John Curl's Blowtorch preamplifier part II

[Esperado]

It's a very nice table- I used an SL15 as well because it came with a superb cartridge (). it did have some cyclic subsonic output,

Due to some resonnance of this particular cartridge and the arm, or the motor of the arm during movements ?
What has become of this turntable, you do not have it any more ?
I'm looking for a replacement head for it, and i have no idea.

 

[SY]

It was from the arm motor. I never noticed it until I got speakers that went a bit lower than ESL-57 or LS3/5A. I ended up giving the turntable away after I got my VPI. I'll bet there's still some around on Ebay...

 

[Steve Eddy]

Using a record jacket at the "null" direction from a pair of dipoles (Quad esl 63's) is pretty close to a test of controlled directivity. The secondary attenuated local reflections seem to be enough to be audible.

As would likely be the case if you removed all the furniture and other stuff from the room.

se

 

[31697B]

If I really wanted one I would just go for Stax. BTW how do planar drivers eliminate the head/driver cavity effect?

The HiFiman has reduced that affect quit a bit... open back, a lot of damping material and who knows. Its a LOT less mushy/blurry sounding in the bass compared to most that use the cavity resonance to boost bass.

Show me the xDSL circuit and I'll go buy a Stax headphone. Thx-RNMarsh

 

[Esperado]

A Stax'O'phone

 

[Kindhornman]

RnMarsh,
I don't see how opening the back affects the cavity side of the headphone except as regards reflected waves back through the diaphragm even if the rear chamber is damped? Unless the diaphragm was perforated how does it change the head side of the cavity resonance?

 

[jan.didden]

Jan, just curious... were you motivated at all to find this chip by the other thread, NXP Semiconductors cleaning house ?

No, not at all, didn't even know that thread.
Just would make my next project a bit easier.

jan

 

[31697B]

RnMarsh,
I don't see how opening the back affects the cavity side of the headphone except as regards reflected waves back through the diaphragm even if the rear chamber is damped? Unless the diaphragm was perforated how does it change the head side of the cavity resonance?

The volume is the volume -- that doesnt change, of course. The affect of fully enclosing the diaphram does affect the bass and its damping. The same way as a sealed enclosure or a tuned port would. They have done a very good job of integrating all the factors with thier driver characteristics. And, I dont hear what is attributed to the cavity space as much as most others. Thx-RNMarsh

 

[Max Headroom]

Max, I might say that while I have experimented with such 'platforms' but I would never have thought that valve springs were useful for them. What is the approximate resonant frequency, anyway, that you normally get? Is it below 5 Hz for example?
.

Hi John, under heavy speakers the resonance is at a few Hz.
Under equipment rack with shelves made of kitchen top stone similarly low resonance.
Works for me.

Dan.

 

[Max Headroom]

Rides Like A Roller...

Max,
It is amazing the lack of understanding of a spring and vibration damping you are demonstrating here. Take your car as an example. Leave the springs in the car and remove the dampers. Now drive down the road and tell me that the mass of the car will stop those springs from going into an oscillation.

The front shocks on my car are rooted. Going over speed bumps or stabbing the brakes can indeed cause a slow oscillation of the body wrt the road.
On smooth roads this behavior is of little consequence, indeed it floats and rides nicely.
Rough surfaces can induce a higher frequency resonance, but that is the unsprung mass resonating (think spring rate/tyre compliance) but still not a lot of transfer into the cabin of the car.

Same goes for internal to an engine. If you have every worked on a cylinder head you would know that there is always more than one spring at a minimum. .

My car has one spring only per valve....that was the case when I last rebuilt the head.

 

[fas42]

One can always play with resonance frequencies to move them to a region where they don't appear to cause a problem. However, I would always prefer to remove vibration from the equation entirely if I can: so for example, couple the speakers to as massive a mass as possible to lower the resonant frequency to irrelevance, like Blu-Tacking them to the top of a safe; or always use viscoelastic materials, to dissipate the energy as heat.

Frank

 

[john curl]

Well thought out, Max. Don't let others give you a hard time. '-)

 

[scott wurcer]

The HiFiman has reduced that affect quit a bit... open back, a lot of damping material and who knows. Its a LOT less mushy/blurry sounding in the bass compared to most that use the cavity resonance to boost bass.

Show me the xDSL circuit and I'll go buy a Stax headphone. Thx-RNMarsh

I've traded 32" of snow for 60 degrees and blue skys for two weeks, one of my guys might have the schematic back home. IIRC jcx did a bunch of xDSL/headphone circuits on one of the head-fi type forums.

 

[Esperado]

Well thought out, Max. Don't let others give you a hard time. '-)

So, for you, spending our time to give experienced advices and technical explanations in order to make people save their time and money and improve their audio system is giving a hard time ?
For me, the 'hard time' comes from people promoting smoke and fraudulent 1000$ parts chasing phantoms at the quantum level, asserting the utility of 'burning raw cables' or pretending that inverting their sens with an AC signal will have an influence.!!!!
You know ? Everything witch cannot be measured and is against all the known laws of physic or the most elementary logic.
Sorry, but your post was just provocative.

 

[Max Headroom]

Empty Vessels Make The Most Sound.....

Well thought out, Max. Don't let others give you a hard time. '-)

Water off a duck's back.

Dan.

 

[fas42]

Better watch out ... the G men are around ...

Frank

 

[31697B]

I've traded 32" of snow for 60 degrees and blue skys for two weeks, one of my guys might have the schematic back home. IIRC jcx did a bunch of xDSL/headphone circuits on one of the head-fi type forums.

Nice here in California, also. Enjoy!
And, if you think of it when you return.... the xDSL/headphone circuit? Meanwhile, I'll hunt for it. Thx -Richard

 

[qusp]

Richard, what he means is the xDSL drivers often find their homes in headphone amps and the same chips used for xDSL are reborn under another name as headphone drivers. like the TPA6120A2

 

[31697B]

Audible effects of TT --

Richard, what he means is the xDSL drivers often find their homes in headphone amps and the same chips used for xDSL are reborn under another name as headphone drivers. like the TPA6120A2

So that is what he was telling me

Did someone say 'mechanical resonances'? See B & K's App Note: "Audible Effects of Mechanical Resonances in Turntables." (turntables/arms/cart). Paper was also presented at AES, N.Y. 1977.

-RNM

 

[qusp]

yep i'm just pretty familiar with this crossover (TPA6120 vs THS6012) and already knew of the designs done by jcx and threads over at head-fi. the TPA isnt the only part, there is a few of the old natsemi DSL parts make nice headphone amps, the loads are pretty similar if you think about it. like the TPA they are often current feedback.

ps. dont be so tense Richard