Symasym 5.3 "AAK model" builder's thread - Page 62 - diyAudio
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Old 26th December 2007, 03:02 AM   #611
Ryssen is offline Ryssen  Sweden
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Location: Sweden--> Here
davidwang,I see you use the same teknik as I to mount the transistors,at least I did something right..

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I bought this Swedish made speakers (XTZ) as I have no other at the moment,I bought them used for about 300$.

Click the image to open in full size.

did some filter tweaking for the mid and high.

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First I used this cable,wich I donīt know the name of.

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The sound is pretty good open and detailed,then I tried this one,at least in Sweden itīs name is EKK,5 solid core leads with 2,5mm2 area each,it is used for electrical power (400v and more)some here in sweden use it and found it sounds good,

Click the image to open in full size.'

To my surprise it didnīt sound good at all!Less bass,less soundstage,not so pleasant treble.....
So I went shopping...

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EKU 2x0,5mm2 solidcore,used for telephones....also used by some here in sweden for speakerwire,AND this one sounds realy good!Maybee som slightly loss in lowbass,but this speakers aint no bassmonsters anyway.. I wish I had some other cables to compare them with..
Any ideas why the EKK didnīt work?I now some donīt belive in cabels "sounding"or if itīs sommething else changing with diffrent cables, is the feedback sensetive for this?

And this amp needs some better speakers to give its best..

And someday maybe.....

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Old 26th December 2007, 04:46 AM   #612
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loek

The symasym emitter resistors is 0.22R/5W. the emitter resistors is 3 Pin leg.
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Old 26th December 2007, 12:00 PM   #613
loek is offline loek  Netherlands
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Default 3 Pin leg

That is what i meant.
Not so easy to find overhere.
Thanks anyway, Loek
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Old 1st January 2008, 09:36 PM   #614
jims is offline jims  United States
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Default Help, Please

Before I start unsoldering and testing components:

One of my amps, I built recently, starting blowing fuses yesterday, always the negative side. I just was poking around and found that the speaker terminal reads 0.1 ohms to ground. Do you think I have a bad output transistor? Can you think of anything else that might be causing the problem?


Thanks

JimS
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Old 2nd January 2008, 01:25 AM   #615
jims is offline jims  United States
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Default part of the problem

The .1 ohm between speaker and ground was due to a piece of aluminum from drilling lodged between 2 speaker posts giving me the short. I am not sure if that was causing the fuse to blow...

JimS
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Old 2nd January 2008, 01:59 AM   #616
Sheldon is offline Sheldon  United States
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Default Re: part of the problem

Quote:
Originally posted by jims
The .1 ohm between speaker and ground was due to a piece of aluminum from drilling lodged between 2 speaker posts giving me the short. I am not sure if that was causing the fuse to blow...

JimS
If the fuses don't blow when you try to drive a 0.1 Ohm load, then there is no point in having them. So, yes it will certainly cause any properly selected fuse to blow.

Sheldon
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Old 2nd January 2008, 09:21 AM   #617
AndrewT is online now AndrewT  Scotland
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Default Re: part of the problem

Quote:
Originally posted by jims
The .1 ohm between speaker and ground was due to a piece of aluminum from drilling lodged between 2 speaker posts giving me the short. I am not sure if that was causing the fuse to blow...
yes, the fuse should blow, but unfortunately the semiconductors can blow even quicker.
You may have permanently damaged the circuit.
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Old 2nd January 2008, 10:25 AM   #618
jims is offline jims  United States
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Thanks

Is there anyway to test the transistors on the board? Assuming that my fuse does not blow when I start it up now that I have removed the short on the speaker terminals, will a good bias reading on the output transistors indicate that everything is OK?


JimS
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Old 2nd January 2008, 10:34 AM   #619
AndrewT is online now AndrewT  Scotland
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Hi,
two sets of measurements should confirm if all is OK.
1. measure the output offset with the input shorted to signal ground.
2. measure the bias current (voltage) in each of the driver and output emitter resistors.
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Old 2nd January 2008, 01:01 PM   #620
jims is offline jims  United States
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Default time to rebuild

I think I will rethink and rebuild. The problems stem from me trying to be clever and mount U3, U4 and the BD139 on to a single piece of aluminum, which is then mounted to the heat sink. This way I could keep the BD139 close to the board and still keep the temperature relatively equal between the 3 transistors. Good idea, but the problem has been that my BD139 ends up shorting to the aluminum regardless if I use mica or a silpad. I think that the holes on the silpad and mica are too large, and the shoulder washers do not fit into the hole in the bd139. Plus it is a PTA to mount. I think once things start to heat up either the screw or the aluminum contacts the back of the BD139. I can not find shoulder washers or pads that fit the onsemi BD139 perfectly.

Given that I just blew the fuse again with some smoke and I have dark solder on the center post of the bd139, I think I will change out my transistors and put the BD139 where everyone else mounts it.

The good news is that when things were working the amp sounds great. I have to keep that in mind as I start to remove the transistors.

thanks for your help

JimS
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