Alpine amp

[caraudioguy2100]

Anyone know what outputs belong in this amp ?

The amp has no model number on it

 

[jkrokenberger]

I'm gonna guess 540/9540. It's a little tall on rating vs real.

 

[Perry Babin]

I think that's a knockoff and not a legitimate Alpine.

They appear to be TIP41C and TIP42C?

 

[caraudioguy2100]

That’s what’s in the amp now just wanted to confirm

 

[Perry Babin]

All I did was zoom in on the photo.

Look at the solder connections. Do they look like original flow soldering or like someone has replaced them?

 

[caraudioguy2100]

Yes they are not original.

I remember reading a post awhile back about this amp and I don’t think the tip parts are the original part numbers .

But I can’t seem to find the post since there is no model number on this amp anymore .

I believe this is the same amp that someone else tried repairing in the area at one point if I remember correctly .

 

[Perry Babin]

What's wrong with the amp?

 

[caraudioguy2100]

It has blown outputs .

 

[Perry Babin]

The TIP42/42 are weak. I'd try the 2N6488/91 if you have to replace them.

 

[caraudioguy2100]

I will give those a try and see .

The power supply is using IRFZ44N’s with 51 ohm gate resistors .

The power supply is also blown if I switch to 3205’s should I also switch the gate resistors to 47 ohm ?

 

[Perry Babin]

If the 51s all survived, they will likely be OK. If any need to be replaced, I'd go to all 47s.

 

[caraudioguy2100]

There is also a resistor missing on 1 side of the amp .

The one that’s still there measures 4.19k on my meter at room temp.

Do you happen to know what value resistor I can add there ?

R16 is the missing resistor

 

[Perry Babin]

Thermistor?

Most cheap amps have only one. Does the other one have anything connected to it in the circuit?

It's rare for a manufacturer to use two different thermistor values for thermal protection in one amp.

 

[caraudioguy2100]

It doesn’t appear to be connected to anything .

As far as the outputs go you told me to try the 6488/6491 in the amp .

I can put bigger outputs in the amp like The TO247 case .

Wondering should I stick with the 6488/6491 or can I try the Tip35/36c ?

 

[Perry Babin]

It was designed to be reliable with TO-220 transistors.

 

[jkrokenberger]

That is most likely a knock-off. The genuine article would have MOSFET outputs and a much nicer board.

 

[caraudioguy2100]

Ok replaced the outputs and power supply fets .

The amp powers up idles fine and plays clean audio on both channels but as soon as I try to bridge the amp the test speaker starts fluttering and amp draws excessive current .

 

[Perry Babin]

Is that with a proper signal source (with a grounded shield) plugged in?

 

[caraudioguy2100]

I touched up all the solder connections on the board and problem is gone .

Amp is up and running thanks for the info on what outputs to use greatly appreciated.


Only thing I noticed with Th is amp is it doesn’t reproduce the low bass notes very well .

 

[Perry Babin]

Since you changed the output transistors (not knowing the originals), you need to run the amp to thermal shutdown, monitoring the idle current regularly as it heats up to confirm that the bias current holds.