SymAsym - "The Sequel", AAK's PCB Builders Thread

Status
Not open for further replies.
Hi Andrew,

I updated the PCB with an extra pad for C7 and C8 with a 10mm spacing. I didn't think it would be such a problem.

Your idea would work fine, but be careful not to drill through the top side trace that connects to ground. The trace comes pretty close to where the drill hole would need to be for a 10mm spacing.

Regards

Al
 
Hi Aidan,

Great to hear the boards and parts arrived.

You should match Q22 with Q23, and Q24 and Q25 to closely distribute the power between each pair. I've not tried using an unmatched pair so I can't say for sure how well it would work. You can also use a single pair until you find a matched pair.

Regards,

Al
 
Hi All

I've added testing procedures to the attached assembly instructions document found in post #1.

Remember if your using the 2SK170s for Q1&Q2 to insert them in the opposite direction then how it's labeled on the board. The flat side of Jfets Q1&Q2 should face inward towards the large PS caps.

I've added a couple pics that should help with the testing.

Regards,

Al
 

Attachments

  • CIMG1238.JPG
    CIMG1238.JPG
    283.2 KB · Views: 1,057
  • CIMG1250.JPG
    CIMG1250.JPG
    321.3 KB · Views: 1,011
  • Assembly_Instr.pdf
    Assembly_Instr.pdf
    16.5 KB · Views: 359
Marc,

Here's a picture of zener diode Zd3 illustrating the correct orientation. For Zd1, and Zd2 follow the labeling on the board. For LEDs L1-L5 insert the longer of the two leads which is the anode into the pad with the circle labeled around it. Look at the parts placement diagram in post #27, you should clearly the see the circle labeled around the pad for L1-L5.

Al
 

Attachments

  • Zd3.jpg
    Zd3.jpg
    82.1 KB · Views: 849
Substitute for L3, L4 & L5

Al,

I have almost done with the transistors matching. I checked my parts bin & found that I don't have enough green LEDs. I do have a bunch of 3mm Red LED (standard low-mcd type), their forward voltage drop are very similar to the green LEDs that I have - around 2.02V.

Is the LED type critical for the SymAsym? Can I use standard Red LED for L3, L4 & L5?

- Stanley
 
Hi Stanley,

The Red LEDs for L3,L4,L5 with a Vf = 2.02 will work but you will have to readjust R19 to drop the LTP current. According to my simulations using the Red LEDs with a Vf = 2.02v compared to the green LEDs with a Vf = 1.8v will increase the LTP current resulting in about 2.3ma across R23, and R24 which is way to high and will cause Q7,Q8,Q9,Q12, and Q21 to overheat drawing over 300mw of power each.

So here's what I suggest you do, for R19 replace the 261-ohm resistor with about a 320-ohm resistor. Then verify the current by measuring the voltage across R23 and dividing that value by 681. This should drop the current across R23, and R24 to about 1.65 to 1.75ma dropping the power draw across the SST to about 200mw. If it's off try some different resistor values until you get it within range.

Let me know how it goes.

Regards,

Al
 
Hi Ed,

The MUR820 is cutting it pretty close, especially if your using 50V rails. If you do use them try not to do any heavy testing at high outputs levels into a resistive load. For music it should be fine as long you don't blast the amps for long periods. For casual listening no problem.

I've tested the MJW1302A/MJW3281A, they worked fine.

Regards,

Al
 
Last edited:
Status
Not open for further replies.