Power amplifier with low thermal distortion

dmatiukas · 19th January 2013, 03:09 PM

Hello,

I create and build this power amplifier.
Ideas for building were to check mr. Lavardin theory about thermal distortions.
I used low feedback, open loop gain about 50db. Traditional distortion is low till half power. Currents for first stage 1mA, for VAS 2,5 mA, for EF 4,6 / 12 / 200 mA.

Sound is clear, voices and instruments have clear separation.
For listening was used Klipsh RF-3 speakers, sensitivity 98db.

I am looking for ideas how to improve this amplifier.

jan.didden · 19th January 2013, 04:53 PM

Can you give some info on how you took care of the thermal distortion?
Did you do any measurements or something to check it?

jan

dmatiukas · 19th January 2013, 05:09 PM

I use method published there: Memory Distortion Philosophies

Dalius

dmatiukas · 19th January 2013, 05:15 PM

Main idea, ensure constant power for gain stages. I use cascode for gain stage and for current sources.

Dalius

Bigun · 06:32 PM

I have looked at these claims before. In the experiments I saw posted on the web, simple topologies are compared with more complex topologies. The use of CFP and of Cascodes. The results seem to be positive - less distortion and clearer sound. The theory makes sense, but it is claimed that memory distortion is an serious issue and that it's removal makes a big difference to the sound.

BUT the issue I have is that the experiments posted on the web do not prove that 'memory distortion' is a real practical issue that affects sound quality.

The reason is that these more complex topologies are inherently superior in technical performance even if you ignore ALL aspects of memory distortion from the analysis. The CFP has very low distortion compared with a single device. A Cascode reduces the Early Effect and greatly reduces Miller capacitance. You can't separate out the huge performance improvements from these more complex topologies due to better linearity and higher OLG from their impact on so-called memory distortion.

These are all very good design approaches and make for good amplifiers. But I don't see any evidence that 'memory distortion' is an issue for sound quality, or that it has been vanquished as an issue with these improvements. But it sure does make for some fun marketing.

I would like to add that the website you linked is very nicely presented and some good quality work is presented there. I admire the effort taken to do the work and share it for us to see.

jan.didden · 19th January 2013, 06:58 PM

Quote:

Originally Posted by dmatiukas

Main idea, ensure constant power for gain stages. I use cascode for gain stage and for current sources.

Dalius

But the greatest thermal cycling is in the power output devices. So that is where I would expect thermal distortion, not in the pre stages.

jan

dmatiukas · 19th January 2013, 07:58 PM

I before modified NAD receiver differential input stage and VAS. Stages become cascode, with low stable ~0,7V Vce for gain transistors. Sound quality was improved. Stable and low Vce ensure low power dissipation changes for gain transistor. Main think is low power dissipation changes.

dmatiukas · 19th January 2013, 08:04 PM

Pre stages have small power changes, bet very great impact (Vout >1V), because gain. Output stage has voltage gain <1, and heat impact make output voltage change ~15mV.

19th January 2013, 04:53 PM	#2
jan.didden diyAudio Member Join Date: May 2002 Location: Great City of Turnhout, Belgium Blog Entries: 6	Can you give some info on how you took care of the thermal distortion? Did you do any measurements or something to check it? jan __________________ /Yes! Its out: Linear Audio Vol 5! I'm not an "accademic", just a plodder who loves a challenge - Ian Hegglun

19th January 2013, 06:28 PM	#5
Bigun diyAudio Member Join Date: Jan 2009 Blog Entries: 2	I have looked at these claims before. In the experiments I saw posted on the web, simple topologies are compared with more complex topologies. The use of CFP and of Cascodes. The results seem to be positive - less distortion and clearer sound. The theory makes sense, but it is claimed that memory distortion is an serious issue and that it's removal makes a big difference to the sound. BUT the issue I have is that the experiments posted on the web do not prove that 'memory distortion' is a real practical issue that affects sound quality. The reason is that these more complex topologies are inherently superior in technical performance even if you ignore ALL aspects of memory distortion from the analysis. The CFP has very low distortion compared with a single device. A Cascode reduces the Early Effect and greatly reduces Miller capacitance. You can't separate out the huge performance improvements from these more complex topologies due to better linearity and higher OLG from their impact on so-called memory distortion. These are all very good design approaches and make for good amplifiers. But I don't see any evidence that 'memory distortion' is an issue for sound quality, or that it has been vanquished as an issue with these improvements. But it sure does make for some fun marketing. I would like to add that the website you linked is very nicely presented and some good quality work is presented there. I admire the effort taken to do the work and share it for us to see. __________________ "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig. Last edited by Bigun; 19th January 2013 at 06:32 PM.

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19th January 2013, 05:09 PM	#3
dmatiukas diyAudio Member Join Date: Sep 2009 Location: Lithuania	I use method published there: Memory Distortion Philosophies Dalius

19th January 2013, 05:15 PM	#4
dmatiukas diyAudio Member Join Date: Sep 2009 Location: Lithuania	Main idea, ensure constant power for gain stages. I use cascode for gain stage and for current sources. Dalius

19th January 2013, 07:58 PM	#7
dmatiukas diyAudio Member Join Date: Sep 2009 Location: Lithuania	I before modified NAD receiver differential input stage and VAS. Stages become cascode, with low stable ~0,7V Vce for gain transistors. Sound quality was improved. Stable and low Vce ensure low power dissipation changes for gain transistor. Main think is low power dissipation changes.

19th January 2013, 08:04 PM	#8
dmatiukas diyAudio Member Join Date: Sep 2009 Location: Lithuania	Pre stages have small power changes, bet very great impact (Vout >1V), because gain. Output stage has voltage gain <1, and heat impact make output voltage change ~15mV.