Coupling of EF86 mic input stage

[rotation]

Hey,

i still don't get this:
"You can put the anode voltage at exactly halfway or put it slightly above or below. On each stage, I'm usually not at the halfway point, but only by a little bit."
Do you mean half of actual 290V or you are talking about relation between anode voltages at // triodes?

Yes, // stages in antiphase are another option for lowering distortion as would be local feedback around ECC99.
My problem here is that i don't have access to good lab very often where i could meassure distortion. I can only test it for real by hearing, but this will not tell much if differences are small, even when monitoring is very good. So i normally have to take decisions based on other's opinions or just copy something i already know (which is not giving me much satisfaction anymore). Well, i used to test some of my gear in very good studio because the owner was interested and never charged for hours. But this takes waaay too much time, i could only afford it if gear was for selling.
Because of this i probably should focus on simple design with ECC99, maybe add some local or global feedback.
Btw, do you have opinion about which option (local fb, global fb or antiphase) would give good improvement/difference if i used ECC99? I will probably try them all with time but for now i would like to start with one.
I still haven't "come" to cathode circuit, i will have some more reading about it because i don't really understand how i calculate cathode resistor after i know anode current...



Miha

 

[guavatone]

I think he means to drop hald the voltage, so if your supply is 300V then dropping 150V with your R(L) or load resistor.

Right PRR?

 

[Winston OBoogie]

I think he means to drop hald the voltage, so if your supply is 300V then dropping 150V with your R(L) or load resistor.

Right PRR?

I'm not PRR but, if you're responding to my post, I meant dropping 150V across the load R yes.  Which would be half of a 300V anode supply.  In reality, I'm usually not at exactly half.

 

[Winston OBoogie]

Yes, // stages in antiphase are another option for lowering distortion

I didn't say that.  I said that if you have an even number of stages (like in your two stage REDDish amp), you can make the stages' non-linearity be in anti-phase to each other which would cancel some of the products.

as would be local feedback around ECC99.

The ECC99 is much more linear than an E88CC.  Try it without a local loop first.  Also doesn't have as much gain to be throwing away.

My problem here is that i don't have access to good lab very often where i could meassure distortion.

The type of distortion measurement is important here.  THD is quite meaningless to me.  A means to look at the spectrum of distortion products is where you want to head I.M.O.

Btw, do you have opinion about which option (local fb, global fb or antiphase) would give good improvement/difference if i used ECC99?

No.  It's not my amp. 
The ECC99 is a quite linear valve by itself - as is - but, besides that fact, I recommended it to you because you were wanting something that would enable you to use a lower ratio output transformer. 

I don't know what your goal is here.  Whatever the goals, there are inevitably trade offs involved.  Pick what's important to you and head down that path.  Juggle the tradeoffs or make them features 

If you just want a different flava mic amp to your REDDish one, start again with another maybe?  Much better and different ways to go than an EF86 input valve too. 

 

[SUPERMAGOO]

http://atvmagoo.googlepages.com/NeveTubeMixer.pdf

 

[rotation]

Yes, // stages in antiphase are another option for lowering distortion

I didn't say that.  I said that if you have an even number of stages (like in your two stage REDDish amp), you can make the stages' non-linearity be in anti-phase to each other which would cancel some of the products.

as would be local feedback around ECC99.

The ECC99 is much more linear than an E88CC.  Try it without a local loop first.  Also doesn't have as much gain to be throwing away.

My problem here is that i don't have access to good lab very often where i could meassure distortion.

The type of distortion measurement is important here.  THD is quite meaningless to me.  A means to look at the spectrum of distortion products is where you want to head I.M.O.

Btw, do you have opinion about which option (local fb, global fb or antiphase) would give good improvement/difference if i used ECC99?

No.  It's not my amp.
The ECC99 is a quite linear valve by itself - as is - but, besides that fact, I recommended it to you because you were wanting something that would enable you to use a lower ratio output transformer. 

I don't know what your goal is here.  Whatever the goals, there are inevitably trade offs involved.  Pick what's important to you and head down that path.  Juggle the tradeoffs or make them features 

If you just want a different flava mic amp to your REDDish one, start again with another maybe?  Much better and different ways to go than an EF86 input valve too.   

Well, my primary goal is learning/making something mine. I also wanted to change OT to lower ratio (later i was told i can go lower with existing circuit if not driving very low impedances) and get different sound from another tube.
I think i have good guidelines about how to do it, so thanks a lot John (and others). Be sure i will come back when i'm done

Miha