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Active Bi-Amping/Tri-Amping FAQ


Chris A
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Well, IIRC, tube preamplifiers don't like to drive low input impedance loads.  If your tube preamplifier has an output impedance that's greater than ~500 ohms, you might have an issue. 

 

If you have a DAC with an optical S/PDIF output, you could bypass the tube preamp and directly connect the DAC to the miniDSP--using the miniDSP as your volume control (you can order an inexpensive IR control for it), thus eliminating one ADC and DAC conversion for all digital sources.

 

The miniDSP 2x4 HD and 4x10 HD also have analog inputs that can be used with an analog source--like a turntable cartridge.  That could use a phono preamp, etc. to do the signal conditioning (RIAA reverse-EQ curve and gain). 

 

Chris

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35 minutes ago, Chris A said:

Well, IIRC, tube preamplifiers don't like to drive low input impedance loads.  If your tube preamplifier has an output impedance that's greater than ~500 ohms, you might have an issue. 

That is exactly the potential problem with a tube preamp -- some have a relatively high output (not input) impedance. But the input impedance of typical amplifiers is on the order of 50K to 100K Ohms, so in those cases there is no problem. 

 

I have a tube preamp with an output impedance of 2.3K Ohm, and some Class-D amps with input impedances of 5K Ohm. In that particular case there is a problem.

 

As long as the input impedance of the amp is at least, oh, maybe 10x the output impedance of the preamp, everything should be OK. It's not a hard and fast rule.

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1 hour ago, Edgar said:

That is exactly the potential problem with a tube preamp -- some have a relatively high output (not input) impedance. But the input impedance of typical amplifiers is on the order of 50K to 100K Ohms, so in those cases there is no problem. 

 

I have a tube preamp with an output impedance of 2.3K Ohm, and some Class-D amps with input impedances of 5K Ohm. In that particular case there is a problem.

 

As long as the input impedance of the amp is at least, oh, maybe 10x the output impedance of the preamp, everything should be OK. It's not a hard and fast rule.

thanks Edgar and Chris, yea I have no idea. Using a mcintosh mx110z. I've gotten the basic info loaded into the minidsp and have attempted to use rew....my lord that software is deep in the weeds for me. Anyway I can't get the sweep sent to the dsp  because it says my biquad input file isn't formatted correctly...yea like I know wth that means. Definitely haven't improved the sound so far. Here is a pic of my graph, looks pretty bad to me but I don't know how to fix it so...

 

 

 

 

 

graph 2.jpg

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1 hour ago, Chris A said:

Well, IIRC, tube preamplifiers don't like to drive low input impedance loads.  If your tube preamplifier has an output impedance that's greater than ~500 ohms, you might have an issue. 

 

If you have a DAC with an optical S/PDIF output, you could bypass the tube preamp and directly connect the DAC to the miniDSP--using the miniDSP as your volume control (you can order an inexpensive IR control for it), thus eliminating one ADC and DAC conversion for all digital sources.

 

The miniDSP 2x4 HD and 4x10 HD also have analog inputs that can be used with an analog source--like a turntable cartridge.  That could use a phono preamp, etc. to do the signal conditioning (RIAA reverse-EQ curve and gain). 

 

Chris

 

22 minutes ago, Madman1 said:

thank Edgar, yea I have no idea. Using a mcintosh mx110z. I've gotten the basic info loaded into the minidsp and have attempted to use rew....my lord that software is deep in the weeds for me. Anyway I can't get the sweep sent to the dsp  because it says my biquad input file isn't formatted correctly...yea like I know wth that means. Definitely haven't improved the sound so far. Here is a pic of my graph, looks pretty bad to me but I don't know how to fix it so...

 

 

 

 

 

graph 2.jpg

 

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21 minutes ago, Madman1 said:

thank Edgar, yea I have no idea. Using a mcintosh mx110z.

It turns out that the MX110 output impedance is quite high; see post #50 here. As @Chris A said, you might have an issue, so I recommend that you follow his advice.

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49 minutes ago, babadono said:

4k output impedance? what?...sure am glad I left that world behind long ago...

What is the input impedance of miniDSP?

From the miniDSP 2X4HD Usr Manual

 

Analog audio inputs
Unbalanced stereo (2 channels) analog audio on RCA connectors
- Max input of 4V or 2V RMS, jumper–selectable

- Input impedance: 10kΩ - THD+N: 0.003% (RCA to USB)

- Dynamic range: 102dB

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I sent a PM to the resident triamping pro on the forum, @Chris A, though perhaps others could also chime in...

 

Very quickly, several rapid fire questions, feel free to give one word answers... My current setup is as follows:  vintage analogue 3 way active crossover (Sony 4300F) and a 6 channel Classe CAV 75 amp. My speaker/driver combo is as follows: QPIE bass bin, Electrovoice Sentry IV-B mid and HF horns, with the A55g as mid driver.

 

The Sony 4300F has allowed me to dip my toes in active crossovers and I love what it's brought so far. Being an analog active crossover it hasn't gotten any provisions for time alignment or EQ, things which I believe are clearly the next step.

 

I have the opportunity to purchase a well priced, functioning second hand Xilica DCP 3060. Knowing that I haven't currently got any subwoofers, do you consider this to be a step up from what I've got, or more of a lateral move? One day I intend on going 2 way with subwoofers, would the Xilica work for that as well? The Classe too?

 

If I purchase the Xilica, I will need to purchase XLR to RCA (balanced to unbalanced) cables, as the preamp and amp are RCA only. Do you see any problem with this?

 

Many thanks for any helpful input!

Daniel

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@Ray_pierrewit, I'm not familiar with the Xilica products so I won't comment.

 

As for the XLR/RCA question, going from unbalanced to balanced you might consider this. Going from balanced to unbalanced you can just leave the (-) half of the balanced source unconnected.

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@Edgar would I be correct to assume that the preamp is not going to have as much effect on the sound when using a minidsp as it would without? I have a couple other preamps that I could try although they may not be ideal, Marantz 2230 and advent 300. 
So I could use just about anything with a volume control and inputs as long as it matches the impedance of the minidsp? 
@Chris A I did try running my dac (no volume control) directly into the minidsp using my laptop as source and volume control with some improved results, it was getting past my bedtime and I was mentally exhausted from using rew. Hope to get some more time in today. 
 

Thanks to you both. 

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17 minutes ago, Madman1 said:

@Edgar would I be correct to assume that the preamp is not going to have as much effect on the sound when using a minidsp as it would without? I have a couple other preamps that I could try although they may not be ideal, Marantz 2230 and advent 300. 
So I could use just about anything with a volume control and inputs as long as it matches the impedance of the minidsp? 

I think just the opposite is true. The preamp will have whatever effect it has upon the sound, regardless of the downstream equipment. But in this case the effect of driving a low input impedance with a high output impedance will also be present. It is hard to predict what effect the impedance issue will have upon the sound -- it may be benign, or it may be worse than what you would get by substituting one of the other "non-ideal" preamps. I suggest that you experiment.

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On 8/31/2021 at 7:13 AM, Madman1 said:

Anyone else using tubes on the front end? 

I was using the minidsp hd for bi-amping the klipschorns with tube amp powering the mid/high and SS the bass bin. It worked OK

 

now, I’ve move to the 4x10 miniDSP and am tri-amping. The tube only powers the squawker and all passives are out of the stream. I have a SS powering the tweeter. There was a noticeable improvement after several iterations of setting crossover points and modifying peq. 
 

still, I did all modifications by ear and looking at levels in the software. I’m sure it would be even better using additional software and a microphone to measure. But the speakers sound the best I’ve ever heard as it is right now. 

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12 hours ago, Edgar said:

@Ray_pierrewit, I'm not familiar with the Xilica products so I won't comment.

 

As for the XLR/RCA question, going from unbalanced to balanced you might consider this. Going from balanced to unbalanced you can just leave the (-) half of the balanced source unconnected.

@Ray_pierrewit Is the Xilica an XP-3060? I'm no expert but I don't recognize the model you mentioned.(NM- Google is a friend sometimes) This is an older unit with 48kHz sampling rate not 96k like the XP models. I believe it would be a definite step up from the Sony as long as you don't have the "anti-digital" meme. It will allow you to do a stereo 2 way set up for now and add subs later if you want. If you are already stereo 3 way there will be no more outputs available for subs. But still getting the ability to time align your current set up will make you smile:) And the EQing of course.

The outputs of the Xilica are impedance balanced already with no active signal on the minus output as shown in the link from Edgar. They will easily take to a properly wired XLR to RCA cable to feed the unbalanced inputs of your power amp. The inputs are electronically balanced and take being fed by an unbalanced source well but best would be to modify your source to be impedance balanced again as Edgar's link shows.

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@babadono

Thanks for your comments. It's a DCP 3060 here is a bit literature I found on the unit:

 

The DCP-3060 is a complete 3 input - 6 output digital loudspeaker
management system designed for the touring or fixed sound installation
markets. The absolute latest in available technology is utilized with 32-bit
(40-bit extended) floating point processors and high performance 24-bit
Analog Converters. The high-bit DSP prevents noise and distortion induced
by truncation errors of the commonly used 24-bit fixed-point devices. A
complete set of parameters include I/O levels, delay, polarity, 6 bands of
parametric EQ per channel, multiple crossover selections and full function
limiters. Precise frequency control is achieved with its 1 Hz resolution.
Inputs and outputs can be routed in multiple configuration to meet any
requirements. The DCP-3060 can be controlled or configured in real time
on the front panel or with the intuitive PC GUI accessed via the RS-232
interface. Software upgrade for CPU and DSP via PC keeps the device
current with newly developed algorithms and functions once available.
Multiple setup storage and system security complete this professional
package.
 
I contacted Xilica and they unfortunately no longer service this model, which is something to think about. For now it will be used in an active 3 way setup, no subs. The subs will happen when I eventually switch to active 2 way. I'm also a little concerned about using the knobs and dials on the front panel to do all the adjusting, as the PC software is no longer available. The seller assures me it's really easy, mind you, he works for a live sound production company and knows way more than I do.
 
I've glanced at @Edgar suggested thread, but honestly didn't take any time to decipher his schematic. I'm still on the fence whether or not to purchase it.
 
I've never heard time-aligned drivers in a home setup before, so I don't even know if it's that important for me. Right now the pressing issue is a bit of EQing and perfecting the crossovers.
 
Daniel
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@Edgar @Chris A   Ok, so I’ve got the preamp situation somewhat resolved now I’ve got a new issue. I’m using Tube monoblocks on the hf sections and class a ss amp on the LF section. I believe I have everything in the minidsp settings identical for both Lf channels and Hf channels but I have to turn the gain up on the tube amp for one speaker to match the volume of the other and also on that same speaker the bass is much “flatter” almost sounds like the polarity is crossed. I’m not sure what I could have wrong that would cause this. I’ve switched the rca inputs, but the poor sound stays with that speaker and doesn’t change. I haven’t swapped the output rcas around yet which I plan to do today, guess that would narrow everything down to the dsp causing this. Any ideas what else to check? You can’t have a different output voltage setting for 1&2 outputs and 3&4 outputs, or can you? I didn’t have the gain difference using a passive crossover, but the bass is dramatically improved on the one speaker using the minidsp. Now if I could just get the other speaker to sound the same I’d be in business. 

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  1. You probably need to double check the connectivity you've got within the miniDSP - left input to left outputs (usually input 1 channel to output channels 1 [low frequency] and 2 [high frequency], right input to right outputs (usually input 2 to output channels 3 [low frequency] and 4 [high frequency]). 
     
  2. Then make sure that the PEQ screens for each match: output channel 1 matches output channel 3, output channel 2 matches output channel 4. 
     
  3. Then check to see that the input channels 1 and 2 have the same PEQ settings (there are, of course, separate input channel PEQs from the output channels).
     
  4. Then check your amplifiers for connectivity to the miniDSP and the loudspeaker drivers.  If you're direct coupling the amplifier outputs to the drivers in the speakers, make sure of the connections.  If you're still using some portion of existing passive crossovers, check to see if all those connections are exactly the same for the left loudspeaker as the right.

 

Bi-amp, active horizontal.GIF

 

Chris

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What @Chris A said; also since at some point you're converting from balanced to unbalanced, make certain that you are using the same signals on all connections. That is to say, you are probably connecting XLR "hot" (usually pin 2) to RCA "signal" and XLR "ground" (pin 1) to RCA "ground". Make sure that one of the connections is not accidentally XLR "cold" (pin 3) to RCA "signal".

 

I hope that made sense.

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13 hours ago, Ray_pierrewit said:

I'm also a little concerned about using the knobs and dials on the front panel to do all the adjusting, as the PC software is no longer available.

For me that would be a Red Flag. Not being able to adjust via a GUI on a laptop and having to do from the front panel. Save up a few more bucks and get an XP 4080.

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@Madman1Which miniDSP are you using? Swapping the inputs made no diff. so the problem is 1) the miniDSP or the settings thereof 2) the output cables from the mini 3) the amp itself 4)the speaker cables 5) the speakers .

Sorry if I am stating the obvious, everyone has different levels of understanding.

You will succeed in figuring this out especially with the help available here.

Where are you switching from balanced to unbalanced and vice versa?

Edited by babadono
I meant sorry if not sorry is
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@babadono

please state the obvious!! Im using the the basic minidsp 2x4, no balanced inputs or outputs. So I think I’ve worked out the gain differences. The polarity invert was clicked on the hf channel for one speaker. This is strange but I physically changed the polarity on the amp to the one woofer and it seems to sound better idk. Is there a basic starting point for my crossover settings?
 I’m using a set of Belles, currently playing with a

Lf=
500hz bw 48db/oct and 45 bw 24/oct

 

Hf=
20000 bw 12db/oct and 400 bw 12db/oct

 

 

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