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Posted

If anyone wants to do a board run of the carbon I would be interested.

 

I don't know who many working carbons are around at the time, but is there anyone who can comment on their strength and weakness compared to our other amps?

Posted

Mine are ready for testing but other stuff has taken over for a while.  Might even be pushed back further for the new Megatron PCB. 

 

As for SMD, if you want resistors that are equal to the RN60D's then they are 1$ each or even more.  SMD was never designed for HV in mind... 

Posted

no difference between the 2sc parts and the pzta or mpsw or mpsa parts

 

1486 does not need heatsinking.  About 188mw

Great, thanks. Just need to check the pin-outs on the parts - hopefully not much twisting will be needed.

Posted

I have Carbon boards as well, but unlikely to have time to do anything with them for at least a couple of months. Even if they are not the newest version I assume they are OK to use?

 

//UFN

Posted (edited)

Just checking the board/schematic around the servo.  Looks good.

 

You can change the label for PZTA28 to PZTA06 (same pin out) or some other NPN.  Keeping the MJF15030 part is a good idea.

 

Also, the 5K pot should probably go down to a 1K (or 2K) POT and also change the 20K to a 24K (TBD) resistor.  Varying by 400 ohms moves the output about 6 - 8 volts.  It's just a matter of making it have enough range, but not being too sensitive.

 

The last thing is that I currently have 2pF caps across both legs of the 2 x 1M resistors on the KGST build.  I'm not sure if this helps or hurts.  I'll try pulling them out this weekend.  I'm hoping the 220pF cap can manage any possible oscillation.

 

I'll confirm the rest of the board then built the LTSpice model next.

Edited by Kerry
Posted

I was also justing looking at the new board and wondered if the lm4040-10 sot package couldn't be replaced by a to92 to make it easier.

 

Furthermore could someone elaborate on the advantages of the new servo? I am really interested in that.

Posted (edited)

certainly can replace the reference with a to92, current datasheet does not list the pinouts.

 

I did trim the emitter resistors to 25 ohms, so there is still about 9v on the servo.

 

But will change values to the final parts when we all decide what those are.

 

also added a pot in series with the 20k resistor to adjust the dc to exactly zero.

 

the 25 ohms decreases the thd a significant amount at 20khz because of the

added gain.

 

let me know which parts and values to change.

Edited by kevin gilmore

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