Any preamp tube gain stages that could drive 2.8 kOhm impedance? Cathode follow, perhaps? I realize much simpler with an op-amp, just trying to see if this would be possible because ideally I'd like to keep my preamp all tube. Thanks.
Yes, you can do this with tubes. You definitely need a complete picture of that load including what capacitance is there, what voltage level is needed, etc.
A high gm cathode follower running a good chunk of idle current isn't going to be bothered by that kind of load.
A high gm cathode follower running a good chunk of idle current isn't going to be bothered by that kind of load.
A good read on cathode followers driving lowish load impedances:
https://www.pearl-hifi.com/06_Lit_A...04/Sec_19/991_White_Follower_Optimization.pdf
https://www.pearl-hifi.com/06_Lit_A...04/Sec_19/991_White_Follower_Optimization.pdf
Cooool. Here's what I've got from the power amp's datasheet:
Load Impedance : 3 ohms
Capacitive Load : 100 nF
Input Impedance Signal Line: 2.8 kOhms
V Audio Input Clamp Voltage: 3V
Load Impedance : 3 ohms
Capacitive Load : 100 nF
Input Impedance Signal Line: 2.8 kOhms
V Audio Input Clamp Voltage: 3V
Holy crap, 100nF is a lot of input capacitance.
You are basically going to need to build a tube headphone amp and use it as a preamp. 100nF is about 80 ohms of reactance at 20kHz, so a transformer coupled tube preamp seems like a wise choice.
...or is that 100nF the maximum permissible capacitive load on the amplifier?
You are basically going to need to build a tube headphone amp and use it as a preamp. 100nF is about 80 ohms of reactance at 20kHz, so a transformer coupled tube preamp seems like a wise choice.
...or is that 100nF the maximum permissible capacitive load on the amplifier?
> drive 2.8 kOhm impedance
"Drive".... how big? How clean?
After all we drive 8 Ohm loads, albeit usually with a transformer.
If you want 2.8V peak in 2.8k at <1%THD, you may want to think abut a small power tube. Or an optimized WCF. Yeah, headphone amps.
> 100nF is a lot of input capacitance.
It does not say Input capacitance. It is right after "3 ohms", which I hope is an Output spec.
I call Insufficient Data.
"Drive".... how big? How clean?
After all we drive 8 Ohm loads, albeit usually with a transformer.
If you want 2.8V peak in 2.8k at <1%THD, you may want to think abut a small power tube. Or an optimized WCF. Yeah, headphone amps.
> 100nF is a lot of input capacitance.
It does not say Input capacitance. It is right after "3 ohms", which I hope is an Output spec.
I call Insufficient Data.
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@audiowize : could very well be, there was "capacitance" near the input parameters so I included. I don't have a ton of history in solid state world so maybe I'm off. Here is the datasheet, the input specs are on page 10-11
https://icepower.dk/download/2431/
https://icepower.dk/download/2431/
FWIW, I read the power board as producing full power, when driven by a "standard" 2 VRMS CDP. Therefore, very little net gain is needed in the preamp.
The low μ (amplification factor) 12B4 is capable of driving the 10 Kohm IHF "standard" load, from its anode. The impedance ratio of a transformer varies with the square of the turns ratio. So, a 3:1 step down transformer coupling a 12B4's plate to the power board would "reflect" 9X the power board's I/P impedance to the triode. IMO, the numbers seem good.
The low μ (amplification factor) 12B4 is capable of driving the 10 Kohm IHF "standard" load, from its anode. The impedance ratio of a transformer varies with the square of the turns ratio. So, a 3:1 step down transformer coupling a 12B4's plate to the power board would "reflect" 9X the power board's I/P impedance to the triode. IMO, the numbers seem good.
