Amplifier Output Impedance (Damping Factor) and Speakers

[DonH56]

Indeed. Do you have any figures for this with a 'typical' amp? I knew how it varied with valve amps due to very limited open loop bandwidth, but always assumed with SS amps that even if the variation was 'large', it was still sufficient even at HF and low LF or it not to have an audible effect.

S

The values used by me in the opening posts are based upon real amplifiers. The data are hard to come by since most manufacturers only spec at a single point. The purpose of this thread was to expose people to what output impedance and thus damping factor meant with some reasonable real-world examples (amps and speakers). I quit following the debate shortly after that so have not kept up with the past few pages of whatever.

 

[sergeauckland]

The values used by me in the opening posts are based upon real amplifiers. The data are hard to come by since most manufacturers only spec at a single point. The purpose of this thread was to expose people to what output impedance and thus damping factor meant with some reasonable real-world examples (amps and speakers). I quit following the debate shortly after that so have not kept up with the past few pages of whatever.

Sorry, I should have gone back to the beginning! After 7 pages I'd forgotten what went before. Damping factor, or as I prefer, output impedance, isn't anything with which I've concerned myself since the days of valve amplifiers. It's always been 'adequate' with any sensible amplifier.

S

 

[Kijanki]

It was mentioned here, that amplifiers with lower DF tend to sound warmer. I do not believe that DF (above 20) has anything to do with the sound, but the way it is obtained does. The easiest way to improve anything, including output impedance is to increase NFB. 40dB NFB will reduce output impedance 100x, but can also introduce some TIM distortions - added higher order odd harmonics, that will make sound brighter.

 

[pogo]

40dB NFB will reduce output impedance 100x, but can also introduce some TIM distortions - added higher order odd harmonics, that will make sound brighter.

According to the T+A A200 description, the NFB is not affected when switching to DF LO!

 

[sergeauckland]

According to the T+A A200 description, the NFB is not affected when switching to DF LO!

It could just switch in a low value resistor.....

S

 

[Kijanki]

According to the T+A A200 description, the NFB is not affected when switching to DF LO!

Sorry, but I don't understand this statement. Output impedance is inversely proportional to amount of NFB.

 

[pogo]

Sorry, but I don't understand this statement. Output impedance is inversely proportional to amount of NFB.

There's probably more to it than adding a resistor value.
The head of development, preferred not to reveal exactly how this reduction in the damping factor of the purifi amp works when asked - it's a company secret.

 

[Kijanki]

I stated that in general the easiest way to reduce output impedance is to increase NFB. I don't question that some companies might do this differently, for instance by adjusting something in the output stage. Increase in NFB might explain brighter sound. Other than class D amps that have inherently low impedance I would stay away from anything that has DF>1000 because it is very likely obtained by deep NFB. DF=1000 is like a keyboard that you can type milion words per second.

 

[restorer-john]

It could just switch in a low value resistor.....

Have a look at Accuphase's first integrated amplifier, the E-202 in 1974.

They implemented switchable (>30, 5 and 1) 'damping' and it works very well (resistors-0v-NFB loop). A significantly aubible difference and beneficial for many sealed speaker systems, particularly large 12" and larger of the time, that were in realively small cabinets with an otherwise limited and 'tight' bass. Or electrostatics.

 

[restorer-john]

The head of development, preferred not to reveal exactly how this reduction in the damping factor works when asked - it's a company secret.

It's hardly rocket science. You can even drive the ouptut stage to a 'negative impedance'. Yamaha did that for a decade (in subwoofers/mini systems) with YST/AST (Yamaha active servo technology). The dedicated HiFi YST speakers came with a cartridge specially configured and you plugged it into the rear of the YST amplifiers. For normal speakers, a flat cartridge was supplied with the amp.

Amazing system but never caught on. Could have been a game changer. We ended up selling the amplifiers, systems and speakers really cheaply when they killed the concept after less than a year.

They still use it in the powered subwoofers IIRC.

 

[Doodski]

It's hardly rocket science. You can even drive the ouptut stage to a 'negative impedance'. Yamaha did that for a decade with YST/AST (Yamaha active servo technology). The dedicated YST speakers came with a cartridge specially configured and you plugged it into the rear of the amplifier. For normal speakers, a flat cartridge was supplied with the amp.

View attachment 176017

Amazing system but never caught on. Could have been a game changer. We ended up selling the amplifiers, systems and speakers really cheaply when they killed the concept after less than a year.

They still use it in the powered subwoofers IIRC.

I used to have one of those CDN ~$1000.00 Yamaha servo mini systems. It sounded fabulous and beat out everything else in the store for mini-systems. I won it in a Yamaha sales contest. Sold it after a week because I had gear coming out my ying yang. Great product. I forgot I even owned one till you mentioned it.

 

[Chr1]

Yamaha YST-C11. Very good sound quality for a boombox/minisystem I reckon. Picked mine up for all of £10. Fully functional with remote.

 

[restorer-john]

I used to have one of those CDN ~$1000.00 Yamaha servo mini systems. It sounded fabulous and beat out everything else in the store for mini-systems. I won it in a Yamaha sales contest.

Which one?

They also had the system 90 with YST. The integrated amplifier in the 90 series system had an onboard D/A converter (18 bit) fibre optic connections and 45wpc.

 

[restorer-john]

Yamaha YST-C11. Very good sound quality for a boombox/minisystem I reckon.

The C11 was the pick. Absolutely an amazing little shelf system.

 

[Doodski]

YS-NC1. The Yamaha rep of the time took pretty good care of us as we were the most loyal crew and biggest account that Yamaha had in Western Canada. (I'm pretty sure it was this one. Been a long time and like I said I forgot I even owned one.)

 

[Chr1]

Mmm. Now wishing I'd got the optional speaker stands too... Damn good deal nonetheless as it is mint.
Mustn't grumble!

 

[Chr1]

Got mine cheap due to everyone nowadays wanting tiny audio gear...even the Yamaha is now seen to be too big. I love it as large high quality hifi gear can be bought cheaply second hand. Splendid.

 

[Doodski]

Mmm. Now wishing I'd got the optional speaker stands too... Damn good deal nonetheless as it is mint.
Mustn't grumble!

It was the best of the best mini-system sound in it's day. I know I used to stand around the front personal electronics counter of the store listening to the Yamaha. I preferred the Yamaha because it was the best to listen to for any kind of music.

 

[DonH56]

I stated that in general the easiest way to reduce output impedance is to increase NFB. I don't question that some companies might do this differently, for instance by adjusting something in the output stage. Increase in NFB might explain brighter sound. Other than class D amps that have inherently low impedance I would stay away from anything that has DF>1000 because it is very likely obtained by deep NFB. DF=1000 is like a keyboard that you can type milion words per second.

Loop gain and bandwidth along with feedback factor, distortion, noise, and stability are affected by feedback and can be a rather complex system of trades. I agree NFB is the way it (reducing output impedance) is done, and often the only practical way, but would not imply it is easy... But, a well-designed amp should not have problems with high feedback, and there are other tricks to improve (reduce) output impedance as well.

 

[DonH56]

Which one?

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View attachment 176026
They also had the system 90 with YST. The integrated amplifier in the 90 series system had an onboard D/A converter (18 bit) fibre optic connections and 45wpc.

John, you scare me sometimes... Go man go!