Damping Factor

[GlennGregor]

For all intents and purposes, your amp is not current drive. We’ve been through this defore:

Current Drive VS Voltsge Drive

I would like to know if anyone has info on Current Drive systems for audio. I have a Current Drive Integrated Amplifier and the sound is amazing. I run a pair of Yamaha S5115HT’s off of it and the music is flawless. These are my house speakers. Their sensitivity is 100. I don’t know if a Current...

www.audiosciencereview.com

Why you still insist it is, is beyond me

I don’t think it’s beyond you.

 

[SIY]

I don’t think it’s beyond you.

The answer to that would not be charitable.

You may want to do a little bit of self-teaching about Thevenin versus Norton sources. I'd suggest a textbook rather than ad brochures.

 

[Cbdb2]

With voltage drive as the voice coil heats up the power into it goes down, with current drive the opposite is true so the coil will burn up.

 

[DonH56]

Sony uses a voltage-to-current inverter. Their A.C.T. circuitry has a few stages. They use a Current Drive type attenuator between the pre-amp and power-amp stage. The pre-amp stage is also powered through a constant current shunt regulator.

Stereo Review did an equipment test report on the Sony TA-F555ES. It’s in the June 83 magazine. I found a .pdf version of it online. Some of the report I don’t understand, but I do understand THD, headroom, and dynamic range. I don’t understand the clipping they talk about, also the second and third order harmonics and some test they did with a phono cartridge to see how quiet the unit was.

The "current drive" part is inside the integrated amplifier, from the preamp section output to the amplifier's input. The output of the amplifier, the part that drives the speaker, is voltage-mode, as shown by the specifications and schematic circuit diagram that @restorer-john provided. It is a nice amp but the speaker output is not current-driven.

 

[DonH56]

With voltage drive as the voice coil heats up the power into it goes down, with current drive the opposite is true so the coil will burn up.

Well, hopefully not! Current amps still use feedback and since the voice coil is passive thermal runaway should not happen, so the voice coil won't burn up. At least not much more than with voltage drive.

For example, an 8-ohm AL voice coil will go to about 10.5 ohms* if temperature rises from room (27 degC) to 100 degC. Of course heat also affects the magnet and other factors... As stated earlier, mechanical distortion in the speaker driver still dominates the distortion, so the type of drive probably makes little difference in the end.

* https://www.allaboutcircuits.com/textbook/direct-current/chpt-12/temperature-coefficient-resistance/

 

[rha61]

here' s an answer from Bruno Putzeys
PSI or Backes & Müller also use current drive in the mid band
the fact is that a part of the speaker THD appears on the current THD

Last question regarding the future directions you might want to explore with purifi: are you going to tackle the task of bringing transconductance/current drive amplification to the DIY and OEM market? I know your new woofer uses special trick to avoid voltage drive distortion, but having a good offering for a current drive amplifier would still be very nice for reducing distortion in "legacy" cone drivers (and maybe even for your woofer, to a lesser degree) in active filtering scenarios

Bruno Putzeys:
I think you are referring to the current drive used in the Kii and Grimm speakers to reduce the hysteresis distortion in the legacy drivers that are used there.

The Purifi woofer doesn’t rely on anything on the amplifier end for its performance, because we don’t want to force people to buy both drivers and electronics from us (or give the impression that we do). But neither would it make sense to give people instructions how to improve the performance of their non-Purifi drivers. Or give the impression that doing so brings them anywhere close to what our driver does. Current drive cleans up the mid-band like a treat but low frequency performance does not improve.

Besides, we sell amplifiers and drivers. If we were to start selling complete solutions, what value is there to be added by the manufacturer that buys our stuff and puts it in a box? It’s bad enough as it is with amplifier companies fearing the inevitable question “so what justifies the price of your amp compared to a DIY build”.

 

[egellings]

The TA-F555ES has a damping factor of 125 so cannot possibly be a current drive amplifier and is with 100% certainty a voltage drive amplifier (so near 0 ohm output R)

That DF implies a stiff (low Z) voltage source to me.

 

[popej]

hat DF implies a stiff (low Z) voltage source to me.

Yes, it is standard class AB amplifier. Voltage to current circuit is for driving volume pot. (I feel sorry for users whose pot contact starts degrading.)

Anyway, speakers are designed for voltage drive. Switching to current will detune speaker box alignment and can affect the crossover characteristic. You can argue about the behavior of a single loudspeaker, but this is not sufficient to assess the actual effects.

 

[egellings]

Yes, it is standard class AB amplifier. Voltage to current circuit is for driving volume pot. (I feel sorry for users whose pot contact starts degrading.)

Anyway, speakers are designed for voltage drive. Switching to current will detune speaker box alignment and can affect the crossover characteristic. You can argue about the behavior of a single loudspeaker, but this is not sufficient to assess the actual effects.

Agree with the speaker statement.

 

[Cbdb2]

Well, hopefully not! Current amps still use feedback and since the voice coil is passive thermal runaway should not happen, so the voice coil won't burn up. At least not much more than with voltage drive.

For example, an 8-ohm AL voice coil will go to about 10.5 ohms* if temperature rises from room (27 degC) to 100 degC. Of course heat also affects the magnet and other factors... As stated earlier, mechanical distortion in the speaker driver still dominates the distortion, so the type of drive probably makes little difference in the end.

* https://www.allaboutcircuits.com/textbook/direct-current/chpt-12/temperature-coefficient-resistance/

I though feedback was to keep the current constant in a current amp?
From: https://www.stereophile.com/reference/1106hot/index.html
Voice coils are designed to with stand 200 degrees C. Copper is 1.7 times more resistive there than at 20 degrees.

Going from 20 degrees to 200 degrees a 100 watts voltage drive will decrease its power to 58 watts while a current drive will increase the power into the voice coil to 170 watts, a substantial amount. The powers got to go somewhere and it will just add more heat to the voice coil.
I agree these circumstances are very rare at home but you get people with big amps at parties turning it up to 11 and poof.
And I sure wouldn't want current drive in a PA system.

 

[KSTR]

Current drive actually keeps air motion transformer tweeters from burning up but for all other types it increases the risk of thermal damage.
SOTA PA amplification constantly monitor current and voltage going to the transducers and stop/reduce output when the transducer starts to behave oddly for whatever reason.

 

[GlennGregor]

The "current drive" part is inside the integrated amplifier, from the preamp section output to the amplifier's input. The output of the amplifier, the part that drives the speaker, is voltage-mode, as shown by the specifications and schematic circuit diagram that @restorer-john provided. It is a nice amp but the speaker output is not current-driven.

Edited by moderator. Got rid of the pottymouth part written by someone who doesn't realize how ignorant they really are:

The Sony Integrated amp I have is a Current Drive Integrated Amplifier, and I really don’t care what your opinion is on that. I’ve tried to explain the technology that Sony uses to incorporate the Current Drive in the integrated amp, and all you want you want to I do is tell me I’m wrong.

 

[Cbdb2]

Bye bye.

 

[GlennGregor]

Bye bye.

I’m not gone yet (bad word)

 

[voodooless]

The Sony Integrated amp I have is a Current Drive Integrated Amplifier, and I really don’t care what your fucking opinion is on that.

It's not an opinion, it's fact. You can rage all you want, but it does not change the facts.

 

[GlennGregor]

It's not an opinion, it's fact. You can rage all you want, but it does not change the facts.

You’re a (bad word deleted) too.

 

[Cbdb2]

I’m not gone yet prick

Why not? Never mind, ignore.

 

[BDWoody]

I’ve tried to explain the technology that Sony uses to incorporate the Current Drive in the integrated amp, and all you want you want to I do is tell me I’m wrong.

Because you're wrong.

Why not?

I had to wake up first.

Good morning everybody!

Goodbye Glenn. Hope your anger issues get better.

 

[DonH56]

I though feedback was to keep the current constant in a current amp?
From: https://www.stereophile.com/reference/1106hot/index.html
Voice coils are designed to with stand 200 degrees C. Copper is 1.7 times more resistive there than at 20 degrees.

Going from 20 degrees to 200 degrees a 100 watts voltage drive will decrease its power to 58 watts while a current drive will increase the power into the voice coil to 170 watts, a substantial amount. The powers got to go somewhere and it will just add more heat to the voice coil.
I agree these circumstances are very rare at home but you get people with big amps at parties turning it up to 11 and poof.
And I sure wouldn't want current drive in a PA system.

Short version: You are right, I was wrong. Oops.

Yes, the feedback is to keep current constant, and I was not arguing that the power does not go up assuming current is held constant. Reading back my response was poorly written, sorry. I was thinking (or maybe I wasn't) in normal use a voice coil rarely exceeds 100 degC (but that's a number I pulled out of a foggy memory so may well be wrong) so the likelihood of destruction was low. I skimmed a bit more, and as you and others have stated, current drive amps do best with drivers exhibiting fairly constant impedance and the ability to handle the extra power, mainly planar-dynamic and compression drivers in my quick search. What I found puzzling is applying to compression drivers, often used for sound reinforcement (PA systems and such), where I'd expect the extra power would be a bigger problem due to the high average power... Mea culpa.

Turning up to 11 at parties is an issue no matter the amp... I got a lot of business in my college days as a repair tech from beer parties.

For others, here are the usual simplified op-amp pictures of voltage and current drive. In voltage mode, the output is a voltage, and feedback is the output voltage through a voltage divider. In current mode, the output is a current, and feedback is sensed as a voltage across a known resistance using basic Ohm's Law: V = Iout*R. Since most speakers are designed for voltage drive and exhibit wide impedance variations driving a typical speaker with a current may not provide optimal results (also stated earlier).

The voice coil resistance usually increases as temperature increases (most all metals have positive temperature coefficients). Recall power P = V^2 / R = I^2 * R so as R increases, power goes down if voltage (V) is held constant, but goes up if current (I) is held constant.

Teach me to enter a speaker discussion, not my area of expertise - Don

 

[NTK]

I though feedback was to keep the current constant in a current amp?
From: https://www.stereophile.com/reference/1106hot/index.html
Voice coils are designed to with stand 200 degrees C. Copper is 1.7 times more resistive there than at 20 degrees.

Going from 20 degrees to 200 degrees a 100 watts voltage drive will decrease its power to 58 watts while a current drive will increase the power into the voice coil to 170 watts, a substantial amount. The powers got to go somewhere and it will just add more heat to the voice coil.
I agree these circumstances are very rare at home but you get people with big amps at parties turning it up to 11 and poof.
And I sure wouldn't want current drive in a PA system.

Isn't that supposed to be the price to pay to minimize your speaker output from "power/thermal compression" (which of course only works when the rest of the speaker system, e.g. magnetic strength, suspension stiffness, etc. are thermally stable)?