Hi,
I'm working towards restoring and bringing a Pioneer SX 680 to a modern standard, one of those thing would be adding speaker protection (if there is a way to) because AFAIK the SX 680 has none
There are a few questions about this
1) Taking a look in the schematic around the A,B A+B speaker configuration (functionality that I would like to maintain if possible), using only 2 speaker protect circuits before the fuses would be enough ? taking into account that most speaker protect circuit protect against DC, the fuses would have to stay right?
2) Is there any recommended Amazon / Ebay protect circuits recommended? (I know about the existence of the Guardian-86 but the pricing seems kind of steep for this project, but I can go for them if there is no cheaper alternative)
3) About powering the speaker protect modules, there are a few in Amazon / Ebay that can use 12 - 24 DC or 10 - 18 AC (those that come with their own regulator, but the comments says that using AC end up being noisy), am I wrong to assume that the 13.6V line is DC? as I see a connection between the diode bridge and the regulator circuit that outputs 13.6V
Thanks
Alex
PD : Attached the service manual
I'm working towards restoring and bringing a Pioneer SX 680 to a modern standard, one of those thing would be adding speaker protection (if there is a way to) because AFAIK the SX 680 has none
There are a few questions about this
1) Taking a look in the schematic around the A,B A+B speaker configuration (functionality that I would like to maintain if possible), using only 2 speaker protect circuits before the fuses would be enough ? taking into account that most speaker protect circuit protect against DC, the fuses would have to stay right?
2) Is there any recommended Amazon / Ebay protect circuits recommended? (I know about the existence of the Guardian-86 but the pricing seems kind of steep for this project, but I can go for them if there is no cheaper alternative)
3) About powering the speaker protect modules, there are a few in Amazon / Ebay that can use 12 - 24 DC or 10 - 18 AC (those that come with their own regulator, but the comments says that using AC end up being noisy), am I wrong to assume that the 13.6V line is DC? as I see a connection between the diode bridge and the regulator circuit that outputs 13.6V
Thanks
Alex
PD : Attached the service manual
I will reference the protection I know--- a design by Bob Cordell that seems very comprehensive. See the video below, starting at about 23 minutes for Bob's discussion of his protection circuit.
https://www.diyaudio.com/community/...-1-audio-power-amp.387115/page-3#post-7338180
Rick Savas (member rsavas) offers a kit of circuit boards to construct the entire amplifier. You might contact him re about the possibility of getting a pair of protection boards (one for each channel, about 4 by 4 inch). I believe the design can be adapted to your Pioneer by changing a few resistor values.
Good luck!
https://www.diyaudio.com/community/...-1-audio-power-amp.387115/page-3#post-7338180
Rick Savas (member rsavas) offers a kit of circuit boards to construct the entire amplifier. You might contact him re about the possibility of getting a pair of protection boards (one for each channel, about 4 by 4 inch). I believe the design can be adapted to your Pioneer by changing a few resistor values.
Good luck!
Thanks, I just bought the STK replacement kit from him so maybe we can ship both things together, I will contact him
the idea of adding a protection ckt, to replace the speaker fuses ( if used) and add turn on-off switching.
What features does one want for the protection ckt?
1) quick turn on,-off relay muting
2) DC offset protection
3) over current, short current protection?
4) HS over temp thermal protection, used on the BC-1 protection design, probably not needed for a sx-680 as pioneer never did it for any receiver design.
Is or was ( not working) there any popping noise from the speakers when you power on-off?
Currently the power on-off muting is performed using a jfet mute gate at the amplifier inputs, as shown in the service manual p9
It's more of a mecahnical challenge than an electrical one for me.
One could use the BC-1 protection design/pcbs but they are not the ideal solution imo because its two rather large pcbs, so mecahnical fit issues, redundant ckts not required etc.
Its probably best to use another protection ckt design and design a specific pcb for the purpose, which I can do but it needs your input on the mechanical aspects since I do not own a sx-680. I have lots of pics but its best to have one to work on.
Where/how to mount the pcb, pcb size etc?
It;'s possible that you make a prototype bread board of the design, I can provide the details, lets see what you think.
I see in some later service manual suppliments, that they removed the fuse holders and shorted them out.
I guess too many nuisance fuses blowing and repairs under warranty perhaps. They could have put the speaker fuses in holders on the back panel at least, but that cost $ 🙂
What features does one want for the protection ckt?
1) quick turn on,-off relay muting
2) DC offset protection
3) over current, short current protection?
4) HS over temp thermal protection, used on the BC-1 protection design, probably not needed for a sx-680 as pioneer never did it for any receiver design.
Is or was ( not working) there any popping noise from the speakers when you power on-off?
Currently the power on-off muting is performed using a jfet mute gate at the amplifier inputs, as shown in the service manual p9
It's more of a mecahnical challenge than an electrical one for me.
One could use the BC-1 protection design/pcbs but they are not the ideal solution imo because its two rather large pcbs, so mecahnical fit issues, redundant ckts not required etc.
Its probably best to use another protection ckt design and design a specific pcb for the purpose, which I can do but it needs your input on the mechanical aspects since I do not own a sx-680. I have lots of pics but its best to have one to work on.
Where/how to mount the pcb, pcb size etc?
It;'s possible that you make a prototype bread board of the design, I can provide the details, lets see what you think.
I see in some later service manual suppliments, that they removed the fuse holders and shorted them out.
I guess too many nuisance fuses blowing and repairs under warranty perhaps. They could have put the speaker fuses in holders on the back panel at least, but that cost $ 🙂
Thanks for your input, I was about to answer you in eBay but I think that makes more sense to talk here
Taking a look into the circuit and with the input from rsavas
1) The fuse is working as a over-current protection
2) The amplifier already has on-off muting
3) The amplifier has no capacitor between the output STKs and the speakers (maybe I'm wrong)
So, the only thing that is missing is DC offset protection, not sure what you mean by HS over temp thermal protection, I don't know what HS means in this context haha
For DC Offset maybe a coupling capacitor will be the easiest fix?
Thanks
Alex
Taking a look into the circuit and with the input from rsavas
1) The fuse is working as a over-current protection
2) The amplifier already has on-off muting
3) The amplifier has no capacitor between the output STKs and the speakers (maybe I'm wrong)
So, the only thing that is missing is DC offset protection, not sure what you mean by HS over temp thermal protection, I don't know what HS means in this context haha
For DC Offset maybe a coupling capacitor will be the easiest fix?
Thanks
Alex
HS is short for heatsink
imo i'd just leave it as is and replace the stk.
I went looking at the designs in that series
sx-580,680,690: fuse protection, some do not use the fuse,
sx-780: PA3004 chip. DC offset and no over current protection, relay
sx-880,980,1080,1280,1980: PA3004 chip, DC offset, over-current, relay
imo i'd just leave it as is and replace the stk.
I went looking at the designs in that series
sx-580,680,690: fuse protection, some do not use the fuse,
sx-780: PA3004 chip. DC offset and no over current protection, relay
sx-880,980,1080,1280,1980: PA3004 chip, DC offset, over-current, relay
IF you want to, there are circuits available on the NET which turn a speaker relay OFF if they detect DC.
Probably somewhere else within the Forum
Relatively simple and cheap, post what you find for comment.
Most basic uses an NPN and a PNP transistor pair to detect excess DC and turn a third transistor ON which activates the relay, nothing more complicated.
If you have 13 something Volts available, you can use a 12V relay.
Or a 24V one with existing amp supply rails.
Insert relay proper between amp board OUT and speaker selection switches.
Probably somewhere else within the Forum
Relatively simple and cheap, post what you find for comment.
Most basic uses an NPN and a PNP transistor pair to detect excess DC and turn a third transistor ON which activates the relay, nothing more complicated.
If you have 13 something Volts available, you can use a 12V relay.
Or a 24V one with existing amp supply rails.
Insert relay proper between amp board OUT and speaker selection switches.
