My 4343's are finally on the way [any one interested in the 300's?]. I have an old Crown VFX-2 crossover that just tested great. The plan is to bridge 2 DC300A's to mono for the lows, a McIntosh 2205 for the rest. Having never undertaken a bi amp project, any and all inputs/ideas/warnings would be greatly appreciated!
Re: 4343' S On The Way!
Congratulations!
Crown VFX-2A
You are gonna love that crossover!
RELIGIOUSLY follow good turn on/turn off sequence with that crossover.
Then again, I promise you'll only make that mistake once.
You might want to use the 1/4 inch balanced inputs, because you have user adjustable gain, and this will compensate for any insertion loss. You have screwdriver adjustments on the back, allowing you to go from unity gain up to +15.5db. If you use the unity gain inputs it might be too dead sounding. Both your amps have input level attenuators, and you will have to balance the level between high/mid and low from here as the VFX has no output level attenuators.
Jus my .02 cents!
If you find a JBL 5234 with correct cards, it has a turn-on delay so the whole system can be turned on/off at will.
In addition the power switch on the crossover works great as a mute ( since we all know how quiet these will be listened to...)
Plus offsetting the VFX filters by the exact amount on both channels is gonna be hard without good test gear ( LP appox 290, HP appox 320 )...
Those controls are 20% tolerance pots and the print is only as accurate as the guy who put the knob on....!
sub
Originally posted by subwoof
Those controls are 20% tolerance pots and the print is only as accurate as the guy who put the knob on....!
A subwoof truism...
bo
"Indeed, not!!"
Speaking of the VFX, I had one years ago. Maybe they were upgraded later, but mine had horrible 741 type quad op-amps and very wimpy power regulation.
At the time I added 7815/7915's, better filter caps and decoupling and TLO74's because it was the best thing to do in those days. I'm sure there are way better quads today, just be careful - wide bandwidth opamps can be a devil if installed in PCB layouts that are not layed out to accomodate high performance chips. We used to call it "green screen" when the HF oscillation was viewed on a'scope.
If you want to be safe, the TLO's at least, were a huge improvement.
C.
Last edited by Chas; 04-22-2004 at 12:40 PM.
Agreed on those quads - someone once sold a 14pin socket with .01 CK5's embedded for decoupling the rails. Great for quicky upgrades.
Those VFX's had none - and the 4 pin regulators ( they were the ONLY manufacturer that used them ) were noisy + could not handle the current. I can't tell you HOW many PSA2's failed because of them.
I think the OP09 also worked BUT the pinout was set to the "other" quad standard???
The last VFX I took the list off had 5532's in it, a bit ancient but a well engineered unit and quite clean for a crossover.
I would tend to have the crossover always on, saves expensive recones. Try them passive just for comparison with the McIntosh 2205, it may sound smoother in some respects.
Ian
All electronic crossover tend to scrub the sound to a certain degree (despite the tighter sounding bass.)
The additional buffer stages, often 4-6 stages add successive noise and distortions. The buffers tend to configured for unity gain with 100% negative feedback which these days is considered a no no for top audio performance.
However years ago most power amps had lousy intermodulation distortion and TID anyway and bi amping cleaned this up a lot and was preferable to 60 uf of Myler caps in series with the mid cone in passive mode.
New crossover parts and better amps, well who knows?
When the parts arrive I will dish up a proto type mini version of this for you guys to try. No I.Cs, full discrete regulation.
Full balanced in and out or unbalance in and out, discrete class A buffers biased to about 10 milliamps (TL074s are AB) with low feedback, the regulator will have 42000uf of passive CRC filtering and zero feedback mosfet series regulators.
I think it will be good.
Ian
Hey, subwoof, I think you jogged my memory cells a little bit, come to think about it, maybe they were an oddball pinout. I think I used TLO75's. Anyway, same family.I think the OP09 also worked BUT the pinout was set to the "other" quad standard???
C.
Yes, the TLO series op amps are an improvement over those 741,s. But, the TLO84 is a better sounding IC than its low noise counterpart, the TLO74! The 84 has better presence and a more solid sound!Originally posted by Chas
Speaking of the VFX, I had one years ago. Maybe they were upgraded later, but mine had horrible 741 type quad op-amps and very wimpy power regulation.
At the time I added 7815/7915's, better filter caps and decoupling and TLO74's because it was the best thing to do in those days. I'm sure there are way better quads today, just be careful - wide bandwidth opamps can be a devil if installed in PCB layouts that are not layed out to accomodate high performance chips. We used to call it "green screen" when the HF oscillation was viewed on a'scope.
If you want to be safe, the TLO's at least, were a huge improvement.
C.
I know Im gonna get shot for this, but its my honest opinion!
Scott,
If you are keen to play with drop in chips on the fly, try the BurrBown opa 2134s or the 2604.
Analogue Devices also have some new chips, just make sure they are Fet input (input low offset).
However the best chips are no chips.
I am hopeful of hearing an XV1 Passlabs crossover in a week or two (as above). The proof will be in the pudding.
Ian.
Ps I wonder if Bo's back door is blue?
BB IC,s are very good and extremely accurate. They do sound different from TLO chips. Yes, I agree that Jfet or FET input is the way to go.
I have several BB IC,s on hand as well as Analog Devices. And still, for one reason or another, I like the way the TLO84 sounds.
Discrete circuits are the best, and the most expensive. Brystons xovers are all discrete and very clean, yet still maintains warmth, and is exceptionally accurate.
Im interested in your xover, Ian, if you can configure some custom stuff in it for me.
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