I am not sure whether it makes more sense to post this here or in the SS section so feel free to move it is more appropriate there. I read through several pages of hits and didn't find what I needed.
I have an AR S108PS 8" "subwoofer" from which I would like to use the 120W plate amp with a 12" system I am putting together. I pulled the speaker wires out to play with it on the new driver and it worked pretty well except that they seem to have put a HP filter at about 37Hz so I am not getting the full potential of the driver. No doubt they did this to protect the little driver.
I have searched the net for a schematic with no luck. So my question is how feasible is it to attempt to figure out their implementation of the filter and disable it? Do most of these amps use similar layout that would help identify the offending circuitry? Does anyone have experience with this actual amp that could help get me started?
I have not pulled the amp to look yet but will do so sometime this week probably.
Any suggestions appreciated as I would really rather use this amp if possible rather than build my own chip amp.
mike
I have an AR S108PS 8" "subwoofer" from which I would like to use the 120W plate amp with a 12" system I am putting together. I pulled the speaker wires out to play with it on the new driver and it worked pretty well except that they seem to have put a HP filter at about 37Hz so I am not getting the full potential of the driver. No doubt they did this to protect the little driver.
I have searched the net for a schematic with no luck. So my question is how feasible is it to attempt to figure out their implementation of the filter and disable it? Do most of these amps use similar layout that would help identify the offending circuitry? Does anyone have experience with this actual amp that could help get me started?
I have not pulled the amp to look yet but will do so sometime this week probably.
Any suggestions appreciated as I would really rather use this amp if possible rather than build my own chip amp.
mike
Hi,
the amp may simply have a high pass filter. Many do this.
But it could be one of the better designs that is a 5th or 6th order alignment that uses a variety of different Qs and filters to extend the bass response and get more volume without overloading the driver.
You must identify what you have.
If you copy a Linkwitz alignment, I think you get the same as a 5th order alignment. You can then design the alignment to exactly suit your new driver.
the amp may simply have a high pass filter. Many do this.
But it could be one of the better designs that is a 5th or 6th order alignment that uses a variety of different Qs and filters to extend the bass response and get more volume without overloading the driver.
You must identify what you have.
If you copy a Linkwitz alignment, I think you get the same as a 5th order alignment. You can then design the alignment to exactly suit your new driver.
I took some pictures today and will get a CD made in the next couple of days but I thought that I would go ahead and describe what I saw.
The circuit board has the following printed on it.
PLAIN REV 5.1
AMI COPYRIGHT 1999
There is a large flat can about like a stack of 30 business cards mounted on its long edge. There is a label stuck on it that says
S53AMI
On the side of the can a number is stamped that looks like
012800
The can has 14 sets of contacts soldered to the board. It appears to be a PC board inside of the can.
Directly below the can are two fairly large (the largest on the board) electrolytic caps of 3300uF 50V.
On the right side of the board where the main power xformer secondary connects to the board there is a small toroid, a bridge rectifier and a couple of green (mylar?) caps labeled
1040 100V
I assume this is the SMPS.
The speaker output has a small cap that looks like a small signal diode (labeled C24) across the two leads. There is a small electrolytic mounted between the output leads also but it is not clear whether it is connected to the speaker lugs or not.
On the lower left of the board is a 14 pin DIP labeled.
LA6324N
9S7
It appears that there is a small CT transformer connected to the negative leg of the speaker output. It appears that one end of what I assume is the secondary is connected there. it looks like the "primary" of this transformer may be connected to a small inductor labeled "L2" on the board. I wonder if this could be part of of filter network like Andrew mentioned.
I can't identify an output device however it/they my be encased in the plastic compartment (sealed with Moose Snot) on the edge of the card where the external connectors and controls are housed.
mike
The circuit board has the following printed on it.
PLAIN REV 5.1
AMI COPYRIGHT 1999
There is a large flat can about like a stack of 30 business cards mounted on its long edge. There is a label stuck on it that says
S53AMI
On the side of the can a number is stamped that looks like
012800
The can has 14 sets of contacts soldered to the board. It appears to be a PC board inside of the can.
Directly below the can are two fairly large (the largest on the board) electrolytic caps of 3300uF 50V.
On the right side of the board where the main power xformer secondary connects to the board there is a small toroid, a bridge rectifier and a couple of green (mylar?) caps labeled
1040 100V
I assume this is the SMPS.
The speaker output has a small cap that looks like a small signal diode (labeled C24) across the two leads. There is a small electrolytic mounted between the output leads also but it is not clear whether it is connected to the speaker lugs or not.
On the lower left of the board is a 14 pin DIP labeled.
LA6324N
9S7
It appears that there is a small CT transformer connected to the negative leg of the speaker output. It appears that one end of what I assume is the secondary is connected there. it looks like the "primary" of this transformer may be connected to a small inductor labeled "L2" on the board. I wonder if this could be part of of filter network like Andrew mentioned.
I can't identify an output device however it/they my be encased in the plastic compartment (sealed with Moose Snot) on the edge of the card where the external connectors and controls are housed.
mike
Well I took off the transformer and the shield so that I could get a better look at the underside of the board. Man it looks like I will have to spend a few hours at the table with a good light and a big piece of paper. A lot of the traces seem to go nowhere so it will be an involved project but very educational.
One of the difficulties is that the inputs and control section of the board is covered by a seal plastic portion of the mounting plate so I can only see the underside at that point (which is where a lot of action takes place.
Right now it looks like a trace coming from the vicinity of the low level inputs goes to op amp number one which is configured as an inverter. The + input is grounded and C13 is connected between the inverting input and the non-inverting input. R40 is connected between the output and the inverting input.
The output of op amp one goes to what appears to be the volume pot. From the volume pot a trace comes back to op amp three. I haven't yet traced that out but it seems to involve a lot of circuitry all over the board and possibly a set of four capacitors. Not sure if this is the low pass section or something else until I get some more time to trace it out.
Will keep you updated as I trace it out further.
mike
One of the difficulties is that the inputs and control section of the board is covered by a seal plastic portion of the mounting plate so I can only see the underside at that point (which is where a lot of action takes place.
Right now it looks like a trace coming from the vicinity of the low level inputs goes to op amp number one which is configured as an inverter. The + input is grounded and C13 is connected between the inverting input and the non-inverting input. R40 is connected between the output and the inverting input.
The output of op amp one goes to what appears to be the volume pot. From the volume pot a trace comes back to op amp three. I haven't yet traced that out but it seems to involve a lot of circuitry all over the board and possibly a set of four capacitors. Not sure if this is the low pass section or something else until I get some more time to trace it out.
Will keep you updated as I trace it out further.
mike
Well here is my first attempt at trying to draw this out. Keep in mind that some of the components are hidden and so some guessing is going on. Some of you filter gurus probably recognize what is going on here but I am pretty baffled.
I am guessing that we can ignore the V++ cap to ground as that was probably just a convenient place to decouple the PS. I don't see anything that jumps out at me and screams high pass but I suspect that U2 and U4 must be forming some kind of bandpass filter.
Does this look like anything you guys recognize?
mike
I am guessing that we can ignore the V++ cap to ground as that was probably just a convenient place to decouple the PS. I don't see anything that jumps out at me and screams high pass but I suspect that U2 and U4 must be forming some kind of bandpass filter.
Does this look like anything you guys recognize?
mike
Attachments
I traced this a little further and added some component values where I could determine them. On some of the caps I could not see the markings and the blue resistors (metal film) had five color bands and so I am not sure that I interpreted them correctly. C2-C5 are listed with values of 100nJ100 as that is what is stamped on the case. I think that it is 10pf but with the "n" in there I am not sure.
I am still a bit baffled by this circuit. For example I am clueless as to why the signal from the output of U1 is applied to both the input and the output of U4. Is this some sort of simulated reactance?
Some of the circuitry that is going off into never never land under the sealed part I have left hanging with a guess as to where it is going. I you think there is something important under there I could try to get access to that part of the board.
mike
P.S. I think that R13 is 11K
I am still a bit baffled by this circuit. For example I am clueless as to why the signal from the output of U1 is applied to both the input and the output of U4. Is this some sort of simulated reactance?
Some of the circuitry that is going off into never never land under the sealed part I have left hanging with a guess as to where it is going. I you think there is something important under there I could try to get access to that part of the board.
mike
P.S. I think that R13 is 11K
Attachments
Of course if I can't figure out their circuitry I could always do my own crossover and tap in at the top of R17 (disconnect r17 from the op amp side and inject my signal there) so that I can use their power amp. Of course I would still have to figure out how to fool their circuitry into turning on the PA since there is no bypass for the auto on circuit.
mike
mike
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