PSU sound?

A few circuits have mentioned there is a sound in PSU, like  drip 175  "this tube rectified design adds a type of beautiful ‘sag’ to the compression and overall tone of the unit"
Can anyone tell me why ?
Of course , if you have a bad PSU desing we have problems, and I call this "problems".

How can a circuit change his sound with differents well designed PSUs ? 
Thanks

it is extremely present in musical instrument amplifiers...


i'm jus sayin...

DAN_000 said:

Can anyone tell me why ?

Click to expand...

I'll be the layman, someone else can elaborate on the finer details. Tube rectifier is not linear, and will not conduct linearly near its design limit.

Look at the image here: http://en.wikipedia.org/wiki/Rectifier

See those green rectified sinewaves (linear full wave rectification). With tube rectifier when enough current is pulled through (in our world, a loud sound) it those sine waves will start to sag, ie. slight limiting will happen to the waveform tops. That means a voltage drop in the PSU.

And now less voltage is delivered to the amplifier tubes. And this happens dynamically with the music.

Sag, a type highly non linear limiting, since the effect of voltage drop for all tubes in the amp can be highly unpredictable. Probably sounds nice and crunchy. But this only really applies to guitar amp power tubes. They can easily knock a rectifier tube to its knees when blasting at max gain.

With a less powerful application, like the 175 compressor, the effect on sound is probably negligible. It will always work in the tube rectifier safe (read: reasonably linear) zone.

The quality of the PSU and the grounding are probably the two most overlooked aspects of audio electronics design.

If the DC rails are not "stiff" enough and/or clean, they can certainly have an impact on the sound. This is particularly true of basic discrete single ended circuits and valve/tube amps. With opamps, discrete (DOA) or monolithic it is somewhat less of any issue due to the typically extensive use of current sources.

cuelist said:

If the DC rails are not "stiff" enough and/or clean, they can certainly have an impact on the sound.

Click to expand...

And this must be taken into account if a guitar amp design wants have the tube rectifier sag audible in any meaningful way. If your PSU has excessive filtering (large caps) the effect of sag will be slow and delayed, useless and undesirable to a player.

Kingston said:

And this must be taken into account if a guitar amp design wants have the tube rectifier sag audible in any meaningful way. If your PSU has excessive filtering (large caps) the effect of sag will be slow and delayed, useless and undesirable to a player.

Click to expand...

Guitar amps are certainly a special case. Here the PSU is an integral part of the sound, same as distortion is part of creative process.

while I'm home sneezing my brains out and too drippy to go out in public (gotta love changes in season) here's an analogy

A power supply is like an audio power amplifier except it's job is to reproduce a dc voltage

Most people can hear differences between power amplifiers and have noted that the various speakers load amplifiers differently and some combinations of speakers and amplifiers work better than others

"stiff" power supplies can be compared to power amplifiers having high damping ratios (low output impedance) and are generally more load tolerant... a stiff power amplifier with a high damping ratio and a very low output impedance can deliver more current on demand so things that have crazy impedance curves like... oh... old B&W 801's... can be driven without the amp pooping out as easily...  as always there are some exceptions here with power amplifiers that achieve their low impedance through copious feedback all at the output of the amp - these might have a high damping ratio in a static resistive load sense but in the real world the complex load might interfere with said feedback and make the amp misbehave and possibly exude smoke...

"limp" power supplies can be compared to power amps with lower damping ratios and higher output impedances...  these amps tend to go non-linear when driving any sort of complex load or simply sag when the filter caps are drawn down - as in guitar amps and nearly all tube amplifiers at some point depending on how hard you push them.

so...  are stiff power supplies always the best thing?  I'd say that in consoles you want stiff supplies and low impedance power supply distribution in the console.  In other applications like guitar amps you probably want the mojo you get from a limp supply...  or in some outboard gear you may find that beefing up the power supply might remove some of the character that you like... 

In my experience power supplies contribute one way or another to the overall sound of whatever they are powering.  Pretty much universally the feedback I've gotten from those who's consoles I've upgraded supplies and power distribution in is quite positive and in most cases I'd say the sonic improvement was not subtle.  I use Acopian supplies - specifically Linear Gold Box "A" version supplies.  Note - with these supplies and large capacitive loads you will likely need to clip out a cap on the regulator board to disable a startup protection circuit...  otherwise the supply may not want to get out of bed.  Todd and other engineers at Acopian know about this so if you order supplies from them you would want to tell them that the load has a lot of capacitance and please remove C7.  The regulators in those are simple and very tight, noise level is low...  Power One and Condor supplies do not sound as good...  to me that is.  I really don't want to start any big arguments - I'm just tellin' you what my opinion is and what my customers tell me...  Also on the PSU and console thing - I've said this a a lot everywhere...  if the console draws 3 Amps you want a supply rated for significantly more, like 6 Amps or more...  you can search some of the forums I used to contribute to a lot and find a pile of my commentary on power supplies and consoles.

In other cases you may want a somewhat limp power supply - but not with consoles...

another digression... I like certain old crappy speakers because I'm used to them...  they suck but I know they suck and I know if I can manage to make anything sound right on them mix-wise it's likely that it'll translate well to most everything else... so...  with Big Reds (these are 16 ohm 604E's in a vented box with Mastering Labs crossovers) you MUST use amplifiers that are a bit limp.  A McIntosh 2120 is a solid state amp with an output transformer that has impedance taps at 2, 4, 8 and 16 ohms and the 16 ohm tap works real good.  These speakers with a modern amp like a Crown Reference can sound very pointy and bad...  I mean they sound bad all the time but I mean unusably bad.  My Westlake BBSM-6's however need a really stiff amp so the 2 ohm tap sounds better - or maybe a Crown Reference 2

Back to gear...  When I was a newbie assistant engineer at Secret Sound Studios in 1976 one of the engineers there was generous enough to turn around and say, while pointing at the 160VU's 'they sound just right when the VU lamps dim a little on the hits' and later he told me that if I ever saw the lamps were burned out that I should make sure they get replaced right away.  At first I bought it...  then later I didn't...  until I "fixed" one and beefed up the supply...  it didn't sound the same when hit hard - it lost some mojo...  and then I did a little A/B on another one with the lights disconnected vs not and hmmm well well...  and much later on when looking at how 1176's worked and what was good and what was bad about them I came to the same conclusion about the zener regulator

and guitar amps...  if you have a tube guitar amp and you like the way it sounds you may not like what happens if you double up the filter caps on the plate supply(ies) because as someone rightly mentioned previously, you will essentially be messing with the recovery time of the power supply.  When you crank an amp up and make it fold up it will take longer to refill the filter caps and that is pretty much like increasing the release time on a compressor - it messes with the timing of your "chunk"  It should also be noted that certain classic transistor guitar and bass amps have a special folding up characteristic...  Mostly I remember one of the guitar players in a band I was in before I moved to NYC had a Kustom 100 that used to completely die when he hit it hard - the blue light on the front would dim a LOT... but it would come right back for the next big chunk...  what a terrible amp...  but it worked "great" and was also responsible for some midrange hearing loss in my left ear.

When you think about it everything contributes to the final sound. The impedance of the power tranny, even the type of tube rectifier can make a difference. The age, size and quality of the filter caps, grounding scheme and so on. A well designed gear is more on the transparent side since the flaws are compensated for.

From Kevin O'Connor's The Ultimate Tone Volume 2 (which I picked up on e-bay);

" .....If you increase the capacitance value of the first filter in any guitar amp supply, the lowest frequencies will be subjectively tighter. However, this will be contrary to the "classic" low-end of traditional guitar tone. ..."

How can the impedance of the PSU transformer make a difference to sound?

Also, every once in a while someone on this forum says a simple CRC network in a tube preamp "sounds better" than CRCRC. I can't see any theoretical or practical difference that would cause it. Is there any?

When an output waveform clips (think guitar amps), the waveform tops are directly modulated by power supply ripple and directly audible.

While less obvious in a class D amp, power supply voltage changes directly modulate the output, but this is typically reduced somewhat by negative feedback.

Opamps are 5 terminal devices. While power supply modulations do talk into the inputs, in good opamps this can be down 90-100 dB.

JR

JohnRoberts said:

When an output waveform clips (think guitar amps), the waveform tops are directly modulated by power supply ripple and directly audible.

JR

Click to expand...

Below from the same book agrees;

" .....As signal level increases, the transients get clipped first, triggering the inherent composite overload characteristic of the amp and power supply. This becomes severe as energy is pulled from the filter caps faster than it is pumped into them. At this point, supply ripple can become extreme and modulate the audio output. This can sound like a sub-harmonic "ghost note". Signal dynamics will be limited until the average signal level drops and the power supply recovers."

Always interesting to me that people avoid the cost of chokes in PSU's for the most part.  Considered a big improvement in some circles, yet almost universally hated with instrument amps.

sahib said:

This can sound like a sub-harmonic "ghost note".

Click to expand...

You can hear that when turning off a "stiff" tube preamp when it's still inline and audio can be heard. The filter caps empty quite slowly and at some point the "ghost note distortion" gradually takes over until the last of the caps are eaten.

I once thought about making this type a distortion a "feature" in a preamp, but couldn't think of anything that would work reliably.

klett said:

Back to gear...   When I was a newbie assistant engineer at Secret Sound Studios in 1976 one of the engineers there was generous enough to turn around and say, while pointing at the 160VU's 'they sound just right when the VU lamps dim a little on the hits' and later he told me that if I ever saw the lamps were burned out that I should make sure they get replaced right away.  At first I bought it...  then later I didn't...  until I "fixed" one and beefed up the supply...  it didn't sound the same when hit hard - it lost some mojo...  and then I did a little A/B on another one with the lights disconnected vs not and hmmm well well...  and much later on when looking at how 1176's worked and what was good and what was bad about them I came to the same conclusion about the zener regulator

Click to expand...

Do you think a zener regulated PSU can be considerated as no linear ? compared to 78xx regulators.

now if you want to look at the Total power supply, the schematic should start with the snow melting.

unless you guys have gone solar already?


i wonder if these solar sub stations with all these inverters are gonna make us use balanced transformers again.  :-*


we might all be on minus 48 if the rivers run dry.

emrr said:

Always interesting to me that people avoid the cost of chokes in PSU's for the most part.  Considered a big improvement in some circles, yet almost universally hated with instrument amps.

Click to expand...

In all honesty I have never seriously considered a choke design. They are usually avoided because of size, cost, etc. They were more popular in old designs I suspect because capacitor technology was less developed and chokes were actually cost effective.

Chokes have some merit for smoothing the current draw from mains, so I recall investigating them briefly when it looked like power factor correction might be mandated for music equipment (in EU). Chokes looked promising for low power gear, higher power PFC would end up using a variant on switching regulation.

In audio design, the choke becomes another source of magnetic fields to corrupt audio signals, while they would reduce peak charging current in reservoir caps that can corrupt grounds.

JR

audio chokes are designed just like output transformers, so they can be a bit more interesting than a black can filled with goop.

DAN_000 said:

Do you think a zener regulated PSU can be considerated as no linear ? compared to 78xx regulators.

Click to expand...

zener regulated supplies use a reversed biased zener diode to shunt enough current to ground to maintain a particular voltage, the "zener" voltage.  If a load is drawing off current the zener reduces it's current to maintain the voltage.  It's a single component regulator and even though it's a semiconductor I view this kind of regulation as nearly passive in the sense that the supply current is not flowing through the device to the load and that there is no feedback or complicated circuitry involved...  just this zener sitting there doing what it does to keep it's reverse bias voltage nearly constant...  the actual voltage you get from this regulator varies a bit depending on how much current is shunting through the device, so it tends to be a little looser in its regulation and the output impedance of the regulator as seen by the load is higher than a monolithic IC regulator because of the series/current limiting resistor that feed the raw supply down to the zener.  There is some interaction between the circuit drawing power from the zener and the zener device itself that is different between that you have between that same circuit and an IC regulator.  Different regulators can have an impact on sonics and in some cases the results from using a zener can be pleasing.  Zener regulation does not work great in high current applications because the devices can cook themselves but you can use a zener as a reference at the base of a pass transistor ... but then you've insert a series component into the regulator and that changes things.  Somewhere in Audio Amateur there was an article or series that explored shunt regulators...  I know I have it on paper - maybe it's up somewhere.  As I recall it was informative.

hey, John, like Wow man! cool!

i'm jus sayin...

you never know around this place...

come back often!

please!

and give me the latest on the best contact cleaners.