Beginner to build an Aleph30 needs some help

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Hello and happy new year to all of you.
I'm new here and quite new to the DIY amp world, but I've already built two different amps (one TA2022, a dual lm3886 (following the optimizations given by Aguilabrava, AndrewT, Pemo...etc on the thread http://www.diyaudio.com/forums/chip-amps/207971-bought-xy-lm3886-kit-13.html thanks a lot to all of them for sharing ;) )
Both sounds really good (especially the Dual Lm3886, although it misses a little power for my rig).

Now I really want to try something witch should be called audiophile....a class A Aleph 30.
I've read a lot about the Aleph and Zen amplifier series (on those forums as well as on the Nelson Pass website...... thank you Mr Pass for sharing your passion and discovers, this is really what knowledge transmission is) But as I am quite new to diy amps and electronics in general, all those information tend to be a little confusing.

To begin, here is my current rig:

AMP:

-Stereo XY Lm3886, XY psu with 4x10000 uf 50v nover capa (20000uf per channels), a 300Va 2x24v/2x15v on 230VAC transformer .
-Two Analog metric speaker protection cards (fed by the 15V secondaries)
-A 10KOhm stepped attenuator (vishay Dale resistors)

Speakers:

-Davis MatisseHD floor-standers; 80W (120W peak) 91db 4 to 8 ohms

Sources:

-Project XpressionIII turntable with Ortofon Red stylus and a speedbox
-Diy scph-1002 (playstation) with modified output stage / psu
-Dynavox TPR-2 Phono and line tube preamp

Now, a list of what I've already on hand for my Aleph 30 project:

- two BrianGT Mini Aleph board (the black one with golden contacts)
- One BrianGT Aleph PSU board (black one with golden contacts)
- A set of paired transistors bought on ebay (12x VISHAY IRFP240, 4+2 VISHAY IRF9610, 4 ZETEX ZTX450)
- Two Hifi2000 300x210x40mm heatsinks given for 0.20 C°/W modushop.biz
- TO220 Ceramic insulator pads (0.3C°/W)
- One 600VA 2X24V 12.5A toroïdal transformer (on 230VAC as I live in Europe)

I'm already on the process of designing the enclosure of my future amp under 3Dsmax (I'm a 3D graphist IRL), witch will be full aluminum (I'll post some pics in the upcoming posts)

Now I have to find out the best settings for the bias/resistors, this is where I need some help from the Aleph experts.
I've used the Aleph-Power.xls by wuffwaff spreadsheet to do my calculations, can you tell me if it makes some sense

An externally hosted image should be here but it was not working when we last tested it.


I've read that to know the secondaries voltage under load with rectifier losses I shall take the secondaries voltage minus 0.5 to 0.7v (rectifier losses) witch leads me to 24-0.5= 23.5, the nearest settings (23.1V secondaries standard) in the spreadsheet gives me 32V DC at rails (23.1V x 1.41 from the capacitor filtering if I'm not wrong)

So I would have to change the 0.47 Ohm resistor from the original BOM by 1 Ohm resistor (3W) to reach the 1.6A Bias (for a 41W under 8 Ohm) right?

However, when i try to simulate the PSU in PSUdesigner I cant reach the specified 32V (with 0.47 Ohm resistor).... Did I made a big mistake here?

An externally hosted image should be here but it was not working when we last tested it.


Witch resistor(s) shall i solder between the two capacitor stages on the psu to obtain the expected rail voltage?, how to calculate them?

I think it' enough for a first post, sorry for it's length, I hope it's not too confusing, but I'm really beginning in this hobby and even if I'm curious and I think a quick learner, the multiplicity of information are a little overwhelming, that's why i'm searching for help here.

Thanks for reading and please excuse me for my English.
 
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Hi,

there will me some much knowledgable guys chiming in to answer your questions.

That being said, I think you are mixing up the bias and the rail voltage somewhere.

Aleph 3 (or 30) runs on 25 DC rails (something like 18V secondaries), so having 32 Rails (from your 24V secondaries) can give you an aleph without any doubt, but not a 3 or 30.

I suggest you use the search function and look for the algar_emi spreadsheet and schematics.

No way you can drop your rails from 32 to 25 V using the resistor in your CRC filter - no use either to do so

Hope that helped a bit!
 
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You're totally right, my project shall better be called Aleph 40 :spin:

I'll take a look at this spreadsheet, thank you

EDIT: I think I've found the schematic http://www.diyaudio.com/forums/atta...eph-x-builders-thread-aleph30by-algar_emi.pdf
But I was not able to find the spreadsheet, however, next to the AXE-1-2.xls i've used to make my calculations, I have another one witch is called Aleph-Power.xls (Aleph-X calculations)
 
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Sorry I've mixed the spreadsheets.
I've used the Aleph-Power.xls to do the calculation and I have another one called AXE-1-2.xls (ALEPH-X calculations)

I don't understand why those two spreadsheets gives me different settings and results with what I think are the same datas

Aleph-Power.XLS
An externally hosted image should be here but it was not working when we last tested it.


AXE-1-2.xls
An externally hosted image should be here but it was not working when we last tested it.


I'm a bit lost here....
 
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Another question, do I have to oversize the capacitors of the PSU (22000uf for Aleph 30) to adapt to my power source (24vac per channels)?

Maybe this post should be a sort of guide for the beginners (like myself), with your help and advices.
 
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For the diodes I plan on using 4 MUR2020CTPBF-ND Invalid Request
as listed in the BOM http://www.chipamp.com/beta1/wp-content/uploads/2013/03/mini-A.xls

I understand your advice to put 22000uf after the rectifier and 44000uf (2X 22000uf) after the resistance, but the layout of BrianGT PSU board calls for the inverse

An externally hosted image should be here but it was not working when we last tested it.


Shall I bridge C5 and C6 with a strap, soldering 22000uf capa on C7 and C8 then 22000uf on C3-C4 with two additionnal 22000uf in parallel (wiring them on the underside of the board)?

As for the results from PSUdesigner witch doesn't gave me the expected 32Vdc at rails, I've just realized I leaved the default 5A for the load, I changed it to 1.6A (Aleph Bias) then I get 31.216 mean voltage (witch seems better)

An externally hosted image should be here but it was not working when we last tested it.
 

6L6

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Joined 2010
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The resistor in your PSU simulation is much too big - the PCB has place for up to five resistors in parallel, making the resistor valuw much smaller than just one resistor. If you were to use the "normal" Pass-style CRC filter you would have (4) 0.47ohm resistors, giving a value of 0.12ohm.

Anyway, don't worry about the simulation - use your parts, assemble the PSU and know that under load your rails will be something close to +/- 32V

You are using 35V capacitors (or better)?
 
I'll probably use those capa Invalid Request
I think i'll bypass the electrolytic with some mks film (like 2.2uf wima) as to speed them up a bit: good, bad?

As for the resistance, I'll be using 4 parallel 0.47ohm resistors per channels (0.12ohm/channel)

Anyway, what about the capacitor arrangement suggested by Zen mod?

thanks again for all your advices
 

6L6

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Joined 2010
Paid Member
The electrolytic caps look very good.

Bypass caps are to your taste, the MKS are fine.

The PCB can't be adjusted to place single cap first, so just use it as designed - it's a great PCB, I've used it in two different projects. I really like it.
 
Those capacitors will be fine. A bit big to mount to the bottom of the board if you want to add after the R. ;) How about mounting them on a small piece of perf board right up at the end of the main PSU board to hold another pair of caps? Either CCRCC or C-RCC

Your net R is in the normal Pass range, should work well.

IMHO, the bypass caps would be better on the amp boards if used at all. On the PSU board it may oscillate with the main caps' self inductance and the power supply lead inductance. There are strong opinions on both sides of the issue, some claiming that it adds life to their amp, others saying it causes oscillation and ringing. At my skill level and limited measurement equipment, I tend to leave it off it it could cause harm if not properly sized, like snubbers. As always, YMMV and it probably wouldn't hurt to try and see if you think it makes a difference.

I agree with Jim (6L6) that is a nice PSU board, It's in a couple projects of mine with more on the way.
 
Those capacitors will be fine. A bit big to mount to the bottom of the board if you want to add after the R. ;) How about mounting them on a small piece of perf board right up at the end of the main PSU board to hold another pair of caps? Either CCRCC or C-RCC

That was precisely what I had in mind ;), 2 additionnal 22000uf capa on a perf board wired to the underside of the PCB, I'll try the CCRCC approach.

Your net R is in the normal Pass range, should work well.

Ok so i'll stick with 4x0.47ohm resistor network on each channel.

I think I can place the order for the PSU parts now :)


I still have to be sure what Bias resistor I should buy; the spreadsheet (on page 1 of this thread) leads me to 1ohm 3W resistors (X12 for two channels) instead of the 0.47ohm ones listed in the BrianGT BOM, is it right?
 
An Aleph biases up to roughly 0.5V across the Source resistors. So if you choose 1R resistors you will have roughly .5A per fet, 1.5A total bias since you are going with three devices per current source. Assuming that you have the heat sink to handle it, you probably will want to go more towards the original 0R47 so that your amp isn't current limited at lower impedances.

You have enough voltage swing with 30V rails to drive ~100W peaks into 8R. At 1.5A total bias, and 50% AC gain you'll be current limited to 27W. At 3A bias (0R47 source resistors) you will be voltage limited.

If you need to limit dissipation but want a little more bias choose 0R68.
 
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I made another calculation with a goal of 0R68 as a target for resistor to Bias fet (gives me 2.6A total bias)
Seems like my heatsinks are just enough for this setting (heatsink= 0.2C°/W for one channel)

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.


Witch value should I choose for source resistor (now 0R82) ?

On the schematic Fet source resistors are R35 to R41 and bias resistors are R18 to R21 right?

What are the purpose of R23 to R26? How to choose their value and number (since you can install a total of 6 resistor here)

I realize that my questions are quite trivial and i'm really grateful that you're taking the time to explain things to me.
 

6L6

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Joined 2010
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If you have 3 pair of Mosfet per channel and 32V rails, you are basically building an Aleph 5.

For source resistors, don't worry too much about changing anything. What Bob says is spot on.

Not knowing what schematic you are looking at I assume that R23-R26 are the (4) 0.47ohm resistors near the output. Those are the Aleph CCS sense resistors. Use (4) 0.47ohm
 
I'd go with 0R68 Source resistors if your heat sinks can't handle the current with 0R47.

Not sure which are which - I don't have that board's schematics handy. The ones whose source resistors connect to the negative rail are the output devices and the ones whose source resistors connect to the output through a bunch of other resistors are the current source's and set bias. Generally use the same values in both places.

Guessing again, but R23-26 are for setting the AC current gain. Are they the ones that connect the junction of the upper and lower transistors to the output? The easiest way to do it is use the same value as your source resistors and as many. In your case 6. (Seeing Jim's note, the goal is to have 1/2 the net resistance of the ACS 3 parallelled source resistors. Using 4 will result in higher AC current gain)

You're welcome of course. hopefully This will help someone else, too.
 
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