Another thread regarding CCS vs BOOTSTRAP

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Similar threads may have appeared here touching the subject of CCS versus Bootstrap configurations and I have simulated and build two identical amplifiers one using a CCS and the other a Bootstrap.

Interestingly enough the amplifiers overall performance is very similar, identical output, band width and overall THD.

However they sound remarkably different the amplifier using a bootstrap has a warmer and friendlier sound while the one with CCS has a more clinical and harsh sound.

Following is the amplifier with CCS, its band width and harmonic distortion at 1kHz, 10 kHz and 100 kHz.

Then follows the amplifier using a bootstrap with its associated illustrations.

The front ends on both amps are identical, current through the VAS, output swing and bias through the output devices are identical.

One can see the difference in sound by observing the harmonics, the one using the CCS reveals higher odd order products.

Yesterday after some of my buddies and I watched :drink: England getting thrashed by the All Blacks,:wave2: we auditioned both amps and seven out of nine preferred the sound of the bootstrap.

Interesting....... :scratch:
 
Amp with CCS

Attached is the simple amp using CCS
 

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Disabled Account
Joined 2006
Hi Nico

Good work, distortion figures like these could also be seen at the patchwork thread. I have one question, did the bootstrap circuit sound as detailed as the ccs one, by detail I mean for example fingers sliding accross guitar strings, that type of detail, not necessarily based on high frequencies? Ive never used bootstrap circuit before, maybe I should try one sometime.

England smashed by All blacks again, I ll drink to that.
:drink: :sing: . I still have a case of Castle I brought with me from SA, for the special occasions. I ll be in London next week again so Ill have plenty to :rofl: :rofl: at the pubs. :devilr: :devilr:

Nico, are you maybe familiar with a SA audio designer in the early 90s based in I think it was Meyerton or Vereeniging??. They had some tube, mosfet and speaker designs.
 
Disabled Account
Joined 2007
Good research Nico,
I was given a hard time in my Patchwork project for choosing the bootstrap. Reasons being better PSRR for the CCS - proved not to be an issue at all for the amp, and reduced linearity at low frequency - as demonstrated to be overblown. I did a little experiment here that compares the performance of the actual bootstrap to the simulated one. While this is not directly related to the CCS vs bootstrap argument, the results do show the shortcomings of the bootstrap to be exaggerated.
I have not had the opportunity to compare identical amps using CCS and bootstrap, as all of the (working :) ) amps I've built have a bootstrapped VAS. I'm not sure that I would hear a difference.
 
Hi Homemodder,

Detail in that respect is the same, but when I say more clinical means a little sharper, 'S' sound is more pronounced. This is a direct attribute to the higher level of the 5th and 7th harmonic.

Higher up in the spectrum this does not matter that much since we cannot hear 50 or 70 kHz, but it is particularly noticed where our ears are more sensitive.

Anyway, I will not conclude that either is better, but the difference is very noticeable on all kinds of music. I think it is a matter of preference as one will notice that the typical specification as one may put it is very much alike.

John,

I will post THD at 100 Hz for both in a moment. Sorry I should have run these as well but I normally optimize where the ear is most sensitive.

Kindest regards

Nico

P.S. if some one feels like building either of these amps I will post the component values, but I did not think at the time that it was important, it is not intended as a project.
 
Here are the numbers at 100 Hz, again the typical performance is almost identical bar the position and level of odd and even harmonics.

http://digisec.co.za/ras/music/CCS THD 100H.pdf

http://digisec.co.za/ras/music/Bootstrap THD 100H.pdf

Again, there are no technical difference really and the sound that the bootstrap makes will be preferred by some and the CCS by others. So there is little room for arguing which outperform the other.

The fact that 7 out of 9 preferred the bootstrap cannot really be explained either. It could have been the type of music that I played.

Nico
 
Hi guys,

one final thing that could also result in the amps sounding different and that was very interesting. Although both amps has the same bandwidth, the CCS is almost twice as fast as the bootstrap but it has some ringing on the rising edge while the bootstrap is a smooth transistion.

Okay that is it, you are welcome debating these facts and maybe even conclude which is best, the bootstrap or CCS.

Kind regards

Nico
 
Andre Visser said:
Very interesting Nico.

Have you tried a Fet CCS, it would be interesting to know the results.

André


No, I did not but you are welcome to play with it. Here are the component values for those interested. The design is loosely based on the quad 303 simplified. I must admit, neither of the amps sound bad at all, in fact I was very surprised at the performance of such a simple design.

Running it with +-50V supplies it will easily give you the magical 100 watts.

http://digisec.co.za/ras/music/CCS Schematic.pdf

http://digisec.co.za/ras/music/Bootstrap Schematic.pdf
 
Nico Ras said:
Hi guys,

one final thing that could also result in the amps sounding different and that was very interesting. Although both amps has the same bandwidth, the CCS is almost twice as fast as the bootstrap but it has some ringing on the rising edge while the bootstrap is a smooth transistion.

Okay that is it, you are welcome debating these facts and maybe even conclude which is best, the bootstrap or CCS.

Kind regards

Nico

Actually what I said here is not quite correct. Have a look at the square wave response and make up your own mind.
 

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Thanks, great work Nico,

I've always used the bootstrap; in listening tests I found it had much less sibilance, and was easier to compensate the amp because of the rapid increase in electrolytic ESR beyond about 200KHz.

I can see it's slower, but that absence of overshoot is a boon.....

According to NP, you get around +/-10% variation in VAS current with a boostrap, and this will make it less linear, particularly at LF.

Swings and roundabouts, perhaps?

Hugh
 
Nico,
How much voltage is across R25 and Q4 under these signal conditions ? (no voltage is indicated on D3)
Did you try adjusting C13 on the CCS version ? (the bootstrap version looks spot on)

Many thanks for the very interesting results ...

dave
 
DRC said:
Nico,
How much voltage is across R25 and Q4 under these signal conditions ? (no voltage is indicated on D3)
Did you try adjusting C13 on the CCS version ? (the bootstrap version looks spot on)

Many thanks for the very interesting results ...

dave

Hi Dave,

sorry about that, D3 is 5V1. Please note that the base bias arrangement for Q1 should be zener stabilized and it is best making R1 variable then off-set can be adjusted for any supply voltage.

Regards
 
AKSA said:
Thanks, great work Nico,

I've always used the bootstrap; in listening tests I found it had much less sibilance, and was easier to compensate the amp because of the rapid increase in electrolytic ESR beyond about 200KHz.

I can see it's slower, but that absence of overshoot is a boon.....

According to NP, you get around +/-10% variation in VAS current with a bootstrap, and this will make it less linear, particularly at LF.

Swings and roundabouts, perhaps?

Hugh

Hi Hugh,

thanks for your comments I appreciate it.

This little exercise was prompted after the debate regarding John's Patchworks thread and to be honest I also prefer the bootstrap.

One can see that there are only slight differences in the harmonic order although the harmonic power density is almost identical, thus the THD of both amps would provide identical specification.

Only when one considers the amplitude and position of the harmonic that one may be able to explain the apparent difference in the character of the sound.

I would suggest that liking or disliking one or the other topology is a matter of preference but this decision can only be made if one could audition each under the same circumstances, so the debate probably remains open forever.

Kindest regards

Nico
 
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