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Old 21st April 2005, 09:38 PM   #1
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Default THD specs

How important is Total Harmonic Distortion (THD) in determining the performance of an audio eqipment? Is 0.05% and 0.005 % is a big difference? Thanks.
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Old 21st April 2005, 09:46 PM   #2
dhaen is offline dhaen  Europe
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THD is an important measurement, but not a good indicator of how equipment will sound. Most valve amplifiers have poorer THD figures than solid state, yet many prefer their sound.
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Old 22nd April 2005, 05:48 AM   #3
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In my case it's a hum eliminator device whose only components is a couple of transformers. This device should ideally be transparent as possible, so for this kind of application, the lower the THD the better it is, I suppose?
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Old 22nd April 2005, 10:21 AM   #4
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Quote:
Originally posted by gndpoints
In my case it's a hum eliminator device whose only components is a couple of transformers. This device should ideally be transparent as possible, so for this kind of application, the lower the THD the better it is, I suppose?
Providing it's well within the level specs for the transformers, the Tx's are of good quality and design and the impedances match then the Tx's should make very minimal contribution to the sonics. How difficult this will be depends on what exactly you're trying to do. Look at the Jensen design apps for serving suggestions.
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Old 24th April 2005, 11:15 PM   #5
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Default You WANT a high THD in musical instrument amps

THD IS your harmonic rating. As in a tube amp is rich in harmonics. This is simply because they have a high level of THD....and while some guys here who know 1,000 times what I do about electronics may tell you I am mistaken, I can assure you I am not.

Any tone guru will tell you a tube amp is superior because of it's high order of even order harmonics. What most don't realise is that harmonic distortion IS your harmonics. There are so many tricks the industry uses to disguise information or mislead even the sharpest of minds when it comes to guitar oriented electronics.

Since you are going by the technical specs rather than your ears, a meter designed to "grade" the quality of your amp sees harmonics as a BAD thing. To the machines, the harmonics are distortion and a distorted signal is bad.....right?

Harmonics are sort of an undertone/overtone of frequencies. Basically if you play your 6th string, the E which hits @ about 80hz, there will be an even order harmonic of 100hz. It adds richness and fullness but as far as meters are concerned, it should not be there. Basically what is distortion to a meter is not distortion to our ears.

An amp with a low THD removes more of these harmonic frequencies which puts the focus on the 80HZ allowing it to have greater clarity and detail but also allowing it to be turned up more without sounding muddy or congested.

High THD amps simply sound better because there actually is more sound. It is richer and fuller. You really do hear more of the music.

Now these harmonics occur within the sound source naturally but what is interesting to point out is if some of these harmonics are not there, the amp will create them.

If you plan to build an amp for a msical instrument, I say always go with a design that has a high level of THD.

Tube amps really aren't all they're cracked up to be by any means. Tube overdrive and the high level of THD is what truly gives tube amps their legendary characteristics. While there is a little more to it, someone wanting to clone the tone and response of a dual rectifier could do so in a solid state model....a chip amp.(because tubes are analog too!) The key thing to the unique tube overdrive is a lot of sustain adding gain before the signal starts to get clipped and dirties up. Plus with all the harmoic distortion there is simply more signal coming through to hear sustain. Hence the reason a tube amp will carry a hammer on so well at a very moddest gain level and a solid state will typically be weak and thin when attempting to achieve the same response at the same signal level settings.

I'd elaborate more but I seriously am afraid of my design being stolen. I've thrown information and designs around these boards and a few others and BAM, my design or innovation pops up in a commercial amp 5 months later! I hope to take my completed design to market some day and it really is everything a tube amp is but with a solid state power amp section and VERY simple preamp with a tube overdrive.

Just remember this, cheap and simple solid state amp designs often have a high THD. Crates power amps have a THD of a whopping 5%!! Most tube amps never break 4% and even the ones that high are rare(2% is the norm I believe). Just keep in mind that with really high levels of harmonics, your amp will break up easier at higher volume levels and you will be forced to sacrifice EQ settings.

Also remember the less parts in your amp, the less the signal is compromised/processed. Don't go by what the meters say, go by your ears. What a meter will call perfect will be crap to us....it's like the signal gets SO cleaned up that is no longer sounds organic....something the instrument producing the signal fundamentally is!
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Old 25th April 2005, 08:23 AM   #6
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thanks for all the informative replies!
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Old 25th April 2005, 09:21 AM   #7
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Default Re: You WANT a high THD in musical instrument amps

Quote:
Originally posted by MrCheeks
THD IS your harmonic rating. As in a tube amp is rich in harmonics. This is simply because they have a high level of THD....and while some guys here who know 1,000 times what I do about electronics may tell you I am mistaken, I can assure you I am not.

Any tone guru will tell you a tube amp is superior because of it's high order of even order harmonics. What most don't realise is that harmonic distortion IS your harmonics. There are so many tricks the industry uses to disguise information or mislead even the sharpest of minds when it comes to guitar oriented electronics.

Since you are going by the technical specs rather than your ears, a meter designed to "grade" the quality of your amp sees harmonics as a BAD thing. To the machines, the harmonics are distortion and a distorted signal is bad.....right?

Harmonics are sort of an undertone/overtone of frequencies. Basically if you play your 6th string, the E which hits @ about 80hz, there will be an even order harmonic of 100hz. It adds richness and fullness but as far as meters are concerned, it should not be there. Basically what is distortion to a meter is not distortion to our ears.

An amp with a low THD removes more of these harmonic frequencies which puts the focus on the 80HZ allowing it to have greater clarity and detail but also allowing it to be turned up more without sounding muddy or congested.

High THD amps simply sound better because there actually is more sound. It is richer and fuller. You really do hear more of the music.

Now these harmonics occur within the sound source naturally but what is interesting to point out is if some of these harmonics are not there, the amp will create them.

If you plan to build an amp for a msical instrument, I say always go with a design that has a high level of THD.

Tube amps really aren't all they're cracked up to be by any means. Tube overdrive and the high level of THD is what truly gives tube amps their legendary characteristics. While there is a little more to it, someone wanting to clone the tone and response of a dual rectifier could do so in a solid state model....a chip amp.(because tubes are analog too!) The key thing to the unique tube overdrive is a lot of sustain adding gain before the signal starts to get clipped and dirties up. Plus with all the harmoic distortion there is simply more signal coming through to hear sustain. Hence the reason a tube amp will carry a hammer on so well at a very moddest gain level and a solid state will typically be weak and thin when attempting to achieve the same response at the same signal level settings.

I'd elaborate more but I seriously am afraid of my design being stolen. I've thrown information and designs around these boards and a few others and BAM, my design or innovation pops up in a commercial amp 5 months later! I hope to take my completed design to market some day and it really is everything a tube amp is but with a solid state power amp section and VERY simple preamp with a tube overdrive.

Just remember this, cheap and simple solid state amp designs often have a high THD. Crates power amps have a THD of a whopping 5%!! Most tube amps never break 4% and even the ones that high are rare(2% is the norm I believe). Just keep in mind that with really high levels of harmonics, your amp will break up easier at higher volume levels and you will be forced to sacrifice EQ settings.

Also remember the less parts in your amp, the less the signal is compromised/processed. Don't go by what the meters say, go by your ears. What a meter will call perfect will be crap to us....it's like the signal gets SO cleaned up that is no longer sounds organic....something the instrument producing the signal fundamentally is!

To be fair you should point out that not ALL listeners want to add loads of harmonics to their sound. It is true that for instrument use, all sorts of deliberate distortions are used to give the sound a unique flavor. And indeed, the attractiveness of tube amps is often quoted as a rich, harmonic structure that is ADDED to whatever is on the CD.

But don't forget that the original aim of hi-fi is to reproduce the music as recorded with as little additions and colorations as possible. Many of us want to hear whats on the CD, not what we think should be there. In these cases, THD is a Bad Thing, because it adds what wasn't there. You can discuss whether .01% is worse than .001%, but the genuine aim is as little THD as possible and that is very logical and accepted.

So the answer to the question depends on what you want to to. Make your own sound? Add THD, filters, wah-wah's, what have you. You want as faithfull as possible reproduction of what's on the CD? You want low THD, no effects, linear speakers etc.

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Old 25th April 2005, 09:56 AM   #8
AuroraB is offline AuroraB  Norway
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I totally agree-- there is a very distinct difference between hifi reproduction an instrument amplification. Particularly for pop/rock guitarists, the choice of amplifier depends very much on the overtone spectrum, better known in these circles as "character"....

Problem with modern CDs and all the modern electronic mumbo-jumbo , is that you just don't have the foggiest idea how the "producer" wanted the music to sound..
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Old 25th April 2005, 10:24 AM   #9
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Hi,
I would have thought that for a power amp the cleaner the better, and add any distortion effects in the pre, meaning you can play extra clean when you want to...
As far as my opinion goes I think that richness etc should already be on the cd, and having a clean low distortion amp won't reduce the richness of the original recording, it just won't make it any richer.
For your application it sounds like an interconnect solution, in which case I'd say lower the better. How audible it is would depend on what order harmonics the system produces though...

And a blanket sweeping statement that all tube amps (and pre's included in that statement i presume) are rich in harmonics...surely depends on topology more that whether solid state or tubes are used. I have a single ended SS headphone amp, and I would imagine the measured THD of that is far far worse than my pushpull tube amp. Anyway, miles off topic for this blokes application...just putting off doing coursework now....

Steve
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