[rajacat]

 I recently added a Crown XLS 1500 to power the woofers (Acoustic Elegance TD15m) in my 2 way bi -amped system. The Crown has an input impedance of 10 kilohms. I've used the Tort's adjustable impedance function over a wide range and I still can't enough volume out the Crown. The Crown has LED signal presence indicators' and the only way I can get them to show a signal is turn the volume very high and then they just flicker. I also ran the gain at max level but to no avail.
 I'm also have insufficient single going to my other digital amp which has 30 kohms Zin. Also my small sub amp signal seems to be not optimum at Zin 900mV.
My tube amp works well with the Tortuga.

My source (MHDT Constantine DAC) has 1.8V, 800 ohm Zout.

[Folsom]

It's not the impedance. The Crown's input volume for the RCA's is really low. A buffer alone won't raise it unless it has gain.

Maybe the 1/4in has more gain? I'm not sure if anyone's tried. I bet you can try an RCA adapter to 1/4in cheaply before buying something with gain. Alternatively maybe transformers for single to balanced, then into the XLR.

[rajacat]

It's not the impedance. The Crown's input volume for the RCA's is really low. A buffer alone won't raise it unless it has gain.

Maybe the 1/4in has more gain? I'm not sure if anyone's tried. I bet you can try an RCA adapter to 1/4in cheaply before buying something with gain. Alternatively maybe transformers for single to balanced, then into the XLR.

Thanks for that. I'll order order a couple of those and hope that that's an easy and cheap solution.

[Folsom]

Oh, you have to order? Darn, I thought they might be locally available!

[33na3rd]

If you are running the Crown (10K ohm) with the other amp (30K ohm)at the same time, then the Tortuga is seeing 7.5K ohms. That's a pretty tough load.

That 10K ohm of the Crown is the only thing that has stopped me from picking one up while they're having these great prices.

I think you might need a buffer if you want to biamp your system.

If you do get a buffer, I hope you'll do a review!

Best of luck!

PS--I see that one of the features of the new XLS 1502, is a lower input sensitivity, but the Zin is still 10k ohms.

[Folsom]

I guess I didn't ask, is the signal being split between all of them? 33na3rd would be right about that being a problem. 1.8v output isn't high, but ok for feeding a single item typically.

[rajacat]

Yeah, the signal is being split to feed the woofer, a 12" sub w/plate amp and a couple of 8" folded horn subs which are powered by one external amp. Hmm... the 12" sub's plate amp can get its signal from speaker level as well as line level. Perhaps I'd be best off feeding it with speaker level signal and therefore less load feeding off of the line level.
Anybody have experience with the Art CleanBox Pro as a solution to increase the line level?

 http://www.amazon.com/gp/product/B003S7T49K/ref=s9_simh_gw_p236_d0_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=desktop-1&pf_rd_r=04KWPPMGYE91AVNNW2Z1&pf_rd_t=36701&pf_rd_p=2079475242&pf_rd_i=desktop

[G Georgopoulos]

your problem is your source is definately loaded when you split the signal
you dont need amplification but an active buffer
this will split the signal with low zout

[Folsom]

Yeah, the signal is being split to feed the woofer, a 12" sub w/plate amp and a couple of 8" folded horn subs which are powered by one external amp. Hmm... the 12" sub's plate amp can get its signal from speaker level as well as line level. Perhaps I'd be best off feeding it with speaker level signal and therefore less load feeding off of the line level.
Anybody have experience with the Art CleanBox Pro as a solution to increase the line level?

 http://www.amazon.com/gp/product/B003S7T49K/ref=s9_simh_gw_p236_d0_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=desktop-1&pf_rd_r=04KWPPMGYE91AVNNW2Z1&pf_rd_t=36701&pf_rd_p=2079475242&pf_rd_i=desktop

You can run from fullrange amplifier binding posts to the line level input of the subwoofer amplifiers by inserting resistors. I prefer to do it this way. I think I used two 22kohm resistors on each wire, for one of my setups this way. It worked nice, gain on sub amps where not high, maybe 1/3.

[G Georgopoulos]

this is what im talking about

the second circuit

http://www.muzique.com/lab/splitter.htm


cheers...

[tortugaranger]

If you are running the Crown (10K ohm) with the other amp (30K ohm)at the same time, then the Tortuga is seeing 7.5K ohms. That's a pretty tough load.

You have 3 resistive devices in series:  Tortuga, MainAmp, Crown. This is what your source "sees" and has to deliver its voltage (audio signal) into.  What the source sees is:  (20x30/50 = 12 => (12x10)/22 = 5.5k effective impedance. With a 800 ohm source that yields a bridging ratio of 5500/800 = 6.9.   This is below the conventional 10:1 bridging ratio guidance  for active (buffered) let alone the 50:1 guidance for passive. Not surprising that results are disappointing. Tough load for the source indeed.

An 800 ohm source with 50:1 would ideally feed into a 40k downstream impedance but you can do quite well even with less than this which is evident with the Tortuga and your MainAmp by themselves (20x30)/50 = 12/0.8 = 15:1.   If you raised the Tortuga pre impedance to say 50k you can improve on this slightly but are ultimately limited by the MainAmp's 30k.  (50x30)/80 = 18.75/0.8 = 23:1 - good enough.

So bottom line is a 23:1 bridging ratio is plenty adequate for good performance with your system with the passive pre but 6.9 is not after adding the Crown. So yes, you need a buffer between the preamp and the Crown....OR...as someone suggested run the Crown off the high level outputs from the MainAmp assuming the Crown accommodates high level signal inputs.

[33na3rd]

I noticed that the Crown XLS 1500 has a Zin of 10K on the RCA's, and a Zin of 20K on the XLR's.

They state that the input sensitivity is 1.4 volts, but don't say at which input.

In light of the different Zin's, I'm wondering if the 1.4 volts is for XLR & perhaps the RCA's are needing 2.8 volts?

Nothing in the manual about this, merely speculation from past experience, but this could muddy up things further. (?)

[33na3rd]

Regarding running subs from the amp's speaker outputs--

I really like this method, as it frees the pre/source from one more load and the sub picks up the flavor of the main amp. It really seems to help the sub blend in with the main speakers.

In the past, one had to be careful doing this with (true) balanced amps, and certain class D amps. In those amps, the negative speaker output is not ground.
With these types of amps you would hook the positive sub input to the positive speaker output, and attach the negative sub input to some point of the main amp's chassis.
Some amps, like the Pass Labs, actually have a ground post just for this.

Not all class D amps have this requirement. I don't know if the Crown has this issue or not.

[rajacat]

Unfortunately the Crown doesn't have speaker level inputs. I seems as though I've screwed myself with lack of planning and attention to detail.  The main problem is that its very hard to employ a passive pre in an active system without the optimum in amp synergy with the source. Now if my DAC output 4v instead of 1.8 then I might be able to get the present configuration to work. I still have to deal with the miniDSP learning curve.

 Hmm....I am due to upgrade my DAC however I don't have the $$ to get a substantially better DAC.

Maybe I should give up on the active system and design a passive crossover and use just one amp. This is getting too complicated for me 'cause I'd have to tackle another learning curve. Audio is starting to eat up too much of my time.

If I had kept my very good active pre, which has a lot of gain, this probably would have worked out well. I wanted to use the Tortuga, which I DIY'ed, because I was impressed with the sound quality. It worked good enough with my tube monoblocks for the tweeters in conjunction with a small digital amp for the woofers. Unfortunately the monoblocks are now having issues. Also I felt that the AE TD15m's could use more power than 25w/channel especially with an active crossover. In addition I suspect that the little digital amp might have been operating a little out of its comfort zone with a low Zin.

So now I need a buffer which, in some ways, defeats the purpose of having a passive plus adds more IC's unless I build it into the Tortuga.

Alternatively, just quit DIY altogether and sell all my gear and just go with a simple system that doesn't require such a time investment which I could better use listening to music and finishing my endless home remodeling project.

 

[Folsom]

You can high level into crown using resistors. And it wouldn't be a problem if it was balanced, you just use XLR input.

[steve f]

You need a buffer.

[rajacat]

You can high level into crown using resistors. And it wouldn't be a problem if it was balanced, you just use XLR input.

Maybe I'll try that.
So I need some XLR plugs and put (2) 22kohm resistors in series on both positive and negative, pins 2 & 3?

[rajacat]

You need a buffer.

That's probably the answer and the easiest route to take otherwise I'll just continue to experiment.

[DaveC113]

The fact you need a buffer and/or rig sub outs from your main amp's speaker level outs to the Crown doesn't take away from the Tortuga's usefulness as a volume control.

My plans include using a Tortuga board for volume and an Aikido cathode follower as a buffer. I currently have a high-gain Aikido preamp and it is very impressive, the buffer is even better as it uses a bipolar power supply:

http://glass-ware.stores.yahoo.net/tubu.html

Also, the voltage out on a source has little do do with it's abilities to produce current, neither does the output impedance. For example there are op amps with low output impedance that can't deliver much current. IMO a good buffer like the Aikido will make almost any system it's used in sound better. I think the combo of the Tortuga LDR and Aikido CF will make for one of the best preamps out there and it'll drive pretty much anything. It doesn't have an ultra low ouput impedance, although it's just a few hundred ohms, but it can deliver about 10 mA of current if used with 6SN7s, other tubes can deliver more...

Broski has written a bit about this in his blog, it's hard to go wrong following his advice. He has the most intuitive feel for circuits of anyone in the world imo. A few days ago I put together an EL34 output stage following his SET design and it's spectacular. Previously I said the Crown was close to my EL34 amp, now it's not even close, the new EL34 is way better.

What I would do if I was you is build an external passive xo, maybe just use the Pi speakers 4pi crossover design, and see if you can beat it with an active setup. The passive will give you a known benchmark to use. With the speaker I'm designing I plan on offering active and passive options.

[Folsom]

Maybe I'll try that.
So I need some XLR plugs and put (2) 22kohm resistors in series on both positive and negative, pins 2 & 3?

I'll make a picture later.