Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › DIY line driver circuit - help?
New Posts  All Forums:Forum Nav:

DIY line driver circuit - help?

post #1 of 14
Thread Starter 

this is at least audio related DIY, and could have to do with headphones. :) but this is in fact for a MiniDSP / amp active setup.

 

The miniDSP is only putting out 1v of audio signal. The amp I paired it up with need more line input voltage, maybe like 4v.

 

 

I need to put together a basic line-driver circuit, with a already-regulated/filtered 5v of DC current.

 

Want to use a 4 channel OPA4134, because the miniDSP is a 4 channel device.

 

I have basic understanding of wiring/building. Have built a couple CMOY head amps, and have modded various electronic over the years.

 

Can I modify the CMOY design for use as a "line driver"?

post #2 of 14

When you say 4V, do you mean RMS or p-p?

Because 4V RMS (sine wave) equates to 11.2Vp-p, so you won't be able to get that out of a 5V single supply.

If you do mean 4Vp-p, then you can achieve this from a single 5V supply, but you will need to use a rail-to-rail capable opamp to get that close to the supply rails, the OPA4134 won't be suitable.

post #3 of 14
post #4 of 14
Thread Starter 

@dsavitsk what would the transformers be used for?

post #5 of 14
4x gain.
post #6 of 14

+1 for transformers. 

 

Not only 4x gain, but galvanic isolation too. 

And (basically) no noise contribution. 

 

You get 2 haiku because transformers are awesome. 

 

Its so much goodness

uses no power supply

I like transformer

 

 

Transformers are great

switching voltage and current

simply elegant 

 

 

It sounds like you are trying to build this into the DAC/source. If you are going to stick with an active solution (op amps, or go all out and design a discrete thingy) why not build it into the power amp instead? I am assuming (there I go making an ass of myself...) that the power amp has more voltage for you to use, which makes everything easier. The only reason I see this being bad is if you have several things that need a 4v input, but 4v is an odd input level so I kind of doubt it.


Edited by nikongod - 3/15/13 at 7:24am
post #7 of 14

Transformer enlightens

Increase pressure reduce flow

More than meets the eye

post #8 of 14

I had to google search the miniDSP, seems like a really cool concept.  I wonder of they could / would develop a tube-DSP module to add even order THD and tube EQ replication?  They could develop digital scripts for various tube distortion types for both gain and rectification.  Guitar amp and cabinet digital modeling has steadily gained popularity over the past ~decade in guitar circles.  It has even to a certain extent overcome the "tube purist mentality", as a workable/practical alternate solution for guitar tone chasers.   I can't see why it couldn't work as effectively in audio industries.

 

Theres quite a few thread topics on the www regarding the .9V-out ceiling for these units.   It seems they can accept up to 2V line in (via configurable jumper), but for some reason the Vout ceiling is only .9.  Not sure why they chose this element.   With USB theres a ~ +/- 2.5V swing at their disposal, and these units have alternate power inputs for up to ~24V.  The smaller SE kit unit  only draws 150ma @5V...????  So on paper it looks like theres voltage headroom to spare.

 

I stopped my google-foo search there, but I wonder if someones modded the output to lift the Vout ceiling... or if its something in the software on the digital side that requires it?

 

Sorry OP I can't help you, but good luck in your search.

post #9 of 14
Thread Starter 

@kramer5150

 

Yeah, the board doesn't output past 0.9v on the output channels, which is disappointing.

 

(BTW this is for a car audio setup)

 

The deck has 4v preouts, which produced a clean, distortion-free signal that got loud when straight to my amp driving the front stage. 

 

When the MiniDSP sits between them, I almost have the deck outputting full volume WITH distortion, and it's not nearly as clear and loud as it was running directly to the amp with a lower volume on the deck. (by maybe five notches, ??dB)

 

Example... the deck has a range of 0-34 notches in volume. 

Without the DSP, I could get to 24 or 25 and it would be plenty for my needs, but it requires me to turn up the deck to nearly 32 to reach that, and at that point has noticeable distortion. The ceiling is definitely different with the MiniDSP in place.

 

The gains on my amp are almost set up max levels. :/

 

The transformer idea sounds pretty interesting if I had confidence that it would fix my problem. I have a hard time understanding how a passive device boosts the output by nearly "4 times" the original input voltage.

post #10 of 14
Thread Starter 

could I use one transformer for stereo? thte schematic makes it look like there are two separate transformers in one (?)

post #11 of 14
Quote:
Originally Posted by ilikepie116 View Post

this is at least audio related DIY, and could have to do with headphones. :) but this is in fact for a MiniDSP / amp active setup.

 

The miniDSP is only putting out 1v of audio signal. The amp I paired it up with need more line input voltage, maybe like 4v.

 

 

I need to put together a basic line-driver circuit, with a already-regulated/filtered 5v of DC current.

 

Want to use a 4 channel OPA4134, because the miniDSP is a 4 channel device.

 

I have basic understanding of wiring/building. Have built a couple CMOY head amps, and have modded various electronic over the years.

 

Can I modify the CMOY design for use as a "line driver"?

 

Quote:
Originally Posted by ilikepie116 View Post

@kramer5150

 

Yeah, the board doesn't output past 0.9v on the output channels, which is disappointing.

 

(BTW this is for a car audio setup)

 

The deck has 4v preouts, which produced a clean, distortion-free signal that got loud when straight to my amp driving the front stage. 

 

When the MiniDSP sits between them, I almost have the deck outputting full volume WITH distortion, and it's not nearly as clear and loud as it was running directly to the amp with a lower volume on the deck. (by maybe five notches, ??dB)

 

Example... the deck has a range of 0-34 notches in volume. 

Without the DSP, I could get to 24 or 25 and it would be plenty for my needs, but it requires me to turn up the deck to nearly 32 to reach that, and at that point has noticeable distortion. The ceiling is definitely different with the MiniDSP in place.

 

The gains on my amp are almost set up max levels. :/

 

The transformer idea sounds pretty interesting if I had confidence that it would fix my problem. I have a hard time understanding how a passive device boosts the output by nearly "4 times" the original input voltage.

 

Quote:
Originally Posted by ilikepie116 View Post

could I use one transformer for stereo? thte schematic makes it look like there are two separate transformers in one (?)

 

You should figure out where and why your system is distorting before you start adding parts to it. Once you know why things don't work it will be easy to fix them. 

post #12 of 14
Quote:
Originally Posted by ilikepie116 View Post

The transformer idea sounds pretty interesting if I had confidence that it would fix my problem. I have a hard time understanding how a passive device boosts the output by nearly "4 times" the original input voltage.

Transformers fix every problem. smily_headphones1.gif

They trade voltage for current and conserve power. Read this http://www.jensen-transformers.com/an/Audio%20Transformers%20Chapter.pdf

Quote:
Originally Posted by ilikepie116 View Post

could I use one transformer for stereo? thte schematic makes it look like there are two separate transformers in one (?)

No.

If you want to experiment, there are cheaper transformers available than the Lundahls. These will do the same thing http://www.edcorusa.com/p/144/wsm600-10k They just won't sound as good -- tough they'll still probably sound better than an opamp.
post #13 of 14
Quote:
Originally Posted by ilikepie116 View Post

@kramer5150

 

Yeah, the board doesn't output past 0.9v on the output channels, which is disappointing.

 

(BTW this is for a car audio setup)

 

The deck has 4v preouts, which produced a clean, distortion-free signal that got loud when straight to my amp driving the front stage. 

 

When the MiniDSP sits between them, I almost have the deck outputting full volume WITH distortion, and it's not nearly as clear and loud as it was running directly to the amp with a lower volume on the deck. (by maybe five notches, ??dB)

 

Example... the deck has a range of 0-34 notches in volume. 

Without the DSP, I could get to 24 or 25 and it would be plenty for my needs, but it requires me to turn up the deck to nearly 32 to reach that, and at that point has noticeable distortion. The ceiling is definitely different with the MiniDSP in place.

 

The gains on my amp are almost set up max levels. :/

 

The transformer idea sounds pretty interesting if I had confidence that it would fix my problem. I have a hard time understanding how a passive device boosts the output by nearly "4 times" the original input voltage.

I have been out of car audio circles for ~15 years now.  When I phased out, the industry was transition-ing over to 4V line outputs/inputs.  Stemming from SPL competitions, where competitors just needed a pure AC signal at some "magical" frequency to excite acoustic resonances in the car for competitions.

 

I imagine today 4V is the norm.  But back then, I think they had "line driver" devices to do exactly what you are asking.  I never owned or needed one, or took one apart, but I think they were nothing more than an OPamp gain stage, to do exactly what you are asking.  They were mainly made as a go between, for those owners who had an old low voltage source and wanted to use modern 4V amps.

 

Yeah turning up your head/source into clipping in an effort to compensate for a voltage level miss-match is a no-no.  Cranking the gains on your amps is also a no-no and can lead to other problems, noise and hiss being the most immediate.

 

Your little DSP box is basically a voltage attenuator.  The company that makes those seems to be pretty on top of things, maybe send them an email maybe theres a simple hack to lift that .9V ceiling?  A jumper-bridge or SMT resistor swap perhaps?

 

There are (or at least were) marketed products out there to do exactly what you are requiring, designed for use in an automotive electrical system which is a haven for EMI and RFI noise.  IMHO a DIY circuit should be your last resort.  of course with these kinds of components you are adding a preamp voltage gain stage... so I don't know if any of the products shown below is really a good solution, more like a band-aid IMHO. 

 

http://www.amazon.com/Peripheral-PAC-LD10-Driver-Booster/dp/B003LWV77Y#productDetails

 

http://www.amazon.com/Rockford-Fosgate-Balanced-Line-Driver/dp/B001P86SJ8/ref=sr_1_2?s=electronics&ie=UTF8&qid=1363645381&sr=1-2&keywords=car+audio+line+driver

 

http://www.amazon.com/PIE-Adjustable-Pre-Amp-Driver-Subsonic/dp/B001AB7HXG/ref=sr_1_7?s=electronics&ie=UTF8&qid=1363645419&sr=1-7&keywords=car+audio+line+driver


Edited by kramer5150 - 3/18/13 at 5:27pm
post #14 of 14
Thread Starter 

Thanks to all who took time to reply with their thoughts, I really appreciate it.

 

I went ahead and emailed the MiniDSP company to see what they say about my dilemma.

 

We'll go from there :)

New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › DIY line driver circuit - help?