Symasym 5.3 "AAK model" builder's thread

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#523
Hi Ryssen,
MikeB's was with the original control, it can be scaled to be more benign.

I am sure the bias circuit values can be reworked to give a reasonable range so that it is not as touchy. I may have to make small boards to fit a control and whatever changes need to be made.

-Chris
 
#525
Hi Ryssen,
I have not even started on these yet. It may be a while also, so I am not familiar with them. If they are anything at all like the SymAsym 5.3, they should sound amazing.

Those boards you had made are very nice. Thank you for making them available to the community.

-Chris
 
#526
anatech,

If you use about 240 ohms for R24 using my BOM, that's a Vbe multiplier range of about 3 to 4.5 which is narrow enough to provide adequate control over the bias even with a 270 deg. pot. But, I still think you should use the multiturns. 😉

Al
 
#527
Hi Al,
I'm on a mission! 😉 No multi turn parts for me. I've beat that horse to death.

I will be building several versions. One board will be close to stock while the other pairs have changes made. In this way I can compare. I will build closely to Mike's so that I can compare his to yours.

So, one pair stocko, the other two for changes. Once I'm done, they will all be changed to whatever works the best.

-Chris
 
#531
HELP! revisited

Colescuttle said:


The thing that first tipped me off that something was wrong was a big imbalance between channels that had not been there previously. With the passive 20K shunt attenuators set at the same level (the attenuators are wired directly to the board with 3" leads; no pre-amp), the right channel was so far down in volume that the "central" image floated only about 6" or so from the left speaker. I couldn't detect any noteworthy distortion from the right channel, just a reduction in volume that I could almost compensate for by cranking the right volume control to maximum. I then tried switching interconnects at the DSP. I got the same result, and while doing so I noticed a large, sharp turn-on thump from the right speaker (dead silence from the left) followed by a more gradual DC surge (over the course of a couple of seconds or so the cone moved as far forward as the surround allowed and then retreated).

The bias on the funky amp checks out OK, but on rechecking the DC offset I find an off-the-scale initial rise (something above 150mV) followed by a return to the 6mV I measured on both boards initially.

I'll reflow the joints as Chris suggested. If that doesn't correct the problem, what should I look for next? These amps sound so good when they're right I can't stand that they're wrong.

George
Click to expand...


MikeB said:
You might have a problem with grounding at the input?
Click to expand...


anatech said:
Hi Mike,
Good thought. The signal ground might now be intermittently floating. Yuk!

-Chris
Click to expand...


I stayed up most of the night working on this thing (couldn't sleep anyway, as I have an awful ear infection), and every joint from from the RCA to the speaker post has been reflowed and cleaned.

The amp is still malfunctioning in the exact same manor. What are the two next most likely things wrong, and what should I do next?

BTW, thanks for your help with this. Without rebuilding the amp I couldn't get this thing working without you.

George
 
#533
Thanks, Chris.

I was wondering if a DC-blocking capacitor is at fault. If the C14 cap can affect both DC and gain I wouldn't be at all surprised if that's it.

Believe it or not, with all those parts left over I don't have another 5pF silver mica cap and will have to order one. Any other suspects? If I need to order or hold back other parts from the spares I've already sold to Al, Ed and Donovan I'd like to do it right away and at least get the parts shipped.

George
 
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