I love tinkering, but it’s good to have design goals, especially since the laws of physics are, um, well, LAWS. and unforgiving. I’m not sure what you are trying to make. Maybe I just didn’t read through everything well too.
I assume you mean the input impedance of the whole circuit; the Baxendall network itself doesn't change. The input impedance is directly inverse-related to the amount of boost. Since you get a tad more boost with the choke arrangement, the input impedance decreases slightly, but only at max boost.Tubetec said:What I still dont fully grasp is how input impedence of my bax network is effected by increasing the gain is such a way with a choke ,does input impedence go up or down ?
It doesn't matter, since the tube operates as a current generator in this current-feedback arrangement.Likewise with triode ul and pentode mode the output impedence of the tube itself will change ,
There's no taming to be done; the Baxendall circuit is unity gain. Inserting a step-down xfmr would imply adding a gain stage.guavatone said:Then a 10:1 output tranny may be in order to tame the output
As indicated on the schemo, it's at the side of the Bax network that's opposite the input.BTW where’s your output? CF?
That is not possible; a rise in open-loop response indeed increases NFB but not as much as the gain increase. You need to make measurements rather than rely on subjective impressions.Tubetec said:looks like the rising impedence at higher frequencies causes more feedback and so a droop in the response.
You can do that; it's commonly done in commercial products.Could I add some extra resistance to the high pot in such a way that the central position of the control yeilds a flat response ?
That would defeat the action of the choke.or could I tame the high load at high frequencies a bit by bypassing the choke to ht line with a suitable resistance ?
That is a necessity at this point.I suppose plotting the frequency response would be a good first move
Check answers #68 & 71 in this thread.I do see some of you have sim'd the Bax ,
You should; LTspice is quite easy to grab.Ive never learned to use spice
Indeed, it can. Are you using an EF86? That's about the only pentode model I have.but if the model already exists can the inductor be added ?
OK, I've done the sim with an EF86. The most striking thing is that with the 10k+1H plate load, the open-loop gain is only 11 (21dB), so the LF boost/cut graphs are very assymetrical at +14/-21dB.Tubetec said:but if the model already exists can the inductor be added ?
OK, I don't think I can find a workable Spice model for it, so I'll use a workaround (putting several EF86's in parallels).Tubetec said:The tube I'm using is a C3g , a German postal pentode,
I would suggest you use REW as both generator and analyzer; synchronizing REW with a hardware sig gen is a PITN.I have a standalone sig gen ,maybe room eq wizard could display the frequency response for me.
I've done the sim using 7 off EF86 in parallels. LF OL gain is about 38dB, rising up to 55dB at 20kHz.Tubetec said:The tube I'm using is a C3g , a German postal pentode,
Just did it. The choke action is felt much earlier (about 20Hz) and reach a plateau at 200Hz. What happens is that the Bax network loads the plate, thus putting a limit to the OLG at about 55dB.Tubetec said:Maybe just for fun try a 75 Hy choke in the sim .
Not really; what happens is that the Bax network loads the plate, thus putting a limit to the OLG at about 55dB.Will the benefits in terms of OL and distortion continue to accrue indefinately the bigger I make the choke ?
Assuming two coils, each of inductance L.Tubetec said:I see some Lundahl anode chokes are bifilar wound and can be connected either series or parallel and either one coil section reversed or normal in relation to the other in such way as the currents cancel or add in the core . I cant figure out which would be the best coil arrangement
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