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Aleph J illustrated build guide
Aleph J illustrated build guide
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Old 13th May 2018, 06:19 PM   #2631
6L6 is offline 6L6  United States
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Aleph J illustrated build guide
What Mark said is completely correct.

The Bulb Tester is a crude but effective tool to keep really bad things from happening if there is a short or some error to make the circuit pull a ton of current. Because the bulb is wired in series with the load, it will glow when a bunch of current is drawn past it, and because it's a resistor, the voltage will be lower on the far end (where the amp is) the lower voltage hopefully keeping things from burning up.

Now the Aleph J is self-biasing to a certain extent, and the pot we use as 'bias' really isn't - it's the AC current gain of the constant current source. But it effects the current flow through the output stage and so it's sorta biasy. So let's consider it bias.

Anyway, because the circuit is setup to bias up by itself and sit there in glorious single-ended Class-A, there is always A LOT of current flowing when the amp is turned on. Which will glow the lamp, which will drop voltage across the bulb and into the amp, which will make it turn on less.

Now, imagine setting the bias pot to read correctly with the Bulb Tester connected - the bias reads low, because the line voltage is being starved, so you turn it up, which makes the bulb glow a bit more, so you turn the bias up even more, and you are fighting a negative feedback loop.

SO, now you have the bias turned up to 11, the bias now is reading in the general ballpark, although low, but everything else seems to be behaving sorta kinda properly, so you unhook the bulb tester and decide to plug it in bare and see what happens.

But remember, the bias is turned up all the way since previously you were fighting the voltage drop of the bulb, and now, with the full AC mains available, it pulls a TON of current since you set the bias pot there, possibly burning things up.

To sum up; The Bulb tester is to catch gross errors. It does this crudely but effectively. If the amp is working properly the bulb tester inhibits proper operation.
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Old 13th May 2018, 11:45 PM   #2632
Blk Dynamite is offline Blk Dynamite  United States
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Quote:
Originally Posted by 6L6 View Post
What Mark said is completely correct.

The Bulb Tester is a crude but effective tool to keep really bad things from happening if there is a short or some error to make the circuit pull a ton of current. Because the bulb is wired in series with the load, it will glow when a bunch of current is drawn past it, and because it's a resistor, the voltage will be lower on the far end (where the amp is) the lower voltage hopefully keeping things from burning up.

Now the Aleph J is self-biasing to a certain extent, and the pot we use as 'bias' really isn't - it's the AC current gain of the constant current source. But it effects the current flow through the output stage and so it's sorta biasy. So let's consider it bias.

Anyway, because the circuit is setup to bias up by itself and sit there in glorious single-ended Class-A, there is always A LOT of current flowing when the amp is turned on. Which will glow the lamp, which will drop voltage across the bulb and into the amp, which will make it turn on less.

Now, imagine setting the bias pot to read correctly with the Bulb Tester connected - the bias reads low, because the line voltage is being starved, so you turn it up, which makes the bulb glow a bit more, so you turn the bias up even more, and you are fighting a negative feedback loop.

SO, now you have the bias turned up to 11, the bias now is reading in the general ballpark, although low, but everything else seems to be behaving sorta kinda properly, so you unhook the bulb tester and decide to plug it in bare and see what happens.

But remember, the bias is turned up all the way since previously you were fighting the voltage drop of the bulb, and now, with the full AC mains available, it pulls a TON of current since you set the bias pot there, possibly burning things up.

To sum up; The Bulb tester is to catch gross errors. It does this crudely but effectively. If the amp is working properly the bulb tester inhibits proper operation.
Ok that makes perfect sense. Thank you for the detailed explanation!
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Old 19th May 2018, 06:08 PM   #2633
DSMStudio is offline DSMStudio  United States
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A while back, I ordered the ALEPH J TRANSISTOR KIT from the store. I forgot that the kit included 6 transistors with the Mosfets and I installed the Zetex ZTX550 and 450s I ordered from Mouser.
Is there any reason I should switch them out for the ones from the DIY store? They don't need to match, do they?
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Old 19th May 2018, 06:09 PM   #2634
wdecho is offline wdecho  United States
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Your good.
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Old 21st May 2018, 09:50 AM   #2635
mcgreg66 is offline mcgreg66  Germany
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Hi all,
First-of all thanks to all who put in here their know-how and experience !
DIY audio is my favourite forum although sometimes hard to follow as English is not my first language.....
I’m attempting to jump on the DIY built of Pass Aleph J (missed the preorder of the aca kit)

Is the BOM on the first page “up to date”?!

Because I find more and more changes whlie reading the built thread!
Like R8 is recommended to be fixex 1kR....

Gregor
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Old 21st May 2018, 03:37 PM   #2636
Blk Dynamite is offline Blk Dynamite  United States
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Big thanks for 6L6 for answering my endless questions as this was my 1st amp build and Papa for sharing his work I was finally able to give birth to a 40lb bouncing baby Aleph J. A few complications in the 3rd trimester but all came out great. Just a few tidbits; I used a transformer from Toroidy and CLC filtering for the power supply. The binding posts, XLRs and chassis RCAs are from Cardas. I was also able to source some Toshiba Jfets as well. For C1 I decided not to use the Wima (I’ve heard them before and didn’t like them, just preference) and instead had Jens Nielsen of Ophelia Caps custom make the film caps for me. Jens spaced out/strengthened the leads to fit the boards and also fortified the casing to withstand the internal heat. Just like the Humble Homemade review the caps really don’t add much to the sound, being a tad warmer from neutral. I tried them w the Elnas and wasn’t my cup of tea (maybe I didn’t let them burn in enough) being congested in the mids but after changing the Elnas w/ Nichicons, everything smoothed out and opened up. I think the Ophelia’s like other parts that are on the neutral side hence why the Humble reviewer had slight congestion, either way I really like this cap as I got no congestion after the change and will use it on other builds if a film cap is needed.


I’ve never heard a First Watt amp so was going on forum members reviews and I must say this is an awesome amp! Very laid back w/ good sound staging and mellow highs. Completely different from the previous bridged Classe CA-100s I was using which were on the darker side in the mids. I look forward to building more of these as the Aleph J needs some siblings!
Attached Images
File Type: png Amp1.png (417.1 KB, 406 views)
File Type: png Amp2.png (405.5 KB, 406 views)
File Type: png Amp3.png (383.5 KB, 404 views)
File Type: png Amp4.png (386.5 KB, 389 views)
File Type: png Amp5.png (394.4 KB, 387 views)
File Type: png Amp6.png (416.4 KB, 148 views)
File Type: png Amp7.png (639.4 KB, 197 views)

Last edited by Blk Dynamite; 21st May 2018 at 03:44 PM.
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Old 21st May 2018, 05:25 PM   #2637
Zen Mod is offline Zen Mod  Serbia
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Aleph J illustrated build guide
well , you even didn't need that cap

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Old 21st May 2018, 05:32 PM   #2638
Blk Dynamite is offline Blk Dynamite  United States
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Quote:
Originally Posted by Zen Mod View Post
well , you even didn't need that cap


Yea I'm not up to your level of expertise. I'm following that build guide to the T haha. I got a lot to learn. Also thanks for the help as well, its greatly appreciated
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Old 23rd May 2018, 02:47 AM   #2639
pggriff is offline pggriff  Canada
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Default Balanced and RCA input wiring

Getting near the end of my Aleph J project, itís my first amplifier and has been a great learning experience, thanks everyone for all of your posts! Question on wiring both balanced and rca inputs in single chassis. I have some 6 conductor wire that is shielded and sports an uninsulated ground wire. I was going to run one wire each from +v rca and xlr terminating each to +v input on board, same with -v . Now Iím not sure if I should use the bare shield wire connected to the ground on the xlr and terminate on the chassis or use one of the other insulated wires in the package. From my reading here grounding is very important with respect to noise elimination, perhaps I should keep it simple and just use some standard wire. Does anyone see an advantage to the insulated cable?
Attached Images
File Type: jpg CFC1ADC9-4D87-40EE-855F-C97A15B7DDAF.jpg (682.5 KB, 231 views)

Last edited by pggriff; 23rd May 2018 at 02:52 AM. Reason: Add picture
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Old 23rd May 2018, 04:07 AM   #2640
mkane77g is offline mkane77g  United States
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I'm not the sharpest knife in the drawer but I would keep them separate from one another and twisted for good measure. Fantastic pic btw
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