Tube with Power IC Output Stage - JLTi

[Pedja]

OK guys, both me and Nuuk overlooked the LPF’s resistor but we’ve been through that long time ago, the accent was now on the way to calculate the effective value of the resistances used in the feedback, and to clarify possible puzzle about this. I hope the link I have provided may give the answer the people may need.

[carlosfm]

Originally posted by Franz G
BTW: maybe the tube is the better buffer than an opamp ?

It may depend on the valve, the op-amp, the implementation...
Taste...

[Joe Rasmussen]

This may help calculating T-Network values versus gain:

Download CircuitMaker Student Version 6:

http://www.altium.com/circuitmaker/d...ds/student.htm

Install it.

Now download this tiny zip file:

http://members.ozemail.com.au/~joeras/diy/T-Network.zip

Unpack and in CircuitMaker open this file.

You will now see a basic diagram of opamp using T-Network inverted feedback.

Double click on any resistor allows the values to be changed. Keep in mind 100k = 100k but 100 = 100 Ohm.

Now choose 'Run' from the Simulation drop-down menu or use F10.

The AC Voltmeter will then show the AC voltage out. Since it is set up with 1V RMS (+/- 1.414V) - the RMS value equals the gain, hence 46.23V means gain = 46.23

See how you go, let me know of any success.

Joe R.

[Nuuk]

G'day Joe,

I downloaded the zip file and unpacked it but when I try and open a file in CircuitMaker I only have the option of opening ckt or binary files. The file in the zip is an XLS!

[Joe Rasmussen]

Originally posted by Nuuk
G'day Joe,

I downloaded the zip file and unpacked it but when I try and open a file in CircuitMaker I only have the option of opening ckt or binary files. The file in the zip is an XLS!

I think you are trying to load Franz's XLS file?

The file in T-Network.zip is called T-Network.ckt and was created by CM Student V6.

What is the XLS full name? If it ends up T-Network.xls - then I am most definitely confused.

If so, edit to read T-Network.ckt . Also it should 4399 bytes.

Joe R.

[Pedja]

Did anyone notice/observe/think how T-network in the feedback influences the relation between the amplitude and phase? I ran some sims with the opamp model that should match relatively well to those commonly used in the GCs (its open loop measurement shows about 3MHz bandwidth and somewhat better phase margin than LM3875’s but with generally similar shape), anyway I think it is good enough to show differences between particular configurations.

Here is its response when used in the inverted configuration and with commonly used IGC feedback of 220k/10k.






Keeping the same gain and going down with the feedback values to match the future T-network’s 10k of summed resistance between the output and the inverted input, i.e. with feedback 10k/454R, the response shows better phase, probably because the pole formed by the input capacitance and feedback resistance is shifted higher.






Now, the same gain and T-network in the feedback (5k/118.8R/5k). Obviously, response disappears earlier, leaving the phase at new unity gain point still better.





Pedja

[carlosfm]

Will you guys still call this a Gainclone?

[Joe Rasmussen]

Originally posted by Pedja

...the response shows better phase, probably because the pole formed by the input capacitance and feedback resistance is shifted higher.

Pedja

Good work Pedja.

So the phase is straighter because, with the lower Z we're more able to drive the input capacitance. That sounds rather rational.

So I got the idea, this is an opamp capable of driving Lo Z speaker loads, hence in a T network can be made really low as it will have no difficulty driving that. So how about making the T 2 x 1K (make these 1 Watt) and One Ohm. With my 4k7 + 18K input Z (22K7 total), this gives a gain of 45.

This not gets maximum drive but should also give low DC offset.

Joe R.

[Joe Rasmussen]

Originally posted by carlosfm
Will you guys still call this a Gainclone?

No, but try to give a different name.... you will just end up with a bloody nose!

[Pedja]

Originally posted by carlosfm
Will you guys still call this a Gainclone?

For quite some time, yes. As long as people call the things with certain names, it is smart to do the same, in the things of language you can’t go against the stream. (It is not that I am proposing this as a universal rule, it is about the language.) Of course, during the time the term gainclone may fade.