CMOS "Tube Sound.....Amp?"

[Bill Mountain]

So....um....would this make sound?



It's a basic sketch of a battery powered hex inverter amp idea I had.

[Bill Mountain]

Double post.

Please Ignore.

[amptramp]

The input of the CMOS device has to be referenced to the output, so the volume control to ground would not work.  A proper volume control would go from output to input and the feedback would be the pot slider.  The frequency controls (EQ) would also have to work that way.  The idea here is that a CMOS device can work as an amplifier over a limited input range which is near Vcc/2 but this has to be maintained via DC feedback.  This is a little like having an op amp with no non-inverting input.  The stage driven directly by the pot to ground would not work - it takes the input of the CMOS device out of the linear region.

[Bill Mountain]

The input of the CMOS device has to be referenced to the output, so the volume control to ground would not work.  A proper volume control would go from output to input and the feedback would be the pot slider.  The frequency controls (EQ) would also have to work that way.  The idea here is that a CMOS device can work as an amplifier over a limited input range which is near Vcc/2 but this has to be maintained via DC feedback.  This is a little like having an op amp with no non-inverting input.  The stage driven directly by the pot to ground would not work - it takes the input of the CMOS device out of the linear region.

Well forget the "volume-control" part.  I was more talking about the "driving-an-output-transformer" part

[teemuk]

In don't see why not. In theory.

But you can't really drive a generic loudspeaker with that. The impedance is way too low and even if you manage to overcome that you are limited to very low current sourcing capability of the CMOS stages.

[Bill Mountain]

In don't see why not. In theory.

But you can't really drive a generic loudspeaker with that. The impedance is way too low and even if you manage to overcome that you are limited to very low current sourcing capability of the CMOS stages.

Thanks.  I was thinking about using it to drive small PC style speakers.  I'm only hoping for 1 watt or so.

I was inspired by all of the mini 1 watt tube amps but I wanted something battery powered.

[jaapie]

You could use a 4069 OD as a preamp into a 386 or other chipamp. I've been meaning to fill up one of the old radio shells i have lying around with a little 4069 driven SS amp, but my short attention span has kept me from getting around to it so far.

[Bill Mountain]

You could use a 4069 OD as a preamp into a 386 or other chipamp. I've been meaning to fill up one of the old radio shells i have lying around with a little 4069 driven SS amp, but my short attention span has kept me from getting around to it so far.

I could but the 386 has a fizzy decay I was hoping to avoid with the inverters.  I may add some gain to the third stage before the phase inverter to make sure there is plenty of "amp" distortion.

[defaced]

In don't see why not. In theory.

But you can't really drive a generic loudspeaker with that. The impedance is way too low and even if you manage to overcome that you are limited to very low current sourcing capability of the CMOS stages.

Thanks.  I was thinking about using it to drive small PC style speakers.  I'm only hoping for 1 watt or so.

I was inspired by all of the mini 1 watt tube amps but I wanted something battery powered.

1 watt?  Not gonna happen with a just CMOS inverter chip.  Looking at the data sheet for the Texas Instrument CD4069 it states you're limited to 500mw per package and 100mw per inverter, so at best, you'll get 200mw with two stages driving the transformer.  Since output power = input power - losses and the addition of a transformer, while necessary to match impedance, is going to cost you power because of losses, so you'll end up somewhere less than 200mw.  You would be better off using these to drive larger transistors which then drive the OT.  But, in the end, what I think you'll end up with is something that looks an awful lot like a CD4069 based pedal in front of a tiny SS OT coupled power amp.  Not that there's anything wrong with that, but that perspective might be more fruitful than going down the path you're looking at. 

[Bill Mountain]

In don't see why not. In theory.

But you can't really drive a generic loudspeaker with that. The impedance is way too low and even if you manage to overcome that you are limited to very low current sourcing capability of the CMOS stages.

Thanks.  I was thinking about using it to drive small PC style speakers.  I'm only hoping for 1 watt or so.

I was inspired by all of the mini 1 watt tube amps but I wanted something battery powered.

1 watt?  Not gonna happen with a just CMOS inverter chip.  Looking at the data sheet for the Texas Instrument CD4069 it states you're limited to 500mw per package and 100mw per inverter, so at best, you'll get 200mw with two stages driving the transformer.  Since output power = input power - losses and the addition of a transformer, while necessary to match impedance, is going to cost you power because of losses, so you'll end up somewhere less than 200mw.  You would be better off using these to drive larger transistors which then drive the OT.  But, in the end, what I think you'll end up with is something that looks an awful lot like a CD4069 based pedal in front of a tiny SS OT coupled power amp.  Not that there's anything wrong with that, but that perspective might be more fruitful than going down the path you're looking at. 

I have 2 inverters left so I could parallel the output stages for more power.

At the very least it might make an interesting overdrive pedal.

I'm going to use of these for experimentation:

http://www.hammondmfg.com/125.htm

[R.G.]

You know, you could fake a tube amp even more. Since you have both true and inverted signals, you could put two N-channel MOSFETs with sources to ground and gates biased for DC after this. The drains connect to the primary sides of an output transformer, the CT of which connects to +v. You feed the gates with the two opposite phases of the signal you already have, and DC bias the two MOSFETs individually.

It's a better mimic of the common tube output stage, introduces crossover distortion like tubes, etc. I've thought about this for a long time, never had time to tinker with it.

N-MOSFETs can have drain characteristics much like pentodes or power beam tubes except for the scaling factors.

[amptramp]

You know, you could fake a tube amp even more. Since you have both true and inverted signals, you could put two N-channel MOSFETs with sources to ground and gates biased for DC after this. The drains connect to the primary sides of an output transformer, the CT of which connects to +v. You feed the gates with the two opposite phases of the signal you already have, and DC bias the two MOSFETs individually.

It's a better mimic of the common tube output stage, introduces crossover distortion like tubes, etc. I've thought about this for a long time, never had time to tinker with it.

N-MOSFETs can have drain characteristics much like pentodes or power beam tubes except for the scaling factors.

ou also have to take into account the non-linear feedback capacitances in a MOSFET.  Tube capacitances are small and do not vary all that much with operating point.  MOSFET's are a different story.  The Miller capacitance requires a bit of power to drive it.  I doubt CMOS will drive anything bigger than a 2N7000 without running into trouble.  Could be a neat form of distortion, though.

[Nasse]

http://www.vt52.com/diy/diypage/aren/fet/aren.html always wanted to try, nver got it done

[PRR]

> CD4069 it states you're limited to 500mw per package and 100mw per inverter

Don't confuse maximum dissipation with Output.

A 100 Watt lamp is rated for 100 Watts dissipation, but you only get 5 Watts of actual light energy from it.

I have not done '4069 math in decades, because it's real depressing.

Using "linear" operation, assuming 10V supply, you can put INTO a load about 3V 8mA. An optimum load is 300-400 ohms. Peak power is 24mW, so 12mW RMS. Two gets you 24mW, four gets 96mW, *if* you can transform to loudspeaker impedance.

A very lame speaker amp.

> 386 has a fizzy decay

If that's the problem, why re-invent 100 years of power amp designs?

1) Use the 10r+0.1uFd network, it's there for a reason

2) Use JRC-made LM386, not look-alikes sold for modems and answering machines

3) Use LM380, you are less likely to get a cheap copycat

4) Use car-radio chips, kin to TDA2003, they MUST sound OK to sell