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Old 26th October 2009, 06:14 PM   #21
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Quote:
Originally Posted by jcx View Post
by the thread title you'd be better off pursuing cascodes:

REDUCTION OF TRANSISTOR SLOPE DISTORTION IN LARGE SIGNAL AMPLIFIERS, M.O.J. Hawksford, JAES, vol.36, no.4, pp.213-222, April 1988

http://www.essex.ac.uk/csee/research...%20cascode.pdf
Thank you very much for this advice. To find the right keywords and headlines to a certainly topic is often difficult. For the same topic sometimes I must use a large scale of keywords to find all informations.
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Old 26th October 2009, 06:39 PM   #22
Gordy is offline Gordy  United Kingdom
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Originally Posted by Wavebourn View Post
Actually, for voltage amplification may be used transformers. Tubes and transistors amplify power. That's why tubes are sometimes preferable: even though transistors have higher transconductance, in order to get the same power amplification factor from stages using tubes VS transistors we need feedback for transistors, tubes perform faster and more linear without any feedback. Also, tube curves are slowly bent, that means low order of transfer function that creates harmonics that are much less audible than distortions created by a transistor stage. Now, if to add a deep feedback to 2-stage tube amp that is already wideband and linear, we are getting equal very strict linearity in the whole frequency band and beyond. And such an amp has high input resistance that is very linear, compared to non-linear input resistance of a transistor stage. Far the more, an asymmetrical design guarantees that the lower is loudness, the less distorted is the sound, that is very significant for audio. Our subconscious perception is much more sensitive than can be found consciously, so even when such distortions can't be caught by people during listening tests, but when listened to the music very fine accuracy of dynamics is vital.
So, using tubes we achieve very low distortions of fine details; adding deep feedback we achieve very low distortions on peak levels that means low intermodulation distortions. Clipping of such an amp would not sound pleasant, it is total b******t that you can read and hear everywhere. However, it is easier to have bigger headroom powering from hundreds of volts than from tens of volts, and it is true, but it does not mean pleasant clipping.

Short reply to a long quotation: Mr Wavebourn I think you say some interesting things.
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Old 27th October 2009, 07:30 AM   #23
AKSA is offline AKSA  Australia
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Agree. I really like Anatoliy's approach; it is balanced, he sees tube and transistors without prejudice for either.

OTOH, feedback does have it's detractors, chiefly the creation of many artefacts of very low amplitude due to tiny intermodulation products.

If you operate transistors from high voltages (100V plus) you have very good headroom too, and generally lower distortion than from rail to rail circuits.

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Old 27th October 2009, 01:14 PM   #24
Bigun is offline Bigun  Canada
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Originally Posted by AKSA View Post
feedback does have it's detractors, chiefly the creation of many artefacts of very low amplitude due to tiny intermodulation products.
Do you need feedback to get IM products ?
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Old 27th October 2009, 01:27 PM   #25
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Originally Posted by Bigun View Post
Do you need feedback to get IM products ?
No, not at all. IM is generated by a non-linear transfer characteristic. Feedback in itself cannot generate IM, unless it is already there. Feedback usually dramatically lowers any IM that occurs open-loop, but it can also generate additional IM products at very low level. Which is better/ less bad is depending on a LOT of factors as well as personal opinion

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Old 27th October 2009, 06:25 PM   #26
Fanuc is offline Fanuc  United Kingdom
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Default Triodes already have local feedback built in. That's why there linear!

Quote:
Originally Posted by Wavebourn View Post
Actually, for voltage amplification may be used transformers. Tubes and transistors amplify power. That's why tubes are sometimes preferable: even though transistors have higher transconductance, in order to get the same power amplification factor from stages using tubes VS transistors we need feedback for transistors, tubes perform faster and more linear without any feedback. Also, tube curves are slowly bent, that means low order of transfer function that creates harmonics that are much less audible than distortions created by a transistor stage. Now, if to add a deep feedback to 2-stage tube amp that is already wideband and linear, we are getting equal very strict linearity in the whole frequency band and beyond. And such an amp has high input resistance that is very linear, compared to non-linear input resistance of a transistor stage. Far the more, an asymmetrical design guarantees that the lower is loudness, the less distorted is the sound, that is very significant for audio. Our subconscious perception is much more sensitive than can be found consciously, so even when such distortions can't be caught by people during listening tests, but when listened to the music very fine accuracy of dynamics is vital. So, using tubes we achieve very low distortions of fine details; adding deep feedback we achieve very low distortions on peak levels that means low intermodulation distortions. Clipping of such an amp would not sound pleasant, it is total b******t that you can read and hear everywhere. However, it is easier to have bigger headroom powering from hundreds of volts than from tens of volts, and it is true, but it does not mean pleasant clipping.
Makes no sense.
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Old 27th October 2009, 06:36 PM   #27
Fanuc is offline Fanuc  United Kingdom
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I join the original poster's desire to see Lender's original circuit (with the current mirror) not variants of it - Borbely et al. The current mirror will make a big difference.

It would be interesting to see what his views/reasoning are on this configuration between the Input stage and VAS. Maybe there is no point having a linear VAS without the Input stage being dealt with first ?

People should stop referring to Borbely's design as Lender's circuit without his original design and knowing the intricate details.

Last edited by Fanuc; 27th October 2009 at 06:43 PM.
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Old 27th October 2009, 07:06 PM   #28
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Quote:
Originally Posted by Fanuc View Post
I join the original poster's desire to see Lender's original circuit (with the current mirror) not variants of it - Borbely et al. The current mirror will make a big difference.

It would be interesting to see what his views/reasoning are on this configuration between the Input stage and VAS. Maybe there is no point having a linear VAS without the Input stage being dealt with first ?

People should stop referring to Borbely's design as Lender's circuit without his original design and knowing the intricate details.
This was actually the main reason for me to start this thread; please read the lead-in of this thread at page 1 - I am very happy, if I get advices to find all there mentioned original articles.
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Old 28th October 2009, 04:03 AM   #29
Bonsai is offline Bonsai  Taiwan
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"by the thread title you'd be better off pursuing cascodes:

REDUCTION OF TRANSISTOR SLOPE DISTORTION IN LARGE SIGNAL AMPLIFIERS, M.O.J. Hawksford, JAES, vol.36, no.4, pp.213-222, April 1988

http://www.essex.ac.uk/csee/research...%20cascode.pdf "


This is the VAS technique I was refering to in my earlier post on this thread.

Using the simple standard current amplifier topology front end, but modding the VAS stage to use Hawksfords technique, I consistently get THD (simmed) below 500ppb. Between the VAS and the load, I'm using a diamond buffer. Hawksfords VAS is really amazing in my view. This weekend, I plan to mod my power current power amp VAS to Hawksford (I was supposed to do it a few weeks ago, but have not had time).
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Old 28th October 2009, 07:34 AM   #30
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The link doesn't work.

http://www.essex.ac.uk/csee/research...%20cascode.pdf
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Last edited by djk; 28th October 2009 at 07:40 AM.
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