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Old 04-22-2017, 11:21 PM   #1
Wachu

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Autotek 99 - Bought for penny, strange repair

Hi guys. At first i must admit that English is not my native language. I know its not at good level, but i hope you can understand what i mean.


I recently bought an Autotek 99 car amplifier, made by Zed Audio 1994.
(The PCB board tell us its Revision C which i cant find on google image)

It cost me 25$. I saw that couple of them was sold on this forum for 100$+, so i thought it was a good price. Seller told me that he is not first owner and he dont know if the amp was repaired, but its fully working. I bought it without asking for photos of inside, just to not waste time (someone else may take it in any moment)


I connected an amp when it arrives. both of two channels works identically, there is no crappy sound or distortions (i only tried to playin at 2/10 of volume, but i hope thats enought to say its working correctly)


When i opened it i did sad face, because it was repaired by someone.

i removed the IMG tags because photos are too big

http://i.imgur.com/nNvoD2Y.jpg

1. Somebody added a capacitor (Nichicon 3300uF 35v). It's probably connected between B+ (12v) input signal and this small black diode.

2. The coil is also smeared with silicon (maybe to reduce the noise of coil?)

3. Im not 100% sure, but also some of the left side transistors looks like they was resoldered (i cant look closer, cause i dont know how to remove those black clips between the transistors and metal. They are very strong and i won't to break anything.)

Questions:
  • Can you explain what somebody wanted to achieve by adding this one more capacitor?
  • Transistors looks like resoldered.. Is there chance that somebody inserted a fake's transistors? If yes, does it means that amp is worthless?
  • I have a chance to replace this Autotek for used Boston Acoustics GTA802, fully working in a good condition. Shall i do it? Im looking for strong mono/2channel amp for my rockford fosgate sub. Which of those two will be better?
  • Also, shouldnt the input level potentiometer act like regular volume control?
  • I mean if i connect this amp in home (i dont have my car audio completed yet), to the PC using 2x cinch > jack cable, even if the input level on amp is at minimum and the windows control is at 20/100 it sounds loud. If i set a input level higher volume get increased by little, so the potentiometer by self is working.

If you need additional informations or photos, just tell me. I would really appreciate your help. I'm starting my journey with Car Audio.

More photos:
http://i.imgur.com/KtJdAVV.jpg
http://i.imgur.com/6FYuZF1.jpg
http://i.imgur.com/LpNTI1T.jpg
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Old 04-25-2017, 09:11 PM   #2
Jimi77

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1) The cap may have been added in a revision. Not sure why, but I've seen work like that in other amps where the manufacture needed to modify the circuit, but wasn't going to print a new batch of circuit boards.

2) The solder job may have been to fix cold solder joints or transistors may have been replaced. It's hard to say if they used "OEM" transistors or an inexpensive knock-off with the clips still in place.

3) The silicon on the coils is probably hot glue used to glue them in place. Usually they aren't so sloppy about it, but gluing down the coil/transformer is a common practice.

4) No comment on your amp's value vs the Boston amp.

5) The input potentiometer is supposed to act like a volume control, but it shouldn't be used like a volume control.

Here is how one should set the input gain, then you use the source's volume control (head unit, computer, etc).

http://www.thesuicidaleggroll.com/gain.htm
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