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TOPIC: Re: Convoluted active system

Convoluted active system 9 years 5 months ago #2231

  • HAudio.
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After months of reading and not satisfied with my first active / passive crossover speaker setup I finally decided to start my second speaker project.
Fortunately I stumbled across the miniDSP on the diyaudio forum and became curious about a 4 way active system.
My limited knowledge with electronics and audio measuring techniques has made the process very slow, but in the bright side I’m learning a lot!


On pic 1 different views of my early prototype. It uses a PC power supply a miniDSP and a 4 X 100 amplifier (hi, mid-hi, mid-low, sub).

Issues I ran into:
 RF noise picked up by the miniDSP. Tracked it down to the PC power supply fans. Turned off the offending fan and the noise was gone. Replaced the fan with another one and the noise was back. Tried with the miniDSP out of the chain by adding a passive crossover after the amp and the noise was gone. MiniDSP back in the chain with a different PSU and the noise was gone.
In my plans the fan on the PSU is critical because that would be the way of getting the heat generated by components out of the system. Just like the cooling concept of most computers.
 Annoying bump (and dangerous for hi freq drivers) when powering up and powering down. I’m currently figuring out a microcontroller and circuit to manage delays when powering up and powering down.

 Very low gain. Cheap mp3 players will make the amps clip at less than acceptable levels. Audio levels from a computer with an E-MU 0404 card were fine. Levels from an Acer netbook were mediocre at best. This issue made me look into preamplifiers and ended up adding two mono pre amplifiers (One for each input channel).


On the 2nd pic the latest setup including the pre amplifiers, new power supply, two miniDSPs and two 4 channel Amps. I know… the AC receptacle with the 2 transformers looks crude.
Will post more as I get time. Suggestions are welcome!!
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Re: Convoluted active system 9 years 5 months ago #2236

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The design changed on the final enclosure to make the best out of the bottom end. Some gluing, clamping, soldering and cutting later and the project is starting to take shape.
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Re: Convoluted active system 9 years 5 months ago #2391

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Update:
Preliminary assembly to test components is done and everything it's working as expected. Even without proper cabinet damping and final sealing the active system sounds with amazing clarity.
The aluminium plate that houses all the equipment has a PC Power Supply Unit, 2 RCA inputs for a stereo line in, 2 USB A headers one for each miniDSP, a speakon 8 pole connector for the second speaker and exposes the controls of the 2 tube preamplifiers.
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Re: Convoluted active system 8 years 9 months ago #4049

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4 way active finally made it to the living room. The thing sounds phenomenal :laugh:

This type of setup is a pain to make it sound good but once you get to the proper tuning the results are impressive.
On thing that I noted is that minidsp (2x4 version) and high efficiency drivers don't match that good. I tried a horn loaded compression driver at around 102 db SPL for Hi freq. and hissing was noticeable at short distances even when bringing the level down. Changed to a 93 db SPL driver (dome tweeter) and had to get the ear on the driver to hear any hissing.


Drivers.
Hi > 6200hz -- Vifa BC25SC15-04 1" Soft Dome Tweeter
Mid Hi 900hz to 6340hz -- Pioneer FB11EC14-51F 5-1/4" cone Mid
Mid Lo 140 hz to 920hz -- 2 x Eminence Alpha-6A 6" Midrange 8 Ohm
Sub < 140 hz -- Dayton Audio SD270A-88 10" DVC Subwoofer at 4 Ohm

Amps
2 x Sure 4x100W @ 4 Ohm TK2050

Crossover/Eq
2 x 2x4 MiniDSP kits

Preamps
2 x ART Tube MP Studio (Moded)

Power supply
Antec TruePower New TP-750 750W (PC PSU)




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Re: Convoluted active system 8 years 9 months ago #4061

  • devteam
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Great seeing some constant progress on your system!

These 2 speakers are looking great! A good project for our "Project Gallery"

DevTeam
miniDSP, building a DSP community one board at a time.
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Re: Convoluted active system 8 years 9 months ago #4065

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Is the noise with compression driver still there without the miniDSP connected? It may well be the amp making the noise (or contributing most of it).

I've just set my compression drivers up with some small TK2050 T1-M amps from Hifimediy and the noise from my signal chain including the miniDSP2x8 is unnoticeable over the amp noise until the gain on the amps is right up.
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Re: Convoluted active system 8 years 9 months ago #4068

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Honestly on this system I didn't test it without the miniDSP and I'm not using the compression driver anymore (Eminence ASD1001 1"), instead I'm using a dome tweeter which is around 10db less efficient.
I do have another miniDSP and amp that I could use to test. I will replicate the chain and post my findings once I get some time.
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Re: Convoluted active system 8 years 9 months ago #4082

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Great work and nice design.
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Re: Convoluted active system 8 years 7 months ago #4504

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Thank you for the compliments.

The compression drivers are gone so I made some quick measurements with a Radio Shack SPL meter and a 93db SPL dome tweeter. The amp is still the same(Sure TK2050).
Please note that I'm just a hobbyist and my measurement tools and techniques aren't top notch.
Three different power sources were used for these measurements. The minidsp and Amp are both powered by the same supply each time.
Ambient noise of 41db -+1db was used as a reference and measurements were taken 1cm apart from the tweeter.

18V Battery:
............Amp --> +3db -+1db
Amp and Minidsp --> +5db -+1db

20V Switching power supply:
............Amp --> +3db -+1db
Amp and Minidsp --> +5db -+1db

12V Switching power supply:
............Amp --> +5db -+1db
Amp and Minidsp --> +8db -+1db

Based on this it seems that the power supply has big influence on the amp's noise and just as findbuddha said it is contributing to most of it. At 1 meter and over measurements didn't represent significant changes.
In all, I’m happy with the outcome and noise is not an issue with the current setup. The only thing I wish for is having preset EQs for movies and music. The 2x8 would be the logical path but I don’t see myself getting this thing apart anytime soon.

Cheers.
Last Edit: 8 years 7 months ago by haudio. Reason: typo
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