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How low do we have to go???

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Posted on November 19, 2014 at 08:39:35
TomWh
Audiophile

Posts: 764
Location: Tucson Az
Joined: August 7, 2003
 Okay have been fooling around with plate and interstage iron in my phono. And as usual more musical come mind when this is done. So the question that comes to mind, when I have been doing the math, is how many hy's are needed.

I have seen rough figures 35 hy's per 1,000 rp to 100 hy's per 1,000 rp. If my math is correct 35 hy's at 1000 would be good to 9 hz. So here are my questions.

1. If your speakers are good to about 35hz (no sub) does this low 9hz have any effect on anything?

2. Short of a pipe organ or cannon shot how low can a lp go?

3. Has anybody done listening tests with various choke values like one that starts roll off at 30hz vs 10hz for example.

There is alot things going on with chokes and transformers that keep me guessing but almost always bring forth a more musical performance. DHT's are also like that.

My holy grail is not the math comes out right, but the tone,texture,attack etc... lights my heart and soul.

Thanks Tom

 

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RE: How low do we have to go???, posted on November 19, 2014 at 09:26:59
Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002
 I may be the wrong person to respond here as I am not a fan of transformers, but the bandwidth thing is something with which I have some experience.

Ideally you want bandwidth to go down below 7Hz. In this way you can include the mechanical resonance of the arm/cartridge combination, which will describe a lower limit of playback.

The reason you want this bandwidth has to do with phase shift. Phase shift in sine waves is not audible, but over a spectrum of frequencies it is. The rule of thumb is 10x the lowest frequency, 1/10th the highest frequency. Now you see why I don't like transformers- they have troubles going from 2Hz to 200KHz.

Now in a phono, you can't expect that sort of bandwidth, but you do want to give it your best shot. On the high end, the RIAA de-emphasis is going to make +100KHz not much of a concern, but on the low end its another matter. If you really want the bass to have the right impact you have to have the bandwidth- even if its not coming off of the LP itself. Its about the phase shift the phono preamp has that we are talking about.

This of course means its a good idea to make sure you get the mechanical resonance right in the arm, otherwise your woofers could be flopping all over the place due to warp and the like.

Our LP mastering lathe has no worries cutting grooves of only 5Hz. We can't play them back though as the tonearm/cartridge combo won't have it, but teh waveforms are clearly visible under the microscope. The limitation is in playback, not record. Our cutterhead is a Westerex 3D, made about 1960.

Kick drums and bass drum whacks can easily be in the lower octave 20-40Hz. Organ pedal tones can be at 16Hz. Synthesizer tones can go well below that. Intermodulations caused by purposely overloaded bass or guitar amps in the recording studio can go much lower. In short, you don't want to limit what music is about. Its not hard to get this stuff right in the phono circuit, and it helps even if your speakers don't have the bandwidth. If your phono preamp design is successful, maybe someday you will get speakers with the bandwidth...

 

RE: How low do we have to go???, posted on November 19, 2014 at 17:06:12
Paul Joppa
Industry Professional

Posts: 7295
Location: Seattle, WA
Joined: April 23, 2001
 #1 (theory) transients such as the thwack of a tympani or pluck of a bass guitar string actually have no practical lower limit - they have at least SOME energy pretty much all the way down.

#2 (experiment) the human ear loses sensitivity as the frequency drops, but the threshold of hearing does not meet the threshold of discomfort until 2Hz.

#3 (theory) the small signal response is relative to the parallel combination of the plate resistance and the reflected speaker load. However, the large signal response (power band) is determined by the load impedance - when the inductive impedance equals the load impedance, the tube has to deliver 1.4 times the normal current, which it usually can't if the amp is designed for maximum efficiency at the design impedance.

#4 (in my experience) A value of 3 henries per kOhm load, or around 10 henries per kOhm plate resistance, usually sounds adequate on most music most of the time but it's not hard to find occasions or music which show the limitation. Twice that makes it hard to detect as a bass-specific issue and the improvements with further inductance increase have a different, more subtle character.

#5 (in my experience) I built a parafeed preamp (6BL7 into Magnequest nickel B7s at 5K nominal) with switcheable inductance and compared 20-24-40-48 henries plate choke and a current source load. The differences were subtle but audible, and several people all came to the same conclusion - more impedance is better.

#6 (theory/experience) transformers get very big very fast when you increase inductance, and the treble response suffers, one way or another. In my experience, the best treble I've heard came from a 3K transformer with only 10 henries inductance.

Not much help, was it? :^)

 

RE: How low do we have to go???, posted on November 19, 2014 at 18:34:06
DanK tubes
Audiophile

Posts: 414
Location: California
Joined: November 9, 2004
 Here is an interesting article from EE times. Check out page 3.

"If an amplifier has high and low frequency roll-offs which begin too close to the audible frequency extremes, it will exhibit phase shifts"

"In general, it is desirable for a good monitor amplifier to have a flat amplitude/frequency response between around 5 Hz and 80 kHz - two octaves either side of the audible frequency range - if good transient responses are to be expected."

Enjoy,
Dan

 

You summed it up (no pun intended!) correctly..., posted on November 20, 2014 at 05:50:21
Dman
Audiophile

Posts: 7211
Location: Kansas
Joined: January 28, 2001
 And certainly put it into words that I would be searching for almost endlessly to explain it.

IIRC, I can also add to that the fact that depending on the level (or mastering "trickery"involved), that bottom end is probably gonna be presented summed up (or in other words, mono).

Dman
Analog Junkie

 

Solution (mine at least), posted on November 20, 2014 at 06:51:28
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012
 Wideband preamp into a very good 4th order electronic crossover set at 125hz. Then you can use about any tube amp to drive the high efficiency mid/tweet through a 12db passive. Very low impedance solid state amp driving 125hz and below into moderate efficiency bass cabinets. The tube amps can be really focused on the mid to high frequency voicing. Without the bass pumping through the tube amp, the clarity improves.

While not a purist approach, it does have a ton of flexibility. It can go from ear bleeding chest thumping disco, to the breathy audiophile junk without missing a beat. Designing a tube amp for high frequency is a different animal.

 

In a similar vein, posted on November 20, 2014 at 07:26:23
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 I would cross over at or below 100Hz and no higher than that. Other than that, 12db passive creates a fairly significant insertion loss and also places several reactive elements in the signal path. So, if anything more than first order crossover is desired, I prefer active vs passive. I agree with the idea in principle, but there is no free lunch.

I have two systems. One is based on a Beveridge 2SW, with which I use home-made transmission line woofers, driven by a vintage Threshold solid-state amp, crossed over at 80Hz using a Dahlquist DQLP1 (18db/octave, I think) for the low pass and the internal crossover in the 2SW (slope unknown but steep) for high pass filtering. (The Bev has a built-in direct-drive amplifier.) I am surprised at how much I like this set-up, because I previously had a strong bias against active crossovers. My other system is based on a full-range ESL with no reactive elements in the signal path; I love that too, and it does sound a tad more "coherent" in the region between the low midrange and extreme low bass.

 

RE: How low do we have to go???, posted on November 20, 2014 at 08:50:49
Sherwood Forest
Audiophile

Posts: 240
Joined: October 7, 2014
 I'm not sure everyone else grasped that you are talking about phono, and not an amp in general. Is that correct?

In the case of a phono, most information below 10Hz is absolute garbage - surface rumble and warp dominate that spectrum. I find that only the most pristine LPs sound clean without at least 6db/octave rolloff below 20hz. Some are better off with 12db/octave

Sure, instantaneous transients go much lower, but those super-low frequency transients are almost DC, and largely make it past the high pass filter anyway.

So, if you're just talking about a phono stage here, if you're flat to 9hz, I'd say you're fine. That's only my opinion, though...


-SF

 

Thanks for the link, however, posted on November 20, 2014 at 09:10:44
Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002
 The rule of thumb, expressed from the article:

In general, it is desirable for a good monitor amplifier to have a flat amplitude/frequency response between around 5 Hz and 80 kHz - two octaves either side of the audible frequency range - if good transient responses are to be expected.

- IME is inadequate. The x10 rule sounds and measures better. That is why I recommend 2-200KHz response. IME its not so important in the speaker as opposed to the electronics.

Thanks again for the link!

 

You got that he's talking about phono reproduction, right? nt, posted on November 20, 2014 at 09:12:27
Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002
 -

 

see my post below, posted on November 20, 2014 at 09:16:13
Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002
 You can easily have bandwidth to 2Hz in the phono reproducer, however attention should be paid to getting the effective mass/mechanical resonance point correct. If you do that, even with 2Hz the low frequency noise will not be a problem. The benefit is that you go get measurably and audibly better bass transients.

If the mechanical pickup is not set up right, that 2Hz bandwidth will suddenly become a liability.

 

Sorry about that, nt, posted on November 20, 2014 at 14:27:07
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 nt

 

No, I guess that the concept of choke loading plates on a phono stage, posted on November 20, 2014 at 15:35:26
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012
 was just a bit too bizarre for me to glance over. Why on earth would someone want to do this? It is a pure voltage stage.

 

RE: No, I guess that the concept of choke loading plates on a phono stage, posted on November 21, 2014 at 23:38:26
Donald North
Manufacturer

Posts: 1296
Joined: February 8, 2001
 "Why on earth would someone want to do this?"

For the same reasons you would want to use a plate choke on any other gain stage: to get full gain and low distortion from the tube without the heat and high B+ from resistive loading or possible solid state sound effects from a CCS, and most importantly for the good sound!

I built a plate choke loaded phono stage earlier this year and can say that, in my opinion, it sounds very good. From a measurement perspective with my AP it has a tight RIAA EQ tracking and low distortion.

 

RE: How low do we have to go???, posted on November 23, 2014 at 11:23:23
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 I don't know if this will help you, but I'd like to relate to you a conversation I had between my original audio mentor, Bob Fulton and myself in the mid 1980s.

Bob marketed a speaker system that went to 12 HZ with low distortion ( double 12's, slot loaded, crossed over at 37 HZ down ), the Premiere speaker. I used those speakers back then. Bob had a highly modified solid state IC phono preamp that could run as either fully direct coupled, or, with a cap coupled output.

Bob, and his group, had a chance to listen to three preamps, identical except the cap couple was at 2 Hz on one, 1 Hz on the other, and either 1/2 or 1/4 Hz on the third.

The listening panel agreed, on demanding organ music LPs, the third, lowest frequency cap couple was quite a bit better.

From that day on, I ran my phono preamp as a direct coupled unit!

Your question does not FULLY relate to my 1980s experience, but I thought it apropos to share this with you and any interested others. I still have the preamp - for my phono playback.

Have fun.

Jeff Medwin

 

Never trust listening tests alone for this, posted on November 23, 2014 at 23:36:52
Triode_Kingdom
Audiophile

Posts: 10044
Location: Central Texas
Joined: September 24, 2006
 Did they ever make measurements to back up what they *thought* they were hearing? It's very easy to confuse subsonic resonance with more powerful bass. In systems that encourage it (such as those with very low frequency coupling caps), such resonance is often excited by, and occurs simultaneously with, low frequency program material. Only test LPs and appropriate test gear can definitively separate the two.

 

RE: Never trust listening tests alone for this, posted on November 24, 2014 at 10:54:49
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 This is the funniest post, perhaps the most ironic, I have ever seen.

Living outside the USA, and at your age, you just never knew who Robert Fulton was, and his audio credentials.

No problem, they all knew what they were hearing. They were musicians T-K, with an audio lab that would astound you !!

Jeff Medwin

 

RE: How low do we have to go???, posted on November 24, 2014 at 12:00:17
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
 Could the IC-based, 1980s-vintage preamplifier to which you refer by any chance have been the one made by Infinity, with the slider tone controls on the front panel? It was the darling of the HP Audio World for a short while. I owned one, briefly. Solid state is about the only way to achieve a direct-coupled phono stage, unless you use a tube-based circlotron, a la Atmas-phere, or some solid state buffer after a tube circuit, I guess. (There may be other ways to do it, of course, with which I am not familiar.)

You don't see any conflict between your here recommending the lowest possible bass cut-off in a phono or linestage and your practice of choosing cathode bypass capacitor values without regard for the optimal capacity to pass bass frequencies, at the input of an amplifier?

 

+1 (nt), posted on November 24, 2014 at 12:47:25
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 .
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: How low do we have to go???, posted on November 24, 2014 at 15:11:55
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Lew,

It was not an Infinity, but rather, the Bravura designed by John Tuttle, and and marketed by FMI.

No, I see no conflict. Good question Lew. Here we are talking about solid state. With tubes, if you do it as theory would dictate, then you may not get the very best overall result. There are trade-offs one must intelligently apply, and test BY EAR, in high performance audio.

An example, the best bass will come from an output transformer with a very large core. But we know this same output transformer won't possibly have the best highs possible. The large core displays mutually-exclusive performance parameters.

The informed, intelligent designer is aware of the formulas, but instead, chooses a design that, to his sensibilities, serves the music the best.

Audio design is an art, not just a pure "by the book" science. If it was solvable by the book, we'd a had perfect tube amps when RDH-4 came out, decades ago, done by an EE. That never was the case, was it ??

Instead, ex stock brokers, and layman make some of the very best sounding amps, without EE degrees, because they can and do think out of the box, and use their EAR as the final arbitrator.

If you fully bypass to a very low frequency the Rk, you have compromised the sonics of the audio amp, just like using the output transformer with the best low end ( biggest core ) compromises the highs.

It takes artistry to do great sounding tube equipment, and an intelligent mind to select what counts the most. To me, always only two things count, is it reliable and...how it sounds.

Good subject.

Jeff Medwin

 

RE: Never trust listening tests alone for this, posted on November 24, 2014 at 16:53:04
cpotl
Audiophile

Posts: 1002
Location: Texas
Joined: December 6, 2009
 "Living outside the USA, and at your age, you just never knew who Robert Fulton was, and his audio credentials."

Could you enlighten us? I tried google, but only came up with THE Robert Fulton, 1765 - 1815, who is credited with designing the first commercially successful steamboat, among other things. I guess he is not the one you are referring to?

Chris

 

RE: Never trust listening tests alone for this, posted on November 24, 2014 at 21:08:28
Triode_Kingdom
Audiophile

Posts: 10044
Location: Central Texas
Joined: September 24, 2006
 The problem is, you're not qualified to translate the event. I don't believe anything you say.

 

RE: Never trust listening tests alone for this, posted on November 24, 2014 at 21:13:48
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Chris,

Alas, the web site dedicated to him is not yet up and running. When it is, I will post an announcement on the Forum.

Robert W. Fulton ( 1925-1988 ) was a trumpet maker, made trumpet mouthpieces, and a long time audio and recording engineer. He was the head recording engineer for a Minneapolis record company called Christian Dynamics.

In the late 1970s, Robert designed a two way bookshelf ( Fulton Musical Industries " FMI 80 " bookshelf ) that was very natural sounding, it honored the tone and timbre of live acoustical instruments.

He further developed a large speaker system called " The Fulton J -Modular " which used the FMI-80 as the mids, and a modified RTR electrostatic ( ESR-6 ) tweeter, and a two way woofer, with a slot-loaded floor firing 12 inch driver, alnico magnets.

This speaker, in its day, and Infinity's Servo Static 1A, were considered State of the Art by J.Gordon Holt, editor of Stereophile. Mr. Fulton was the earliest person I know of in consumer audio to make special speaker wire for audio. In the 1970s, most of the better audiophiles ran his wire.

He made wonderful choral records. He later developed more complex speakers, the J-Modular morphed into the Premiere speakers, a seven way design with linear wideband response from 12 HZ to 80 KHZ. He invented a turntable mat called the Fulton Kinetic barrier, to this day it is outstanding !!

The story goes on and on. Robert died in 1988, bone cancer, and the small company was liquidated. He was a fabulous person, good Christian, and he touched many people in audio in a positive way. Sadly missed by many to this day.

The web site will have a LOT of cool information. In the meantime, do a whole-AA Forum search under "Fulton", "FMI 80", "J-Modular" and Kinetic Barrier " and you will gain an insight.

Jeff Medwin

 

Do you ever get tired ??, posted on November 24, 2014 at 21:30:01
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Of flaming people, or, me in particular ?

You are evil, my man !!!

Jeff Medwin

 

RE: Do you ever get tired ??, posted on November 24, 2014 at 21:42:53
Triode_Kingdom
Audiophile

Posts: 10044
Location: Central Texas
Joined: September 24, 2006
 You know what's happening here, and you're *not* the victim. Stop spewing this arrogant nonsense disguised as expert advice. The problem will remedy itself.

 

RE: Do you ever get tired ??, posted on November 25, 2014 at 15:47:19
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Only in YOUR negative mind, and, as usual Mr. Cathode Follower, you are wrong about that.

----------------------------------------------

"ME - a perverted psychopath, but Doctor ( EE ) YOU are the one who is drawing all these dirty pictures !!"

RIP.

Jeff Medwin

 

RE: Do you ever get tired ??, posted on November 26, 2014 at 10:22:22
Triode_Kingdom
Audiophile

Posts: 10044
Location: Central Texas
Joined: September 24, 2006
 The degree of negativity in my responses is commensurate with the degree of BS in your posts.

 

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