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dlwearl
12-11-2007, 08:12 PM
Hi everyone,

I'm building a 4-way stereo system with an active crossover and therefore need an amplifier that will handle the duties of 10khz or so on up.

The drivers are JBL 2405h and so far the system consists of two Yamaha power amps (M-80 and P-2200) and one Crown Com-tech 800.

I would prefer something with xlr inputs but RCA inputs are also ok. It need not be rack-mountable. Preferably under $500, and vintage equipment is fine. I would also like it have a frequency response through 100khz.

I was personally considering a Yamaha B2 but that's partly because I can actually find specs for the damping factor at 20khz (50). Neither it's THD nor it's S/N ratio are terribly close to those of my M-80 although I've read that it produced wonderful sound.

Thanks,
David

pos
12-12-2007, 02:21 AM
Hello dlwearl, welcome to this forum!

here is what Greg Timbers (4345's designer, among many other great JBL speakers) has to say about it (from the 4345 club thread):

The ring radiator hates passive networks. A major improvement in the upper range would be to drive the 2405 from its own little amp. You only need 3 or 4 v rms. The 2405 does 110 dB for 2.83v. It is padded way down in the system. There is little real power at those frequencies anyway. You only need to know the voltage output of the amp, power is irrelevant. The 2405 is about 12 ohms and won't draw much current. I would use some little chip amp with a 2ond or 3rd order low level highpass in front of it. Take off the passive network to the ring and just feed it straight. Make sure the amp doesn't make a DC thump on turn on or turn off. That will fatigue the diaphragm. The amp will also have to have really low noise characteristics as any hiss will be really loud directly into the ring. I used to use an old Marantz 1030 integrated amp to run my rings. I could separate out the power amp section and the tweeters always sounded really good.I think that Ian wanted to try some class A chip amps on his slots, integrated into the cabinet, but I don't know the results.
I have tried the T-amp (cheap/chip amp) on my compression drivers, but it had too much hiss for such sensible drivers, and more importently, it emitted a nasty "click" (not DC thump I think, but still annoying) when turned on/off. I think the "Super T-amp" uses a relay to avoid this.

I've also read that some members here use crown d75 or d45 to drive there slots.

Are you going to use protections caps on your slots?

matsj
12-12-2007, 03:03 AM
If you can build something, try this. I can really recomend this.

http://www.audioheritage.org/vbulletin/showthread.php?t=18253

mats

SMKSoundPro
12-12-2007, 02:40 PM
Dear dlwearl,

I am using the Yamaha P2200 family of amps and really love them!

I am using a P2200 for lows, P2200 for low-mids, P2100 for mid-highs and P2050 for tweets.

I use a dbx 234 three-way crossover with a dbx 120 to do the 120hz and lower sub driver.

The amps are cheap and easy to come by. It really sounds great in my shop stereo at work!

If Crown is your thing(and mine too) Try the D60 or D75 for the top. It has always been a classic amp in my small world.

Good luck!

Scott.

scott fitlin
12-12-2007, 05:13 PM
For cheap off ebay, Crown D-75 amps are a great match for JBL tweeters, and sound great to boot. I use Crown Power Line 2,s, an enhanced D-75, I have been using these since 1985, and I have tried many other things, and always put the Crowns back.

And they are pretty cheap on ebay!

:)

Baron030
12-13-2007, 03:20 PM
Hi dlwearl,

In my own quad amplified 4 way system, I use a Crown D75a to power my 2405s.
And in my opinion, the Crown D75a is a match made in heaven for the 2405s.
Absolutely great sound and they can effortless keep up with other 960 watts/channel within my system.
So, the D75a would be a great choice for your own project.

But, I would not recommend that you wire the 2405 drivers directly to an amplifierís output terminals.
Amplifiers can produce noises during turn on and/or turn off cycles.
You can call them pops, clicks or thumps, these noises do contain a lot low frequency energy, which can damage diaphragms.
So, install a high pass filter between the amplifier and the 2405 driver for protection.
In the schematic pictured below, is the high pass filter that I use in my own system.
It utilizes charge coupled and by-passed caps for really low distortion and a damping resistor that helps with the transient response.
Actually, in the case of the 2405 driver, the 40 ohm 10 watt damping resistor is really optional.
And the reason why I say this is that the 2405 does not have any large resonance peaks within its impedance.
But, for other drivers, adding a damping resistor can make a very noticeable difference.

In side by side listening tests, the circuit pictured below sounded just as good as having 2405s wired directly to the D75a output terminals.
So, the added expense of using charge coupled caps really is worth it.

Baron030 :)

dlwearl
12-15-2007, 07:55 AM
I had no idea Crown made smaller amps...I'll look into that.

Thanks so much,
David

Allanvh5150
12-16-2007, 12:50 AM
I will go with a crown D60 as well. Years ago I ran a sound reinforcement rig for a live band. We had 2000 watts below 80Hz, 1000 watts from 80 to 800, 125 watts from 800-5000 and the little old D60 from 5000 up. It had no problem at all keeping up.:)

BMWCCA
12-16-2007, 07:17 AM
I'd been considering a small Crown for years for HF duty using Crown VFX-2A crossovers, but the price was always so high compared to larger Crowns (double a PS-200 for instance). I asked, on this forum, why this was and Subwoof gave a good answer here (http://audioheritage.org/vbulletin/showthread.php?p=190556#post190556):



The D75 is *one* rack space. The D150 is *three*

size matters to the space limited audiophile.

The circuit, design and components are nearly *identical* BUT for the size of the power supply ( and therefore the output power ). Same output transistors. Same drivers. Same input chip ( except for the extra balanced ckt on the 75 ), same circuitry. Look at the schematics on line:

http://www.crownaudio.com/gen_htm/legacy/legacamp.htm

The D150AII would be a better choice since it has more headroom ( you do NOT need more power ) so it can handle transients better. READ THIS:

http://www.jblpro.com/pub/technote/lowpower.pdf

Get it??So now I intend to use either a D150A-II or PS-200 for the HF with the advantages outlined by Subwoof and since I already have spares of both. Once you start looking at D75A and D60 prices, compare them to D150A-II or PS-200 and maybe (if space is not an issue) the bigger amps make even more sense for your application.