Patchwork Reloaded: Circuit Optimization and Board Layout.

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#461
andy_c said:
It can't possibly sound good if it doesn't have a French name, like "Le Monstre". And where are the boutique capacitors, boutique resistors and so on? Does the chassis have boutique screws? 🙂
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Hi Andy and John, what about "Le Abominable" 😀 ... hehehe ...

Definitely, Le Metal Film Resistor and Le Cap are all components of John's "Le Abominable". sarcray blur 😀

🙂
 
#462
MJL21193 said:
I considered renaming it after myself - L'un Misérable. Doesn't 'ave a good ring to et! 🙂

With the proper French title, we could step up to high end bolts and such. One must use the caps and cheap resistors I have chosen, as it is the "voice" of the amp. To replace any of the parts that I have personally selected is to run the risk of harshness and fatigue from listening!
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High-end bits are useful for assuring repeatable results; because, the performance is usually documented and guaranteed. That can be a sort of performance enhancement.

But, it sure has led to some craziness. Unfortunately, such things are often used for decoration because the audiophile consumer is prone to mistakenly reverse cause and effect.

Howabout the "Specially Matched Spherical Walnut Audio Equipment Isolation Stands. $48. Buy Now!" These are ordinary black walnuts. Fortunately, that's a sale price. 😀

Of course the height of those feet could help the airflow a bit, but some of that stuff is just nuts. 😀
 
#464
homemodder said:
Hi Nico, how did you come to the values of R2 and R3 ?? Is it to balance the LTP?? Is the ltp unbalanced with the values MJL21193 used??
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Microcap has an optimization feature that you can run on a host of components and chose what outcome you require. for example balance in the LPT, lowest THD, etc.
 
#465
homemodder said:
Hi Nico, how did you come to the values of R2 and R3 ?? Is it to balance the LTP?? Is the ltp unbalanced with the values MJL21193 used??
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John,

I am not slating the design, please don't be offended. If you have a real amplifier that performs quite differently from the sims, why even bother with sims obviously all the other data will be equally useless such as low THD, Slew, PSR, etc.

I have looked at the 4.7 Ohm 100 uF combination, what are you filtering 100 Hz ripple? This filter will do nothing.

If the 200K makes a slight difference on the THD, even in the sim it is fractional considering that the amp performance is already at 0.003%, in the real amp it probably is non existent, why 200k, what about 150K or 220K.

I cannot imagine how you could have a 10 mV off-set in the real amp if you have a 1:3 current ratio current in the LPT which is determined by component selection not coincidence.

Anyway, I think as it stands now this is a pretty nice amp and may be considered by other DIY enthusiasts as a very nice project.

Kindest regards

Nico
 
#469
Hi MJL21193

I was wondering how that ccs mirror performed. When I saw you apply it my immediate thought was that the ltp would be unballanced. What was confusing me was that you found this to bring a distortion reduction so I tried to sim it on a blamess type design, it didnt work at all, the imbalance was so great everything was a mess. So I balanced that ccs mirror by manupulating the resistor values and got some figures to compare with a std current mirror. The standard was better in THD figures.

So I went to look again at my design where I have this ccs mirror applied to a vas compaired to a std mirror. Its a ltp vas, and here I have it applied as a balanced mirror, by manupulating the resistor value after the diode I have 0 percent imbalance. Im not using it to boost gain like in that technics paper (only read it today) and their is only a 4ohm difference between the resistor values. in this application it gives better results than a std mirror. :scratch: Why would it work better in one and not the other?? , keep in mind using it balanced. I dont use a diode in real its a transistor connected as a diode I have a few comercial designs schematics that have applied this current source too, always in the vas, in some it is bootstrapped and has the effect of raising 2nd harmonic.

Seeing the values that nico suggested I couldnt see how the amp could possible work. If you look at the technics paper they have some interesting nfb values, I guess this is for balancing somehow.

As for the the resistor in ltp current source I have found again that it works in some applications and not in others. Bootstrapping the ccs ltp on a amp like roenders fc brings distortion down, but it does not function on a blameless design, with a resistor ccs I havent tried. This is also true when applied to a vas that uses ccs. You could try this with your fc too. 😕 Im still not sure exactly whats at play here.
 
#470
danielwritesbac said:

Did the lower THD at high output feature work in practice in any way that affected the amplifier's presentation or increase the likelihood that it would perhaps be used at high output?
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Hi Dan,
I didn't try the mirror mod on a real amp so I can't say for certain what the overall effect would be - good or bad. Simulations can get some things wrong.

danielwritesbac said:

but some of that stuff is just nuts. 😀
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Holy! Did you just say something normal?? 😀
 
#472
Nico Ras said:

I am not slating the design, please don't be offended. If you have a real amplifier that performs quite differently from the sims, why even bother with sims obviously all the other data will be equally useless such as low THD, Slew, PSR, etc.
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Hi Nico,
If it weren't for the simulator, we wouldn't be having this conversation. 🙂 I wouldn't have any amp design or redesign, I wouldn't know diddly squat about any of this.
The amps that I have built completely agree with the simulations, right down to the measured voltage and current. I have been diligent about using accurate models in the sim to give the best prediction. Some things may be slightly off, but not by much.

I know there was some confusion and that you were under the impression that I was still using the revised mirror. I have thrown out that idea and will stick with the standard mirror.


Nico Ras said:

I have looked at the 4.7 Ohm 100 uF combination, what are you filtering 100 Hz ripple? This filter will do nothing.
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My simulation and real world results say otherwise. This filter works to improve PSRR at higher frequencies. Increasing the resistance to 22 ohms and capacitor to 220uF will make it effective at a lower frequency. I suggest you look at this in Microcap. It should be very apparent on a PSR plot.


Nico Ras said:

If the 200K makes a slight difference on the THD, even in the sim it is fractional considering that the amp performance is already at 0.003%, in the real amp it probably is non existent, why 200k, what about 150K or 220K.
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The bootstrap resistor value has been optimised for the last version of this amp. I can see if it needs adjustment for this version.
It has a positive effect, not a negative one. It lowers THD at high frequency. Whether this is a simulation only result is unclear. I would sorely love to have a distortion analyzer to verify these things. Maybe in the new year.


Nico Ras said:

Anyway, I think as it stands now this is a pretty nice amp and may be considered by other DIY enthusiasts as a very nice project.
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Thank you Nico. 🙂
 
#473
Nico Ras said:
have you considered a capacitance multiplier, or what about a series shunt regulator. It may give you that 100dB PSR.
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Hi Nico,
I'm not looking for PSRR that low. 🙂
Others are, but I believe the best way to accomplish this is to improve the power supply. Leave the amp itself as simple as possible.

homemodder said:
Hi MJL21193

I was wondering how that ccs mirror performed. When I saw you apply it my immediate thought was that the ltp would be unbalanced.
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Hi homemodder,
Unbalanced would seem to be the intention of the original design.
I don't know if it will bring the improvements that I saw in a real amp circuit, I don't know if it will have a negative impact on PSRR in a real amp circuit. If I had a distortion analyzer I'd take the time to add it to a working amp and see what the actual results would be. Until then, I'll forget about it.
IF it does as it shows in my sim, it is worth pursuing. The PSR can be dealt with and the DC offset can be handled with a simple pot of even a servo.
 
#474
MJL21193 said:

My simulation and real world results say otherwise. This filter works to improve PSRR at higher frequencies. Increasing the resistance to 22 ohms and capacitor to 220uF will make it effective at a lower frequency. I suggest you look at this in Microcap. It should be very apparent on a PSR plot.
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I have ran the sim with a few different values for the RC filter:

PATCHWORK_PSRR.png


The green trace is with no filter. The yellow is with 4R7 on the rails with 100uF.
The blue is 10R on the rails with 220uF and the red is 22R on the rails and 220uF.
 
#480
danielwritesbac said:


Then it can be a nice surprise. I updated the post for more specific information that just came out of the Dick Smith ESR meter when I measured the caps. Its still an estimate, though.
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You're slipping again Dan! Didn't you take your meds today? 😀

We are talking about power supply ripple rejection of the amp circuit. The resistors and caps form a filter to drive the effects of this ripple from the power supply down in audibility.
 
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