In this discussion we say only about of current-drive instead of voltage-drive, but effect of discontinuance spurious feedback with output stage with hi-impedance isn’t the subject under consideration.
Sorry, bad translate.
Spurious feedback, stray feedback, parasitic feedback.
In above mention paper
1. Mills P. G. L., Hawksford M. 0. J. Distortion Reduction in Moving-Coil
Loudspeaker Systems Using Current-Drive Technology. — JAES, vol. 37, ¹3,1989, March,
p. 129—148.
2. Mills P. G. L„ Hawksford M. 0. J. Transconductance Power Amplifier Systems for
Current-Driven Loudspeakers. — JAES, vol. 37,¹ 10, 1989, Oct. p. 809—822.
authors writes about decrease distortions in output stage with common base.
Output stage with common emitter or collector has this parasitic feedback from load to input because of low own impedance if we used their in current-source.
Spurious feedback, stray feedback, parasitic feedback.
In above mention paper
1. Mills P. G. L., Hawksford M. 0. J. Distortion Reduction in Moving-Coil
Loudspeaker Systems Using Current-Drive Technology. — JAES, vol. 37, ¹3,1989, March,
p. 129—148.
2. Mills P. G. L„ Hawksford M. 0. J. Transconductance Power Amplifier Systems for
Current-Driven Loudspeakers. — JAES, vol. 37,¹ 10, 1989, Oct. p. 809—822.
authors writes about decrease distortions in output stage with common base.
Output stage with common emitter or collector has this parasitic feedback from load to input because of low own impedance if we used their in current-source.
Hi alex
An amplifier for current drive does not necessarily have to be a transconductance amplifier.
You can use almost any ordinary amplifier and current feedback instead.
Regards
Charles
An amplifier for current drive does not necessarily have to be a transconductance amplifier.
You can use almost any ordinary amplifier and current feedback instead.
Regards
Charles
Why on earth do all electronics terms have two or three different meanings?
Phase_accurate,
when you use the phrase "transconductance amplifier" in the sense that Cherry and Hooper and Nordholt define it, it simply means an amplifier with a high input and high output impedance having an accurate voltage to current transfer (in other words, a voltage to current converter), regardless of how you implement it. In this sense, an amplifier with a floating load and with feedback from a sense resistor in series with the load is a transconductance amplifier.
Millwood, I'm not sure if I understand what you mean, but I think compensating for the level dependence of the loudspeaker impedance in the equaliser in my proposed self-equalising amplifier system is the last thing you'd want. This would bring back all the compression effects you got rid off by using current drive. The equaliser should simply be adjusted according to the small-signal impedance, which can for example be measured with a simple tone sweep just after switch-on.
Phase_accurate,
when you use the phrase "transconductance amplifier" in the sense that Cherry and Hooper and Nordholt define it, it simply means an amplifier with a high input and high output impedance having an accurate voltage to current transfer (in other words, a voltage to current converter), regardless of how you implement it. In this sense, an amplifier with a floating load and with feedback from a sense resistor in series with the load is a transconductance amplifier.
Millwood, I'm not sure if I understand what you mean, but I think compensating for the level dependence of the loudspeaker impedance in the equaliser in my proposed self-equalising amplifier system is the last thing you'd want. This would bring back all the compression effects you got rid off by using current drive. The equaliser should simply be adjusted according to the small-signal impedance, which can for example be measured with a simple tone sweep just after switch-on.
Hi Marcel
O.K. I agree with your general definiton of a transconductance amplifier.
But I think the effects Alex writes about are minimal with an ordinary amplifier combined with current feedback taken from a shunt resistor compared to more exotic solutions.
Regards
Charles
O.K. I agree with your general definiton of a transconductance amplifier.
But I think the effects Alex writes about are minimal with an ordinary amplifier combined with current feedback taken from a shunt resistor compared to more exotic solutions.
Regards
Charles
Mills and Hawksford use a rather exotic amplifier having a class-AB complementary current follower with floating power supplies driving the loudspeaker. The only advantage I see is that since the open-loop output impedance is high and since they don't need a Zobel network (Boucherotnetwerk), the high output impedance is better maintained at high frequencies, assuming that the transformer capacitance of the floating supplies doesn't spoil it. I also wonder if this is really worth the trouble.
Thanks, phase_accurate and Marcel
For the first experiment I decide to use simple TDA7293 with current-sense in my 3-bands active loudspeaker.
For the first experiment I decide to use simple TDA7293 with current-sense in my 3-bands active loudspeaker.
Hi Alex
Maybe you will check with cheap drivers or resistors before hooking up the real ones.
Because it can be quite expensive when "things get interesting"*!
Rergards
Charles
*copyright by NP
Maybe you will check with cheap drivers or resistors before hooking up the real ones.
Because it can be quite expensive when "things get interesting"*!
Rergards
Charles
*copyright by NP
New method of current-drive loudspeaker
In this patent for current-drive authors used bridge of one amplifier as voltage-source and other - as current-source. Patent in Djvu-format in Russian with abstract in English.
In this patent for current-drive authors used bridge of one amplifier as voltage-source and other - as current-source. Patent in Djvu-format in Russian with abstract in English.
Are there any DIY kits or plans for a decent (low distortion, very low high-order HD or IMD) current source amp?
I would have thought an 8 year old abandoned thread would be a good indicator of there being no plans.
I briefly tried high impedance drive on a 3-way once - it sounded awful.
Hi 454Casull
Your fellow Canadian member Duo started to plan a kit for a very interesting variable impedance current drive amp last year. It had received some favourable comments.
'Not heard his progress since then as he was setting up a website - perhaps he would be good to contact.
Your fellow Canadian member Duo started to plan a kit for a very interesting variable impedance current drive amp last year. It had received some favourable comments.
'Not heard his progress since then as he was setting up a website - perhaps he would be good to contact.
My experimental current-driven loudspeaker with motional feedback from a second voice coil worked rather nicely. Pity I didn't have a practical application for it.
Another way to get rid of the response peak around fundamental resonance is to just equalise it out with a filter (Linkwitz transform circuit or other type of filter with two zeroes and two poles). The problem with this is that the filter zeroes will never be exactly on the loudspeaker poles. As a result, you will get some small ringing that damps out slowly.
Another way to get rid of the response peak around fundamental resonance is to just equalise it out with a filter (Linkwitz transform circuit or other type of filter with two zeroes and two poles). The problem with this is that the filter zeroes will never be exactly on the loudspeaker poles. As a result, you will get some small ringing that damps out slowly.
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