1.5 ohm resistor in series with speaker

[rebos123]

A gentleman by the name of G.A. Briggs also suggested doing something similar. I have attached a scan from his treatise on open baffle speakers. Mr. Briggs knew a thing or two about sound.

 

[Grainger49]

Dr. Gizmo (as far as I can tell) pretty much single-handedly drove the resurgence of interest in DHT SE amplifiers, at least in the US.

As to the even/odd order harmonic distortion... this is NOT a tube/transistor difference; it is a single-ended/push-pull difference. Even-order harmonics cancel out in a push-pull amp; but not in a single-ended amplifier. Tube amps tend to have proportionately more lower-order harmonic distortion. Put those two factoids together, and the even/odd order fallacy just seems to spring up.

http://www.audiokarma.org/forums/showpost.php?p=2905128&postcount=31

Note: so the pitch known as "concert A" in music has by convention a frequency of 440 Hz. That's the A above middle C for those as musically challenged as I. Folks would call the base frequency of 440 Hz (A440, aka "A4") a "fundamental" (tone) if you struck that key on the keyboard. Double that frequency is 880 Hz. You might be tempted to call that the "first harmonic" but it is in fact referred to as the second harmonic (which is the first even order harmonic distortion product of the fundamental). 880 Hz is also the fundamental frequency of "A5", i.e., the "A" note one octave above A440. Needless to say, if you have a single-ended amplifier (tube or solid state) with a significant amount of second harmonic distortion, the result will be "euphonious" -- the note and its partner one octave up. Is it accurate? No. Is it pleasant to hear? Yes.

http://en.wikipedia.org/wiki/Piano_key_frequencies
http://en.wikipedia.org/wiki/A440

I agree, I had glaringly omitted that push pull cancels second harmonic. There is a lot of confusion about first overtone/second harmonic out there. Of course 880 is one octave above 440 and is an overtone of 440, the second harmonic, and first overtone. Both are correct but often misused.

Regardless, we have skidded way off topic of the OP and the 1.5 ohm resistor here.

 

[vibroverbus]

As to the even/odd order harmonic distortion... this is NOT a tube/transistor difference; it is a single-ended/push-pull difference. Even-order harmonics cancel out in a push-pull amp; but not in a single-ended amplifier. Tube amps tend to have proportionately more lower-order harmonic distortion. Put those two factoids together, and the even/odd order fallacy just seems to spring up.

+1. well clarified.

 

[vibroverbus]

that you can make any good quality amp sound like a tube amp by inserting a 1.5 ohm resistor in series between the positive erminal of the amp and the speaker.

I see your 1.5 ohms, and Nelson Pass raises you by 45.5 ohms.

http://www.firstwatt.com/downloads/cs-amps-speakers.pdf

Actually that's a whole different concept - Current Source driving modern full-range speaker drivers, and then emulating a Current Source amplifier with a 47ohm resistor.

But hey, it's still interesting, geeky, and involves series resistors, right?

And not to be a complete Pass fan-boy, but here's another interesting link if you want to groove on the nitty gritty of even/odd distortion components:
http://www.passdiy.com/pdf/articles/distortion_feedback.pdf

 

[mhardy6647]

You can doo far worse than to be a Nelson Pass fanboy!

 

[vibroverbus]

You can doo far worse than to be a Nelson Pass fanboy!

(and seriously that NFB / distortion piece is a great read... just a random tidbit - blind testing shows people split between preferring small amounts of 2nd and 3rd order distortion aka SE vs. PP... so much for the commonly accepted "even order always sounds better" rule.)

 

[M Jarve]

(and seriously that NFB / distortion piece is a great read... just a random tidbit - blind testing shows people split between preferring small amounts of 2nd and 3rd order distortion aka SE vs. PP... so much for the commonly accepted "even order always sounds better" rule.)

It's when you get into higher harmonics (4th, 5th, etc.) that even-order sounds less offensive. High amounts of either 2nd and 3rd harmonics will "richen" and "detail" the sound in an undesirable, yet subjectively good way, in the same way that a well-tuned 12-string guitar sounds "fuller" than a six-string counterpart.

I've also heard of the Pass method, and while I've not read his results, my own indicate that the effect is largely dependent on the speaker. Some speaker sound like $hit doing it (otherwise sounding fine) whereas others did seem to benefit and gain a tube-like euphoric presence.

 

[vibroverbus]

It's when you get into higher harmonics (4th, 5th, etc.) that even-order sounds less offensive. High amounts of either 2nd and 3rd harmonics will "richen" and "detail" the sound in an undesirable, yet subjectively good way, in the same way that a well-tuned 12-string guitar sounds "fuller" than a six-string counterpart.

Yep. It's in the article. Higher order even and odd are generally universally agreed to become more offensive, and it's the high order inter-modulation distortion that 'kills you' in a poor system. On top of that ill designed feedback might take out the relatively 'harmless' (even possibly desirable, depending on your preference) 2nd/3rd while having little effect on the higher-order distortion. Great read as I said.

I've also heard of the Pass method, and while I've not read his results, my own indicate that the effect is largely dependent on the speaker.

Yep he says it's only for specific examples of these modern full-range speakers (for ex: Lowthers, Fostex, etc.) that a current source is ideal, and the implication up front that conventional speakers may well still sound best with conventional voltage-source amplifiers (makes sense as our conventional audio gear has mutually evolved to work together). Read the article - he tests a whole number of specific drivers and comments on results of each... (Note to self: get going on that full range Fostex driver speaker build this fall... )

 

[Tripqzon]

Holy crap guys. With my clogged up allergy head your getting a little too scientific for me. I have to read some of the posted article links when my head clears.

I get the point about using non inductive resistors. I use them for testing amplifiers. But for now I will use 25 watt sand resistors just to try this experiment out.

 

[OvenMaster]

I would think that you'd want to use noninductive resistors for best results.

Mark, I remember reading at the time that wirewound types were specified because the resistance element coil winding added inductance to the mix, and that was the primary reason for the treble rolloff, leaving the bass unaffected.

I wish I could remember precisely where I saw the original article, but it was around the early 80's or thereabouts.

Tom

 

[badbadbad]

I tried it...I like it better, as my highs were a tad bright anyway...but Im still listening.

 

[Tripqzon]

I tried it...I like it better, as my highs were a tad bright anyway...but Im still listening.

What type of resistors are you using?

The sand resistors I ordered haven't arrived yet. Not a big issue as my head is stuffed up from my cold/allergies. This really sucks.

I realize the packages say 390 ohm but the pic is for illustration purposes only.

If a different type resistor is required I will buy those if I like the results.

 

[Tripqzon]

Mark, I remember reading at the time that wirewound types were specified because the resistance element coil winding added inductance to the mix, and that was the primary reason for the treble rolloff, leaving the bass unaffected.

I wish I could remember precisely where I saw the original article, but it was around the early 80's or thereabouts.

Tom

Tom,

What you say makes sense. Bob Carver didn't specify what type resistor to use though. It'll be interesting to see what Mark has to say about this.

Paul

 

[badbadbad]

Im using sand versions

 

[whoaru99]

Tube amp = (generally) output transformers. Output transfomers = (relatively) high output impedance. High output impedance = low damping factor and more deviation of the amp's frequency response due to interaction with impedance swings of the speaker.

Put a resistor in series with the typically low output impedance of a SS amp and you have what Carver describes by primarily emulating the higher output impedance of a tube amp. This is what is done in the Sunfire amps having both current source and voltage source outputs. The current source outputs have higher output impedance.

 

[ferninando]

I find it amusing, not critisizing, just observing, how some SS amp owners want them to sound like tube amps. Seems to me if you want tube sound buy tube equipment and be done with it. Personally I wasn't able to distinguish between a tube amp and my SS sansui integ. amp. But to be honest , the tube amp at 5 watts sounded good as SS 65 watts. albeit only 1 watt was being pumped. Go figger. But my ears suck anyway.
Additionally, if its the highs thats to be rolled off by tubes, then just knock the treble down abit on an SS amp. But that's probably too simple. The even/odd order harmonics are at work in there.

 

[cornhulio]

My magnepan 1.6qr's came with resistors for the top end. I didn't like the 1 ohm. I'm using the 2 ohm and I'm not sure it's enough. I may try a 3 ohm one of these days. It does warm up the sound by lowering the intensity of the highs but that's about all it does. It's definitely worth a try for a few bucks. Caps can also be used to tweak the x-over point of the highs which prevents the harsher mids from reaching the tweeters.

 

[mhardy6647]

Let's just be really clear on this. Any decent tube amplifier is not rolled off at high frequencies. Further, you won't find more extended HF response than via a vacuum tube preamplifier. The modest EICO HF-85's quoted frequency response (per the manual, available at the EICO Yahoo group) at high level inputs to outputs is +/- 0.3 dB at 5 to 200,000 Hz

 

[Tripqzon]

If that's what it sounded like I was saying that was not my intention. I deleted my last post because after thinking about what I wrote it just sounded wrong to me. You read it before I got a chance to delete it.

I've read specs on tube amps and know that they have very good frequency response.

This thread was started only because I was curious as to what Mr Carver said. I know a SS amplifier can never sound like tube amps and apologize to the tube fans out there if I said anything that makes tube amps seem less than anything they are. It just seems that some associate "warm" sound with rolled off high. I think it's just easy to associate less treble with warmer sound.

This thread is all about a simple experiment and nothing more.

 

[mhardy6647]

I associate tube sound with good sound. Something like a stock ST-70 can have that bluesy, boozy, warm, bloated "tube sound" that the denigrators, umm, denigrate. But you can fix that.

A good one sounds like music.

A good ss amp sounds like music, too.

Coincidence? I think not.