Damping adjustment questions

JonTee

Well-Known Member
Hi members,

Some of the tube amps i have recently acquired have a adjustment on the back for damping of the bass frequency. the manuals included with these amps (vintage) state this adjustment may be used to alter bass damping from more 10 to a factor of 2. The mauals go on to state that this may be used with newer (these were 1959 and later amps) compact speakers that have a higher damping factor built into them.

When would I want to use this feature?

What kind of speakers would lowering the damping factor work best with and what kind of results can be expected from lowering the damping factor?

I noticed a relatively newer solid state amp (Accuphase E202) had this feature also.

Thanks in advance for your help:)

Jon
 
Loudspeaker damping from the amplifier

Jon,

Loudspeakers with piston cones will continue to move in the direction they are pushed from cone inertia when the drive signal has stopped. The idea of electrical damping is to use the output circuit of the amp which connects to the voice coil to act like a low impedance short circuit to the voice coil after the drive signal is gone. This makes the voice coil, working now like an electrical generator under heavy load to come to a faster halt, reducing its tendancy to ring or overshoot. The sound of percussive events like kick drums will sound mushy if the loudspeaker is underdamped.

You can demonstrate this for yourself by taking a woofer and carefully pushing/pulling the cone from the edges with your fingers. It will move fairly easily within the limits set by the spider and surround. Now take a wire and short circuit the speaker terminals and repeat the test. Now it will be noticeably more difficult to move the cone in and out. You have turned the driver into a generator and it is convcerting the work you are inputing with your fingers into electrical energy that is being converted into small amounts of heat in the shorting wire.

Solid state power amps typically have high damping factors whereas vacuum tube amps have rather low damping factors.

One way to increase the damping factor of any amp is to add negative feedback. Solid state amps mostly employ huge amounts of negative FB which in part explains their high damping factor. If a tube amp manufacturer places a user adjustable negative FB control on the amp they could conceivably label it "Loudspeaker Damping Control". Best to set this control while listening to music with good percussion and set this control for most pleasing, tight reproduction with whatever speakers you are using.

Some speakers are highly damped by the air against the cone, especially the case in horns. This explains why horns can sound so good producing tight 'fast' sound with tube amplifiers despite the generic lack of good damping in tube amps. My number one speaker recommendation for use with a low damping factor amplifier? Large full-range horns!

Rob
 
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My number one speaker recommendation for a low damping factor amplifier? Large full-range horns!

Rob,

So if I were using horns and set the damping factor to 2 the resulting sound would be more open, larger sounding? I am thinking horns for mids and highs thru my vintage tube amps, and electronically crossing -over to a solid state amp for LF.

This may be a speaker forum question, however, when going in the horn direction, what horn(s) and drivers would AK members recommend for this? The tube amps I will be experimenting with are push-pull designs from 12 wpc to 40 wpc.

Thanks for your replies:)

Jon
 
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Jon,

I don't know anything about the size of your room or the kind of music yo like to listen to and how loud so I can only be somewhat helpful in my recommendations. I can tell you that I had a pair of Altec 500-B horns (802-8D?) drivers ) running on a 20 watt/ch PP tube amp and two 15's in an infinite baffle sealed box for many years. I drove the woofers from a SS Marantz 240 (120 watts /ch)and used an 18 dB/octave active crossover at 500 Hz in front of the power amps. I really liked that system and it worked well even in smaller rooms. It would go as loud as you wanted and more. It would drive your ears into limiting well before it would run out of SPL's.

A set of big Klipsch corner horns might be the ticket if you have the room and just drive the whole box on one of your 40 watt tube amps.

I was all into tri-amping in my previous system and have gone back to full spectrum, single amplifier configuration for the simplicity and safety factor it provides. Putting a full range power amp directly on a compression horn driver without a HP filter between can wipe the driver if you ever have a 60Hz hum accident with an input cable in a loose RCA jack. This happened to my system when it was in someone else's hands.

I made a set of full-range front loaded horns that load down to 50Hz (measured out in the open outdoors, corner placement makes them go lower) just over a year ago that I am very happy with. They are very efficient (over 100dB) and fill a large listening room with a small SET amp in the 5 watts RMS range no problem as loud as I need. The bass is very fast and articulate. I used a 12" coaxial pro-sound driver from Parts Express. It is just like a smaller version of the legendary 15" Altec 604 coaxial. Has a 2" titanium compression driver on the very back firing through the woofer magnet into a small horn in the middle of the woofer cone. These speakers were custom sized for my home theater and have to be partially disassembled to get them down the stairs. I made them as big as absolutely possible to achieve low frequency extension. They are 75" high, 29" wide and 5 feet deep. I offer this as an example of a superb horn speaker that sinergizes extremely well with low to medium power tube amps. Photo included.

Altec made some outstanding home speakers like the Model 19. 511B horn upstairs and a great 15" woofer in bass reflex downstairs. These are easily bi-amped if desired. In fact there was a whole lineup of 2 way speakers from Altec in this configuration, all which deserve a listen. You might like a set of Altec A-7 Voice of the theatre speakers if you have a really large room. Klipsch made some smaller horns like the LaScala that might be right for you.

Best to move this over to the speaker forum. There is a large experience base here at AK with good loudspeaker systems.

Regarding the damping control. I won't make any setting predicitions. Best thing is to twiddle it while listening to your system and set it where it sounds best, not where a particular damping factor number is indicated.

Rob
 
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Rob,

Thanks for your input. I will move this over to the speaker forum once I get my amps up to speed.

Those are very impressive horns you've built:jawdrop: ! Nice work!

Jon
 
Some homebrew tube amp and speaker rambling

Thanx Jon. Are you scratch building your tube amps? If so I'd be curious what you are building.

I'm designing a hi-end SET right now with a proprietary circuit (I've been fiddling with this circuit for over 6 months) that uses four 6080/6AS7's per side and happily drives loudspeaker loads from 16 to as low as 3 ohms! My design has user adjustable NFB from Zero through about 6 dB. I really like the sound of the prototype in the shop on my test speakers at around 2 dB NFB. Unlike many SET amps this one has negligible 2nd order HD. I have hopes of making a very limited number of these available for sale. I've also prototyped a very nice (IMO), highly efficient speaker (100dB club) that can work great with low power tube amplifiers excepting that it has a 4 ohm impedance at low frequencies and this limits one's choices of suitable tube amps. I could change this to more friendly 8 ohm territory by using 16 ohm woofers if I could find some. I saw this instead as a challenge to design a suitable tube amplifier.

Despite the 4 ohm issue I am able to use a homebrew stereo tube amp that I also really like on my big 8 ohm horns. This amp uses the Dyna MK-2 circuit but recently got rewired from P-P ultralinear to P-P triode 6CA7's and I've added plate choke load in the 6AN8A input amps. The power output dropped to 14 watts/channel but I'll put this amp up against 300B SETs for midrange magic with a bonus of P-P bass (zilch 2nd order HD) and good inherent triode damping factor to any challengers. It drives my new difficult tube load speakers very, very well. I did an A-B comparison with these speakers again last night with this 6CA7 tube amp against my Sansui 9090. The tube amp wins by a light-year despite the huge power advantage of the Sansui.

My new SET amp is significantly more costly component wise and complex to build than the modified Dynaco MK-2 circuit so I hope that it is noticeably again a plateau better than the modified Dynaco. If not I will still be in audio heaven. I'm really into the area of diminishing returns now with this setup, and these new speakers are not even horns. :eek:

Rob
 
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Well, you've sold me...!!!

Do you have a 2 years same as cash plan:D?

My plans are much more modest than that. Electronics has always been an interest to me, however, until now I didn't have the time to develope the skills and knowledge many of you at AK have. I am a novice at this point, trying to teach myself basic electronics and circuitry.

The bug for tubes overtook me when I salvaged a 6v6 tube amp from a Magnavox and started playing it in my garage with some thrift store speakers. I found it amazing that this little amp could sound so good.

Started collecting vintage Sherwoods after that based on recommendations from this site and others. Collection includes:

S-5000-II stereo integrated
S-5500-II stereo integrated
S-1000-II mono integrated
s-4400 mono integrated with stereo pre (anybody know where I can find a S-360)
S-2100-II tuner
S-2200 tuner
S-8000-IV receiver

Plus a ugly little Pilot 240 that sings so sweetly you've got to love it despite its looks.

Do you think I'm...you know:screwy:...

I've got this sacd player I want to hook into the first three Sherwoods listed, down in my basement listening room, to do multichannel as well as stereo. The room isn't very large, 12X14, but will be expanded to 24x14, hopefully, next year.

Millerdog and others here have suggested the Bottlehead SET amps as a starting point into amp building, although, I don't feel I'm ready for that yet. Meanwhile the Sherwoods, Pilot, and the little 6v6, continue to sound way better than something that old should.

Jon:)
 
Don't overlook vintage Bozak speakers for tube amps!

Jon,

You have a nice Sherwood museum there! I have been eager to hear the S5000 and S5500 for a while now. I almost bought one several times but now the prices are inching up and I really don't need 'em since its only to compare to what I'm building.

It just occured to me that you might also wish to look out for a pair of vintage Bozak loudspeakers. I have a pair of cabinets that have the B199A, 12 inch woofer on a 15" flange plate that supports a pair of B209 tweeters with a simple oil cap first order HP filter crossover. They are in an approx 4-5 cu.ft. box and sound amazing on some of the tube amps I've tried. They were of course voiced just for tube amps of the early 60's and have high efficiency. I think mine are called B301's. Bozak made some bigger ones like the B310. The lower cutout behind the grillecloth is not a reflex port, it is a blocked hole used for a 5" midrange driver in the next model up.

Rob
 
Here is the inside of the Bozak speaker cabinet. These are a completely sealed infinite baffle enclosure.
 
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