Schematic? Sundown SAZ-1500, Elevation Audio DX1500.1, RD 1750.1, Atomic AT-1600.1D

[ThyDntWntMusic]

Does anyone have any info on these amps?
They all use the same board, and I have a ReSponse branded amplifier here, that also uses the same board.

I've used two of these amps in the past at 0.5ohm daily, no issues, never went into protect, no matter how much abuse I gave them. Even blew all the fuses in one.

Nevertheless! I've recently bought two second hand, brand new, never used, amps, and they don't like 0.5ohm at all... and thats what I bought them to run at!

SO, I'm hoping to modify the protection circuit to make it less sensitive, a schematic would be excellent, or even just a little info.

Thanks for any input!

 

[NickParr666]

I know you've used these amps in the past into 0.5 ohm but the manual states they are only stable down to 1 ohm. If you modify the protection cct surely you're going to cause more harm than good?

 

[Perry Babin]

I agree but if you can't use the amp like it's supposed to be used, find the 8 pin op-amp that has pin 4 connected to the negative rail. There will be a voltage divider across the shunt resistor. That voltage divider feeds the inputs of the 8 pin op-amp. Compare the resistors of that divider in the old and new amps. If they're the same, compare the voltage on the reference terminal. The reference terminal will be the input to the op-amp that has more voltage than the other input terminal. Measure the voltage with the black probe on the negative rail. The reference voltage will be very low (less than 0.2v, likely) so measure carefully.

 

[ThyDntWntMusic]

I don't think you mentioned where exactly the shunt resistor is

 

[Perry Babin]

They look like this in most amps.

 

[ThyDntWntMusic]

I figured they did.

It has four, all appear to be on the negative rail? is that correct?

 

[Perry Babin]

Probably so.

 

[ThyDntWntMusic]

ok, it seems that no opamp in the whole circuit has pin 4 connected to the negative rail.

 

[Perry Babin]

There should be one near those resistors. If not, follow the small traces away from those resistors to see if they lead you to an op-amp.

It may not be an 8-pin but I can' remember them using anything else.

 

[ThyDntWntMusic]

it only has 8 pin opamps.

http://www.diyaudio.com/forums/car-audio/176660-sundown-saz-3000-d-2.html

is this the opamp I'm meant to be looking for? that section of the circuit is the same (or very similar) between the 1500, and 3000watt amps.

 

[ThyDntWntMusic]

The shunts are different sizes....

the amps that go into protect more have higher shunts... so they're longer, while being the same thickness... meaning more resistance, greater voltage drop, and therefore, go into protect more easily?

Which explains why I can't find any differences between the two amps component values...

 

[Perry Babin]

You're likely right about the increased resistance. If you can find the op-amp (may be a comparator, not an actual op-amp), you should be able to work out the values or install a pot to make it just barely hold on the 0.5 ohm load (so a slight overload would allow the amp to go into protect).

 

[ThyDntWntMusic]

Thing is, the subs I was running at 0.5ohm per amp, were rising to 1ohm per amp at the frequency I was playing anyway :/ and even scrolling the volume up, one amp still went into protect.

So how does this short circuit protection actually work then?

 

[ThyDntWntMusic]

You're likely right about the increased resistance. If you can find the op-amp (may be a comparator, not an actual op-amp), you should be able to work out the values or install a pot to make it just barely hold on the 0.5 ohm load (so a slight overload would allow the amp to go into protect).

did you see my last post on the previous page?

 

[ThyDntWntMusic]

 

[Perry Babin]

I'm not familiar with that amp and the photo was so bad that I couldn't tell anything from it.

The circuit is likely (again, I have no information on this amp) a simple voltage comparator. There is a reference voltage on one input of the op-amp/comparator and a voltage produced across the shunt resistors on the other input of the op-amp. When the input from the shunt resistors exceeds the reference voltage, the amp shuts down.

 

[ThyDntWntMusic]

where does the reference voltage come from? the positive rail with a voltage divider?
and when you said "find the 8 pin op-amp that has pin 4 connected to the negative rail"
did you mean the amps full negative rail? or the regulated -15volts?

thanks.

 

[Perry Babin]

The voltage divider is generally taken off of the 12v zener connected to pin 8 of the op-amp.

The negative rail (-100v or whatever it is).

 

[ThyDntWntMusic]

The 1000 watt monoblock has three opamps with the main negative rail directly connected to pin four, also has a Zener diode.

While the 1500 watt I was looking to modify appears to have neither...

 

[ThyDntWntMusic]

Do you think it would be alright to just wrap a bit of solder around the shunt to reduce the voltage drop?