AV800 + clipping , etc ...

[darkm4n]

Hi ,

I'am building the AV800 amplifier ( from Holton ) and i want to add a clipping indicator , a speaker protection ( maybe i will use uPC1237 ) , soft start , a signal leg ( like on the QSC amplifiers and other ) .

With the clipping indicator the problem was that my amplifier use 90V ( 2 x 65V AC and 2500 W supply ) ... the clipping indicator from http://sound.westhost.com/project23.htm it's for 70V maximum .. and on the last table i don't know the formula to calculate the resistor for 90V . Anyone know a better solution ?

Another problem was the short circuit protection , I know that the uPC1237 can do this but i don't know how ...

Thanks .

[edl]

Hi,

let's use these values:

"Resistor Value For Power Supply" 3,6k
"Resistor Value For 3V Clipping Reference" 56k
"Opamp Input Resistors" 9k1

Regards,

[darkm4n]

Rod Elliott sayed : The transistors must be rated for the supply voltage. For most systems (less than +/- 70V) BC639 - NPN (Q2) and BC640 - PNP (Q1) will work happily. They are over the top in power and current ratings, but we need the 80V rating. I do not know of suitable (readily available) devices for use at higher voltages.

I searched over the net for other transistors but i couldn't find ....

[richie00boy]

Maybe 2N5401 and 2N5551 could be used? They have reversed pinout but as no PCB layout is done it shouldn't matter.

[darkm4n]

Thanks !!! The problem with the clipping indicator is solved .

Now only the speaker protection circuit remain . I found uPC1237 , a speaker protection IC but i don't know how good it is . Maybe someone know a better protection circuit with short circuit protection ( 4 Ohm is the minimum impedance for this amplifier , it can support 2 ohm only if the supply voltage is reduced ) . As i found in professional amplifiers after a shot circuit or overload is produced the amplifier go in protect mode and after 5 seconds is operating again .

Another thing i want to integrate in this amplifier is a signal led ( as found in professional amplifier , when signal is detected a led blink such as a VU METER ) . I don't want a full VU METER , only a single led .

Softstart is OK , i will use the schematic on Rod Elliott site .

If anyone think that i should integrate anything alse than soft start , clipping indicator , speaker protection , short circuit protection , thermal protection , signal led in this amplifier let me know .

Thanks .

[kubeek]

Does anyone know some newer brother to the obsollete uPC1237?

[jacco vermeulen]

uPC1237C, $1.5 the piece.
AFAIK, they've only discontinued the 8-in-line package(HA version)

[kubeek]

Where I live, there are only two main parts shops, one doesn´t have it at all, the other has 0 pieces in all stores, and says it is not to be used in new applications. So is there anything similar, but newer?

[AndrewT]

Hi Dark,
you can change the thermal protection to latching thermal shutdown.

Try adding a DC block and interference suppression to the input of the transformer.

What about an orange LED flashing @-3db and the red LED @-1db or -0.5db?

Add a delay (50mS) on the LED so you can see the flash.

[edl]

Originally posted by richie00boy
Maybe 2N5401 and 2N5551 could be used? They have reversed pinout but as no PCB layout is done it shouldn't matter.

Or MPSA42/92 (MPSA43/93)...