VSSA Lateral MosFet Amplifier

[Kindhornman]

BYRTT 8 PCB set
CaféNoir 6 PCB set
ColinAlex 8 PCB set
DavorXXL 6 PCB set
DuffyDawg 4 PCB set + 4 SMPS400
electromf 4 PCB set
badrisuper 2 PCB set
volavola 2 PCB set
JethroTull 2 PCB set
kp93300 2 PCB set
momomo67890 4 pcb set
ua3grn 6pcb set
mj777 2pcb set
mkusan 2pcb set
Odysseas 4pcb (2 pairs)
hcbonfim 2pcb set
Albrerta 2pcb set
dw1narso 2 pcb set (1 stereo) + extra output device pairs & isolators (for stereo if possible)
supernet 2 pcb set
milandks 4pcb set
tjencks 2pcb set
quanghao: 2pcb set
audionootje: 4pcb set (2x stereo)
tritosine 4pcb (2 pairs)
Bobo le Chat 2 pcb set
AP2 2pcb set+2pcb empity (i need this also)
Meganinja 2 set ( stereo )
coolewater 2 pcp set
mikvous 2 pcb set
still4given 2 PCB set
Rick G 2 PCB set
kindhornman 2 boards

 

[coolewater]

BYRTT 8 PCB set
CaféNoir 6 PCB set
ColinAlex 8 PCB set
DavorXXL 6 PCB set
DuffyDawg 4 PCB set + 4 SMPS400
electromf 4 PCB set
badrisuper 2 PCB set
volavola 2 PCB set
JethroTull 2 PCB set
kp93300 2 PCB set
momomo67890 4 pcb set
ua3grn 6pcb set
mj777 2pcb set
mkusan 2pcb set
Odysseas 4pcb (2 pairs)
hcbonfim 2pcb set
Albrerta 2pcb set
dw1narso 2 pcb set (1 stereo) + extra output device pairs & isolators (for stereo if possible)
supernet 2 pcb set
milandks 4pcb set
tjencks 2pcb set
quanghao: 2pcb set
audionootje: 4pcb set (2x stereo)
tritosine 4pcb (2 pairs)
Bobo le Chat 2 pcb set
AP2 2pcb set+2pcb empity (i need this also)
Meganinja 2 set ( stereo )
mikvous 2 pcb set
still4given 2 PCB set
Rick G 2 PCB set
kindhornman 2 boards

 

[ravid]

BYRTT 8 PCB set
CaféNoir 6 PCB set
ColinAlex 8 PCB set
DavorXXL 6 PCB set
DuffyDawg 4 PCB set + 4 SMPS400
electromf 4 PCB set
badrisuper 2 PCB set
volavola 2 PCB set
JethroTull 2 PCB set
kp93300 2 PCB set
momomo67890 4 pcb set
ua3grn 6pcb set
mj777 2pcb set
mkusan 2pcb set
Odysseas 4pcb (2 pairs)
hcbonfim 2pcb set
Albrerta 2pcb set
dw1narso 2 pcb set (1 stereo) + extra output device pairs & isolators (for stereo if possible)
supernet 2 pcb set
milandks 4pcb set
tjencks 2pcb set
quanghao: 2pcb set
audionootje: 4pcb set (2x stereo)
tritosine 4pcb (2 pairs)
Bobo le Chat 2 pcb set
AP2 2pcb set+2pcb empity (i need this also)
Meganinja 2 set ( stereo )
mikvous 2 pcb set
still4given 2 PCB set
Rick G 2 PCB set
kindhornman 2 boards
ravid 2 pcb set

 

[Esperado]

PMI, i believe L.C. had followed the same road as me. First, suspicious with SMPS, then convinced with the sound improvement he could hear, comparing the two.
Why this improvement ? We can try to understand.
The first track is the much shorter time between the decrease of voltage, due to current consumption of the amp, and the next refresh increase due to the power supply following pulse. Like a 12 cylinder car will always be smoother, at the same RPM, than a 4 cylinder, (switchnig frequency) whatever the quality of the vibration filtration of the transmission (PSSR).

The second is, as you noticed, a better rejection of various AC hf pollution.
About the evils of the switching frequency of SMPS, i'm not sure they are greater than the ones induced by the rectifier cut off with the big trasfo, that you can only cancel partially with complicated and precise circuitry and soft recovery expensive rectifiers.

As you said, this little improvement in definition can be observed with voltage feedback traditional amplifier as well. PSSR rejection of the two can be as high as possible, they are not absolute. And the difference in quality between the two PSUs is at a subtle high quality level.
As each time something rely on transients reproduction, (like the difference between VFA and CFA) it is very difficult to demonstrate the things you can hear in an obvious and definitive manner.

 

[tinitus]

I will use a soft-start circuit on anything using toroids over 300VA.

if only we could get good IE-core trafos
less aggressive than toroids

 

[PMI]

@Esperado: I keep forgetting what size toroids you guys are using...

I believe that what causes an issue during recovery from a dip, also causes the temporary bit of noise from the SMPS mentioned in the other thread. I've seen the same thing in other, non-audio applications of switching supplies. The transition time from high-load to low-load is problematic. MrEvil's design for the cap multiplier has that licked quite effectively. Not sure if that was by design, or a fortunate accident. You have to read back through his two threads to get the whole picture, but it works very well.

I agree on the rest, the diode switching noise can be just as hard to get rid of as the SMPS switching noise, and sometimes harder (been there, done that). In this case, the supply rails are not as much the issue as the grounds. To see that, I would have to make or buy a current probe which is sensitive enough, and unfortunately, that won't happen soon... Wish I had more time...

 

[Esperado]

I believe that what causes an issue during recovery from a dip, also causes the temporary bit of noise from the SMPS mentioned in the other thread.

Considering the trasfo inductance in a SMPS, in a lot less amplitude and damping time.
I too, use cap multiplier in my amp (with a zener to limit the voltage) as it brings a reel improvement.
To be compared with an SMPS.
But you, guys are buying so many VSSA that L.C. is fully occupied to packet and post you orders instead of working.

I will send a horse head for he explore more PSUs solutions.
A single double power one vs two for both channels, Linear + cap mutliplier Vs SMPS+ cap multiplier, Connex (stabilized) Vs Hypex.

 

[pinnocchio]

LC, any news on the chassis?

Ciao!
Do

 

[PMI]

I will send a horse head for he explore more PSUs solutions...

Is this encouragement, or a threat?

 

[Esperado]

Is this encouragement, or a threat?

Just an invitation he can not refuse ...(where the hell is the clown icon ?)

 

[PMI]

Just an invitation he can not refuse ...(where the hell is the clown icon ?)

See, this is what happens when you start sending out horse heads, they take all your fun icons away

Just type it w. the colon... : clown : =

 

[tinitus]

would it change anything to have a bank of power supply caps between SMPS and amp ?

 

[PMI]

would it change anything to have a bank of power supply caps between SMPS and amp ?

That would depend on the SMPS. LC apparently went in the direction of replacing the stock caps, rather than adding them. One of the posts in the thread I referred to above was suggesting a common mode choke, which seems interesting. You can pull one out of any old tube TV. I decided to go with the cap multiplier in part based on comparing to a linear regulated bench supply.

I believe you would have to be careful adding caps to the output of the Hypex supply, after seeing what happened to the series resistors on the VSSA boards. If the output voltage rise time is fast enough to blow a 10R, I would be concerned with what might happen to a large capacitor bank.

(visions of irresistible force meeting an immovable object come to mind... ).

 

[tinitus]

ah, ok

I'm planning my future amps to have extern power supply
so even if build with linear supply, I can still plug in a SMPS if I want to

but amps will have their own power supply caps
and the reason why I ask

 

[Esperado]

I'm planning my future amps to have extern power supply
so even if build with linear supply, I can still plug in a SMPS if I want to
but amps will have their own power supply caps
and the reason why I ask

Well, you will be faced to a problem.
As long wires between rails and power supply acts like inductances, you rare, indeed, obliged to add caps near rails. You will rely on them for fast feeding currents to the amp, less to the quality of the PSU.
With SMPS, you are limited by the max current they are able to provide to those caps, both on a reliability point of view, and the quality of the signal, depending on the way they are designed. Usually, SMPS can't afford much more than two time the capacitances in their outputs.
You'll have to consider, too, the added impedance of the connectors between your two units (amps and PSU).
Remember, too, that you have to consider differently the capacitances when you use SMPS, with a switching frequency of some >50 Khz than the 100Hz of a linear PSU. All the advantage of SMPS is, indeed, to save money on capacitance values.
Just my two cents for tracks of reflexions.

 

[PMI]

...All the advantage of SMPS is, indeed, to save money on capacitance values.
Just my two cents for tracks of reflexions.

I am pretty sure there are other advantages, too...

It probably seems that I am coming down just on one side of a linear v. switch-mode debate, but that was not actually my intention. In either case, there is some noise generated, and has to be filtered out. No free lunch when it comes to power supplies (chuckle).

 

[Esperado]

About noises, i make a difference between them. Omho, continuous noise, even composed of random frequencies is less prejudicial (and sometimes bring some advantages, example dither) than a noise composed of spaced peaks, like the one generated by the schitching off of the diodes in a linear supply.
Note too that HF noise in not audible.
I am, of course, unable to explain with a definitive demonstration why one SMPS can make an amp sound better, (Who knows precisely our our ears works, or even what's exactly happens in an amp during big transients), but it seems obvious than a current tank refreshed 50 000 time/s will behave better than a one refreshed only 100 times in the same interval.

I believe L.C. did a much simpler and pragmatic study: tried both solutions, and chose the best.

 

[AP2]

About noises, i make a difference between them. Omho, continuous noise, even composed of random frequencies is less prejudicial (and sometimes bring some advantages, example dither) than a noise composed of spaced peaks, like the one generated by the schitching off of the diodes in a linear supply.
Note too that HF noise in not audible.
I am, of course, unable to explain with a definitive demonstration why one SMPS can make an amp sound better, (Who knows precisely our our ears works, or even what's exactly happens in an amp during big transients), but it seems obvious than a current tank refreshed 50 000 time/s will behave better than a one refreshed only 100 times in the same interval.

I believe L.C. did a much simpler and pragmatic study: tried both solutions, and chose the best.

Hi,
If smps has a frequency of 80kHz, this must be seen as a sub modulation of 100Hz. therefore also on the smps, needs to be fixed at 100Hz ripple. of course there are various ways to get a low ripple (100Hz), such as various ways to get a low harmonic content of the output smps.

 

[PMI]

About noises, i make a difference between them. Omho, continuous noise, even composed of random frequencies is less prejudicial (and sometimes bring some advantages, example dither) than a noise composed of spaced peaks, like the one generated by the schitching off of the diodes in a linear supply....

This was partly what I was trying to get at with my previous question. With reference to VSSA, MrEvil's Cap Multiplier seems to suppress the two sources of noise which I found of potential concern. The switching noise from the diodes, and the normal sags in supply voltage during current demand peaks. I say "potential" because I do not actually hear evidence of this from the speakers, but it is easy to see with an oscilloscope.

Test results are posted, here:

-> Cap Multiplier and Diode Noise

-> Cap Multiplier and Rail Sag

A similar test can be done with the SMPS, or any similar regulated power supply. I do not have a Hypex power supply to test with (although after this discussion I should probably get one... )

The switch-mode power supplies I have tried in the past basically traded one set of problems for another. This does not make SMPS a bad choice, just not necessarily better than linear (well, cheaper to manufacture in quantity, cheaper to ship, and using less energy, less copper etc., which is also important).

Here is an independent comment from another thread, about one of the SMPS often mentioned in this forum:

I'm testing a Connexelectronic SMPS800RE (+/- 60V) PSU with the honey badger. There is a tiny bit of noise evident on sensitive speakers for a few seconds after playing loudly and then cutting the sound...
...The Connexelectronics PSU does seem a good unit, but I may need to investigate filtering if I still get audible levels of noise. Plan B is back to a linear PSU...

That noise comes from how the SMPS responds to a momentary increase in current demand, and what happens when the demand for extra current stops.

Basically, unless you filter (or regulate) the power rails VERY extensively, there will be some noise. Whether you notice it or not with one particular setup, is another question... If the noise is in the bandwidth of the amplifier, it will change what you hear. If frequencies above 20K did not matter, then we would not be concerned with maximum slew rates, square wave tests, etc.

 

[Kindhornman]

A couple of questions here on this amplifier that may have already been posted but I am new to the thread. I was talking to Christophe in a PM and we discussed using this amplifier in a bridged mode. Has anyone already designed the circuit to use the boards this way? Also if you do this what do you need to do about the power supply? Would you need two smps supplies to do this or would you use a higher output smps for that application? If this has already been discussed in the thread does anyone know the approximate page number where I can go read about this?

I'll need to double my boards if this is a viable alternative.