Symasym 5.3 "AAK model" builder's thread - Page 3 - diyAudio
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Old 28th April 2007, 01:41 PM   #21
AAK is offline AAK  United States
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Here's the BOM again without some many blank pages.
Attached Files
File Type: pdf symasym_aaks_pcb_bom.pdf (15.0 KB, 374 views)
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Old 28th April 2007, 02:40 PM   #22
AAK is offline AAK  United States
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Hi MBK.

The only thing that I'd like to add to post # 13 has to do with L//R on the output. It's there to keep the amplifier from oscillating when driving a capacitive load, which could result from using long speaker cables or even the load itself. My amp works fine without it.

But if it does become an issue the best place to put it on my PCB version is between the amplifiers output terminal and your speaker output connector. It can also be installed under the board by cutting the trace that goes to the output terminal and putting it between the two.

Here are the Instructions from MikeB's site on how to build the output L//R listed as L1 and R7 in his schematic.

Around R7 is wounded a 0.6mm isolated (enamelled) copper wire forming the output coil. (~12 windings)

http://www.lf-pro.net/mbittner/Sym5_...ymasym5_3.html

Al
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Old 28th April 2007, 03:07 PM   #23
MBK is offline MBK  Singapore
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Hi Al,

thanks again. Just for completeness sake, I take it that IGND and AGND are not separate, thus no R2.
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Old 28th April 2007, 03:40 PM   #24
EUVL is offline EUVL  Europe
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> Post #8
> Cascoded input stage..

If you are prepared to add a Zener, then I would suggest using MOSFETs for the cascode instead (e.g. ZVN3310A). Amongst others, it can take much higher voltage.

> Simpler..

You will find that most 2SK246s would not give you much more than -2V Vgs at 2mA, and the 2SK170s ideally would like to see at least 5V, preferrably >7V Vds. I suggest you try J111 instead. But then this does not solve your voltage problem (see above).


Patrick
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Old 28th April 2007, 04:01 PM   #25
AAK is offline AAK  United States
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That's right. No R2.
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Old 28th April 2007, 07:04 PM   #26
Ryssen is offline Ryssen  Sweden
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Quote:
Are the heatsinks from Conrad?
Yes.

Quote:
For my version of Symasym you'll need two transformers
Isn´t possible to parallel the input to the rectifiers?(the AC side)
Otherwise I´ll have to buy another one.
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Old 29th April 2007, 02:25 AM   #27
AAK is offline AAK  United States
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Hi Ryssen,

No, I wouldn't recommend that. The amps will most likely develop a really nasty AC hum because they'll be sharing a common ground. Your better off buying a second transformer.

Al
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Old 29th April 2007, 02:58 AM   #28
MBK is offline MBK  Singapore
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You mean, you can't run several rectifiers off a single transformer's AC side? (just for the record. It's not aproblem for myself, I'll be using a central outboard rectifier beacause I already have it set up this way for existing amps).
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Old 29th April 2007, 03:34 AM   #29
AAK is offline AAK  United States
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If you had success doing that way then give it try. See what happens.
You'll then have to bypass D3 and connect your outboard rectified positive rail to the terminal nearest D3, and bypass D1 for the negative rail. Ground would be connected to the center terminal.
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Old 29th April 2007, 04:53 AM   #30
MBK is offline MBK  Singapore
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OK. What I am doing now is having a central rectifier and large smoothing caps, then going to a pair of chip amps with mid size (220uF) bypass close to the chip. No ground hum or such, but I was very careful with the grounding logic. Only problem is the long wire runs (several inches) due to point to point wiring, which I "conceptually" don't like, although there is no obvious problem. But, without oscilloscope, I have no means of testing whether some minor oscillations might have sneaked in.
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