My new SymAsym PCB design Rev_1.3

[lgreen]

When?

Here's the dual pair OT version in an enclosure using two transformers, one for each channel.

I'd actually like to make this version (posts #32 and #34) as I would like a higher powered variant. Not to hijack the thread; but this in my view would be more popular. When do you think the boards /parts for dual output transistor version will be available?

 

[AAK]

Hi Igreen,

I agree the DTV is the way to go. I'm still working on some of the fine details like the silk and BOM. Luckily for the BOM I was able to find all the parts to complete the amplifier at Mouser, but I did have to modify the PS on the PCB to accommodate the slightly larger United Chemi caps. The UC's are about $1.75 cheaper a piece at Mouser than the Panasonics from Digikey so it was worth the trouble.

I'll be checking on line and making some phone calls to get some PCB quotes today.

At the moment for the group buy I have a count six boards. It would be nice to get up to about 50 boards to get the price down.

Regards,

Al

 

[nigelwright7557]

Here's a pic of the PCB layout, THD plot at 150watt/4ohms, and the prototype boards.

Why the long tracks from c1 and c2 to the ground plane ?

 

[AndrewT]

good question.
Long tracks equals added inductance. the R+C becomes R+C+L across the output leads.

 

[AAK]

Hi nigelwright7557,

I just wanted the ground side of C1 and C2 to be as close as possible to the PS main ground labeled GND on the board. The trace length including the 45 degree turn is slightly less than 2 inches. I don't think inductance should be an issue.

Regards,

Al

 

[AndrewT]

that sounds like an excellent reason for moving the R+C to where it is needed.

 

[sng001]

I also added two full wave rectifier circuits before the PS caps on each edge of the board for those that would like to add a speaker protection or soft start circuit using the main transformer.

Al,

Pls correct me if I am wrong. I suspected that the polarity of the diode D7 and D8 should be reversed on both the schematics on the post #38 and the PCB layout on post #3.

- Stanley

 

[AAK]

Hi Stanley,

The polarity of D7 and D8 is correct on the board and the schematic. I put these rectifiers on each side of the board for easy access regardless of which side the amplifiers is on. But you can rotate diodes D5,D6 or D7,D8 180 degrees if you have peripheral device that requires a negative voltage.

Regards,

Al

 

[AndrewT]

it's the label V- that causes confusion.

 

[AAK]

Thanks Andrew for pointing it out. I've made the correction on the new DTV board.

Regards,

Al

 

[sng001]

Will this amp with with 52V rail

Hi Stanley,

The polarity of D7 and D8 is correct on the board and the schematic. I put these rectifiers on each side of the board for easy access regardless of which side the amplifiers is on. But you can rotate diodes D5,D6 or D7,D8 180 degrees if you have peripheral device that requires a negative voltage.

Regards,

Al

Thanks Al for the clarification.

I have a couple of 37.5V (160VA) toroids, that will give +/- 52V. The new amp will drive a pair of 8-ohm speakers. Do I need to change some resistors value and/or output devices?

Regards,
Stanley

 

[sng001]

Thanks Hugh, I really appreciate it.

BTW, I was wondering with your expertise if you have any ideas as to why the 2nd harmonic output in my design is less the input? You can find the THD plots in post #31.

Regards,

Al

Al,

I am a newbie to diyA. I just read the beginning of the related thread: http://www.diyaudio.com/forums/solid-state/87609-symasym-sequel-2.html

I don't know how much your design has evolved since October 2006, post #15 & #17 in the "Symasym - the sequel " thread may answer your question with regards to 2nd harmonic.

Regards, Stanley

 

[AAK]

Hi Stanley,

No you shouldn't have to change anything. But keep an I on the rails to make sure they stay at +/-55V or less. The 160VA for 100watt amp is little small but unless your planning to use them in a disco tech you should be fine.

As far as the 2nd harmonic, I don't think it's the cascoded VAS becaues I see the same thing in my original design.

Regards,

Al

 

[sng001]

Hi Stanley,

No you shouldn't have to change anything. But keep an I on the rails to make sure they stay at +/-55V or less. The 160VA for 100watt amp is little small but unless your planning to use them in a disco tech you should be fine.

Al,

I agree that 160VA is a bit small. I bought the transformers some time ago with the intention to build two mono-blocks. I like your layout with the on-board PSU as the wiring is so neat with one transformer per channel (post #32).

Best regards, Stanley

 

[alibear]

Hi everyone, I appologise if this is slightly off thread but can anyone help me. I am building the symasym 5.3 and I want to change the input transistors from MPSA18 to 2SK170, my question is does collector = drain
emiter = source
base = gate.
I think the pinout is different between the two as well.
Thanks for your help
Alan

 

[AAK]

Hi Alan,

You have it right.

Collector = Drain
Base = Gate
Emitter = Source

The pin outs are different but all you have to do is rotate the 2sk170 180 degrees compared to the MPSA18 so that flat side of transistor is pointing in the opposite direction.

Regards,

Al

 

[AAK]

Hi All

Here's the BOM for the DTV version. I still have to find a heatsink suitable for the drivers from Mouser. You'll need them if you don't mount the drivers to main heatsink.

Al

 

[sng001]

Hi All

Here's the BOM for the DTV version. I still have to find a heatsink suitable for the drivers from Mouser. You'll need them if you don't mount the drivers to main heatsink.

Al

Al,

I found the following heatsink from mouser:

532-577002B00
19.05 mm L x 13.208 mm W x 6.35 mm H

It look like that may fit.


Best regards, Stanley

 

[sng001]

If you would like to use external PS (illustrated in post#34) the on-board capacitors will provide 9400uf of extra AC filtering per rail. You can even use a 0.1ohm or 0.2ohm resistor in place of one of the rectifiers on each rail to provide some additional filtering.

I’ve attached a schematic to illustrate how to configure the on-board PS when using an external PS.

Regards,

Al

For those of you who go for the external PS, you may consider the following 5W resistor to replace a TO220 rectifier:

Mouser part#280-PRM5-0.22-RC

The lead spacing is 5mm.

- Stanley

 

[AAK]

Hi Stanley,

The price quote is for the DTV with four capacitors for the PS on-board.

Part number 532-577002B00 looks right on; I'll add it to the BOM. I really appreciate the help.

Regards,

Al