Explendid amplifier designed by Michael Bittner, our MikeB

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#3,464
I was listening to my favorite music "The Best of Elvis Presley" with my Symasyms and I found that the one made with 2sc 2922 in the output have the deeper and nice bass compared with one with 2SC5200.

The amp with 2SC5200 is quite powerful, It makes the speaker move up and down a lot, but the bass is not warm and thick enough. I think there 's smt vibraton in the sound was missing.

If you have a clue pls tell me. I'm eagle to have the answer to this.

Regards,
 
#3,465
Spirtos said:
Hi,
better export the files in more common formats like jpeg or bitmap, otherwise anyone who likes to see them must have protel s/w .

Regards😉
Click to expand...

For schematics and other images with sharp edges and uniformly colored areas, GIF is a much better option for a given file size.

JPGs do work but they have to be much bigger (read low compression) than GIFs to avoid fuzzy areas close to edges.

JPGs are of course better than GIFs for photos.

/Peter
 
#3,468
Sorry for my bad english, n my bad question. i am newbie

I have finished to build Symasym 5.3, but i have several question

1. why the bias ( V at 0R22) voltage always changes. If the first time turning on, the bias about 8mV. but if the heatsink go to warm, the bias about 14mV. its normal?

2. I try to separated the heatsink of MJE n TOSHIBA (as like as AAK version) but the temperature of MJE about 60 degree celcius. is it normal to? (the heatsink on MJE in my amp is little bigger than I see in AAK model)

3. I used input voltage at 30.6V. should I change the bias? or just same as the normal voltage (12mV)?

Thanks
 
#3,469
idle current

If your idle current stay stable at that value then (14mv measured across output Emiter resistor), you have no point to change a thing, just adjust the idle current to your desired value. Remember you will adjust only when the amp thermal is stable. If stable stage is not reached, try to find out if smt wrong with the servo bias.
 
#3,470
crt said:
Sorry for my bad english, n my bad question. i am newbie

I have finished to build Symasym 5.3, but i have several question

1. why the bias ( V at 0R22) voltage always changes. If the first time turning on, the bias about 8mV. but if the heatsink go to warm, the bias about 14mV. its normal?

2. I try to separated the heatsink of MJE n TOSHIBA (as like as AAK version) but the temperature of MJE about 60 degree celcius. is it normal to? (the heatsink on MJE in my amp is little bigger than I see in AAK model)

3. I used input voltage at 30.6V. should I change the bias? or just same as the normal voltage (12mV)?

Thanks
Click to expand...

Please put the drivers on the same heatsink with output transistors. It will fix the bias.

Mihai
 
#3,471
sorry for my very bad english

BD139 is mounted on same heatsink of toshiba transistor.

In my amp, the bias is going stable when the "BIG" heatsink go warm, about 12-13mV. and keep stable when heatsink going to HOT mode.

I have another question.
-Can I change the resistor value?
10r to 8r2
33r to 30r2
47r to 50r
220r to 229
150r to 160r
500r to 2*1100r parallel.
and the other resistor, but the value is near.
is it making trouble to symasym?
because is hard to find good resistor value near then original value in my town.javascript:smilie('🙁')

Thanks.
🙁 🙁
 
#3,476
I had a check on feedback compensation cap (47pF). This have to be adjust according to the type of transistors I'm using. For this amp, oscillation occurs when I use 68 pF. I decided to use 47pF then reduced to 33pf to keep the amp's sound bright enough. Without this cap, the sound is somewhat dull and lack of liveliness.
 
#3,477
If the sound is somewhat dull and lack of liveliness, the amp is oscillating. This single feedbackcap is not enough for compensation, its just a "helper". The original 330pf and 100pf around the vas where the main compensation. I am sure your amp is very undercompensated an might even be the source for your dc-offset.
There is no reason why the amp should put out 100mv dc-offset.

Mike
 
#3,478
Hi Mike, could you give me some steps to take to make my amp better in that way, it might me up to some oscillations. If I can eliminate this problems, my amp could be better.
Now first could you show me some more traces of oscillation: burn, high buzz, increase quiescent current . . .
How will I know about this.

thanks,
 
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