there better capacitors selections?
· What are the best capacitors to by-pass the 220uF electrolytics?
· What are the best capacitors to by-pass the power supply electrolytics?
· Is it best to the negative side of the 220uF C9 be connected to the emitter of Q5 (like most of the other Alephs) instead of to the Out+?
· What are the critical components that make sense to spend the money to upgrade?
· Any advice regarding binding posts, assuming solid silver speaker cables (homebrew). Cardas?, WBT?, other?

Power supplies for both channels in a single box sounds ambiguous to me, and perhaps also to Nelson. Are there four caps for each channel, or for the two combined? This might be why Nelson is saying twice the capacitance.
If you want 1% (or even tighter tolerance) load resistors, consider Caddock.
Yes, the Digikey blue 3BK Panasonic resistors are the ones Nelson uses.
Whether the 220 uF across the NPN goes to the emitter or the ouput line makes little difference, as there is only the value of the nominal resistor array at the output between those two points.

I thought you didn't mentioned what type of solder you are going to use but after careful reading your post I noticed that you covered that angle too.;)

When choosing binding posts I wouldn't recommend spending too much money. I'm using Music Posts from Michael Percy because they probably cheapest quality posts around.

As to resistors the tolerance is not really important as longas you measure your resistors and use the same values for your output devices. Panasonic 3W are probably the best deal around and I'm using them too. I bought a 100 from Digi-Key and found at least 20 matched to 0.1%. The other alternative I'm considering are Mills wire wounds from Micheal Percy.

As to electrolytics bypass you can try smaler electrolytics (in PS) like 120u and maybe 1u film and 0.1u film. But experimenting is recommended. Check the post:

If you really into p2p wiring check my latest project at:
To clarify the outboard power supply issue.

My intention was that in that single box (for both channels) there would be:
2-1000VA transformers
8-24,000uF Caps, each with 1.5uF Polypro by-passes
4-2mH air-core inductors

When Nelson suggested twice the capacitance, was it because of the added Pi-filter? (2-caps, inductor, 2-caps per rail per channel)
From a sound quality point of view it would be advisable. I also came with that idea and in some Alephs the value of parallel resistors is really close to 0.1ohm.

Which brings the question I am interested in too. Is there any relation between the value of paralleled output resistors and the value of the source resistors? Can 0.1ohm approximation be used in any Aleph?
Caddock has a .075 ohm, which would be closer to 6x.47 in parallel (about 4%, anyway).
Yes, the value matters. The formula is in the patent, but in general you want the value of the output resistor array to be half the cumulative value of the Source resistors for the current source MOSFETs.

Caddock current resistor

I don't thinK you need a Caddock for this. Spend money on the feedback resistors instead!

RWF-LVR3-.08 .08 ohm 1% 3w WW Resistor 3.00

"Caddock has a .075 ohm, which would be closer to 6x.47 in parallel (about 4%, anyway).
Yes, the value matters. The formula is in the patent, but in general you want the value of the output resistor array to be half the cumulative value of the Source resistors for the current source MOSFETs"

It seems that it wouldn't hurt to use a bigger current sense resistor and change the value of the AC feedback resistor to compensate for it. Resistor values under 0.1 ohms are hard to find. Don't forget to take your feedback from as close to the resistor body as possible or your wire resistance will change the value of the resistance that the feedback in the current source is measuring across. This is a real concern for resistor values this low and some resistors come with seperate sense leads for this purpose.

Resistors for poets

"That resistor is in the signal path, would 3W be enough?
I don't thing it's less important than source resistors for which you are using $40 Vishays."

Ah......resistor envy, it's a terible thing. Actually where it is in the signal path probably makes it little less important. 3 watts should be more than enough. (0.1 X 30 AMPS!) Many low value precision wire wounds are actually very good and I would not hesitate to use the Mills non magnetic wire wound other good wire wound for this resistor. I have plenty 0.5 ohm and 0.25 Vishays, maybe I will trade you for some other parts.

" How is TEX X coming? I first want to finish my Aleph 5 mono."

Finish the Aleph 5s first, maybe we should wait for Grey. It is a lot of work and I am gathering parts as I build, I know it will not look as nice as yours though and will listen to it in the dark. Some joker out here will probably blind side all three of us!

If you're interested in Caddock parts, but can't find the values you want at retail, Caddock will sell directly to the public.
They've got more values than you can shake a stick at, but they aren't exactly cheap. However, they are one of the best resistors out there. I seem to recall that Erno Borbely prefers them to Vishay; says they're more neutral.

When mounting MOSFETs on an anodized heatsink, is there any reason to use a mica insulator?

I would assume that it would be better to mount the MOSFET with thermal grease only, since the surface of the heatsink is NOT electrically conductive (have double checked with VOM). That being said, in the past I have had a MOSFET go bad when I was probing (and probably touched an anodized heatsink of a MOSFET without a mica insulator).
mounting MOSFETs on an anodized heatsink

I would not do this! The anodized layer is pretty thin and a high point in the aluminum or transistor case, a scatch, a void in the anodizing ,or a small chip of metal from drilling or deburing any holes could punch through the anodized layer when the transistor is screwed down snuggly. I really think this begging for trouble and it won't take long to find it.

Brittany Spears might not like this idea

She says you wait till your married, but if you just can't wait to use protection, a girl has got to be careful..... Use the Mica washers. Live heat sinks are asking for a different problem, like the first time someone accidently touches a speaker wire to a sink with power supply voltage on it. Jam is just trying to see if I am paying attention..... Shame on you jam!!
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