KGSSHV Carbon Build Thread

[johnwmclean]

Yes Identical bias for all 4 phases, I have it all out on the bench now and will test and probe to see what I can find. As well as implementing simmocon’s mod for 400V.

Edited March 29, 2022 by johnwmclean

[johnwmclean]

I dialled back the bias from 20mA to 17.2mA, installed a 562k resistor in parallel over one of the 175k resistors and achieved 24.8V bias voltage across the 20k resistor and Vce of the PZTA42 is 13.25V. Thanks to simmocon on this for the ground work for the 400V Carbon! The offsets on troubled board (after dialling down the bias) drift slowly down from around 5V. Still not sure why at 20mA bias I was getting no drift, I’ll leave that a mystery.

[audiostar]

Uff... Mouser delivered today only 4 from 6 backordered C2M1000170D, so I guess my Carbon boards are going to wait more months before first power on.  I even have the LSK389's stuffed in there.

Edited April 5, 2022 by audiostar

[Reima]

My custom r-core transformer from Custom Magnetics has arrived. It is the same one that Laowei used.

 

[audiostar]

On 4/10/2022 at 4:34 AM, Reima said:

My custom r-core transformer from Custom Magnetics has arrived. It is the same one that Laowei used.

Nice one. Any particular reason why you have chosen R-Core over Toroid? 

[Reima]

12 hours ago, audiostar said:

Nice one. Any particular reason why you have chosen R-Core over Toroid? 

From what I have read they are low noise, low flux leakage and high efficiency. I have never used a R-core before.

[audiostar]

1 hour ago, Reima said:

From what I have read they are low noise, low flux leakage and high efficiency. I have never used a R-core before.

With the R-core having primary and secondary windings on opposite legs, the capacitance is low, but the leakage inductance is high. Where the toroid has a high(er) capacitance, but lower leakage inductance. 

Now, because of the tight coupling between the windings, the toroid couples RFI.
But because of the low leakage inductance, it has a much lower external magnetic field. 

The R-Core is better for not coupling RFI between windings.
But the leakage inductance is much higher, so may cause hum problems. 

[audiostar]

Hi Kevin, in a Carbon GRLV with 15VDC output, can I get away with not bolting the MJW21193/MJW21194 pass transistors to anything? Don't have enough space on the bottom plate... or any flat, horizontal heatsinks I may use instead of bolting them to the bottom plate? @kevin gilmore

Or I can bolt them to the bottom plate, but left and right of the GRLV PCB by extending their leads for about 2-3cm...

Edited April 30, 2022 by audiostar

[mwl168]

Kevin can confirm but I am pretty sure you'll be fine - the current draw is very minimal like a few 10mA IIRC. Unless you are dropping some unusually high voltage through the GRLV there is not much heat to dissipate for the MJW21193/21194.  

[audiostar]

Thanks, Michael! 

Or something like this, but still on the edge of available space. Best would be mounted straight up on the PCB without heatsink.

Edited May 1, 2022 by audiostar

[mwl168]

I don't know what Martin thinks but Michael thinks freestanding on the PCB will be fine 😉

[audiostar]

2 hours ago, mwl168 said:

I don't know what Martin thinks but Michael thinks freestanding on the PCB will be fine 😉

That's what I wanted to say, Michael 🙂 Thanks for confirmation! 

[Kerry]

For the +/-15v supplies, the pad transistors do not need heat sinks. 

[Reima]

On 9/17/2020 at 10:47 PM, Pars said:

The BOM that was posted by jamesmking uses 4 x 470uf 550V Kemets. Is there much difference between the 680uf and 470uf in terms of sound or anything?

Did you ever get an answer to this question?

I am collecting parts to build a Carbon and have the choice between Kemet 680uF 500V and Kemet 560uF 550V. My transformer has 360VAC@350mA X 2 18VAC@200mA X 2. should I just use 4 x 560uF 500V capacitors?

[Pars]

I chose 2 x 680uf 500V and 2 x 470uf 550V Kemets for this. I hadn't looked at the 560uf / 550V and might have chosen a pair of those instead.

[Reima]

8 minutes ago, Pars said:

I chose 2 x 680uf 500V and 2 x 470uf 550V Kemets for this. I hadn't looked at the 560uf / 550V and might have chosen a pair of those instead.

Thanks.

[audiostar]

For the 400V Carbon, the input cap should be 550V rated and down to 450V is fine for the output cap. Other than that I am not sure if you will hear any difference between 560 and 680uF.

I have chosen four identical 680uF 550V FTCap/Mundorf caps.

PS: with 360VAC secondaries it looks like you are building a 450V Carbon where 500V caps are pretty much a nogo.

[Reima]

2 minutes ago, audiostar said:

For the 400V Carbon, the input cap should be 550V rated and down to 450V is fine for the output cap. Other than that I am not sure if you will hear any difference between 560 and 680uF.

I have chosen four identical 680uF 550V FTCap/Mundorf caps.

Unfortunately 680uF 550V caps are no longer available unless you buy them in large quantities.

[audiostar]

You could use 1) two caps in series or 2) just go to 400V PSU.

or

570VDC 560uF Vishay
https://www.mouser.at/ProductDetail/594-MAL219390125E3

Edited May 6, 2022 by audiostar

[Reima]

1 hour ago, audiostar said:

You could use 1) two caps in series or 2) just go to 400V PSU.

or

570VDC 560uF Vishay
https://www.mouser.at/ProductDetail/594-MAL219390125E3

The Mouser page says 570VDC but the data sheet says that it is rated for 500V. They are also out of stock in the US. I plan to get four of these Kemets:

https://www.mouser.com/ProductDetail/KEMET/ALA7DA561EF550?qs=IS%2B4QmGtzzosEBZF0Z4Lbg%3D%3D

[Pars]

Yeah, those should work as long as they are the same footprint as the others.

 

[Reima]

Anyone know where I can find the gerbers for the pcb for Alps RK50?

[audiostar]

7 hours ago, Reima said:

Anyone know where I can find the gerbers for the pcb for Alps RK50?

I have a couple PCBs left, PM if you need some.

[Reima]

Anyone tried these connectors (the black one): https://www.mouser.com/ProductDetail/571-7969495

[mwl168]

These are only rated for 300V so need to be mindful where they are used.