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Taming Hum on two pre-owned Aleph Mini's
Taming Hum on two pre-owned Aleph Mini's
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Old 9th January 2019, 03:52 PM   #11
Dennis Hui is offline Dennis Hui  Canada
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Taming Hum on two pre-owned Aleph Mini's
You can build a fine power supply with a centre-tapped transformer like the Hammond.
Its power rating is a bit low for both channels but I wouldn't discount it.

For PS boards, please check that they support the size of caps you intend to use.
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Old 9th January 2019, 10:35 PM   #12
mpmarino is offline mpmarino  United States
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Hard to tell the scale, but do you think one of the chassis can handle 4 channels of heat? If so, you could make one chassis for the amps and the other for the PSUs. Even quieter for your horns.

Edit - I might have a set of brianGT boards buried somewhere if you want to make it all the same. Mine are blue i think.
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Last edited by mpmarino; 9th January 2019 at 10:41 PM.
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Old 13th January 2019, 12:12 AM   #13
rhthatcher is offline rhthatcher  United States
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I have spent time this week studying and documenting the boards in my amps. After doing all that, I found a goldmine in this thread.
Aleph with BrianGT boards - diyAudio

The spreadsheet that thread with cross references between Aleph J schematic, BrianGT Schematic, and BrianGT PCB label would have saved me hours. It is gold. I learned a lot in the process, though. The good news is that the spreadsheet an the schematic posted by bobodioulasso regarding using BrianGT’s boards for an Aleph J lined up with what I found. Once I moved on the green boards, that went super quick.

PDF/Pix are of:
My documented “As-Built” schematics for both amps, plus pix of boards with component locations. This will be useful for any work at the bench now or in the future.

Pix of schematics from bobodioulasso’s post. One is the Aleph J on BrianGT Boards. The other is titled “Aleph 30 mod” and had red X’s on parts not included.

Questions that I need input on:
- What is R0? I have a 3 Ohm R0 resistor on the BrianGT board amp on the board, and 2.7 Ohm from board to speaker negative terminal on the other amp. It is not on bobodioulasso’s build, and crossed out with a red X on the other schematic. I’m thinking I remove them… Thoughts?
-

My amps dosn’t have the R27 on the boards. It’s open. I understand that is used for setting Bias. Should I put in a 68.2k resistor? Bias now is at 1.378A on one amp, and 1.355A on the other. Maybe a non-issue. Thoughts or experience on leaving R27 out?


- bobodioulasso’s drawing shows R27 (on his drawing R13 68k2) with a dashed line. Any clue on what the dashed line is?

Since I'm going to get in and tweak, are there any parts on the boards that could benefit from premium parts? I could imagine caps are candidates. Any favorite flavors?


Open items:
- Swap R14 and R16 on “Shorty” amp. It appears they’re backwards
- Jumper SG to –IN on "Shorty"
- Address R27 68k2 resistor when I know the right thing to do.
- Address R0 / mystery 2.7Ohm resistor when I know the right thing to do.

- Order Parts and update
- CRC PS
- Pots for R8 (DC Offset Adjust)
- C6 10uF on “Shorty”
- 2.5A 250V fuses

@mpmarino - What would you want for those boards?
Attached Images
File Type: jpg aleph j brian gt bobodioulasso .JPG (169.8 KB, 206 views)
File Type: jpg Aleph 30 mod.JPG (110.2 KB, 202 views)
File Type: jpg Shorty Schematic As-Built-00a.jpg (109.6 KB, 197 views)
File Type: jpg Shorty Board As-Built-00a.jpg (245.4 KB, 191 views)
File Type: jpg Tallboy Schematic As-Built-00a.jpg (287.8 KB, 185 views)
File Type: jpg Tallboy Board As-Built-00a.jpg (220.3 KB, 72 views)
Attached Files
File Type: pdf Shorty Schematic As-Built-00a.pdf (94.9 KB, 8 views)
File Type: pdf Shorty Board As-Built-00a.pdf (168.4 KB, 4 views)
File Type: pdf Tallboy Schematic As-Built-00a.pdf (90.0 KB, 6 views)
File Type: pdf Tallboy Board As-Built-00a.pdf (147.9 KB, 5 views)
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Old 21st January 2019, 03:26 PM   #14
rhthatcher is offline rhthatcher  United States
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Weekend progress.



I gutted "Shorty" amp. I installed transformers, bridges, and a terminal block with AC mains in, cap, thermistors.



I'm stuck on the PS boards until my PCB spacers show up. My first amazon order is apparently coming from China, because delivery date is weeks out. Ooops. I have a batch set to come in on Wednesday. Perfect timing from return from a short biz trip.



I made some updates on the amp PCBs, too. Updated 'lytic caps, added missing caps, installed pots for Bias and DC offset, and swapped the resistors that were backwards.



Hopefully by this weekend I can fire it up for testing.


I bought a tap set for this. My wife is already sick of the "I'll tap that" jokes.
Attached Images
File Type: jpg IMG_9764.jpg (987.8 KB, 77 views)
File Type: jpg IMG_9746.jpg (994.4 KB, 74 views)
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Old 26th January 2019, 01:43 PM   #15
rhthatcher is offline rhthatcher  United States
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I rebuilt the “Shorty” amp – pic is below.

It tested the output on some cheap speakers, then hooked it up my eXemplar horns. Good news: the hum in the speaker output is tamed. Sound is great.

The bad news – these Hammond transformers buzz louder than original speaker hum.

Is this a normal thing for Hammonds? Could it be the wiring job, or layout? If you see the picture you can see the AC mains going to a terminal block, then a thermistor and wire going to each transfomer. I had an orange drop cap at the terminal block, but pulled it.

Thoughts on how to fix it? Real estate is tight in this chassis, I opted for the hammonds because I measured up and all of the torroid options I looked at were extremely tight squeezes.

Power supply voltage = +/- 20.3V (was +/-17V before mods)
DC Offset 25mV Left, 30mV Right (was 34mV / 37mV before mods)
Bias Voltage = .592V / 1.26A (was .637V / 1.355A before mods)
I haven’t played with pots to tune the bia or offset, I want to solve the buzz first.
Attached Images
File Type: jpg Shorty As-Built Hammonds.jpg (1,008.4 KB, 66 views)
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Old 26th January 2019, 01:53 PM   #16
mpmarino is offline mpmarino  United States
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I'd try extending the wiring and pulling them out of the chassis. Maybe getting them away from right against that wall, or rotating one or both may help?
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Old 26th January 2019, 07:01 PM   #17
rhthatcher is offline rhthatcher  United States
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MPMarino - thanks for the suggestion! I went to bed stumped about this, and woke up thinking about it. Your post got me inspired to try some things. After lunch I played around a bit.


- Transfomers out, no thermistors. Transformers still hum/buzz regardless of how I move them around.
- I found a corcom filter in my bag of tricks and thought "what the hell". I tried that between the switch/fuse and the transformers. Transformers still hum/buzz.


With the trannies out of the amp, it's quite easy to hear that it's the transfomers. And the speakers (in another room with long speaker cables) make great music. So it now comes down to figuring out the transfomers.


Before I bought the Hammonds I cut out circles the size of AnTek, Plitron, and Avel Lindberg torroids. The AnTek and Avels' won't fit on the bottom (traditional mounting) or standing up.



It looks like I could bolt a Plitron to the faceplate or maybe to an L bracket and have a couple millimeters to spare. Tight, but possible.



I could also try to put it on the bottom and move the PS boards perpendicular to their current configuration. I have a feeling the caps might not clear the binding posts or the amp boards. It would be a very tight squeeze.



Any other ideas on transformers? I'm assuming these won't work, so I'm looking for a "one and done" solution. 2x 15V or 16V or 18V @ 200VA-ish
Attached Images
File Type: jpg Shorty Hammonds Out Test.jpg (984.6 KB, 45 views)
File Type: jpg Shorty Hammonds Out Corcom.jpg (1,004.8 KB, 32 views)
File Type: jpg Plitron Tempalte.jpg (986.1 KB, 30 views)
File Type: jpg Plitron Tempalte 2.jpg (928.0 KB, 31 views)

Last edited by rhthatcher; 26th January 2019 at 07:19 PM.
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Old 26th January 2019, 07:36 PM   #18
mpmarino is offline mpmarino  United States
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Overload or DC on mains usually causes buzz. A toroid is much worse with DC on mains.

Maybe your secondaries are out of phase with each other. try reversing secondaries on one perhaps?

Recommend a light bulb (60-100) in series with mains so nothing get's too hot - in case.
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Old 26th January 2019, 08:33 PM   #19
rhthatcher is offline rhthatcher  United States
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I played with swapping secondaries. Buzzz
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Old 27th January 2019, 06:24 PM   #20
rhthatcher is offline rhthatcher  United States
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Today's experiment.


I decided to try and go back to original transformer (25VCT) with single rectifier bridge into the new CRC filter. So center tap to star ground, + from bridge to V+ input on the boards, - to V-.



Fire it up.



+/- 16.9V to rails. Good. 0.1V drop with CRC filter compared to original.



Plays nice music.



Transformer doesn't buzz. But I hear hum from the speakers when music is paused. Back to the original problem.



That leads me to conclude the dual rectifier bridge setup is key for noise reduction. I saw that when reading here Dual Bridge Rectifiers in PSU - why?


Side note. With the bias pot in, not "freewheeling" as original, the bias voltage was pretty close to previous dual rectifier / transformer and higher voltage rails. Good to know that it's doing its job.


Here are some options I'm thinking about now;
- Get a Plitron, see if I can stuff it in
If not, get a new chassis to hold 2 torrids and use that to feed both of my Aleph Mini-J's.
- I could consider transplanting all the guts into an all-new properly sized chassis, but that's the high price solution. I want to make what I have work before I go that route.


Thoughts or advice?
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File Type: jpg Shorty Single Rectifer CRC.jpg (994.6 KB, 48 views)
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