What's the best way of applying amp protection for power and speaker's 4 Project

[Paulflan]

Hi, I'm interested in learning how to apply both speaker protection (DC on the output) and power supply protection to an amplifier to protect against short circuit and any other issues, would be nice to also monitor bias values

what's the best practice to apply this please ?


I've got the power supply and main 7 channel power amplifier module successfully working removed from a non working Onkyo TX-875 however now it has no protection what so ever, all i have left is 12v relay's to trigger for controlling power and 7 more to connect the speaker output's and just need a way of monitoring the amplifier and power supply to use it safely as a power amp connected to another preamp

This power amplifier has 7 really high quality individual channel driver boards each driving 2 2sa1962 and 2 2sc5242 so that's 28 2sa1962 and 2sc5242 genuine output transistor's and a huge high current power supply with 2 separate B+/B- secondary winding's and appear's to be easily salvaged and reused !!
as i understand it, onkyo used the same amplifier and power supply setup in a couple of it's different higher end model's and it removes from the casing as a hole unit separate to the rest of the AVR receiver leaving all the complexity and digital logic board's behind and leaving a power supply and power amplifier with just main's in, 7 line level input's, 7 speaker output's and a bunch of 12V relay's to control,

Here's a link to the service manual however i'm only interested in pages 14 to 19 as everything else that's complicated has been removed

https://www.manualslib.com/manual/10...page=18#manual

can someone please tell me how/if i can reuse the PROTECT (IPRO & VPRO) and VOLH sense lines coming from the power amplifier that would normally go to the microprocessor that now no longer exists in the circuit to apply my own protection please ?

Please help me as i'm not trying to redesign the wheel here, just make a protection circuit for a beast of a modular power amplifier stage I've salvaged from another unit because how well its designed and how easily i got it to work just powering the main transformer and the right relay's and providing a volume controlled audio signal input and old speakers on the output's for testing,

I just need a way of protecting the speaker outputs reusing the 12V relay's already provided and mean's of monitoring the power supply for possible short's ect to control the power supply relay's

I'm really hoping someone is going to step up and help, support and guide me to a workable solution.....

Cheer's

[Paulflan]

Re: What's the best way of applying amp protection for power and speaker's 4 Project

Here's some pictures of the service manual covering the main part's im using, hopefully it will help....

here's the circuit layout from 1 of the 7 identical driver board's, please note i'm wanting to know if/how i can possibly use the IPRO & VPRO and VOLH sense lines for building my own protection circuit

https://www.dropbox.com/s/ngkt81vhy2...Board.png?dl=0

Here's the circuit layout of the X2 2sa1962 and X2 2sc5242 output transistors

https://www.dropbox.com/s/l758lcp3de...board.png?dl=0


and here's some more covering the rest of the IPRO, VPRO & VOLH sense lines and also power and temperature sense and control lines also power relay's for B+/B- from secondary winding's also the 7 line level input's

https://www.dropbox.com/s/wrcdfp5bx1...d%201.png?dl=0

https://www.dropbox.com/s/amml26syma...0VOLH.png?dl=0

Please could anyone have a look over them for me and give any advise,

please let me know if you can't load the pictures

[Paulflan]

Re: What's the best way of applying amp protection for power and speaker's 4 Project

Think i'm just going to settle for fuses in the power supply and standard DC speaker protection board's you get cheap from china in order to use it safely,

Would anyone with experience paralleling output transistors just check this out for me please,

here's a link to the pic of the driver board circuit and i'm interested in knowing if the 6 pin connector to the right of the pic that connect's to the circuit with the main output transistors and is shown on the link below that would be safe to connect to another channel's output transistor's using the same 6 pin connector and joining both speaker output's together and running them in parallel for the higher current for driving a 4 ohm's load please ??

Driver board...
Dropbox - Onkyo TX-875 Amp Driver Board.png

The output transistor circuit layout...
Dropbox - Onkyo TX-875 Power Amp transistors 2SC5242 & 2SA1962 layout board.png

Yes there's questions if the drivers have enough current to drive 4 pair's of 2sa1962 / 2sc5242 unless someones got any ideas of modifying the second driver board to keep both in perfect sync in order to drive the output transistors in parallel,

My idea was to cut the traces on the second driver board at the bases of Q6036 & Q6046 and (inject/modify) drive the transistors with exactly the same signal coming from the base of the driver transistors on the driver board im actually using to provide the extra current to drive the extra 2 pair's of 2sa1962 / 2sc5242 and joining the speaker output's together to run them in parallel ?

can someone please give thoughts an advice please ?

cheer's

[Paulflan]

Re: What's the best way of applying amp protection for power and speaker's 4 Project

the modification is working under test (still to dig my old scope out and test with a sign wave for possible crossover distortion) and showing no constant DC values on the speaker output's apart from 37mV
My aim with this project is to create a monster power amp for my home theatre modifying 2 (already done) or possibly 3 (yet to try) of the 7 channel's to create a single channel capable of driving a single subwoofer @4 ohm's powered from a separate toroidal transformer providing independent 65v-0-65vdc and separate rectifier with it's own 6 6800uf cap's on board i already salvaged from a Cloud VTX 750w RMS PA amplifier leaving the remaining 4 channel's and with the Onkyo Transformer having two separate B+/B- secondary winding's i'm thinking of splitting them and interdependently rectifying them with a couple of nichicon 10000uf 80v capacitors on each rail and splitting it for driving 2 for the left and the other 2 for the right and running the speaker's Bi-amped

Anyone else into salvaging and reusing part's ????

[Paulflan]

Re: What's the best way of applying amp protection for power and speaker's 4 Project

unfortunately i was wrong about the Onkyo transformer it appears to have 3 secondary winding's providing 3 different voltages to the amplifier stage all split rail out, +/-24Vac Gray Wires, +/-33Vac Yellow wires and finally +/-48Vac and a common black wire centre tapped rail coming from the transformer and the +/-24Vac is hard wired straight to it's own rectifier then to the B+/B- of the amplifier,s reservoir capacitors, then the +/-33Vac is controlled by 2 relay's again going through it's own rectifier before connecting to the same B+/B- of the amplifier,s reservoir capacitors and the same is repeated for the +/-48Vac with it's own pair of relay's and rectifier before connected to the B+/B- of the amplifier,s reservoir capacitors,

would this be used when you set the speaker's ohm's rating's or required power power output and how do i stand having all 3 supply's connected at once as that's what's thrown me, the lower +/-24Vac supply is constantly connected and the other two are relay controlled ?

Scrap's my idea of using the different winding's to power different channel's for left and right as i wrongly presumed they was all the same however added up to more current capability however what's peoples ideas on using this setup with 3 controllable voltages to power 4 channel's aimed at Bi-amping a stereo pair of speaker's and i'll just add to the already 18'000uf reservoir capacitors and drive the remaining modified channel's run in parallel from the separate power supply as stated in a previous post

would this be used when you set the speaker's ohm's rating's on the receiver or for required/demanded power output to the speakers

once i've sorted this final hurdle I'll go ahead and order the speaker protection boards and enclosure from amazon UK to finish the project