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Old 16th August 2011, 04:56 PM   #241
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Salas,

I ran several bias simulations and it would appear as if the harmonic distribution remains unchanged between 120mA and 1,4 Amp with second harmonic predominant and smooth decay of all higher orders.

Dropping the bias below 110 mA third, fifth and ninth harmonic becomes dominant and THD increases by an order of magnitude.

I will make measurements on the week-end as I do THD measurements manually and it is a tedious process.

Regards

Nico
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Old 16th August 2011, 05:10 PM   #242
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Salas,

I tried to optimize bias for best harmonic distribution but as I said it remains almost constant. I conclude that there is no benefit to run a bias current higher that 140 mA. I am referring to my circuit only, Lazy Cat may have different results using the isolated gate set-up.

Regards

Nico
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Old 16th August 2011, 05:44 PM   #243
Salas is offline Salas  Greece
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Nico thanks for the info. I got some laterals on the way in and I hope that I will be able to experiment on the amp in due time too.
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Old 16th August 2011, 06:30 PM   #244
Bigun is offline Bigun  Canada
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Is anybody building the all-BJT version of this amp, I am very tempted to use this for my next project ?
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Old 16th August 2011, 07:00 PM   #245
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Hi Bigun, welcome here. Although Lazy Cat has mentioned an all BJT design I do not think anyone else has built anything yet. Lazy Cat did suggest that all three types could be available in the near future and I think much is going to depend on Alex's willingness and time to assist in laying three different PCBs.

Nico
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Old 16th August 2011, 07:18 PM   #246
Bigun is offline Bigun  Canada
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Hi Nico, I don't want to ask for time from Alex when priority is the 'popular' version of this amp - besides I may need to make my own pcb yet, in order to suit the physical constraints. If I go ahead with this project I'll be fitting 3 channels into an old Onkyo stereo chasis. But I was hoping there may be some practical experience of building the all-BJT version I could learn from and so help me decide which amp to make.
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Old 17th August 2011, 12:11 AM   #247
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Quote:
Originally Posted by Nico Ras View Post
In simulation it is actually 29nS. I doubt if one can do much better than 33nS, Lazy Cat that is excellent!!

Nico
Yes, indeed excellent, Nico.

I was surprised too, so I double checked and 33ns it is, as you said almost the same as 29ns from simulation, very close to the theoretical limit.

Closed loop gain and phase shift are perfect at 100kHz and far beyond, which is clearly audible as a "no amp present" effect, music only.

So what I have here is super fast, linear and stable amp, but still easy to built even to a DIY newbie.
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Old 17th August 2011, 12:18 AM   #248
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Quote:
Originally Posted by Nico Ras View Post
Salas,

I tried to optimize bias for best harmonic distribution but as I said it remains almost constant. I conclude that there is no benefit to run a bias current higher that 140 mA. I am referring to my circuit only, Lazy Cat may have different results using the isolated gate set-up.

Regards

Nico
I run an amp with bias current set at 150 mA all the time, lower is non-sense, higher will check.
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Old 17th August 2011, 12:32 AM   #249
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Quote:
Originally Posted by Bigun View Post
Is anybody building the all-BJT version of this amp, I am very tempted to use this for my next project ?
Bigun please reward us with your active presence to this thread, an all BJT version of SSA could be yours participation to DIY-ers, since I will prepare mosfet driver/BJT output version
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Old 17th August 2011, 01:15 AM   #250
Bigun is offline Bigun  Canada
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I'm very tempted, not sure I can keep up with you guys though as I have other projects on the go but I will investigate this option more seriously now...

I'm curious why this amp produces predominantly 2nd harmonic when it is symmetrical (from Nico's simulations) ? is this a consequence of generally poor complementary matching between n-type and p-type FETs. One reason I built only asymmetrical to date is because I like the harmonic signature.
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Last edited by Bigun; 17th August 2011 at 01:17 AM.
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