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Kofi Annan in: "Tube Amp for Multi-Way Speakers"
Kofi Annan in: "Tube Amp for Multi-Way Speakers"
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Old 17th September 2019, 09:55 PM   #91
scott17 is offline scott17
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Old 22nd September 2019, 11:57 PM   #92
Kofi Annan is online now Kofi Annan  United States
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More to come soon, but wanted to share what I believe to be the final design of the top plate of the amplifier.

I was unable to justify using the M O N S T E R power transformer from Hammond and no other EI I could find ready-made would do the job right, so I went with the Antek AS-2T300 - 200VA 300V toroidal as it meets both the power and heater current requirements.

I became concerned about the ventilation of the toroid as I ordered the accompanying steel cover. Initially, I had added some ventilation holes underneath the toroid, however I thought that it might be venting *inside* the warm chassis and would wind up getting warmer or maintaining its heat rather than cooling.

My current plan is to raise up the transformer and cover off the top plate a few mm and have it vent into the cooler air above.

Comments? Questions? Ire?

KOFI

Holy cow! A lot has happened!

Here's a status:

All parts have been received and I'm now only waiting on the Edcor OPTs. I finally pushed the button on the chassis and it looks incredible (take a gander!).

While the toroidal transformer would not have been my first pick, I think it looks really nice on the chassis.

I'm currently wiring the heaters and remembering how much I HAAAAAAAATE wiring heaters. That's always the worst part to me, but so far so good.

The Sifam meters really do look neat-o and will be illuminated by a 12V LED and bounce around to the music and stuff. I wound up getting an op amp buffer circuit PCB from JLM audio which I'm hoping will prevent distortive feedback to the signal when running the meters.

Lots of wiring to come soon!

Kofi
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Old 4th October 2019, 09:43 PM   #93
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Looking really good! Nice nomenclature work. Looking forward to the updates.
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Old 5th October 2019, 08:04 PM   #94
nerdorama is offline nerdorama  United States
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A fun project. It looks great.
John
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Old 5th October 2019, 09:16 PM   #95
Kofi Annan is online now Kofi Annan  United States
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Quick question on the Anteck toroid. There are dual secondaries for the heater supply, which I had originally intended to parallel, however each secondary is wired with the same color (BRN - BRN for one secondary and BLU - CLU for the other).

Is there a way I can determine the phase for each same-colored wire so I can parallel these?

Kofi

Kofi
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Old 5th October 2019, 10:40 PM   #96
kevinkr is offline kevinkr  United States
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Kofi Annan in: "Tube Amp for Multi-Way Speakers"
I would double check the datasheet (it seems that for some of the larger ones there are no data sheets) because that's not usually how it is done with Antek transformers.

I've used a lot of them and usually you parallel the same colored wires from the matching secondaries to place in parallel.
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Old 6th October 2019, 12:23 AM   #97
nerdorama is offline nerdorama  United States
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If you don't have a scope, connect them in series and measure the voltage across the series pair without any load connected. If it's 12V, your good. If it is around 0V then they are backwards.
John
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Old 6th October 2019, 01:14 AM   #98
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I've also used a lot of the Anteks, and yes the wire colors often differ than what is shown on the drawings. I can't absolutely guarantee this to be true in every case, but I've found that the winding wires exit the xfmr body in order of the windings. So in order, the first and third heater wires would pair with the second and forth wires if your going to parallel them. That would be a good starting point to try as nerdorama said.

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Old 13th October 2019, 01:04 PM   #99
Kofi Annan is online now Kofi Annan  United States
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Thanks, all. Much appreciated.

If all goes will I will be firing it up today and will address the heater AC as you described.

On another note, I was reading up on star grounding last night and I'm challenging my own method based on what I read.

Normally, I make 'local' star grounds for each stage (preamp / power) and attach them to the chassis at the BACK of the amplifier along with the PSU ground (one connection to chassis). Then I attach the earth connection to the chassis right next to the AC inlet (second chassis connection).

Based on what I have been reading, it may be better to attach both signal and power - near the SIGNAL input rather than at the PSU negative. I have seen that some people float the signal return rather than connect it to the PSU negative and chassis but that seems scary to me.

Any guidance?

Kofi
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Old 13th October 2019, 11:47 PM   #100
scott17 is offline scott17
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I wire amp grounds similar to what you have described.
All inputs are isolated from the chassis. The input signal grounds only connect to the input jacks (not the chassis) and run back to the preamp section signal ground, including the volume control signal ground. That ground goes to the main star ground, with the star ground isolated from the chassis. Same for the power section, back to the main star ground. The speaker output ground also goes to the star ground point. It is important to run the main rectifier ground directly to the first filter capacitor, and then to the star ground point.

I had a problem once with a laptop power supply injecting noise onto the signal ground, so I have been using a ground breaker for connection from the signal ground to chassis ground at the power entry chassis ground point. No more noise. I use what is described here in point #9: Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

Last edited by scott17; 13th October 2019 at 11:50 PM.
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