Dr Z EMS Touch Control - what is it?

[echuta13]

To me, this stuff is getting closer to the fringe or maybe in the realms of "gilding the lily"?!?

Doesn't mean its not interesting and shouldn't be explored though! 

There are other areas you could also explore plopping a film cap in (just to play devils advocate).  What about the bypass of a cathode biased output section?  I know some people have tried larger bypass caps (1000uf+) in that section to emulate fixed bias.  Maybe a 1uf film in addition could add that extra "something".. or maybe just trying a big' ol fattie film cap in there might be interesting.

[shooter]

maybe start with a SS PS, tweak values for tubes, then remove one cap at a time n evaluate 

[Willabe]

Here's the link;

https://www.aikenamps.com/index.php/grounding

[Willabe]

So Jordan, by the time we are downstream at the filtered node for V1 we have 0V AC.
But, coming straight out of the rectifier we have some AC ripple voltage.
The cap you mention just shunts some highs from the AC signal to ground whereas this cap in question shunts AC ripple to ground.
That's what makes it thread worthy. A closer look at why the mighty Dr. Z thought this was worth a front panel switch.

Sounds like Mr. Aiken agrees with us.

No, I don't so. I think it's another thing. Curve ball. It's only the "very high reactances at frequencies within the range of a distorted guitar". Heavy distortion generates a lot of very high frequencies that some lytic caps can't decouple from the B+. 

I don't think he's talking about ripple on the 1st stage, there's not enough of it there.

[SILVERGUN]

Sounds like Mr. Aiken agrees with us.
Maybe we need a switch with a cap on each stage. 

I think you may have missed the highly sophisticated sarcasm in that post?
I don't think this is a mystery anymore.

Let's give it a name:
Output Stage Transient Snubber

And a new abbreviation: OSTS

sluckey, please add that to the Official Amp Acronym List or OAAL as I like to call it

[Willabe]

I think you may have missed the highly sophisticated sarcasm in that post?

Well, that's because I would have to be highly sophisticated. 

Let's give it a name:Output Stage Transient Snubber

But it doesn't snub the transient, it alows them by responding faster that the lytic.

And a new abbreviation: OSTS

sluckey, please add that to the Official Amp Acronym List or OAAL as I like to call it.

NO!!!!!! NO MORE Acronyms!!!!!!!         

I can't remember 3/4's of them now!      
There's a reason we use letters to make words. Everything is backwards these days!!!!!

[SILVERGUN]

Ok, lets just call it the Dr. Z Touch Switch. 
Or DZTS?

[Willabe]

The Ditzs switch?     

[SILVERGUN]

Let's give it a name:Output Stage Transient Snubber

But it doesn't snub the transient, it alows them by responding faster that the lytic.

One of us is off here and it makes me nervous that pdf64 liked your post. I looked up the definition of snubber in case I was using it incorrectly.

I used the term "Snubber" because:
"Snubbers are used in power circuits to suppress harmful voltage transient spikes"

[Willabe]

Edit; I'm talking about the ac signal component, its transients, not the dcv. Read the Aiken quote again.

Let's give it a name:Output Stage Transient Snubber

But it doesn't snub the transient, it alows them by responding faster that the lytic.

One of us is off here and it makes me nervous that pdf64 liked your post. I looked up the definition of snubber in case I was using it incorrectly.

I used the term "Snubber" because:
"Snubbers are used in power circuits to suppress harmful voltage transient spikes"

That's what I'm saying, I think you have it backwards.

Lytic caps have flaws in their ability to filter the very high and low ends of the frequency spectrem. After a certain point, the higher and lower the frequency goes the less able they are to filter those frequencies. And high distortion creates lots of hi end harmonics.

The film cap can respond much faster and in the high frequency range that lytics can't. So the initial pick attack, spike in the ac signal, is not rolled off, it is not snubbed. 

[pdf64]

I’m sceptical that the cap could have anything more than a negligible effect on the amp’s transient response.

[Willabe]

Hi-fi guys have been doing it for years. (Yes they do some wacky things.)

Same type of thing as using all film caps for the B+ filtering. KOC and some of the guys that hung out at his old forum, built amps with all film caps and talked about the difference in sound and response/feel. And like I said Carr amps does the same with a few models. His amps are highly respected. 

 

[pdf64]

Indeed but no matter how venerable the source, it still only seems to amount to so much idle hypotheses. And highly respected builders don’t have to be EE superbrains.
Transient response is something that can be characterised, analysed and differences be made quantifiable. Isn’t that what the impulse response testing of the different speakers is all about?
The resources to do that are beyond the scope of most DIYer’s test bench, but surely, if so minded, those people could put some evidence behind their hypothesis?
 

[shooter]

Hi-fi guys have been doing it for years.

the A/B switching in sand is different than glass, therefore a different "take" (see schematic reply #51) on making DC stay DC


one of the "ball buster" cal's I had to accomplish, make the DCV go from 0 to 320V in 60mS. measure n meet spec at all 5 TC's (time constants) on the way UP. once that was done, make 320VDC stay 320 VDC +/- .5v for ANOTHER 5 TC's (0-200(IIRC) seconds)


any time we switch Volts or current on/off fast, especially into inductors, (coils), transients can n do happen, in music that might produce a happy "sound".  In constant source DC, they are never welcome.  N, ya PDF64, the math is crazy and doesn't help AT ALL for calibrations

[Willabe]

None of this matters if you can't hear it of feel it when you play. Have to experiment to see what you hear. Not a big deal.

The evidence is what you hear. They wouldn't build amps with poly film power supply caps if they and their customers didn't hear anything different.

If an audio amp is basically a modulated power supply, then the PSU is the foundation of the amp. So the PSU would have a big influence on an amps overall sound and performance.

Speed players complain about being able to out run certain amps, PSU.   

Still, with bypass film caps in the PSU, it's probably pretty subtle, not a massive change, as it's only a small change to the whole PSU. Changing to full film caps, not just a small bypass film cap, would probably be more noticeable. 

[pdf64]

...
Speed players complain about being able to out run certain amps, PSU.   
...

That seems like another example of hypothesis that I query the credibility of.

[Willabe]

That's been long expressed by speed players. They change amps because of it.

It's the sag and compression, they want more articulation. So they go to amps with a stiffer PSU, SS rectifier, larger filter caps, even going to 6550's. Larger wattage speakers, less compression, more articulation. Larger PT B+ reserve, mAs, larger OT's. Any/all of those make can help make for a stiffer amp.   

They don't need the sag/compression, they play fast note's not long sustaining bent string note's that bloom, like blues/rock players.

I had a Mesa MkII C, never liked it, way too stiff for me, too articulate, I could hear the smallest little pick attack thing, extremely unforgiving. The least little subtle pick mistake, you could hear it. Now some guys would love that. And I played a BF SR for years, main amp, not exactly a weak PSU in those those amps. But certainly more grace than that Mesa.         

[High Voltage]

You'd be surprised how many brand new filter caps have very high reactances at frequencies within the range of a distorted guitar. Sometimes you can take a "bad" filter cap and bypass it with a 0.1uF cap and it will sound fine. It never hurts to have good high-frequency decoupling at all nodes.

This is a super interesting thread. However could someone please explain to me how the reactance of a cap at the B+ node could interact with the frequencies of the signal? I don't understand that.

[pdf64]

…how the reactance of a cap at the B+ node could interact with the frequencies of the signal?

Standard circuit analysis assumes that power supplies have zero impedance to 0V circuit common.
High value caps (usually ecaps) are used to achieve something hopefully close to that in real world. But if the impedance is not so low as to be negligible, then as 2 or more stages might share the same power supply node, and the impedance of that node becomes significant, then unexpected interactions between those circuit stages will occur. Because signal paths occur where none should be.
It’s a similar scenario to the circuit board losing its insulative property.

[sluckey]

Electrolytic caps are great for filtering out low frequency 120Hz and even audio signals from the B+ line. But their response time is too slow to effectively remove high frequency stuff such as noise spikes that come in on the power line or rectifier diode switching spikes, or square waves, etc. Small film caps have a much faster response time to high freq stuff so they are much more effective at removing high freq noise spikes, etc from the B+ line.

[pdf64]

…
It's the sag and compression, they want more articulation. So they go to amps with a stiffer PSU, SS rectifier, larger filter caps, even going to 6550's…         

Thanks, whatever makes people happy I suppose!
A vintage type amp still works fine at full load though, can put out continuous max power until they run out of notes or whatever.
The HT supply doesn’t differentiate between a continuous single note and an continuous stream consisting of different notes; full load is still full load, I don’t see how the HT cap type would make a difference?

[shooter]

^^^^
agree, I think one "magic genie" is current demand over a short time cycle, a PT that just barely meets the load requirement verses one that is 2X the load required would go further on sag/response than a cap time constant.   Transients are better dealt with with fast response caps as Sluckey pointed out

[Willabe]

A vintage type amp still works fine at full load though, can put out continuous max power until they run out of notes or whatever.
The HT supply doesn’t differentiate between a continuous single note and an continuous stream consisting of different notes; full load is still full load, I don’t see how the HT cap type would make a difference?

That's not what I said, it's not about full power. It's about sag, compression and not rounding off the very front end, the initial attack, of the notes envelope. I also said SS rectifier. You can still have full power and be well into the amps PSU sagging, the OT compressing the far ends of the frequency spectrum more and more and the speaker into compression too. In fact you get more power as the sine wave squares off. As this happens the very 1st pick attack gets more and more lost, diminished, yet you can still have full power output.   

It's a matter of feel. You have to get behind the wheel and play through the amp. Some love 'grezzy' amps, weak PSU, squishy/saggy amp. If you can have that end of the spectrum of an amps feel, you can have the other end too. Amps are tools, and as such can be under-powered or over-powered for the job.   

A friend of mine and I were A/Bing speakers 1 time. When he was playing I could hear some difference in sound/tone, but nothing drastic. But when I got behind the wheel, there was a huge difference in how the speakers responded to pick attack.

Another time, had a BF Dual Showman, had a gig, set up, turned on the amp, something was wrong. Sounded odd. There was a guy who came to see us and sit in. He was playing 2nd guitar for Buddy Guy and Jr. Wells, had played for them for several years at that point. He got up and played through my Showman, after I asked him if he thought the amp sounded odd, he thought it was fine.    And he was a Fender BF guy.    I took the amp into the shop, before I worked on amps. One of the 6L6GC's died. I heard it, he didn't, my bass player didn't. The bass player played with me for several years, so he knew that amps sound.   

Depends on how you play, what style you play and how developed your style and ears are.

I had a Mesa MkII C, never liked it, way too stiff for me, too articulate, I could hear the smallest little pick attack thing, extremely unforgiving. The least little subtle pick mistake, you could hear it. Now some guys would love that. And I played a BF SR for years, main amp, not exactly a weak PSU in those those amps. But certainly more grace than that Mesa.

How do you explain this? This was way before I had read anything about PSU's, sag, etc.

Do you play? It's in the hands, ear, not paper that you get to know these things.

[PharmRock]

It's in the hands, ear, not paper that you get to know these things.

Along these same lines, my shipment of caps arrived earlier this week (Thanks Doug for quick shipping) and I plan on moving up to a 0.1uf cap on the switch to see if I notice anything. Maybe try a 0.047 to 0.1uf in parallel.  I'll report back what I find.

Thanks to all for the comments and replies on this thread.  I've been doing my best to keep up with the more technical aspects of the discussion and have learned some things along the way.

[Willabe]

Since it's an experiment, and you have the film bypass cap on a switch, I'd try it at different volumes, even if you don't normally play at those settings. Leave the tone settings the same on the 1st test. Looking to see if PSU sag plays into this in any way, it might. 

I'd try starting at low volumes going to higher setting, so your ears don't fatigue.

Maybe start at 3 flip to bypass, then 4 flip to bypass and so on all the way up to 8 or more. I'd also try it latter again, ear fatigue recovery, with the treble set higher. It might revel it self clearer in the higher frequencies.

And I'd also be listening to hear if the very front end of the note, initial pick attack, changes, is clearer, crisper, more percussive, responds differently to your pick attack, etc.

I was thinking and wondering if maybe, that at least part of what the bypass cap does, if it does anything, is removes enough/all the high frequency line noise that was masking the initial pick attack? 

Take your time, it may be subtle. It may be more feel, touch response, than heard, or it maybe some of both.   

[PharmRock]

This morning I soldered in a 0.1uF cap on the switch.  Amp was set up for high gain, but this amp cleans up nicely with the guitar volume control.  I used a Washburn superstrat with a JB and Jazz, and also a partscaster with Lollar Blondes.  The amp went into a reactive load with headphones attached so I could hear the details better.  To minimize any bias, I had my wife switch the cap in an out while I played, with me not knowing whether it was switched in or out of the circuit. Towards the end she let me know whether the cap was switched in or out.as she operated the switch.

To my ears, there is a subtle but noticeable difference with the 0.1uF cap switched in.  The pick attack was more clear and the top end less ratty/fizzy, especially on the higher notes.  Not sure if I would call it smoother, but as SG said previously, not as harsh.  It was more evident at higher gain settings.  But even with low gain there was a noticeable difference. 

Currently the switch is located on the side of the chassis.  I think I will leave it there for a while and if it seems like I am using it a lot, I may relocate it to the front panel, or maybe convert one of the tone controls to a push/pull. 

One more experiment is to switch the 0.1uF and 0.047uF in parallel, just for curiosity's sake.  I'll try that later today and report back.

[Willabe]

That test is fair in 1 way and not another. I believe you are hearing a difference, but can you hear the same difference through the speaker as you are hearing with head phones? The speaker might mask or filter what your hearing? Have to try the same test through the speaker you have.

Did you try the test you did with the .047 cap? I wonder if you could still hear it with the smaller value cap? 

That caps value is way to small to affect the PSU's ripple, and the ripples frequency is to low, so it has to be affecting some other component of the sine wave or ridding on the sine wave.

Edit: I mean the total magnitude of the ripple.   

[drew]

Let's give it a name:
Output Stage Transient Snubber

And a new abbreviation: OSTS

sluckey, please add that to the Official Amp Acronym List or OAAL as I like to call it

Official Forum Amp Acronym List would yield a somewhat better acronym.

[PharmRock]

That test is fair in 1 way and not another. I believe you are hearing a difference, but can you hear the same difference through the speaker as you are hearing with head phones? The speaker might mask or filter what your hearing? Have to try the same test through the speaker you have.

Did you try the test you did with the .047 cap? I wonder if you could still hear it with the smaller value cap? 

That caps value is way to small to affect the PSU's ripple, and the ripples frequency is to low, so it has to be affecting some other component of the sine wave or ridding on the sine wave.

Edit: I mean the total magnitude of the ripple.   

So its been almost a month, and I've been playing the amp pretty much cranked through a reactive load/attenuator, listening either through headphones or a more neighbor-friendly volume through a 2x12 closed back cab (amp is still cranked, but attenuated).  I changed the switch to a On-Off-On, so I could compere either the 0.1uf or the 0.047uf to no cap at all.  I'd play, mess around with the switch, play some more.  Then come back the next day not remembering what position I left the switch in and playing some more (switch is mounted on the side of the chassis...can't easily see it). 

I am just not hearing a whole lot of difference overall especially through the speakers.  It is very subtle at best. 

After doing a little more digging, similar to what Sluckey found about the Bassman reissue that has a 0.047uf cap, I discovered that the JTM45 schematic dated 2001 (reissue?...see attached) has a 0.05 right off the rectifier to ground.  I've come across this before with the Mojotone JTM45 kit schematic, and it is shown on the attached PDF as well as a schematic I found on Marstran website. 

[Willabe]

After doing a little more digging, similar to what Sluckey found about the Bassman reissue that has a 0.047uf cap, I discovered that the JTM45 schematic dated 2001 (reissue?...see attached) has a 0.05 right off the rectifier to ground.  I've come across this before with the Mojotone JTM45 kit schematic, and it is shown on the attached PDF as well as a schematic I found on Marstran website.

Yes, Marshall was doing it years ago, Kevin O'Connor has it in his books from the 90's. But it was for B+ line noise like Sluckey said.

[pdf64]

Didn’t Marshall just copy it off the 5F6A?
My guess is that it was intended to take some stress off the rectifier from the hot switching standby.

[Willabe]

Didn’t Marshall just copy it off the 5F6A?
My guess is that it was intended to take some stress off the rectifier from the hot switching standby.

Fender shows a .05uF cap before the standby.

How is that small a value cap going to take any stress off the standby switch?   

[pdf64]

Fender shows a .05uF cap before the standby.

So does the JTM45, it looks the same to me 

How is that small a value cap going to take any stress off the standby switch?

I was thinking the rectifier rather than the switch. ie the little cap will charge up to the peak unloaded HT winding voltage in standby. Then when switch is closed, the little cap will dump its charge into the main reservoir, so the initial peak rectifier anode current won’t be quite so high.
Ok, it’s tenuous, but it’s my hypothesis and I’m sticking with it 

[Willabe]

I was thinking the rectifier rather than the switch. ie the little cap will charge up to the peak unloaded HT winding voltage in standby. Then when switch is closed, the little cap will dump its charge into the main reservoir, so the initial peak rectifier anode current won’t be quite so high.
Ok, it’s tenuous, but it’s my hypothesis and I’m sticking with it 

Ok, that's your story and your sticking to it. 

Oh, yes the diodes. I read that wrong.