Hi everyone,
I am looking at making a DIY of the GRR or Rhythmik type of servo subwoofer.
I see that there are various types of 'special' plate amp offered by those 2 companies for these drive units, that have the necessary servo connections.
But what if I want to use a different plate amp? What is the necessary modification to use it with the above servo sub drivers?
Has anybody done this at home? What's involved?
Cheers
Arg
I am looking at making a DIY of the GRR or Rhythmik type of servo subwoofer.
I see that there are various types of 'special' plate amp offered by those 2 companies for these drive units, that have the necessary servo connections.
But what if I want to use a different plate amp? What is the necessary modification to use it with the above servo sub drivers?
Has anybody done this at home? What's involved?
Cheers
Arg
Do you already have the woofers?
If so, Rythmik appears to take its feedback signal from a sensing coil. This signal must first be cleaned from crosstalk from the voice coil, shaped to a certain response and then it is fed (together with the desired signal) to a difference amplifier, which drivers the amplifier. You can read about feedback systems and loop shaping in any textbook that covers the basics of control theory.
If not, what kind of feedback method would you like to apply? A sensing coil? The output of an accelerometer that is mounted to the voice coil?
If so, Rythmik appears to take its feedback signal from a sensing coil. This signal must first be cleaned from crosstalk from the voice coil, shaped to a certain response and then it is fed (together with the desired signal) to a difference amplifier, which drivers the amplifier. You can read about feedback systems and loop shaping in any textbook that covers the basics of control theory.
If not, what kind of feedback method would you like to apply? A sensing coil? The output of an accelerometer that is mounted to the voice coil?
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Several good threads in the subwoofers forum on motional feedback or MFB. Not clear what the consensus is quite yet, but maybe accelerometer sensing.
Design using current feedback (one little resistor in series with driver used for feedback) is quite simple to implement. Any good ordinary amp you own can be used. Just needs a little op-amp mixer and ability to EQ. Of course, all MFB systems are bi-amp'd, as should be all systems now a days.
It is an understatement to say it is rare to hear anything but great enthusiasm among those who try MFB.
B.
Design using current feedback (one little resistor in series with driver used for feedback) is quite simple to implement. Any good ordinary amp you own can be used. Just needs a little op-amp mixer and ability to EQ. Of course, all MFB systems are bi-amp'd, as should be all systems now a days.
It is an understatement to say it is rare to hear anything but great enthusiasm among those who try MFB.
B.
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Hi Guys, yes I am looking at the Rhythmik / GRR type of driver that uses a sensing coil. I don't own the drivers yet.
Thanks for describing gate type of circuit needed. I don't think I am up to designing it myself. I would need to see an actual circuit, ideally a reverse-engineering of what Rhythmik or GRR actually use in their servo plate amps.
I basically want to be able to copy what they do, and apply it to amps other than the ones they supply.
I tried to search the site for prior threads, but didn't see what I needed, although I might have missed it.
cheers
Thanks for describing gate type of circuit needed. I don't think I am up to designing it myself. I would need to see an actual circuit, ideally a reverse-engineering of what Rhythmik or GRR actually use in their servo plate amps.
I basically want to be able to copy what they do, and apply it to amps other than the ones they supply.
I tried to search the site for prior threads, but didn't see what I needed, although I might have missed it.
cheers
As far as I know, there are no off-the-shelf drivers with dedicated feedback windings, other than proprietary ones that you might buy. It is a good way to generate MFB. But making the "spare" winding on dual voice coil drivers aren't suitable.
(There is one older Sony driver with a purpose-built MFB winding out there in eBay-land.)
B.
(There is one older Sony driver with a purpose-built MFB winding out there in eBay-land.)
B.
If you want MFB, an accelerometer seems to outperform a sensing coil, as the former is what most people are using.
Bentoronto, would you happen to have any examples of circuit diagrams for the current feedback circuit? How hard would it be to tailor it to a particular amp/driver combination?
I had a play years ago with a similar amplifier from a local speaker manufacturer, and it really opened my eyes as to how well it can work, also on less than ideal drivers.
I’m currently using Rythmik subwoofers (which I absolutely love), but would still be interested in the current feedback style.
Regards,
Matt.
I had a play years ago with a similar amplifier from a local speaker manufacturer, and it really opened my eyes as to how well it can work, also on less than ideal drivers.
I’m currently using Rythmik subwoofers (which I absolutely love), but would still be interested in the current feedback style.
Regards,
Matt.
No special amp or driver needed. Some folks also think any kind of box (or no box) will also work fine. Amp does need good low freq output (phase and power) and maybe 25 dB voltage gain, so even tube amps work nicely (and won't destroy your driver, see below). You must become bi-amped of course.
Sorry, no circuits close at my hands this moment but several out there. Nothing but a .5 Ohm resistor, (or less if 4 Ohm driver) an op-amp, and a 6 dB/8ave bass boost. If you need too much more info than that, you may not know enough to keep from destroying your driver with the power of erroneous feedback (please don't take that "personally").
(I have a feeling somebody smarter than me could rig up current MFB using their mic mixer and DSP. I've been trying it with an accelerometer and have some results. Really boffo if you could use the phantom power supply too, eh.)
B.
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Attached is a schematic for a variant using a Wheatstone Bridge. Not sure bridge adds anything to ordinary current feedback but helps get articles published in journals. The "differentiator" is just EQ and better handled in your DSP/XO. Not sure you need anything but the first IC and a pot.
I built it pretty much identically, worked fine for a few decades.
Like I said, you can use any ordinary driver and any ordinary amp.
Reference: C J Adams and R. Yorke, Motional feedback in loudspeaker systems. Monitor - Proceedings of IREE, March, 1976. Article says it all and more.
I built it pretty much identically, worked fine for a few decades.
Like I said, you can use any ordinary driver and any ordinary amp.
Reference: C J Adams and R. Yorke, Motional feedback in loudspeaker systems. Monitor - Proceedings of IREE, March, 1976. Article says it all and more.
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