F4 power amplifier

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#2,522
My tall tower has worked very well, but it is 6" square, and allows a lot of air flow through it- in fact more than normal because of the stack effect. A finned heatsink won't get this kind of air flow as the channels are relatively small.. Note that Nelson uses his fins horizontally, offending all purists, and they work fine. The tower gives a small footprint and like a big V8 engine, it works by having lots of inches! - about 25% more surface area than Nelson's commercial F4's. Magura predicted disaster for it and insisted on additional heatsinks, but it works fine even after I scraped the extra sinks off... I am rebuilding it for a second time and it is finally of a quality that I can live with. The show version was a mess and needed to be rewired..
 
#2,524
Variac said:
My tall tower has worked very well, but it is 6" square, and allows a lot of air flow through it- in fact more than normal because of the stack effect. A finned heatsink won't get this kind of air flow as the channels are relatively small.. Note that Nelson uses his fins horizontally, offending all purists, and they work fine. The tower gives a small footprint and like a big V8 engine, it works by having lots of inches! - about 25% more surface area than Nelson's commercial F4's. Magura predicted disaster for it and insisted on additional heatsinks, but it works fine even after I scraped the extra sinks off... I am rebuilding it for a second time and it is finally of a quality that I can live with. The show version was a mess and needed to be rewired..
Click to expand...

I personally liked the channels hanging off the chassis. Kinda like christmas tree ornaments. They had a good pic in the AudioXpress article that covered the event.

Chris
 
#2,525
Yeah, but the boards kept getting moved around so various pins broke off the output devices. That's kind of sad. The repairs to the amps should have been done in a week, but I have a lot of other stuff to do like knocking member's heads together, sortin the Off Topic Pumpkin thread, etc. Also I wanted to take the time to make them something that I would feel are finished.

Certainly shorter, vertical heatsinks are more efficient- in fact I was considering
cutting some of the PAss heatsinks I got at Burning amp to use them vertically on a new project but then decided: naah! they have wide fin spacing, and I think, as I mentioned above, that increases the airflow..
 
#2,528
Ok, my PSU-trip continues...today I changed the setup of the 4-pole Jensen's and paralleled them, so that each input is in parallel and each output as well. Before, the output of one 47000uF was connected to the input of the next one, so that the current need to go through the each of them which multiplies impedance.

Some technical observations: BEfore, I have on the 24v+ 0.3mV ripple (when having them in series). Now I have 80mV ripple.

Again, No CRC, both setups have no resistor or coil/choke.

I put as well on the output of the Jensens a 0.1uF Mundorf Supreme MKP Cap (more or less inductance.free).

So, how did the sound changed ? MAybe I need to relax more, take more time. My iitial impression:

More power and basis in the bass department. IN total warmer sounding, blacker. On the down-side: Less resolution, less refined, less 3D-space. The formerly huge soundstage is now more flat, more 2D. Instruments / voices seems to be bigger.

Can that be ? What are your experiences when playing with the PSU ?
 
#2,533
There is a potential difference between the grounds at the input
connectors, either as a result of their grounds attached at points
which are at different potentials or as a result of the transformer's
magnetic leakage making for circulating currents to the Source from
one channel and back through the other.

What happens if you hook up a source on two channels but disconnect
the input ground on one channel only?
 
#2,535
Some pics

I just wanted to show you some pics of my F4...

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.
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.
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.


That big and ugly star grounding, in the middle of the PSU board, does work great. The amplifier is dead silent, I have 98.5 dB/W/m speakers and can't hear anything at all, even if I put my ear near the drivers. I'm impressed with this, never achieved such a result with other equipment (mainly tubes, you know...).

It's got about 20 hrs mileage, once burned-in I'll bypass those Cerafine's with a few nice polyester caps, courtesy of Jacco 😎

By then, I'll post some sort of listening test too.

Giacomo
 
#2,538
@Jacco: hahaha 😀 err, I meant polystyrene :angel: Thank you for the hints, I'll follow. About my creative insulators cutting: for drilling them, I used that stupid toy which is intended to make holes in paper sheets... Not so precise, and I had only thin strips of insulator, so that's the result. And I also used curved electrician scissors, so that's the top end 😀 but I can guarantee that they're entirely coupled to the heatsinks, I checked.

@Magura: Those two resistors are actually soldered together. They're two 1.5k in parallel, to obtain the 750 ohm R. I didn't find a better way to place them, so the first one sits in the PCB, and the other one is soldered "above" on the pins.

Thank you both. 😉

Giacomo
 
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