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Old 5th April 2013, 04:41 PM   #1
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Default Direct driving Apogee Full Range speakers

Hi
I've owned several Apogee's off and on over the years and now have a pair o the Full Range. Even in their stock configuration they are impressive speakers. But i know they can do better with active 3-way XO and direct driving the ribbons. I think i have sufficient amps for the job: 2 pr of Krell KRS 200 for the bass and MR and Clayton S40 for the TW. the KRS should handle the bass directly no problem and i think(?) the Clayton can handle the TW directly as well. the big question, as always, is the MR. I am very concerned about damaging the ribbons and do not want to run the MR directly despite the KRS probably ability to handle it. My question is whether to use a series resistor on th MR (and maybe the TW?) to raise the resistance up to approx 1 ohm, OR use a Speltz Zeroformer to do the same? I view these options as being sonicaly superior to using a full on transformer. Yes? So i would greatly appreciate some feedback/guidance on these alternatives, or some other approach?

Lastly, i repeat my concern for ribbon safety - will either the series resistor or the Zerofromer provide any protection for the MR and TW ribbons? the very last think i want to do is re-ribbon these speakers. Would adding in-line fast-blo fuse be advisable?
thanks!
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Old 5th April 2013, 09:45 PM   #2
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Putting a 1 or 2 ohm non-inductive resistor in series with both the Midrange and Tweeter ribbon will have very little negative sonic effect and should protect them from damage. Matching SPL levels can be done at the active Xover.


To protect the ribbons you want to avoid any amplifier clipping, plus all power-up and power-down DC or AC THUMPS. To protect the ribbons you want to keep low frequency BOUNCE off the midrange and tweeter ribbons. The original Apogee Xover included a series capacitor to protect the delicate tweeter ribbons. When the tweeter ribbons are directly connected to a large amplifier a small series resistor provides some damage insurance.

To protect the midrange and tweeter ribbons from stretching due to low frequency BOUNCE you want to use crossover slopes much steeper than the 6db/octave in the original design. You can get 18db/octave from a single amplifier stage. Discrete ClassA active crossovers, like the Krell KRX-1, provide a modest number of amplifiers for the crossover function such that 18db/octave is often used for 3-way speakers. The popular LR4 and LR8 steep slopes are typically constructed from IC opamps. Anything is possible with digital Xover.


Over the Full Range production lifetime Apogee made a few minor changes to the construction of the Bass Panel, midrange ribbon, and tweeter ribbon which affected their resistance, efficiency, and resonance.
MY SPEAKERS:
Bass Panel = 1.86 ohms
Midrange Ribbon = 0.14 ohms
Tweeter Ribbon = 0.88 ohms
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Old 5th April 2013, 10:02 PM   #3
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thanks Line Source - very much appreciated. a couple quick follow up questions:

what current rating should i get on the resistors? Was thinking 5 amp.

What exactly is low frequency bounce?

i currently use a Pioneer D-23 crossover in 2-way mode at 6 db slope (replaces stock passive XO). i plan to use it in 3-way mode to tri-amp. It does have the ability to run 18 db slopes, but wont i need to do something about phase shift around the XO points if i go 18 db?

Thanks again. Love the FR!
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Old 5th April 2013, 10:28 PM   #4
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I have to chime in here.

Do NOT overlook any DC offset at the amp output - this will move a direct coupled speaker in one direction or another (in or out) possibly more so with a ribbon which may offer little resistance to the force.
This could stretch your tweet ribbons in particular .
I raised the issue (unsuccessfully) of "wobbly' low freq output driving my direct coupled ribbons by my diy pas a5.
i was using a series resistor att he time and ended up going back to transformer coupled to avoid dc offset in particular..

Cheers
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Old 6th April 2013, 03:35 PM   #5
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thanks George. Ya, i will b measuring the dc offset today and see where i come out. a friend pof mine had FR's and was direct driving using tube amps with autoformers. every time he turned his amps on/off the MR and TW ribbons flapped around. any idea how much offset is acceptable?
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Old 6th April 2013, 06:20 PM   #6
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HI guys
i measured my amps for dc offset and they ranged from 1.5 mv to 25mv. Would obviously want to use the amps with higher offset on the bass panels. i also meausered the ribbons:
bass - 2.2 ohms
MR - .5-.6 ohms
TW - 1.2 ohms
These measurements were including the pigtail wires.

So i am thinking of padding the MR with 1.5 ohm resistor and the TW with 1 ohm. That way amps will all see approx 2 ohms. I do not know whether the dc offset will be an issue when using the series resistors or not. Does the power rating of the resistor have any impact on both sonics and level of 'protection'. I.e would a 5w resistor be better/worse than 20w? My listening levels are such that peaks are in the low 80's db. If these speakers are as inefficient as has oft been reported then i should think 5w might be too low. Would appreciate your feedback.

Thanks!
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Old 7th April 2013, 12:34 AM   #7
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Padding the ribbons up to a 2 ohm load is a good idea. You can always experiment with 1 ohm loads after safe operation has been proven over many hours.

I would purchase 25W or 50W non-inductive resistors from Caddock or Dale. Resistors this size often require some heat sinking for full power, so read the specs on free-air vs. chassis mounted power rating.
==========


Starting with just the resistors on the amp outputs would allow you to test the amplifier chain for poor servo DC, or DC/AC turn on/off transients under load.


I use the term ribbon BOUNCE for the large physical midrange ribbon movement when a deep bass transient is run through a shallow 6db slope Xover. The tweeter ribbon also shows some bounce off midbass transients. Transient ribbon bounce will quickly stretch out the ribbon pleats, requiring taking off the speaker grill_sock and re-tensioning the ribbon at the bottom clamp point. This will change the ribbon resonant frequency. If possible, I would start with 18db or 24db slope Xovers. The ribbons are resistive loads, so you will get very good transient response from these higher order slopes.

When your amp can effortly push 2,000 watts into 1 ohm
Be Afraid!
Be Very Afraid!

P.S.
Your measured resistance values are higher than "typically reported" on this forum. You may want to log onto the Apogee forum and ask if the Apogee factory started to use thinner Al foil on late model production.
bass - 2.2 ohms
MR - .5-.6 ohms
TW - 1.2 ohms
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Old 7th April 2013, 02:49 AM   #8
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thank you Line Source.
i have used both pr of KRS on my Scintillas (1 ohm version) and never noticed any transients from turning on/off. But the Scintillas do have capacitors in the passive XO so that may have muted any transient.
My ribbons are original as far as i can tell and already have a fair amount of movement in them, so re-tentioning is probably in the not too distant future. They need new socks anyway. Are there any specs and/or instructions for proper tensioning? When you consider that Graz has several different versions and they are all probably different from OEM it gets a little confusing as to what the proper tension would be , not to mention different impedances.
Anyway, i will order up some power resistors and see if i can get these guys singing wihtout screaming in pain. As a test i was thinking i could leave one leg of each speaker cable unattached to MR and TW ribbons, then power everything up and very briefly touch the unattached lead to the MR ribbon pigtail and see if there is any movement at all. If not then i may be in the clear. Do the same for TW ribbon If it moves then its back to the drawing board
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Old 7th April 2013, 04:16 AM   #9
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Quote:
Originally Posted by 90493m View Post
Are there any specs and/or instructions for proper tensioning?
As a test i was thinking i could leave one leg of each speaker cable unattached to MR and TW ribbons, then power everything up and very briefly touch the unattached lead to the MR ribbon pigtail and see if there is any movement at all. If not then i may be in the clear. Do the same for TW ribbon If it moves then its back to the drawing board
I would never "hot" connect an open amp onto a speaker. Perhaps consider putting an 8 ohm dummy load resistor across the amp output before you switch in the ribbon circuit for test.

Ribbon Tensioning: I once read a spec where "V" bent plastic coated solid copper wire, as used in home power wiring, was slipped onto the ribbon foil between pleats just below the bottom clamp as a weight to set the tension. I do not remember what AWG was used ... probably 12. Gratz would be an expert in ribbon tensioning techniques.
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Old 7th April 2013, 02:09 PM   #10
tyu is offline tyu  United States
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Thanks for this post....
I have Had A pr of Duettas an from the 90s 5 pr of the stages..
The pr of Stages i have now were made in the 93...the MT have always moved as the Duettas did all over the place...an yes we think it All has to do with the 6db crossover letting low fre in the the MT ribbons....
You would think looking on paper at the passive crossover this is the case..
I have been looking at this in my Apogees speakers an have found a way to stop About 80% of the movement....
I have found that if the Crossover coiles are not gluded down... Like all are ..thats with one side of the coils pressed down to some type of board....or what ever
I have pull the coils lose in the MT Stock crossover an then put 1/2 rubber spacers in only two pr coil... an glued the rubber to the coils an then the board..
This stops this from moving a Lot...
Now I too thought it was the Base driver that was adding a LOt to the movement in the MT...if it is it the other 20%..
An there is know more Twesting of the MT ribbon with this setup...

Now when the movement stops the MT the sweetness of the passive crossovers relly come in...Jason liket the passives crossover sound better than any other...
I got in to this becaues My Magnepans true ribbons Move more than any ribbon i have ever owened...way to much to give the best sound ..an i found that geting the coils lose from the boards stop this 50-60%...an the Maggy ribbons are nothing the wind can kill one..
Just one ribbon lovers finding....Good luck
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