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TO-3 SYMASYM

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#1,181
Rotundo: nice job.

You have already cut the PCBs!
If you are planning to do a dual-mono build: use one 4x25VAC transformer or two 2x25VAC transformers and use both PSU PCBs.
If you are planning a standard-SYMASYM-build: use one 2x25VAC transformer and one PSU PCB and power both SYMASYM-channels from this one PSU.

Can you please give me by PM your EMail-address?
I will then send you the Builder's Manual.

Best regards - Rudi
 
#1,182
Today i've tested one channel of Symasym. I was able to adjust very nice the current thru power transistors but i am i bit confused about one thing. Tried to test the thermal compensation heating up the heatsink with hairdryer but the current is increasing with temp is not compensating like in FC100. After i stopped the forced heating up the current started decreasing to the adjusted level. Is that behaviour normal ? I'm using a BD139-10 made by St Micro for temp comp.
I measured between 0.5-2mV Dc output
 
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#1,183
Rudi_Ratlos said:
You have done a good job so far, Adrian, allthough I would have preferred to use MPC74 as output-emitter-resistors 🙄.
Go on with your build, and you will happily listen to a very good (one of the best-sounding) DIY-amplifiier.

Regards - Rudi
Click to expand...
Rudi - Forgive my ignorance, but what is the significance of using the MPC74 style .22 ohm resistor as the emitter-resistors over, say a regular round style resistor. You had sent me 8, but I will need 8 more for my other channel. Doing a quick look on Mouser, I could not find that style using the MPC74 designation. I will keep looking and try and cross-reference with Reichelt.

I also assume that at .22 Ohm there's a reason for such a small resistance. However, when I measured the 8 you sent me - with a reasonably decent DMM, all of them were reading .5 ohm or higher. That's more than double the .22 Ohm spec'd requirement. Will they work as directed, or should I look for some that are within much closer tolerance than 100%!

Also, do you have a full-size schematic (8.5 x 11) as a separate document or image you could upload? The one shown and printed in the build guide is barely readable when I print it out.

I'm starting to populate the PCBs.

Thx, Rick
 
#1,187
Rudi_Ratlos said:
Rick, I have attached the SYMASYM-schematics as a .pdf-file.
Best regards - Rudi

P.S.: Capacitor C4 needs to be rotated by 180°.
Click to expand...
Thanks so much for the schematic. I did note that capacitor needs to be rotated. You had mentioned it in an email.

BTW, where did you source those MPC74 0R22/5w resistors? I don't need anymore for this build, but would like to have some on hand. I can't find those specific ones on Reichelt, Mouser, or Farnell. 😱

Rick
 
#1,194
Adrian, I agree to your judgement of the 2SK170BL as frontend differential pair.

I do not agree to what you say about bypassing the CAP-multiplier.

This is why I have not added the option to simply bypass the onboard cap-multiplier and use the backend-rail-voltages for the frontend in the "Black-Beauty - SYMASYM" layout.
Leaving jumpers JP1 and JP2 open on the BB-SYMASYM PCB gives you the option to feed the frontend by an external power-supply through the 3-pole connector on the left side.

Best regards - Rudi
 
#1,197
redjr said:
Thanks so much for the schematic. I did note that capacitor needs to be rotated. You had mentioned it in an email.

BTW, where did you source those MPC74 0R22/5w resistors? I don't need anymore for this build, but would like to have some on hand. I can't find those specific ones on Reichelt, Mouser, or Farnell. 😱

Rick
Click to expand...
Bump...

I'm still looking for ANY 0R22 (.22 Ohm) wire wound resistor rated at 2 watts. These things are rarer than hen's teeth 🙂 Seriously, anyone have a source in the USA? I need 8 pieces. Even eBay didn't turn up anything. Do they need to wire wound, or will metal film work?

Thanks, Rick
 
#1,200
I just use 1r0, 600mW, 1%, 100ppm, metal film in parallel combinations, rather than stock lots of low value, high wattage Re types.

2off 1r0 = 0r5, 1.2W
3off 1r0 = 0r33, 1.8W
4off 1r0 = 0r25, 2.4W
5off 1r0 = 0r2, 3W
6off 1r0 = 0r17, 3.6W
and all are <1% tolerance with 100ppm tempco.
If higher dissipation is required for 0r5, I would use series/parallel combination.
 
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