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Old 27th July 2012, 01:24 PM   #1
srmoska is offline srmoska  Mexico
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Default Fisher CA-39 trashing speakers in the right channel

Hello guys,

I have a Fisher CA-39 Integrated Stereo Amplifier, a firend gave it to me becasue it was damaged, the left channel wasn't working. It originally had a STK4191II amp, but it was damaged and the fuses were missing.

I replaced the Amp it with a STK4192II, it has the same pins (18 pins) and it has the same Specs (Stereo 2x50 watts), some people says that the 4192 just distorts a bit and that the 4191 sounds cleaner.

After changing the amps and replacing the fuses (4 Amp like indicated in the PCB) the Amp is working again, both channels are working, to be honest I'm using 8 ohm/3 watt speakers right now, because i don't have the original speakers. and the amp has messed up 2 speakers, both on the right side.

My friend will give me the original speakers but i'm affraid of busting them if there's soemthing wrong with my amp. Also is there a prob if I use 4ohm speakers? My STK is "OEM" so I'm pretty sure its a Fake one (they offered me both the SAnyo and the Generic one when i bought it)
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Old 27th July 2012, 02:52 PM   #2
johnr66 is offline johnr66  United States
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Okay, so what is the question? Are you saying it blew the speakers after replacing or beforehand. It is probably fine if no damage and sounds good to your ears after fixing.
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Old 27th July 2012, 02:59 PM   #3
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Test for DC across the output terminals.

If it is close to zero (ie less than 10mV) then it is probably fine.
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Old 27th July 2012, 03:00 PM   #4
srmoska is offline srmoska  Mexico
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After replacing the STK, I'm using 3 watt speakers to test it, it sounded fine, but I noticed the right channle started to distort, then after some troubleshooting I noticed its the speaker that is damaged, it has happened to me two times and it was in the same channel with tho different speakers.

I want to know if it is normal because i'm using very small speakers or it is because there's something wrong. Also the amp gets very hot after being on for a while, I was told it is normal but I don't have a referene to tell if its normal or it is getting overloaded
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Old 27th July 2012, 03:01 PM   #5
srmoska is offline srmoska  Mexico
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Quote:
Originally Posted by KatieandDad View Post
Test for DC across the output terminals.

If it is close to zero (ie less than 10mV) then it is probably fine.
I get around 55mV DC on the left channel and 42mV DC on the right channel

Last edited by srmoska; 27th July 2012 at 03:12 PM. Reason: missing info
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Old 27th July 2012, 07:14 PM   #6
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by srmoska View Post
I get around 55mV DC on the left channel and 42mV DC on the right channel
That sounds OK for the STK modules.

Even 100mv was considered acceptable some years ago although nowadays designers try to aim for lower.

The heat is probably normal too (I'm trying to think back as we serviced countless STK based music centres in the 90's). The STK modules were a common failure item across the board.

As long as the supply voltages are OK (correct voltage selector setting if it has one) and the STK has some fresh thermal paste applied you should be fine.
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Old 27th July 2012, 07:19 PM   #7
srmoska is offline srmoska  Mexico
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Quote:
Originally Posted by Mooly View Post
That sounds OK for the STK modules.

Even 100mv was considered acceptable some years ago although nowadays designers try to aim for lower.

The heat is probably normal too (I'm trying to think back as we serviced countless STK based music centres in the 90's). The STK modules were a common failure item across the board.

As long as the supply voltages are OK (correct voltage selector setting if it has one) and the STK has some fresh thermal paste applied you should be fine.
So the speakers that got busted in the right channel it's because i'm using very small speakers?

The STK has fresh silicone thermal paste
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Old 28th July 2012, 07:07 AM   #8
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by srmoska View Post
So the speakers that got busted in the right channel it's because i'm using very small speakers?

The STK has fresh silicone thermal paste
Impossible to say...

If the STK module has failed and was outputting DC across the speaker then that would damage the speaker in seconds.

The STK may have just failed naturally with no obvious cause, or failed through overdriving (and so overheating) or through something like a short on the speaker output.

Overdriving a small speaker will damage it eventually. If the coil develops shorted turns through the excess heat then that is like a short (or near short) on the amplifier output and so could again cause failure of the STK.
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Old 28th July 2012, 02:16 PM   #9
srmoska is offline srmoska  Mexico
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Well, thge first time I busted a speaker a fuse blew up (that time I went the speaker was starting to distort so I started to turn up the volumen and I got as far as 9 of 10 in the volume knob), I changed both the stk and the fuse just to be sure, and the "new" speaker started sounding weird again so I wrote this post.

Las night I got the speakers made for this amp (Fisher DS-810) I have a volume of 1 and it sounds like a level 3 with the small Speakers

I'll be testing them today, It has been on for an hour and I feel like the amp temp is lower. With any other speaker the resistance next to the amp got really hot in seconds. Let's see what happens and thanks for the replys
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