Heres an odd one....

[hesamadman]

Im toying with the notion of using this solid state class D amplifier I have and building a tube preamp for it. The power amp says it has an ideal input impedance of 60k. I think the suggestion is a power amp should have 10x input impedance of the preamp. So i would need an output impedance of roughly 6k. That is if I am understanding correctly the article I just read. Is this something that would be a huge pain in the butt to accomplish?

[pompeiisneaks]

I doubt it in theory, many amp manufacturers make hybrid amps.  Some have used SS Preamp with power output, others have done all or partial tube preamp into the power amp.  The new Vox nutube ones use a nutube for the preamp and a class D for the power stage.  I'm not totally sure about the point of the impedance difference you're referring to.  I was under the impression they had to match exactly.  I.e. if the class D expects 60k the output of the preamp should be in that range, you may need to add something to balance the impedance some, but that's where I get out of my depth :)

~Phil

[hesamadman]

I was just basing my info off of this quote.


"[color=rgba(40, 26, 23, 0.85098)]If you are adding a tube preamp and hooking it up to an amplifier,[/color][color=rgba(40, 26, 23, 0.85098)] the input impedance of the amp should, in general terms, be ten times (or more) the output impedance of the preamp. If it isn’t 10X, or maybe it’s close, you may still get incredible performance."[/color]

 If it does have to match, according to the output impedance calculator, I can get 60k by using a 12ax7 with a 100k plate resistor and a non bypassed cathode using an 820ohm resistor.


I thought it might be cool to try and build a small bass amp if I could get this to function correctly.

[PRR]

Low-Z. Cathode follower. Or sand buffer.

[hesamadman]

That's what I was guessing.

[DummyLoad]

12AU7 will push 50Vrms with 5.5k Z out into 60k load. AV is ~ 11. conditions: Va 250V; Ra 27k; Rk 1.2k; Ib ~4mA


--pete

[kagliostro]

12AU7 will push 50Vrms with 5.5k Z out into 60k load. AV is ~ 11. conditions: Va 250V; Ra 27k; Rk 1.2k; Ib ~4mA

Ciao Pete - Ahemm ..........

in CF configuration or do you mean with Plate output ?

Franco

[DummyLoad]

12AU7 will push 50Vrms with 5.5k Z out into 60k load. AV is ~ 11. conditions: Va 250V; Ra 27k; Rk 1.2k; Ib ~4mA

Ciao Pete - Ahemm ..........

in CF configuration or do you mean with Plate output ?

Franco

the values for the plate and cathode resistors are for a plate drive. it doesn't seem that we'd be able to swing 50Vrms with a 1.2k cathode resistor now does it?   


--pete

[labb]

So what do the folks that build the rack mount stand alone pre amps do for this?

[kagliostro]

Thanks Pete

I've never be very skilled and in the last few days (since I spent the last night, last Sunday, in the emergency room of the hospital) I take a medicine I need (I still hope only for further few days) but sometime I miss a bit of synchronism with the brain 

 

Franco

[pompeiisneaks]

no bene!  Take care our italian stallion!

~Phil

[kagliostro]

L'erba cattiva non muore mai (or, at least, I hope so)


  


Thanks Phil


Franco

[pompeiisneaks]

Had to translate that, LOL

The bad grass never dies :)

~Phil

[DummyLoad]

Thanks Pete

I've never be very skilled and in the last few days (since I spent the last night, last Sunday, in the emergency room of the hospital) I take a medicine I need (I still hope only for further few days) but sometime I miss a bit of synchronism with the brain 

 

Franco

my thoughts are with you. hoping you're on the mend soon. do take care franco!


regards,


--pete

[PRR]

> The bad grass never dies

In English, we usually turn the meaning around: "Only the good die young".

See my lawn: the Bluegrass and even the Tall Fescue are stunted, the Crabgrass and Plantain (Plantago) are doing well.

Hoping Franco stays on the "bad" side of the lawn, and out of the hospital.

[kagliostro]

Many thanks to all, my friends

things are improving

 

Franco