Re: bias at choke current handling
Yes, usually ready-made PSU chokes are designed to operate not so much below saturation. At low frequencies the max. peak current through the choke may raise and the choke must be capable of handling this. So it wise to stay lower than the maximum current rated to have some headroom. Also distortion raises a lot at low frequencies when you bias close to the maximum rating of the choke.
Cheers
Yes, usually ready-made PSU chokes are designed to operate not so much below saturation. At low frequencies the max. peak current through the choke may raise and the choke must be capable of handling this. So it wise to stay lower than the maximum current rated to have some headroom. Also distortion raises a lot at low frequencies when you bias close to the maximum rating of the choke.
Cheers
My power supply is a 500VA 22vac (IIRC) feeding 4x30 amp 300v ultra-fast ST diodes then a choke of approx 1mH then 104 paralled 2200uF 35v electros. Ripple at 7 amps load is about 100mV p/p but it is a sinewave shape (much lower audibility) thanks to the filter choke, not a sawtooth like in a cap-only filter.AudioGeek said:
The output coupling cap voltage needs to be only as great as the voltage drop across the choke.
One great feature not mentioned yet about choke loaded amps is that if it all of a sudden decides to go belly-up then if your choke is sufficiently low resistance it prevents too much dc voltage being developed across the speaker until such time as the fuse blows.
source follower PSRR and input cap.
for a IRFP240N running at around 28vdc 3A or so... what is the PSRR with a 100mH choke as an inductor??
trying to figure out minimum ripple I should have on PS.
Also, I want to use a IT and a tube to drive the gate. should I use a 1:1 or a 2:1 for some current drive???
what current is required for decent slew rate at 30Khz?
Thanks!!!!
for a IRFP240N running at around 28vdc 3A or so... what is the PSRR with a 100mH choke as an inductor??
trying to figure out minimum ripple I should have on PS.
Also, I want to use a IT and a tube to drive the gate. should I use a 1:1 or a 2:1 for some current drive???
what current is required for decent slew rate at 30Khz?
Thanks!!!!
Can´t answer the PSRR question except for the obvious: As low ripple as possible. As i mentioned before I had a similar amp (very similar, actually) that had about 0,1Vp-p ripple out from the PSU but nothing audiable on the output.
A stepdown IT seems to be a great idea. You´ll hardly have any use for all the voltage swing that a decent tube stage can deliver, so trading some swing/gain against better drive capability must be a good thing.
I had similar plans for my balanced project, but I changed my mind towards a balansed Zen linestage. Might try tube/IT in the future, though.
A bit of current though the driver tube can´t hurt, I´d say a few tens of mA. What tube are you going to use?
And while we´re at it, what IT?
BTW: A resistor across the IT secondary migh be useful to damp out resonances and stuff.
A stepdown IT seems to be a great idea. You´ll hardly have any use for all the voltage swing that a decent tube stage can deliver, so trading some swing/gain against better drive capability must be a good thing.
I had similar plans for my balanced project, but I changed my mind towards a balansed Zen linestage. Might try tube/IT in the future, though.
A bit of current though the driver tube can´t hurt, I´d say a few tens of mA. What tube are you going to use?
And while we´re at it, what IT?
BTW: A resistor across the IT secondary migh be useful to damp out resonances and stuff.
EP?
There should be plenty of good tubes to use in this circuit.
6C45, EC86, ECC88, E55L, E81L, plus probably a few hundred that I can´t remember right here and now
Integratad or plain power amp, well, that´s up to you alone.
Separate chassis are way less messy, though.
May I suggest that you put all tube circuitry (preamp + driver) in one chassis and the power follower in another?
There should be plenty of good tubes to use in this circuit.
6C45, EC86, ECC88, E55L, E81L, plus probably a few hundred that I can´t remember right here and now
Integratad or plain power amp, well, that´s up to you alone.
Separate chassis are way less messy, though.
May I suggest that you put all tube circuitry (preamp + driver) in one chassis and the power follower in another?
Hi,
Depends, there are several options regarding tube configurations: SRPP, Mu-stage and interstage transformer. For a Mu stage and 1:1 interstage transformer you need a mu of app. 20 for a gain of 20. So unless you are intending to use feedback, look for tubes with a mu of around 20. The EC86 has a too high mu of 68. The new ECC99 looks promising as well.
Also have a look here for some ideas of driving stages:
http://www.wdehaan.demon.nl/hybrid.html
Cheers
Depends, there are several options regarding tube configurations: SRPP, Mu-stage and interstage transformer. For a Mu stage and 1:1 interstage transformer you need a mu of app. 20 for a gain of 20. So unless you are intending to use feedback, look for tubes with a mu of around 20. The EC86 has a too high mu of 68. The new ECC99 looks promising as well.
Also have a look here for some ideas of driving stages:
http://www.wdehaan.demon.nl/hybrid.html
Cheers
trying to decide on ouput coupling caps.
ok... BG's are waaayyyy to expensive for me.
so looking at the Nichion Muse caps. Michael Percy has some 2200 and 4700uf caps.
any recommendations for caps and what to bypass them with??
also what should I bypass my supply caps with??
supply is 68,000uf - 2.2mH choke - 68,000uf cap per channel.
probably a 22vac tranny at 5A per channel for supply.
comments???
Thanks!! you have been a great help.
ok... BG's are waaayyyy to expensive for me.
so looking at the Nichion Muse caps. Michael Percy has some 2200 and 4700uf caps.
any recommendations for caps and what to bypass them with??
also what should I bypass my supply caps with??
supply is 68,000uf - 2.2mH choke - 68,000uf cap per channel.
probably a 22vac tranny at 5A per channel for supply.
comments???
Thanks!! you have been a great help.
I have good experiences using Elna RJH low impedance electrolytics as output caps.
Want something cool for bypassing? Try to find some good old paper in oils. I doubt that anything better exists.
68000uF - 2,2mH - 68000uF should be enough to keep the ripple and hum down. Put a few thousand uF next to the Mosfet, too.
Want something cool for bypassing? Try to find some good old paper in oils. I doubt that anything better exists.
68000uF - 2,2mH - 68000uF should be enough to keep the ripple and hum down. Put a few thousand uF next to the Mosfet, too.
With 10gauge wire, properly sized and wound (dimensions, etc.), you'd be somewhere between 1 and 2 ohms for 100mHy. With 8 gauge, you could probably bring that down to the vicinity of an ohm. And no solid core inductor could equal it in sound quality. Also, you could run 10 amps bias easily with such an inductor. Of course, you'd be looking at a fairly sizable, heavy part, but how much of a concern is that in the pursuit of excellence?
Hi, Fuling -
That could work. Also, if a little compromise in inductance is acceptable, Solen will sell you a 10ga 30mH 'perfect lay' choke ready made with less than 1 ohm dcr Of course, I would just buy the wire, wind a slightly larger choke to, say, 50mH and pot the result with epoxy to avoid the possibility of windings vibrating under higher current ac signals, myself.
That could work. Also, if a little compromise in inductance is acceptable, Solen will sell you a 10ga 30mH 'perfect lay' choke ready made with less than 1 ohm dcr
Of course, I would just buy the wire, wind a slightly larger choke to, say, 50mH and pot the result with epoxy to avoid the possibility of windings vibrating under higher current ac signals, myself.
If you limit the use to mids and high that is viable. Then say your SE class-A is for above 100 - 300 Hz where it counts most and a more beefy class AB for the low end. You need filtering in front of the amps then. But I doubt how such a coil will perform at high frequencies, it is not made for it.
Cheers
Hi, Pjotr -
Usually, air core coils have HF performance comparable to or better than that of solid core coils with similar ratings, especially those with laminated cores to minimize AC eddy currents. You can parallel two or more smaller gauge windings to further improve air core HF performance while keeping dcr low, also. An exception to this would be ferrite cores, but ferrite has a well deserved reputation for relatively high levels of nonlinearity and poor sonic performance when applied to audio.
Usually, air core coils have HF performance comparable to or better than that of solid core coils with similar ratings, especially those with laminated cores to minimize AC eddy currents. You can parallel two or more smaller gauge windings to further improve air core HF performance while keeping dcr low, also. An exception to this would be ferrite cores, but ferrite has a well deserved reputation for relatively high levels of nonlinearity and poor sonic performance when applied to audio.
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