Classic Aleph Amplifier for Modern UMS Chassis Builder's Thread

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GKT - This is quick and DIRTY....

I just grabbed the closest Aleph I could find. It's on a cold heatsink... and as you can see... it's wired (ahem) temporarily with the stuff I had within arms reach. This is ONLY to show the type of behavior I see with a properly biased Aleph when ramping up with a Variac.

What I did (in addition to what Mike is suggesting) is that I turned the bias pots 'all the way down' even though the starting point is middle. Once I verified that there were no shorts etc, I ramped the voltage on the variac up to full mains, then I set the bias.

Let me know if this link works.


Edited to add - I wasn't standing on my head... I have no idea why it's upside down... LOL! Hopefully you can see what I'm talking about. I've still got it hooked up if you need anything else done / slowed down.

For those that know what they're doing... maybe they can shed some light on the "immediate rise to a higher voltage than for the normal bias" then ramping back down past a point as the DC supply increases to the normal voltage. I've tried to figure it out... maybe I will some day. Given the 10 or so Alephs I've been fiddling with over the last few weeks, it's just something I noticed that they all had in common.
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What a helpful thing you've done for me! Thank you so much. That is exactly what I observed, even down to the approximate bias voltages. I'm going to try it on the DBT first, and see if the current draw equilibrates enough for the circuit to settle and not just draw from the bulb. If not, I'll switch in the second bulb in series and see if it settles.
Back in a few...
AWESOME! Thank you!
I'm a happy camper.
On either the Variac at lower AC or the DBT leash, the circuit never equilibrates, but more interesting, the bias pot has no influence at all.
Off the leash, the bias voltage spikes, but then settles quickly. I'm now trimmed at 311mA dropping a bit - now at 304mA as the outputs and heat sinks warm up. They are all within a degree or 2F an total line current draw is 1.26A.
Last night, Jim suggested as much, but neither he nor Randy wanted me to go further without doing all of the QC checks (thanks again for the help, gentlemen). Glad they passed, and this is just normal behavior. Next will be all of the other adjustments after I get the left channel hooked up and tested.

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Thanks, Jim!!

Guess what? Left channel is working properly, with numbers right in line with right channel!

Bias is 17mV, without touching P1. Adjusting that now.

I'll follow Randy's offline advice - get the bias stable, assemble the heat sinks and front/rear panels, get all connections made, then adjust AC gain. Pots were preset accurately, so it should be close.
Remaining wiring and full assembly was finished late yesterday, including adjusting offset to about .3-.5mV (correction to my comment above - offset, not bias was 17mV before adjustment).

I have to cut down a trimmer adjuster - the two V8 power supplies fill the chassis pretty well. These will be used for our SLOBs, so I have to make some longer interconnects from the crossover to the new amp. Should be up and running later today.

Many thanks to Randy, Jim, Patrick and everyone who provided comments and input - I do appreciate it.

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@GKTAUDIO That looks really nice and very inspiring to watch your posts. I'll eventually be giving a similar project a go (not anytime soon though), likely Aleph 60 in separate chassis, and sharing your journey will most certainly help guild my future efforts.

One question I have is to understand why you have 2 sets of fuses, the two internal fuses available to the IEC inlet, and two external fuses. I suspect it's my lack of understanding of the fuses in the IEC, or just that you want individual protection for each circuit.

I have a separate question that I've yet to fully understand for the broader community and that's why I most often see the transformer(s) at the front of the amp chassis, and not at the back close to the AC input. My first thought is to minimize length of AC wiring, I'd want the primary wires of transformer as close to the IEC inlet as possible. I'm sure there's a valid reason to have them at the front and wanted to ask as I've yet to find an answer in the many threads I've read through.
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The location of the transformer question is a good one! In rack mount gear, having the transformer near the front, puts it closest to mounting screws, which is good. Also the front panel tends to be thicker than the rear, so the overall chassis strength is higher at the front. Of course, most of us don't actually mount our rack gear, so you could ask why we stick to a 17in wide chassis as well! On the electrical noise front, you probably want the input stages further from the transformer, which would imply having them on the opposite side from the transformer. Putting the transformer at the front, allows the input stage to be at the back, and the shortest connections for the input wiring.
This is all just off the top of my head, and I'm sure this topic could be an entire thread on its own!! Any other thoughts?? Dave
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@birdbox: Thank you very much! I was inspired by Randy and Jim, who spent time with me understanding the intention for this amp. Since I have large 200-250wpc amps for our Eminent Technology LFT8-c speakers and was finding that for our SLOBs I wanted a little more volume at less distortion than the ACA Minis I built, their wisdom was the Aleph 30 - yeay!

I am using one fuse for each power supply and amp channel. Since this is a completely dual mono build, I wanted protection for each channel.

@DCtoDaylight answered your question for me - I wanted the large magnetic fields of the two transformers further away from the input section of each board, which are at the rear. Many of my good quality commercial amps are laid out similarly.

By the way, I have built a lot of tube guitar amps, and the topology I follow is much the same - the power transformer is as far away from the sensitive input stage as possible, and the output transformer is closer to the output tubes. These toroids are pretty darn big for a 30 watt stereo amp, so I definitely wanted them far from the input pair, etc. I also rotated the transformers to position the AC inlets close to the CL-60 boards, and the rail outputs to the front corners, angled away from the boards. This seems to have been the right choice - it is very quiet,and has no hum.
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Oh - forgot the status report. After fine-tuning the Iq and DC offset I put the amp in service with our inefficient 87dB panel speakers first, since I have to re-configure and rewire the current crossover/amp setup for the SLOBs. It sounds wonderful. Beautiful clarity in the mids and highs, great detail, and no unpleasant characteristics. I played a variety of music styles through it - acoustic guitar, vocals, piano, jazz.

My wife came in the house after the amp was playing for an hour, and before taking two steps in, she said "Oh, it's working." I asked her how she knew that it was the Aleph 30 playing, and she answered "it has really clear highs and mids." After literally 2 seconds walking in the door, and not even seeing the amp.

Sure, it is underpowered for the panel speakers, but it will be in use with the full range drivers in the open baffle speakers, so should sound absolutely incredible.

Thanks again to Randy and Jim for the inspiration and encouragement, and to Randy for the great boards and matched actives.
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My light pipe material arrived a few minutes ago, so here it is, installed. No extra wires or current draw, mounting delicate LEDs in the front panel. Nice, focused blue light.



Also received two different feet - silver and black - so, still deciding which ones to use. The taller, much more expensive ones (of course) intended for this amp were apparently lost in the process of my several concurrent shipments being aggregated into one package. :(

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Now have Aleph installed on a new audio stand, temporarily in my guitar room until we move the system into another room. Since the room is filled with guitar amps and speakers, the SLOBs are not spaced properly.

Not surprisingly, the new Aleph brings a lot more clarity, volume and definition to the full range speakers compared to the ACA Mini Redux previously in the system. Lovin' it!

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Quick update. I've had the Aleph powering the FRS Moths in the SLOBs and they sound incredible. Very detailed and clean, and of course, the drivers are efficient so the Alephs are not cranked. I followed @rhthatcher's instructions for initial and subsequent adjustments, and got them lifted 2.5" off the shelf for better convection, per @6L6. Slight adjustments of the active crossover were needed, but this seems like a great combination. Cheers!
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