Amp needed for measuring speakers with laptop - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 23rd February 2005, 09:29 AM   #1
JohanH is offline JohanH  Netherlands
diyAudio Member
 
Join Date: Dec 2003
Location: Noord Brabant
Default Amp needed for measuring speakers with laptop

Hello all,

I am looking for a small DIY amp that I will use to hook up to my laptop or PC soundcard.
The reason for this is that the built in amps are not good enough (I think) to use when measuring with software as Speakerworkshop etc.

Power should probably be somewhere around 2 to 5 watts.; mono is ok. Distortion should be low etc.

My question also is: should it be constant-voltage or constant-current based?

For ease of project I would prefer a chip-amp, but I'm not sure if they are suitable for measuring loudspeakers.

Thanks very much in advance for your input.

Johan
  Reply With Quote
Old 23rd February 2005, 11:27 AM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
I mounted an LM1875 into a small Bud-box just for that use. Powered off an 12VAC wall-wart. A volume control is a good idea. My total cost was about $10.

You want constant voltage- the CC is simulated with a precision series resistor.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 24th February 2005, 09:25 AM   #3
JohanH is offline JohanH  Netherlands
diyAudio Member
 
Join Date: Dec 2003
Location: Noord Brabant
Default Low Impedances?

Hello Sy,

thanks very much for your answer.

How does it cope with low impedances? I am asking because I used to have a ESL with an impedance of 0,8 ohm at about 8000 Hz that would bring most measuring equipment to its knees.

Although I don't own it anymore I would like to be able to measure loads like ESL's in the future.

Johan
  Reply With Quote
Old 24th February 2005, 04:09 PM   #4
scone is offline scone  United States
diyAudio Member
 
Join Date: Nov 2004
Location: Austin, TX
The lm1875 would have serious trouble coping with a .8 ohm impedance. All of the other national audio opamps would as well. Even a parallel design (using a 4780 or something) would crack under a load like that. Not have I've ever tried this, but looking at the spec sheets this would seem to be the case.

You might be able to do something with a series power resistor to raise the overall impedance level as seen by the amp. This is terrible for efficiency, and I'm not sure what it would do to the test results. Perhaps others can comment. It's quite possible that you'll have to settle for testing "normal" 4+ ohm loads with a simple amp based on the 1875, and will have to use a fancier one for your electrostatic experiments.
__________________
audio projects
  Reply With Quote
Old 24th February 2005, 05:47 PM   #5
JohanH is offline JohanH  Netherlands
diyAudio Member
 
Join Date: Dec 2003
Location: Noord Brabant
Default Maybe this would work..

After some searching through datasheet I found the TDA2003.
Supposedly it will be able to drive loads down to 1.6 ohms, so that's probably close enough for my purposes.
It does however have a poor PSRR so it would need a battery or regulated PSU.
Also some experimenting might be needed to get a decent frequency response coupled with good stability.

And a plus: there's a Velleman kit that's cheapish so I could build it.
So for a quicky it looks ok.

Johan
  Reply With Quote
Old 24th February 2005, 06:10 PM   #6
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
At a certain point, you might just shrug and buy an extra power amp secondhand.

0.8 ohms? That's a speaker which needs some serious redesign.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 24th February 2005, 06:25 PM   #7
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
0.8 ohms is plain stupid. However, if you measure using the pseudo constant current method (large series resistor) then it won't matter even if your speaker is 0.00001 ohms as far as hurting your amp is concerned. The issue will merely be getting a readable/reliable measurement.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 24th February 2005, 06:28 PM   #8
JohanH is offline JohanH  Netherlands
diyAudio Member
 
Join Date: Dec 2003
Location: Noord Brabant
Hello Sy,

don't get me started on redesigning the ESL: its high-voltage multiplier was directly connected to the mains. Sounded nice though.

The reason for wanting to build an extra (small) amp is that I don't want to have to haul my spare integrated amp everywhere for testing loudspeakers.

But then again, maybe you're right and I am going overboard by wanting to have yet another amp,

Johan
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Laptop as measuring device ? Jan Dupont Everything Else 7 15th February 2009 07:05 AM
Measuring a speakers efficiency pjpoes Multi-Way 14 30th January 2009 03:35 PM
laptop internal speakers mrybczyn Multi-Way 1 25th May 2008 07:26 AM
WTB: Mic + preamp for measuring speakers Saurav Swap Meet 2 6th October 2004 06:13 PM


New To Site? Need Help?

All times are GMT. The time now is 03:59 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2