Simple, no-math transformer snubber using Quasimodo test-jig

[Mark Johnson]

is there a correlation between best perceived sound and the amount of damping?

diyAudio member fglabach has answered your question in this very thread: In the case of his tube preamp + his subjective listening judgement + his various snubbing experiments -- Yes!

I recommended, not sarcastically, that he create a diyAudio thread whose title is chosen to be easily findable with standard searches, discussing what he did, and how he did it, and what his subjective listening results were.

There are several diyAudio members who, I am absolutely certain, could construct an audio preamplifier (or power amplifier) that sounded exactly the same whether the power transformer's secondary was underdamped, critically damped, or overdamped. For that piece of audio gear, I am absolutely certain, there would be no correlation between best perceived sound and secondary damping.

Thus the answer to your question also depends on the audio equipment. Member fglabach's tube preamp? Yes. The preamp of the preceding paragraph? No.

 

[Mark Johnson]

Anyone ever heard of this from the old days of 'ham radio'?

Not me, sorry.

I offer, as a pleasant "thought experiment," the Sutherland 20/20 phono preamplifier: mfr's web page. This is an extreme example of minimalism; it's dual mono construction and each channel gets its very own DC power supply. These are a pair of wall-warts (!!) that perform AC to DC conversion.

Imagine opening up those wall-warts in an attempt to install Andrew Nehan's sound improver capacitors! Wow.

From the owner's manual:

 

[fglabach]

Mark that wasn't fair
I did not do it by ear to find the resistor value

I used an old tectronic scope with the expensive plug in differential amp that measures down to micro volts


I clipped the scope leads on the secondary wire insulation
To pick up radiated noise

Used bandwidth limiting function in scope to only see the ringing


I only listened to the caps

Yeh I did listen to the resistors too but with the same value

And I bought the Quasimodo

I love it as it gets me there faster

I am just saying you should still listen to the part choicesin circuit once you get the right values from Quasimodo

Any know where to get small value Teflon caps

The rti were great but don't sell them anymore

 

[Mark Johnson]

I praised your bravery and congratulated you on your results. Sorry you feel that was unfair. It was not at all clear in your message #791 that you had used an oscilloscope when testing; you didn't mention scopes at all, and you asked someone else to show you the ultimate resulting waveform, which sounded like you had no scope.

Please allow me to congratulate your can-do attitude and your careful testing, again. Well done!

By the way, a diyAudio member here made a wonderful suggestion for viewing the ringing on high voltage transformers, at voltages so high that you hesitate to make a direct electrical connection with your scope probe. He suggested using a high pass filter (series capacitor, shunt resistor) whose cutoff frequency is much much higher than the mains frequency, yet lower than the oscillation frequency. This eliminates the high voltage 60Hz sinewave, leaving the low voltage oscillatory ringing. I wish I could remember the person's membername and/or the post# here, but regrettably I can't. Naturally the series capacitor needs to be a high voltage type.

 

[jameshillj]

Yeah, playing around with those caps is a real pain in capital letter, even if you have the space to add plug in connectors and accurate measurement facilities - not the friendliest aspect of diy - mind you, having the ability to quite significantly alter the bass content or the treble balance with such a simple technique is 'sort of' fascinating in it's own way - it takes me back to when operating any electronic equipment meant squeezing everything possible out of the power supply designs as the components back then were quite limited but lateral thinking was highly prized - things have changed so much since then but it's good to see some of that thinking is being revisited...

These days your tester has allowed simple inclusion of critically (or whatever) damped snubbers in nearly any power supply (and at negligible cost) and takes the guesswork out of this area and so can concentrate on other areas of the supplies

I really appreciate your 'little gadget' design and continuing active thread support - I take my hat off to you for this and again, many thanks

 

[fglabach]

Mark I apologize for my iPhone sloppy texting
I tried every cap I could find
The cap director across the secondary I looked for a cap that cleaned up the broadband noise with short leads

Small Teflon the best

It reduces high frequency noise

The tuned cap with the resistor actually affects the midrange
Even the voice

The high quality golden ratio ceramic caps cleaned up the signal the best

But they wete far less acoustic sounding

I used a polypropylene here

The metal film resistor was too hard

I preferred a radio shack carbon film

This is highly subjective

But I would not use cheap parts in the b plus of a tube preamp

You can hear everything in that location

I have an old Eico capacitor resistor box

It lets me put the resistor and cap in series

First I would get resistor right

Then vary cap

Very useful if you can find one

I did this with the scope attached and music playing


Snubbing is the finishing touch to the supply

To go off the thread a little
The power transformer is very impotent
You want the lowest inter winding capacitance but also good regulation
They are somewhat contradictory requirements
But I believe in really overating the transformer if you want your system to sound big and majestetisl

I tried a triad super low capacitance split bobbin
A huge Hammond slit bobbin with 20 amps on a solid state crossover that draws 1 amp
And a new torroid medical step down with shield from triad

I used a laboratory grade ground on the shield

I preferred the oversized Hammond split bobbin even though the capacitsnce at 250pf was a little high

The torroid was clean and fast and edgy



The

 

[Mark Johnson]

Congratulations on your good results! After you find the transformer(s) that sound best, maybe another fruitful path of exploration might be EMI/RFI filters between the AC mains and the transformer primary here is a datasheet

 

[fglabach]

Thanks mark
I will use your Quasimodo to snub this and the turntable motor supply
That uses and old great sounding transformer from
A huge lambda power supply

I will try your try filter

I am shears concerned with any impedance between the power cord and the transformer primary

I will compare the Shaffer from a huge 50 amp one i got from
A salvage house


I hope you know mark that if the transformer has low capacitance for line isolation then the noise levels are lower and the benefits of snubbing more audible

 

[trobbins]

I moved house to be closer to the nearest distribution transformer - that way I get the lowest supply impedance.

I also put all my audio gear in the room next to the house switchboard, and use the wall outlet closest to the switchboard.

Patti Smith has never sounded better.

Can't wait to add a snubber now that I've done the big cost items.

 

[fglabach]

Your right how about being closer to the distribution transformer
Also try to have copper wire from the transformer
If your All copper then be sure your split bolt connections to the house are all copper too
Don't want any aluminum if you can avoid it

 

[fglabach]

Mark I think your right you want to be critically damped
I think when you go past critically damped you may create more problems than you solve with the snubber

I also think you want to have your dissipation to a minimum because a circuit sounds better not overly loaded down

You want an effortless unencumbered sound

So if you have low capacitance transformer and rectifiers it might be better to use a ,005 for cx and .1 for cs if you can still get good snubbing on the scope


My expert says want t to keep the total capacitance of the transformer rectifier to a minimum

There is no doubt sonically that even super soft diodes benefit from snubbing

Don't the soft recovery Fred's have more capacitance so you have to use a larger cx cap to swamp it


My expert suggests that your are better off using low capacitance cheap diodes
And then critically snubbing then soft recovery types that require more power dissipation to snub

Does anyone have any theory or listening experience to support these ramblings

I think you want to minimize dissipation of the snubber circuit particularly on a high voltage step up transformer in a preamp

Apologize for the ramblings

Mark I'm a good rambler
But I trust your application of theory which is beyond me

 

[DIYspaceW]

Are the PCBs still available somehow?

 

[Mark Johnson]

Please look at post#1 at the very beginning of this thread.

 

[fglabach]

I played with the Quasimodo
There was some jagged stuff ridding on the sine wave
It went away with a slightly bigger cx cap
I'm not sure it was lower dissipation or higher value cap as I had to do both
I moved up to a ,068 polprop
Allied electronics has a good assortment of asc series x363 caps
That cleaned up the jaggedness

I am going to try to take the first cap up to ,022 instead of .068
And then raise the other cap to .22 or .47
And see if this sounds better
Just as mark told us the .15 did not work well with the .067



I have a sneaking suspicion that with a .022 it will clean up
The high frequency better than a .01

We will do some serious listening and report back

I bet I like the .022 ,22 combo better than the .01 ,15 combo

I'd I do I'll try the .,047 ,47 combo

All these caps in axial lead are available from allied electronics

 

[fglabach]

Cornell dublier white paper on snubbing recommends carbon composite or carbon film resistors because they are lower inductance

I recommend the big radio shack 1\2 watt bag of carbon film resistors
You can make a resistor very close to your pot critically damped value

They are a little warmer sounding than metal film

 

[AndrewT]

Carbon film are helix like metal oxide and metal fim.
They are not any lower in inductance.
Generally carbon film tend to be slightly longer and slightly bigger diameter for the same power dissipation. That would make carbon film higher inductance than either of the metal types.

 

[Mark Johnson]

A good engineer would calculate how much parasitic inductance inside the snubbing resistor, is needed to change the circuit's behavior by 0.5% (or 0.1%). That number is "L_toobig". Then she would compare "L_toobig" against the datasheet inductance of a 400 milliwatt metal film thru-hole resistor, a carbon film resistor, a metal foil resistor, and a carbon composition resistor.

Maybe ALL resistor types are bad? Maybe they all have more than "L_toobig" nanohenrys of parasitic inductance?

Maybe none of them are bad?

A good engineer would calculate this.

 

[fglabach]

Mark

I loved your post 143 that really helps us to identify critical damping

If you look at the critically damped photo there are still high frequency wiggles on the wave

Those go away completely with a lower dissipation cap for cx

Or a slightly larger cx

I'm going to critically damp with cx at ,01
,022
And

.047

I will use correspondingly larger cs

I will report back as to the sound differences

Is this a fruitful endeavor?

I know you have high standards of a good engineer

I do not pretend to be

 

[Mark Johnson]

fglabach, please post oscilloscope photos which show the transformer secondary waveform before, and after, your circuit changes which give improved listening pleasure.

You could label the photos with captions such as, "A. Sounds OK" and "B. Sounds Much Better"

 

[fglabach]

I will do so in about 7 days

Hopefully we will dime correlation between snubbing and sound

We will be using the atc polypropylene caps


We may try and old black beauty with Kraft paper for the fun of it