Voltage sag - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 3rd July 2007, 02:25 PM   #1
Banned
 
Join Date: Jul 2007
Default Voltage sag

Hi I am new here, I would like to know about voltage sag

What does it do to the wattage of the amp?

What does it do to the impedance output?

Can a capacitor on the speaker compensate for the sagging source voltage?

I am assuming both wattage and impedance drops.
I don't have a "True RMS" wattage meter to check the voltage. My meter doesn't seem to pull an impedance reading off my amp like it does my speakers.
Not exactly pretty results when I pushed it to higher levels, it broke up..or shattered really. Moderate levels sounded fine but volume for large sound projection is totally unusable.
In one experiment, I got a tremolo or volume fanning effect from pushing too much volume.

I have to live with the voltage sag on this amp due to the circumstances of it's location but knowing what's fully going on might offer solutions.
  Reply With Quote
Old 3rd July 2007, 03:19 PM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
you don't need a true rms meter.

Measure the Vac on the amplifier terminals when the load is connected.
Measure again when you disconnect one end of the load.
The change in voltage when on load and off load tells a lot about the amplifier.

Similarly you can measure the Vdc of the supply rails (at the smoothing caps and at the the amplifier connection to the output transistors) on load and off load. This will tell you a lot about the PSU and cabling.

I would use a dummy load that is non reactive for these tests.
It must be able to dissipate a lot of power while you take the measurements.
Quote:
What does it do to the wattage of the amp
it reduces the watts a lot but has much less effect on the maximum SPL which for normal music is very short term.
Quote:
What does it do to the impedance output?
probably very little if the amp is any good.
Quote:
Can a capacitor on the speaker compensate for the sagging source voltage?
no.
__________________
regards Andrew T.
  Reply With Quote
Old 7th July 2007, 07:57 PM   #3
Banned
 
Join Date: Jul 2007
Well say I cut the impedance in half.
This is a 24 volt amp running on a 12 volt power supply. I haven't gotten a chance to run the tests but the factory RMS wattage is something like 5 or 10 watts..I'm not sure it's worth the trouble but obviously it would tell me what I'd like to know.

I'm running a 2 ohm load on it which dramatically improved and increased volume. Obviously adding the second 4 ohm speaker has plenty to do with that but the volume increase of the initial woofer was still quite tremendous compared to before, it suddenly had bass and density.

I guess my assumption is that it is safe running like this and not worth the trouble of upgrading the power supply which would only complicate things more on this most primitive of Frankenstein creations. Such low power input and output, I'm inclined to believe I won't likely ever have any issues and if I do, it won't be for a decade or more.

Can this be concurred?
  Reply With Quote
Old 7th July 2007, 10:30 PM   #4
jnb is offline jnb  Australia
diyAudio Member
 
Join Date: Dec 2006
Quote:
Originally posted by 1400WATTSRMS+
it suddenly had bass and density.
Were these two identical speakers, placed side by side?
Quote:
upgrading the power supply
This would reduce the sag. It can also improve the performance of your amp. Not all amps are the same but improving a power supply is normally a worthy cause. Maybe your 2 ohm load is a reason to have a good supply?

I can't comment on reliability without seeing the supply.
  Reply With Quote
Old 8th July 2007, 05:00 AM   #5
Banned
 
Join Date: Jul 2007
nah I'm sure it's fine man.

One speaker is in the front of the cab, the other is in a rear duct of the cabinet and running almost as a "free air" full range woofer.
The volume increase to the front woofer was probably triple what it was before and it now has much better bass and clarity.

The rear woofer shows similar performance but due to the only possible mounting set up, it doesn't get much compression for the low end.

The power supply is a 12 volt sealed battery rated for 7 amp hours. A single charge seems to last a good month or more, even with frequent use.

At some points though, the voltage sag does seem to give a sloppy, dirty signal. A better preamp helps but not as much as I'd like. I should try experimenting with different cap values in the equalizer I'm sure.

I wouldn't mind the voltage sag effect so much if it didn't get so sloppy and dirty sounding at higher levels. I'm still a bit curious about the impedance drop being my best mod to this mess.
I think impedance varying is an overlooked problem solver to sound and volume quality in plenty of situations.
  Reply With Quote
Old 8th July 2007, 06:12 AM   #6
jnb is offline jnb  Australia
diyAudio Member
 
Join Date: Dec 2006
Quote:
Originally posted by 1400WATTSRMS+
I'm still a bit curious about the impedance drop being my best mod to this mess.
I think impedance varying is an overlooked problem solver to sound and volume quality in plenty of situations. [/B]
Could you explain a little more of this problem and how you plan to fix it?
  Reply With Quote
Old 8th July 2007, 10:20 AM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
placing a second driver in parallel to the first halves the load impedance.
The amp will try to send twice the current into the lower load value.
A good amp will increase volume by about 2db to 2.5db when driving a half impedance load. That makes your two driver conbination sound a little louder.

When you add two drivers together, you have doubled the cone area. At low frequencies the extra cone area makes the speaker more efficient with the result that the combination sounds about 3db louder than the single driver, but only over a restricted range of frequencies. This frequency range is determined by the distance between the drivers. By putting the physical size of your box between the two drivers you are pushing this extra efficiency to a range that is restricted to lower bass.

The combined effect of the twin drivers producing upto 5.5db of extra output is what you have heard. But the poor little amp is having to draw nearly twice the current from the supply to achieve this.
Because you have reduced the supply voltage by half the stress on the output stage (and drivers) is probably similar to 24V and single speaker driver, so reliability is probably no worse.
Improve the power supply substantiallyt and you will increase the stress on the output stage and you may run into reliability problems.

A single high efficiency driver that is probably twice as big as your present drivers will make the batteries last longer if this becomes an issue.

How this thread has changed as the originator has (too) slowly released more information about his "problem".
__________________
regards Andrew T.
  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
845 Low voltage SE AMP =maximum= Tubes / Valves 16 20th January 2013 02:31 AM
Should I use high voltage value zeners or multiple lower voltage zeners in series? jarthel Parts 7 30th May 2006 04:56 PM
Rail Voltage to Capacitor Voltage Mermprin Parts 6 20th September 2004 03:56 PM
secondary voltage vs. primary voltage Stocker Parts 5 11th March 2004 07:41 PM
Rail voltage compared to transformer voltage SteveG Solid State 4 22nd July 2002 11:50 PM


New To Site? Need Help?

All times are GMT. The time now is 12:21 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