Explendid amplifier designed by Michael Bittner, our MikeB

[ulfheden]

I would suggest 10k pot (log).

Probably most of you have already seen this, but some might not.

There is an alternative way, using lin pots which have better precision/tracking than log pots.

This is a way to make lin pots behave log.
http://sound.westhost.com/project01.htm

 

[dexter]

mike,

Greetings again.

I'd changed the i/p tr (bc 550 to 2sk30).
The dc offset climbed into 279mV.

I put back in the input Tr bc 550.
Now i heard some faint whistling probably oscilation?
reduig the bias didn't help.

more questions,
I'm wondering
is it true that fet need to be carefully matched more so than bipolar ?

Can I use 2sk43 instead of 2sk170?

Thanks and best rgds,.

 

[hcbonfim]

symasym driven by a BZLS preamplifier

Hi MikeB , i am building a symasym v5.3 and i intend to use with
BZLS pre amplifier. The symasym gain is too high i guess. Is it ok to increase r30 from 500 ohms to 1k and insert
r16/r19 ? witch value 22r or 33r ?

best regards

hcbonfim

 

[MikeB]

Hi, yes, that's the way to half the gain. you might prefer 33r to be on the safe side.

 

[hcbonfim]

thanks for the repply MikeB ! I will do that to decrease the gain.

Best regards

hcbonfim

 

[Buzzy]

Can the symasym be used to power a 4 ohm subwoofer ?

 

[PhongVuTuan]

Too bad

My beloved symasym has passed away yesterday for rail short circuit leaving 2pair of sc2922-sa1216 dead bodies. It's so painful. I must have left a metal dust on the back of the power device. It did work for a year now, and one day, things break. what I found after the disaster were smoked devices, and a burn metal dust on the back of 2sa1216.
That's too bad.

 

[MikeB]

Sorry to hear that!

 

[PhongVuTuan]

re. 2sc2922 replacement

Hi Mike
I'm recovering my amp but I don't have the SC2922-Sa1216 now so I have to apply Sc5200-Sa1943. The amp is up and running now, but there's something not desirable. The sound is less detailed, the bass is not as powerful as the previous version. I think the sound resolution is lower. Can you tell me a way to make that better.

thanks,

 

[roender]

mje/mjw/njl 0302/0281

 

[MikeB]

Re: re. 2sc2922 replacement

Hi Mike
I'm recovering my amp but I don't have the SC2922-Sa1216 now so I have to apply Sc5200-Sa1943. The amp is up and running now, but there's something not desirable. The sound is less detailed, the bass is not as powerful as the previous version. I think the sound resolution is lower. Can you tell me a way to make that better.

thanks,

Have you verified that it is not oscillating? Are the sc5200/sa1943 genuine? Maybe more parts than the outputdevices were blown.

Mike

 

[PhongVuTuan]

Ya, I don't know if they are genuine but the devices sa1943-5200, I bought from digikey. There no harm to the pre-drive section. I think there must be some thing with the gain. I find out that I have to put 20% more on volume knob to get the desired sound level. There 's no trace of oscillation, not getting too hot, the bass is quite warm clear treble. The quiescent current of the power device is 80ma. but the bass is not powerful enough and the high mid (3khz) is somewhat blur in comparison with the earlier version.


I have tried to use 1 pair of 2sc2922- SA1216 for each channel. the sound is just right but I don't think they could withstand the load, as a result, I have to put 2pair of 2SC5200 per channel.

I have read in some posts about ring emitter device (2sc29322) with high gain, high bandwidth. Will it be the cause of this. Can you tell me some trick to make this better.

regards,

 

[bluevas]

Hi guys,

Can I use 2SC4029 and 2SA1553 as final output?

 

[AAK]

Hi PhongVuTuan

You'll need to drop C14 to less than 10pf to prevent oscillation when using 1943/5200. I had the same problem and so did Pavel. Here's his site.

http://web.telecom.cz/macura/symasym.html

Regards,

Al

 

[PhongVuTuan]

Hi,
I have finished my amp rebuild work, but I have found that, my sound system can not provide satisfied sound for my room.

Room: is about 50m2: 7.5m x 6.8m and 3.9 m height.
speakers: I use a pair floor stand speakers with 8 ohm (90W woofer; 80w mid range; 39w treble)

Amplifier: 2 channels symasym built with 50V rail supply with 2 pair of 2sc2921+sa1215 each.

my sound system provide good performance when the room is quiet, with the distance of 3.5m in front of the speakers.

when I have some guests, the sound is so bad, even when I push the amp to the limit.

can you give me some advices on how to improve my system. Can I make things better with another amp.
I have tried with a 100w commercial amp, and things are more disappointing.
thanks

 

[AndrewT]

either take out the ear plugs or get more efficient speakers.

 

[Nordic]

If it is not obviously clipping, maybe you can up the gain a little?

 

[PhongVuTuan]

Gain? I'm thinking of reduce the gain because, the amp always works with less than 1/4 turn of volume knob. The sound is so detailed, I can hear the sound that I could never hear before. the voice is clear and high, warm bass.

By the way, I want to ask. My system with symasym make the nearby glass door vibrate a lot when there' s a bass sound. especially sound of the double bass. the bass is poweful warm, distinguished and firm. (I have fixed the door). I think the current must be very high. Will that reduce the sound density in my room. If not, will some more big rectifier caps improve the situation

 

[Nordic]

sorry, I thought you were haveing low output due to sensitivity issues..

 

[AndrewT]

My system with symasym make the nearby glass door vibrate a lot when there' s a bass sound. especially sound of the double bass. the bass is poweful warm, distinguished and firm. (I have fixed the door). I think the current must be very high. Will that reduce the sound density in my room.

Hi,
try moving the speakers to a new location. Move them away from the corners, move them away from the walls, lift them off the floor. Try to get the distance from the driver to the floor/to the nearest wall/to the 2nd closest wall, all to be different.