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Old 11th December 2010, 03:56 PM   #2841
sendler is offline sendler  United States
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Default Volume control

Quote:
Originally Posted by pumpkin1 View Post
Sendler-correct, that post, and I think it's the only negative one I've seen so doubt the measurements as he has gone on to post a number of other questions on the Minidsp's own forum. My problem however will be the same-ultra efficient 4 way horn system well over 100db efficient. I also am confused about how to control gain using the minidsp board- are you supposed to wire in a physical knob to control it? Is it ok to go from a Rogue tube preamp to the analog in's and still get good s/n when playing low, will that cause issues between low and high volume? I'm not an electronics guy, more of a speaker builder. Their website does not seem to clearly explain as they assume more electronics knowledge than I have.
I haven't really studied the Minidsp products but think that you will find the same volume control concerns as DCX users. Digital in or analog in, either way, the best sonics require matchable controls on each amp channel to set the sensitivity so that your max listening level occurs with -0db digital volume settings and/ or full-ish analog input meters. The cheapest way is to experiment with fixed resistor pads, best placed inside the amps input connectors to minimize the passive's interaction with any following cable which will be none at that location. I use direct stepped attenuators which install on the amps inputs and maintain matching at any volume setting. Jan's active output board is also very handy and gives remote volume control. Doing a simple direct out mod to your DCX will also reduce the hiss as the stock DCX outputs are adding a lot of noise to the output of the dac chip. I use either a simple, one leg cap coupled out with no ultrasonic filter which is a very cheap mod, or transformer coupled output. I have found great sound from Jensen JT-11-EMCF or FMCF. Six of those gets expensive though.
.
If the hiss/ hum from your amps alone is too loud into your high sensitivity horns even with the inputs unplugged/ shorted, you may have to consider adding passive pads at the drivers which will also be beneficial in flattening impedance peaks.
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Old 11th December 2010, 04:04 PM   #2842
doug20 is offline doug20  United States
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Is passive pads on my CDs to control the noise floor issue. I liked the MiniDSP because I had a complete unbalanced setup in my office (Outlaw amp, pre/pro) and there simply was no need for any pro audio components.
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Old 11th December 2010, 04:18 PM   #2843
Davey is offline Davey  United States
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Signal levels are much more 'consumer' friendly with the MiniDSP. Maximum output limited to 0.9VRMS and with much lower noise than a stock DCX unit. Attenuators between MiniDSP and power amp(s) should not be required in most cases.

Cheers,

Dave.
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Old 11th December 2010, 04:54 PM   #2844
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Default Minidsp

Understood- though implementing some of your suggestions for a non-electronics guy is not possible without step by step instructions. I've found that the folks on this site, like yourself, have fairly advanced knowledge about electronics so there doesn't tend to be a how to faq created as I've enjoyed with Tapped Horns for example. Unless someone takes the time to explicitly show how they added attenuation, how to pick the right resister or parts, etc, it's just not possible for me or others like me to implement.

But what appealed to me is the fact that the Minidsp shows it's own gain/vol control-so if that is physically controlable in real time, it would be a very cheap solution vs. having to build separate vol controls for each channel. I do have gain controls on a couple of amps so I can match them to my main tube amp.
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Old 13th December 2010, 01:32 PM   #2845
doug20 is offline doug20  United States
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Just saw this

Quote:
Originally Posted by paulspencer View Post
Recently I've participated in some listening tests of various active crossovers over two separate days in two systems.

We compared
Behringer Ultradrive DCX
Behringer Ultradrive DCX with the Pilgrim audio mods
MiniDSP
DEQX

We did two tests:
1. digital conversions
2. digital active crossovers

We used an instant switching level match box that switches both inputs and outputs. For the first test, we let the units simply act as digital converters of an analogue input - ADC then DAC. We compared to a loop through wire.

For the second, we set up with the same settings and measured to ensure we were comparing level matched and with the filters doing the same thing. It's quite time consuming to set up an event like this, so it was not the last word on perfect accuracy. We did not match to within 0.1 db but we took a decent stab at matching.

We didn't do the test blind. While this may disappoint some, but I felt that using instant switching would be revealing enough. We did this test for our own curiosity, but no one had a point to prove. In a previous informal comparison, I found that was enough even with levels obviously not matched. No one in that test could hear a difference with the digital conversions vs a loop through wire, not even one person there who was certain a difference would be heard.

Our extended tests did show differences, but I'd call them subtle. At certain times, I noticed a difference in imaging where there was a small shift. The instant switch during a sustained note is quite revealing. MiniDSP appeared to have increased treble detail compared to DCX, despite mreasurements showing that it rolls off more above 20k. The measurements from what I recall didn't seem to reveal why that might be the case.

The full write up is here in my blog:
Red Spade Audio: Active crossover listening tests
and there are more comments in the linked SNA thread.

My findings if I can sum it up in a nutshell?
MiniDSP is the first one you want to try out of these.

DEQX sadly didn't quite get a fair trial, we had time limits and something wasn't quite right.
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Old 13th December 2010, 01:34 PM   #2846
doug20 is offline doug20  United States
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Quote:
Originally Posted by pumpkin1 View Post
Understood- though implementing some of your suggestions for a non-electronics guy is not possible without step by step instructions. I've found that the folks on this site, like yourself, have fairly advanced knowledge about electronics so there doesn't tend to be a how to faq created as I've enjoyed with Tapped Horns for example. Unless someone takes the time to explicitly show how they added attenuation, how to pick the right resister or parts, etc, it's just not possible for me or others like me to implement.
There is a learning curve or you can buy a product like this

NHT Professional PVC Pro Passive Volume Control

Quote:

But what appealed to me is the fact that the Minidsp shows it's own gain/vol control-so if that is physically controlable in real time, it would be a very cheap solution vs. having to build separate vol controls for each channel. I do have gain controls on a couple of amps so I can match them to my main tube amp.
Currently the MiniDSP does not have real time volume control or atleast I know mine do not.
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Old 13th December 2010, 01:45 PM   #2847
Pano is offline Pano  United States
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I thought you just had to connect a linear pot to drive the volume control portion.

EDIT: Quick look at the manual says yes. 10K linear pot connected to pins 6, 12, 22 of the expansion connector. You can drive multiple boards with the same pot.

Last edited by Pano; 13th December 2010 at 01:53 PM. Reason: found info
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Old 13th December 2010, 02:20 PM   #2848
doug20 is offline doug20  United States
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Quote:
Originally Posted by panomaniac View Post
I thought you just had to connect a linear pot to drive the volume control portion.

EDIT: Quick look at the manual says yes. 10K linear pot connected to pins 6, 12, 22 of the expansion connector. You can drive multiple boards with the same pot.
Yes sorry, I wasn't clear. If you are not buying the prebuilt one then you can do some of that electrical stuff.
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Old 13th December 2010, 02:37 PM   #2849
Pano is offline Pano  United States
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OK, I should have figured that!

Yeah, does not look like you can easily do it on the boxed version.
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Old 13th December 2010, 02:48 PM   #2850
doug20 is offline doug20  United States
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Thanks for the post, I forgot about the expansion connector. Maybe some EOM would like to add a Volume control or maybe MiniDSP will add one in the future.
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