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Old 1st May 2013, 05:17 AM   #11
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Quote:
Originally Posted by 90493m View Post
direct drive the TW should be easy - can either just use series capacitor to block dc (Clayton s40 amp should handle the 1 ohm load ok)
I do not recognize any of the pictured circuits as a DC servo. I just do not see the large non-polarized caps used for DC integrators that I normally use. Perphaps another reader will know how to adjust the DC offset level. Your DC direct ribbon experiments prove how important a 1-2mv DC offset is for optimal direct drive safety. I would not personally put a DC servo on the RELAY PCB on the rear panel, but Krell engineers might have selected that location because of access to the output signal.

Your Clayton S40 amp only has 4 output transistors per channel. Your owner's manual would likely spec the maximum continuous power into 1.2ohms. My DIY ribbon amps have 20 * 180-watt outputs/channel for a 1 ohm ribbon. You may end up using the Apogee 4-ohm tweeter interface to avoid damaging the Clayton S40.
==========
Let’s suppose you want to experiment with the reduced driver overlap of a 24db/octave acoustic slope.

FOR MID-TWEET… you use the standard Apogee Xover box wired for Tri-Amp which has a 4-ohm impedance that the Clayton S40 will like, and the Apogee capacitor-based passive 6db/octave slope at 4000hz. You program your active Xover for 18db/octave at 4000Hz and together you have a 24db/octave slope acoustic Xover. This combination is NOT EXACTLY the Linkwitz Riley ganged equation. For the midrange ribbon Xover, you use the 4-ohm transformer connected to the Krell KRS200, and program your active xover to 4000Hz at 24db/octave to match the tweeter. Again, maybe not a perfect match to the tweeter.

FOR BASS-MID: You program your bass active Xover for 24db/octave at 200Hz for both the bass and midrange. A 24db/octave Xover at 200Hz will put less bass energy on the delicate midrange ribbon than the original 6db/octave crossover at 400Hz. Direct drive the 1.8 ohm bass panel. Use the 4-ohm transformer for the midrange ribbon, adjust Xover gain for equal SPLs.

One Xover experiment completed! No amp destruction! No ribbon destruction!
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Last edited by LineSource; 1st May 2013 at 05:20 AM.
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Old 1st May 2013, 06:27 AM   #12
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thank you LS
as always your knowledge and insight are most appreciated! I think we are getting to the point where i am well armed to find the best combination of amps and crossover components.
I will keep everyone informed of my progress!

PS - will ask Krell where and how the dc offset is adjusted as well as the bias. one piece of good news - i measured all the caps on the driver boards and they are all within 5%.
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Old 6th May 2013, 04:31 PM   #13
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LS-
have you replaced the caps in your transformer box? if so i would be interested in what brand cap you used to replace them with. If i just stick with bi-amping the logical upgrade, other than possibly re-winding the MR transformer to 1 ohm would be to upgrade the stock caps and resistors. Just wondering what your experience has been with upgrades?

Thanks again LS

PS - even in their stock form the sound from the FR with the KRS is really lovely.
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Old 10th May 2013, 03:00 AM   #14
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Quote:
Originally Posted by 90493m View Post
LS-
have you replaced the caps in your transformer box?
I have not replaced the standard capacitors. They are now about 20 years old, and I do not hear any distortion. Good time to measure them for deterioration.

"Out of sight, out of mind".. :-)



Have you experimented with a steeper Xover slope between the bass panel and mid-tweet Xover? LR4 24db/octave slope at 200Hz should be a safe, simple experiment with your active Xover hardware. An experiment like this might help your future decisions for mid, tweet Xover slopes and frequencies.
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