What audio circuit would you build to intentionally produce high IMD?

Help Support GroupDIY:

JohnRoberts

Well-known member
Staff member
Moderator
Joined
Nov 30, 2006
Messages
20,245
Location
Hickory, MS
For the record the OP is trying to make distortion not reduce it.

Modulating the full range bypass by a LPF pass band into a simple multiplier might work. The IM we experience is generally caused by HF riding on top of a LF envelope that pushed its peaks of the HF signal into nonlinear transfer function region.
 

jacomart

Well-known member
Joined
Sep 13, 2017
Messages
161
Location
Tuscany, Italy
For the record the OP is trying to make distortion not reduce it.
True, my reasoning was based on my experience of designing intermodulation precorrectors in RF amp stages where a complementary distortion to that generated by the amplifier is normally introduced to linearize its response. This is why I said that a precorrector itself is an intermodulation generator.

Cheers
JM
 
Joined
Sep 24, 2017
Messages
11
I was going to suggest ring mod, but there are more intelligent opinions already posted than my guessing whether it's a relevant suggestion related to IMD.

But, while on the topic, I heard a guy explaining what a ring modulator was in the hierarchy of guitar effects, closing with (paraphrased) 'Not advisable at a wedding reception you're performing at, but if you choose to, it's on you, not the guy who introduced it to you'.
 

ricardo

Well-known member
Joined
Apr 28, 2011
Messages
1,429
I was involved in these Intermodulation Distortion Listening Tests which went on well after this paper was published. IIRC, it used a multiplying modulator. IMD doesn't sound nice.

You have to be careful about the order of IMD you are trying to generate which is sorta related to the order of simple harmonic in circuits with flat response.

The hidden gem in this paper is the tests on Delayed Resonances. The false prophets Floyd & Olive replicated & confirmed Peter's results some 2 decades later. These are the most important speaker distortions.

If you are after a 'nice' effect, the simple diode clipper (1 resistor & 2 parallel back-2-back diodes that JohnRoberts & squarewave suggest), has been tested in many DBLTs including mine and found worthwhile. More difficult to dial in the amount of IMD you want though ... and it has large amounts of simple harmonic distortion too
 

gswan

Well-known member
Joined
Sep 18, 2006
Messages
892
Location
Sydney, Australia
Ed Cherry presented a really good paper at the AES convention in Melbourne in 1984 which may be worth examining ("Amplifier Distortions: Audible and Inaudible"). Here he presented different styles of music and introduced different amounts of different types of distortion during listening. Most were actually very pleasing and enhanced the sound, with the exception of crossover distortion which sounded pretty objectionable.
 

JohnRoberts

Well-known member
Staff member
Moderator
Joined
Nov 30, 2006
Messages
20,245
Location
Hickory, MS
Ed Cherry presented a really good paper at the AES convention in Melbourne in 1984 which may be worth examining ("Amplifier Distortions: Audible and Inaudible"). Here he presented different styles of music and introduced different amounts of different types of distortion during listening. Most were actually very pleasing and enhanced the sound, with the exception of crossover distortion which sounded pretty objectionable.
+1... I recall seeing and reading more than one AES paper from Cherry about amplifier design back last century. Very instructive, but as I recall those papers were about objective measurable phenomenon.

JR
 

Matt Syson

Well-known member
Joined
Dec 17, 2005
Messages
84
Location
France
My guess at a 'start' could be made by using the transistor network that was dreamed up (meticulously designed) as the core of early VCAs so about half a dozen transistors but then intentionally unbalancing things and possibly filtering of the 'sidechain' and/or a slight delay or phase change.
'Unbalancing' a VCA can give 'warmth' which might be useable. Things like the Valley People EGC 'VCA blocks used well matched transistors as their goal was minimal distortion .
But what do I know?
 

Latest posts

Top