[laikadog]

Hello all,

I'm trying to figure out if I'm going to have any compatability issues by using a tube preamp to run my 440EX. Does anybody happen to know the input impedance of the 440EX? Probably going to use a vintage Scott pre (355 preamp/tuner combo or LC-21), which at this point I don't know the output impedance of either. Any and all advice is welcome. Thanks.

[avahifi]

The input impedance of all OmegaStar solid state amplifiers is 24Kohm pure resistive load.  It should be easy for any preamp to drive, tube or solid state.  The input impedance is not affected by the feedback loop and does not vary dynamically like many amplifiers do. The input impedance of Fet Valve hybrid amplifiers is 1 Meg ohm

An interesting test for an amplifier is to drive both channels with a 10KHz square wave at about half power into an 8 ohm load, with a 1 uF capacitor in parallel with that load on one channel only.

This will cause a leading edge overshoot and ring on the channel with the capacitive load with most amplifiers.  Then move the scope probe to the input of that driven channel, the same overshoot will likely show up at the input because the feedback loop is modifying the input impedance of the amplifier, which then affects the preamp performance too.  For a further test move the scope probe to the channel that does not have a capacitive load attached, many amplifiers will show the ringing here too, reflected from the other channel, and at the second channel's input too.

Now explain to me how your reactive (multistrand woven) speaker cable, which is making the output of the amp different from the input (the name for this is distortion) is making your system "sound better".

Caution with the square wave test, it can cause some amplifiers to fail quickly.

Frank Van Alstine

[WEEZ]

Hey Frank,

Thank you for responding to laikadog's question. (You may have read my similar question on another thread-re:using a T5R w/ a solid state amp). As both you and Larry have said- using such a combination will work well but the question of cables 'that complete the chain' are important so as not to screw-up an already good thing. I am interested in learning more- so I hope you can shed some additional light on this so I- and everybody- can learn more.

As I mentioned on the other thread- I was (am) aware of the importance of low capacitance in cables- and as I stated- most of us have no idea what the "specs" of most of these cables are so it's no wonder that people can be sold on the "magic stuff"- 'cause nobody knows the difference- and how to predict the performance (whether a cable will help or hurt).

Now, after that rambling intro....
What would be a reasonable range of capacitance in a 1-meter pair of interconnects- say between a source/preamp and/or a pre-amp/amp?

Secondly (and hopefully lastly)- I have been recommended to use a speaker cable that has the following specs:
    .037 uh/ft/loop inductance
     347 pf/ft capacitance
     Q-Factor of 9.2
      9.5 awg

I would need 10' for each speaker- which are 8-ohms (min 6.5, max 14)

Can you comment ?

I'm sure I speak for most of us out here- but for myself- I want to learn how to make my existing system and more importantly my next system work best and to it's fullest potential.

Thanks in advance....

WEEZ

[Christophe35]

Hi everyone,

What are the output impedance of the T5, T6 and T7 preamplifier ?

Thanks for any information,
Christophe

[WEEZ]

I believe it's 560 ohms for all - at least that's the output impedence of the T5- per Larry @ AVA.

WEEZ

[avahifi]

347 pF per foot cable capacitance would be a real nasty load.  Times 20 feet would be a .069 microfarad capacitor tied across your amplifier speaker terminals.  That is enough to generate a significant leading edge overshoot with most amplifiers and cause some (not ours) to go into full bore oscillations.  This will change the sound but not for the better.  Try this with a square wave generator and a scope on the test bench and you would never ever use this kind of cable.  Or simply buy a couple of .05 uf 100V film capactiors for 20 cents each and tie them across the speaker terminals and use conventional low capacitance lamp cord for speaker wires and achieve idential sonic results.  The world of gonzo speaker wire is simply snake oil and fraud.  Yes it changes the sound, but on the test bench you can learn exactly how it is changing the sound and you won't like what you learn at all!  The output impedance of all T series preamps is 560 ohms pure resistive.  Frank Van Alstine

[avahifi]

347 pF per foot cable capacitance would be a real nasty load.  Times 20 feet would be a .069 microfarad capacitor tied across your amplifier speaker terminals.  That is enough to generate a significant leading edge overshoot with most amplifiers and cause some (not ours) to go into full bore oscillations.  This will change the sound but not for the better.  Try this with a square wave generator and a scope on the test bench and you would never ever use this kind of cable.  Or simply buy a couple of .05 uf 100V film capactiors for 20 cents each and tie them across the speaker terminals and use conventional low capacitance lamp cord for speaker wires and achieve idential sonic results.  The world of gonzo speaker wire is simply snake oil and fraud.  Yes it changes the sound, but on the test bench you can learn exactly how it is changing the sound and you won't like what you learn at all!  The output impedance of all T series preamps is 560 ohms pure resistive.  Frank Van Alstine

[WEEZ]

Frank,

You confirmed my suspicions- I too thought the capacitance to be out of line- but the inductance was low, which is an important factor too, isn' it?

What I-and maybe others- would like to learn, is more about what electrical characteristics we should be looking for with cables and wires so that we can get the best out of our equipment.

I am not a proponent of gonzo or magic wire either- that is why I have hijacked this thread ...

But I do think it would be useful for us to have some guidlines from an expert such as yourself. How much capacitance is too much? Like I mentioned on another thread- I thought inductance was a major factor with speaker cable, and capacitance was more of a factor with high impedence connections. I don't mind being wrong

Just trying to learn so I and others don"t get screwed by "snake-oil" salesmen.

Any guidlines you can offer would be helpful- and appreciated

WEEZ