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Author Topic: Best way to do a transfer function of an amplifier output?  (Read 6212 times)

John Penkala

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Best way to do a transfer function of an amplifier output?
« on: June 18, 2018, 02:29:40 PM »

I'd like to do a transfer function of an amplifiers output to "see the processing". How are folks padding down the output of the amplifier to a level that a USB I/O can handle? Any help is appreciated.

JP
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Nathan Riddle

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Re: Best way to do a transfer function of an amplifier output?
« Reply #1 on: June 18, 2018, 02:46:15 PM »

You can connect it directly, just don't exceed 24v or so (for an interface with line level inputs) :P

(I've done it, just be careful of the gain knob ;) )

Any *nearly voltage divider will work though.
http://www.epanorama.net/circuits/speaker_to_line.html/

If you really don't want to blow up your equipment then isolated transformer is best way to go.

If you want to run the amp (depends on max voltage) into clipping then you'd need higher value resistors and wattage.

good luck have fun!
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Ivan Beaver

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Re: Best way to do a transfer function of an amplifier output?
« Reply #2 on: June 23, 2018, 02:09:55 PM »

I built a box that has a pad on the amplifier output, then that goes into an old Altec line level transformer.

The main reason for the transformer is to provide physical isolation between the amp and the interface input.

This way you can look at bridged outputs, or amps that have both output terminals floating.

Be sure to use a high quality transformer to avoid saturation.

The pad size will depend on the size of the amp being looked at.  But if you calculate it to get to around a -10dBu or so, the transformer should be fine.

Or you can simply turn the amp down.

It all depends on exactly what you are trying to measure and why.

BTW I use this method when setting up/matching transfer functions of amps with DSPs in them.
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David Sturzenbecher

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Re: Best way to do a transfer function of an amplifier output?
« Reply #3 on: June 23, 2018, 03:43:09 PM »

I have always used the VIbox from linearX in the past with great success. Unfortunately they are no longer available due to the passing of the companies owner.


Sent from my iPhone using Tapatalk Pro
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Hayden J. Nebus

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Re: Best way to do a transfer function of an amplifier output?
« Reply #4 on: July 18, 2018, 05:39:50 PM »

I'd like to do a transfer function of an amplifiers output to "see the processing". How are folks padding down the output of the amplifier to a level that a USB I/O can handle? Any help is appreciated.

JP

Most DSP amps have some sort of handle to turn it down, just turn it down by about 30dB. Stim near -20dBfs/0dBu and you should be well above the noise floor still and near unity gain.
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Lyle Williams

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Re: Best way to do a transfer function of an amplifier output?
« Reply #5 on: August 01, 2018, 11:57:43 AM »

You really should have a dummy load that can handle full amp output (some great heatsunk monster) and have a voltage divider across that.

But the result will be very very flat.  If there is DSP it will be textbook-perfect EQ and resulting phase shift.
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Ivan Beaver

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Re: Best way to do a transfer function of an amplifier output?
« Reply #6 on: August 01, 2018, 07:01:33 PM »

You really should have a dummy load that can handle full amp output (some great heatsunk monster) and have a voltage divider across that.

But the result will be very very flat.  If there is DSP it will be textbook-perfect EQ and resulting phase shift.
With solid state amps you don't need to put a load on it.
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Justin Segbers

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Re: Best way to do a transfer function of an amplifier output?
« Reply #7 on: August 13, 2018, 03:13:46 PM »

I'd like to do a transfer function of an amplifiers output to "see the processing". How are folks padding down the output of the amplifier to a level that a USB I/O can handle? Any help is appreciated.

JP

Put a countryman Di with it selected to speaker input.  May not be perfectly flat? but I had no issues reverse engineering some l'acoustics presets to load them onto some crown amps for some extra rental flexibility.
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Chris Grimshaw

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Re: Best way to do a transfer function of an amplifier output?
« Reply #8 on: October 23, 2018, 05:35:29 PM »

With solid state amps you don't need to put a load on it.

While true in theory, I think an interesting part of testing amplifiers is when you push them to the ragged edge with 2ohm (or worse) testing and see what they do.
Most amps are capable of low distortion, flat response, etc. The good ones will keep doing that when the rest have overheated and shut down.

I just wish I had a load bank capable of dissipating the multi-kilowatt power levels required.
My last load bank (some fairly big aluminium-clad resistors bolted to heatsinks) did okay until a big Crown amp got all the resistors to go open-circuit in less than 20 seconds.

Next time I'll probably just get some oil-filled electric radiators and put a few in parallel.

Chris
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Mark Wilkinson

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Re: Best way to do a transfer function of an amplifier output?
« Reply #9 on: October 23, 2018, 05:44:00 PM »


I just wish I had a load bank capable of dissipating the multi-kilowatt power levels required.

Chris

Lowes https://www.lowes.com/pd/Utilitech-Water-Heater-Screw-Element/3693202#362342

16 ohms, $6 bucks.....I just stick em, however many needed for load desired, in a 5 gal paint pail full of water...
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ProSoundWeb Community

Re: Best way to do a transfer function of an amplifier output?
« Reply #9 on: October 23, 2018, 05:44:00 PM »


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