Servo amp ACE Bass

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Hello everyone.
I was able to find the ACE Bass Audiopro B1-45 wiring diagram. I would like to isolate only the ACE bass circuit to implement it on a speaker (not subwoofer) of my construction. The idea is to extrapolate that part of the circuit and use it with an existing amplifier. Has anyone had any experience with this?

b1-45.png
 
If I understand the circuit, that op-amp in the lower right corner is the MFB. Not a whole lot about how it works is related to frequency per se.

MFB is dramatically beneficial for bass but I actually have no knowledge of consequences for mid-range. Wish I did.

"MFB" comes in various flavours, but it relates to motion of the cone (OK, the dust cap) which can be satisfactorily sensed any number of ways. And for subs, getting the cone motion happy then gets the sound output of the driver happy.

For a mid-range, the relation of dust cap and sound quality (and their phase relationship) are more complex. And there is no horrible bass resonance to wrangle - one of the glories of MFB.

So, many of us will be very glad if try and if you provide measured results back here.

Hint: use an amp that can supply no more power than the driver can handle. DAMHIK.

B.
 
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The values of the components in the circuit must be tailored to whatever driver is used, and the amplifier gain. Also, the system will suffer from a response irregularity around a couple of hundred Hertz. This is why Stahl's circuit is limited to subwoofer applications.

If these characteristics of the ACE-BASS circuit are not familiar to you, I suggest that you can download the US patent Stahl filed to get more info. I think Stahl published an article in JAES or other audio/electronics journal as well.

I attached a schematic diagram that I think is from the patent (can't recall exactly). This is one form of the ACE-BASS circuit. The simulation program Basta! can be used to simulate the circuit and then find appropriate component values for a given driver and amp.
 

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  • Stahl 1-op-amp circuit.png
    Stahl 1-op-amp circuit.png
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That circuit is standard current feedback MFB. Standard. And it matches the post #1 circuit (note the .1 Ohm series resistor in the corner).

At least with a Wheaststone Bridge circuit (Werner, 1957) you do simulate the stationary parameters of a driver and therefore you are matching the circuit to that driver. Not so much with that drawing except maybe as plain-vanilla EQ or converting velocity to acceleration sensing.

If I recall seeing the patent application, it was all the standard MFB plus a lot of double-talk intended to sneak it past the patent office clerks, like a lot of audio "inventions".

B.
 
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merovingio search for Karl-Erik Ståhl, he is the inventor and did the patents.
You should be able to find both the patent and AES presentation online (otherwise PM me).

bentoronto .... not sure why you want to down play the achievements by Karl-Erik Ståhl, and say it is not a real invention!!
The circuit and implementation does indeed lowder distortion a lot and this still with the benefit of a vented design. Done in 1977 where you more or less had to do everything by theory, pen, paper and pocket calculator!

I stopped playing with AceBass, as my class d amp's had the habit to start switching at much higher frequency, caused by the extra fb loop. Still want to re visit, as I think it is a really cool circuit, and will also work with passive radiators.
Will need to sort out the effect on the extra loop wrt class d.
 
...bentoronto .... not sure why you want to down play the achievements by Karl-Erik Ståhl, and say it is not a real invention!!
The circuit and implementation does indeed lowder distortion a lot and this still with the benefit of a vented design. Done in 1977 where you more or less had to do everything by theory, pen, paper and pocket calculator!..

It is unacceptable that you attack my motivation in posting about ACE stuff as if I had a conspiracy ("why you want to down play...."). But I do tend to be allergic to exaggerated patent applications. Perhaps I might ask just why you are such a proponent of Karl-Erik when all the principles were well known decades earlier?

Instead of attacking me, perhaps you could explain in what way the system differs from other current sensing methods? Good chance I've missed reading something important in that long patent you think we should all read.

And perhaps you could also explain how a current sensing approach accounts for the divergence between cone motion and bass output in a BR in the frequencies below, at, and just above tuning?

B.
 
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