Question.....If I have a SS Class A/B vintage amplifier (B&K ST140 for instance)....And it is known to not play well with low impedance speakers (Magnapans for instance)......Could I put a Xohm resistor on the speakers to show a higher impedance to the amplifier?
Adding series resistance to a speaker is a "Brute Force" Method for impedance matching.
Supposedly all Resistors sound different (Metal Film, Carbon Comp, etc), and the higher wattage type you would be using (ceramic) directly in the signal path, may sound questionable.
BUT these are the same resistors used in the Magnepan Crosovers!
Try with and without. I doubt the amp would have a hard time unless overdriven...
Supposedly all Resistors sound different (Metal Film, Carbon Comp, etc), and the higher wattage type you would be using (ceramic) directly in the signal path, may sound questionable.
BUT these are the same resistors used in the Magnepan Crosovers!
Try with and without. I doubt the amp would have a hard time unless overdriven...
Adding a series resistor between the amp and the speakers severely drops damping factor and squanders power.
Best regards!
Best regards!
Are you throwing Maggies in as an example or are these what you actually want to use with the amp?
I see the B&K is a lateral FET design and all I can say is my own amp (Lateral FET) has no issues driving B&W703's which can apparently dip down to 2.8 ohms.
I bid on a B&K ST140 (2nd generation) and I'm aware of the low impedance issue with this amplifier. I will be using it with KEF LS50 Metas and Magnepan LRS...
So KEF quote a 3.5 ohm minimum so I don't think that should be a problem. From what I'm reading I would think it should be fine (unless you are into extreme SPL).
This is what I found on the Mag's vs the B&W's I use which read as a more difficult load tbh. All you can do is try it 🙂
This is what I found on the Mag's vs the B&W's I use which read as a more difficult load tbh. All you can do is try it 🙂
Electro static speaker will have series resistor and matching transformer already in design.
Opinions vary. FET was somewhat new technology in 80s
so the amp would be considered robust for low impedance loads.
I believe it only has single pair of output devices.
If I was to design amplifier for low impedance
Would use multiple pairs for lower distortion, less beta drop.
As far as vintage amplifier, likely capable of driving low impedance.
As with any vintage amplifier, most would be concerned about power supply health
and maybe clean and update thermal grease.
otherwise brand new, that amplifier can drive 4 ohms no problem.
Some electrostatic may dip down to 2 ohms.
As with any amplifier, low impedance load has heat concerns
and can create more distortion. Just observe amplifier temperature.
Opinions vary. FET was somewhat new technology in 80s
so the amp would be considered robust for low impedance loads.
I believe it only has single pair of output devices.
If I was to design amplifier for low impedance
Would use multiple pairs for lower distortion, less beta drop.
As far as vintage amplifier, likely capable of driving low impedance.
As with any vintage amplifier, most would be concerned about power supply health
and maybe clean and update thermal grease.
otherwise brand new, that amplifier can drive 4 ohms no problem.
Some electrostatic may dip down to 2 ohms.
As with any amplifier, low impedance load has heat concerns
and can create more distortion. Just observe amplifier temperature.
The lateral fet's are now available as modern double die' parts with a 16 amp rating and I would think they would be a direct replacement with only a tweak of the bias current needed. It is certainly something to consider.
Having said that I looked at the ever popular diy amp from the 80's (the Maplin lateral fet amp) which uses the original single die 2SJ/2SK parts and that is rated at (gulp) 150 watts rms into 4 ohm and 100 watt into 8 ohm.
This generation has single pair of FETs...The next generation (3rd Gen) has two sets of FETs ....just so it can drive low impedance loads more easily.
(Magnepans are not electrostatic.....)
"Put a 4E woofer in series instead of wasting power?"....Now THAT is an interesting idea!
(Magnepans are not electrostatic.....)
"Put a 4E woofer in series instead of wasting power?"....Now THAT is an interesting idea!
The double die FET's are just two standard ones in the same package.
https://www.profusionplc.com/parts/ecf20n20-s
https://www.profusionplc.com/parts/ecf20p20
https://www.profusionplc.com/parts/ecf20n20-s
https://www.profusionplc.com/parts/ecf20p20
That is pretty cool actually.
And the Maplin/Hitachi style amplifiers being such a DIY favorite.
Would be a perfect candidate for a double die project.