Preamp CCS

[pre65]

I was reading a forum post (not on here) about using an Ixys 10m45s CCS chip on a preamp.

It seemed to suggest that if the 10M45s was the anode load you could ground the cathode, as the chip set the current.

Or could I have misunderstood ?

Also, I've read of cascoded 10M45s being better than a single one, can anyone point me to information on that ?

[Nick]

Must be true, it s on the net.

Grounding the cathode will force it into grid leak bias. it will work for some values of work.

Cascoding CCS's will create a composite CCS with higher impedance and better power handling, so yes, it is "better", but you need to know if it was good enough before, or if the weak point is somewhere else.

[Mike H]

It seemed to suggest that if the 10M45s was the anode load you could ground the cathode, as the chip set the current.

I imagine the anode Voltage will fall to the point where it stabilises at that current, which could be quite low, depending what valve it is, not sure I like that idea. I'd still want to bias the valve 'properly'.

Also grid will behave like a diode to ground for input signals.

[pre65]

It seemed to suggest that if the 10M45s was the anode load you could ground the cathode, as the chip set the current.

I imagine the anode Voltage will fall to the point where it stabilises at that current, which could be quite low, depending what valve it is, not sure I like that idea. I'd still want to bias the valve 'properly'.

Also grid will behave like a diode to ground for input signals.

Talking of diodes, if one wanted to use diodes instead of a resistor at the cathode, is it a case of adding up the forward volts till one gets to the desired voltage ? And then no bypass cap is needed ?

I could be suffering from information overload.

[Mike H]

Must be true, it s on the net.

There are still a few oases of sanity in a sea of dross, but I've noticed the increasing weight of the latter is reinforcing the impression that the former is dwindling. Though it probably isn't, just seems like it

[Mike H]

Talking of diodes, if one wanted to use diodes instead of a resistor at the cathode, is it a case of adding up the forward volts till one gets to the desired voltage ? And then no bypass cap is needed ?

This is like using LED's isn't it?

Not tried it but I'd worry that the diode(s) impedance is non-linear vs changing current, and probably also frequency. Although I've seen it done in transistor circuits, but then the base-emitter of the transistor is also non-linear and anyway global NFB would be applied to compensate.

[pre65]

Talking of diodes, if one wanted to use diodes instead of a resistor at the cathode, is it a case of adding up the forward volts till one gets to the desired voltage ? And then no bypass cap is needed ?

This is like using LED's isn't it?

Not tried it but I'd worry that the diode(s) impedance is non-linear vs changing current, and probably also frequency. Although I've seen it done in transistor circuits, but then the base-emitter of the transistor is also non-linear and anyway global NFB would be applied to compensate.

Some bod tried it with Shottky diodes and reckoned it was ace.

As we know, must be true.

[Mike H]

I used to have enough aggro making things work from magazine articles, now with the Internet it's 1,000 times worse

[pre65]

I used to have enough aggro making things work from magazine articles, now with the Internet it's 1,000 times worse

I have enough aggro (or I used to have) making things work when following a known working design.

[little eddy]

I was reading a forum post (not on here) about using an Ixys 10m45s CCS chip on a preamp.............. Also, I've read of cascoded 10M45s being better than a single one, can anyone point me to information on that ?

See my Snail PreAmp thread. I used a pair of cascoded 10m45s on both ECC82 gain stage and CF, in that instance both running at 5mA without any heatsink. Went straight to the cascode because the cost of an extra chip and resistor seemed a cheapish thing to do.

[Mike H]

There, knew I'd seen it done somewhere

[little eddy]

Knew I had a photo. Set resistor was 520R for 5.0mA.

[coolboz]

Refer the datasheet of the IC