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Old 9th October 2011, 05:13 PM   #1101
Bigun is offline Bigun  Canada
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TGM5 has only a single output pair, no parallel outputs. It does have an extra pair of driver transistors making the output a Triple. I guess this is more complex, but I feel it's worth the effort because this output stage does not load the VAS like a 'regular' Double output. You could leave that out and go with the Double. You can also chop out the input cascode devices. Athough this would no longer be the LazyCat front end, it would behave the same and be the simplest possible arrangement. Simpler even than the original SSA. It might be interesting to give this a try.

TGM = 'The Great Machine', a reference to the Krell.
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Old 9th October 2011, 11:34 PM   #1102
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Originally Posted by Bigun View Post
TGM5 has only a single output pair, no parallel outputs. It does have an extra pair of driver transistors making the output a Triple. I guess this is more complex, but I feel it's worth the effort because this output stage does not load the VAS like a 'regular' Double output. You could leave that out and go with the Double. You can also chop out the input cascode devices. Athough this would no longer be the LazyCat front end, it would behave the same and be the simplest possible arrangement. Simpler even than the original SSA. It might be interesting to give this a try.

TGM = 'The Great Machine', a reference to the Krell.
dah..... maybe i really have no idea how to breakdown a circuit operations....
what will cascode input does, compare to normal pairs ? The double/triple VAS, what will help ? saw a Q7 in the middle , is it the Vbe Multiplier ?

Well.... maybe its more simpler, but the sound quality is not worth of doing that ? but i agree that it is interesting...... anyone can do the simulation, or teach me how to use simulator (by using which ? previously used simulation software are complicated.....)
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Old 10th October 2011, 12:14 AM   #1103
Bigun is offline Bigun  Canada
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I think you have a pretty good idea about circuits, but sometimes the way they are drawn makes them look complex.

I've never used Cascode before so I don't know much about it - it came with the Lazy Cat design so I've decided to use them. As far as I know, they are simply another stage of amplification after the input devices, only they are in 'common base' configuration. When used like this these cascode devices lower the voltage and reduce fluctuations in the voltage at the collector of the input devices, allowing them to operate at higher current without overheating (good for increasing transconductance and linearity) and they reduce the affect of parasitic capacitance (good for lower phase shift and h.f. roll off). You kind of get them for 'free' in this design because the bias circuit for them is used to bias the emitters of the input devices so deleting them only saves you two transistors - which is less than $2 where I live.

The Triple helps in several ways. The TGM5 is all-BJT whereas the original SSA in this thread has a FET output. FETs isolate the amplifier from the load impedance, they have a high input impedance. The VAS has to drive the output stage, so an output stage with high input impedance like a FET is good. The disadvantage of FETs is that their inputs are essentially a capacitor, which has to be charged and discharged so at high frequencies they need current. Anyhow with TGM5 the output is a BJT and it has a relatively low input impedance compared with a FET. By having a Triple with 3 stages there are more devices to buffer this impedance. The VAS now has an easier job and distortion will be lower. In a Class AB amplifier the output devices are rarely both active at the same time, but alternatively switching from one output device to the other, they present a non-linear load to the VAS so it helps a lot to isolate it with a Triple. I've used a particular kind, I've used a Sziklai pair/CFP for the drivers. Compared with two emitter follower stages this offers less voltage drop (so you can swing closer to the supply rails), is vastly more linear at high signals. Triples aren't all plain sailing, they can be susceptible to local oscillations which is why I have a pair of capacitors in there.

Is the sound quality better ? - I've no idea ! - haven't built it yet and I don't have a lazy cat version to compare with. The Roender amplifier uses the same output stage I am using and those that have heard it say it sounds superb - I regard it as one of the benchmark designs on this Forum. I've used this output stage before, on my TGM3 amplifier, the best sounding solid state amplifier I've made so far, it also has current feedback so TGM5 is more a less an extension of TGM3 to a symmetric input - I think it's going to sound just fine
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Last edited by Bigun; 10th October 2011 at 12:18 AM.
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Old 10th October 2011, 12:46 AM   #1104
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Originally Posted by Bigun View Post
they reduce the affect of parasitic capacitance (good for lower phase shift and h.f. roll off). You kind of get them for 'free' in this design because the bias circuit for them is used to bias the emitters of the input devices so deleting them only saves you two transistors - which is less than $2 where I live.
Yes, they isolate the parasitic caps like would do a ground between two wires. About removing them, i think it would be a bad idea, as bandwidth is an issue, and parasitic caps is an open door for instability, and less bandwidth induces IM distortion. I know no other way to design a good fast Amp driving power Fets without cascodes. And they sound transparent. That i love with "Crazy Cat" ;-) is his choices respect all i've experienced on my side in matter of good sound and good design practices: Cascodes, Current feedback, over sized currents sources, symmetrical design, power FETs and keeping-it simple with good parts.
SSA !
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Last edited by Esperado; 10th October 2011 at 12:48 AM.
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Old 10th October 2011, 08:12 AM   #1105
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Originally Posted by Nico Ras View Post
I have completed the L-MOSFET with drivers. It sounds really good, clean, open and dynamic. It is stable and can operate into dubious loads. Again my compliment Lazy Cat it is a job well done.

Regards

Nico
Hi Nico, Can i use irfp240/9240 output in your mosfet design? (LazyCat/Nico Ras) I have a pair of irfp240/9240. What modification should be made? Thanks in advance.

Note: I have a pcb design by alex mm with your mosfet schematic (LAZY CAT-NICO RAS AMPL/Lazy Cat Refined R01)


Regards,
Boyet
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Old 10th October 2011, 09:08 AM   #1106
MiiB is offline MiiB  Denmark
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No you can't use vertical fets with out changing the circuit...They will heat up and thermally ruaway...
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Old 10th October 2011, 10:31 AM   #1107
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so.... its a good arrangement in conclusion. ohh yeah, we need to thermal coupling which pair ? (there are 4 units)
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Old 10th October 2011, 10:47 AM   #1108
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Originally Posted by Esperado View Post
Yes, they isolate the parasitic caps like would do a ground between two wires. About removing them, i think it would be a bad idea, as bandwidth is an issue, and parasitic caps is an open door for instability, and less bandwidth induces IM distortion. I know no other way to design a good fast Amp driving power Fets without cascodes. And they sound transparent. That i love with "Crazy Cat" ;-) is his choices respect all i've experienced on my side in matter of good sound and good design practices: Cascodes, Current feedback, over sized currents sources, symmetrical design, power FETs and keeping-it simple with good parts.
SSA !
Less bandwith does not induce IM distortion, where did you get this belief that it does or maybe you´d care to prove this ???

Read up on the subject by well known professionals youll find on this forum, Bob Cordell, D Self, Scott Wurcer and many others.
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Old 10th October 2011, 01:22 PM   #1109
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Originally Posted by homemodder View Post
Less bandwith does not induce IM distortion, where did you get this belief that it does or maybe you´d care to prove this ???... by well known professionals...
Sorry, but i do not want to argue about such an evidence, known by every knowledgeable people in audio, and, for sure, by those people you are referring to like god.
When your amp is unable to follow your signal transients, if it uses CR, that's what happens. So, you will have to reduce the bandwidth of the signal applied to it before it enters in active devices if you want to get rid of IM. And that is all the purpose of Current feedback (or error correction) designs: higher slew rates.
I'm not well known by you, but, as a "professional" during 40 years, i don't care with "well known" or not, audio electronic is not a matter of fashion or VIPs. Unless you are a consumer of special sounding loudspeaker's cables ;-)
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Last edited by Esperado; 10th October 2011 at 01:24 PM.
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Old 10th October 2011, 01:29 PM   #1110
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Esperado View Post
Sorry, but i do not want to argue about such an evidence, known by every knowledgeable people in audio, and, for sure, by those people you are referring to like god.
When your amp is unable to follow your signal transients, if it uses CR, that's what happens. So, you will have to reduce the bandwidth of the signal applied to it before it enters in active devices if you want to get rid of IM. And that is all the purpose of Current feedback (or error correction) designs: higher slew rates.
I'm not well known by you, but, as a "professional" during 40 years, i don't care with "well known" or not, audio electronic is not a matter of fashion or VIPs. Unless you are a consumer of special sounding loudspeaker's cables ;-)
You should read Bob Cordell book.
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