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Discussion in 'The Workbench' started by 67Mopar, Jun 27, 2019.
I was kidding since these things are nothing but layers and there can be only one outer foil.
With all due respect, I will try to explain this.
And please understand that this is a discussion - we do not intend to make an argument or create a bad feelings for our fellow forum members.
We appreciate every member and their experience and input. So please do not misunderstand what we are trying to explain.
In a low sensitivity audio amplifier the induced AC noise (noise in the audio path) is not considered a big problem.
But as the sensitivity of the amplifier input is increased, the induced AC noise from external sources (such as AC filament wires) becomes much louder. This noise is amplified as it is combined into the audio signal path.
Plexi Amplifier input sensitivity = 10 mv for full output
JCM 800 amplifier 2203/2204 input sensitivity = 5 mv for full output
DSL amplifier input sensitivity = 2 mv for full output
The more sensitive the input, the more this noise is amplified.
Then, as the sensitivity increases the more precautions are taken to reduce the potential final noise.
Yes it does make a large difference in low frequency (hum and buzzing) noise. (not hiss)
And this noise is chiefly the magnetic field of he filament wires or other AC power sources.
The magnetic field of these AC wires crosses the wiring and other components in the circuit, causing AC noise to be induced into the audio path.
Using the capacitor in the proper orientation can reduce this induced noise by 50% sometimes more.
1. The test to find the outside foil of the capacitor is a valid and important test.
[ careful research has shown that the "hiss" is caused by the resistors used in the circuit, and that this is the thermal noise of the resistor which is being amplified]
2. Although capacitors are not marked with "Polarity," there is no polarity actually.
(so please everybody, stop calling this "polarity.")
3. The capacitor is marked with "outside foil." "polarity" is not the proper nomenclature.
4. The outside foil of the capacitor was considered very important during the era of tube amplification, up to about 1964 and sometimes beyond.
5. Shielded coupling capacitors were also manufactured which had a third terminal for a ground connection to the shield.
Maybe I should re-word what I am trying to explain:
We are standing on your shoulders, Mr. Underwood.
You created the art and now we are building onto what you created to push that art forward.
we would never have started in the first place.
Without you there would be nothing for us to build upon. Your work was the basis of our inspirations.
This information about connecting capacitors so that the outer foil acts as a shielding ground is the sort of institutional knowledge that's not found in many electronics textbooks but it's a real characteristic and should not be lost, just as circuit constants and transformer orientation are real factors that may not be easy to find in the same textbooks. I've seen home brewers do such unwise things as orient both the power and output transformers in the same plane, not realizing that they magnetically couple to each other when you do that. Your PT, choke, and OT should all be oriented in different planes to keep them from talking to each other.
I've seen one manufacturer, a big name, one that I won't name but its first letter stands between O and Q in the alphabet, and is six letters long, that would in some cases attach brackets to the transformers by having the steel brackets WELDED to the transformers. Right across the laminations. There is a reason why transformer cores are made of many thin laminations of steel and it's not for ease of assembly. It's to reduce eddy currents and hysteresis and improve performance. Welding across those laminations runs counter to the very reason FOR those laminations.
Needless to say, it would appear that their mechanical design engineers had no transformer design experience whatsoever.
This Exactly. In addition I avoid coplanar layouts when possible. It is always possible.
I suspect that the reason for the laydown transformer arrangement in early Marshalls was specifically to avoid a coplanar layout.
I'm not sure why you'd move away from that if you already had it. But Marshall did that in the early 70s changes.
Taking into consideration communications with one of the founding fathers of Marshall engineering (Mr. Ken Underwood) on this very thread I hesitate to think avoiding coplanar designs between the laydown to standup dual bell PT came into play.
If we leap forward to 1990 and the JCM 900 we see the Laydown come into use again but this time Transformers were laid out on each end of the chassis for the physical reason of balancing weight while being carried.
Just my $.02
Here is a link shared with me by Mark Cameron. For those really wanting to dig in this is a great read. I have gone through it 3 times & will read it a couple more I am certain.
Great for developing understanding IMO.
This is a interesting subject. I tested some .022 for a build years ago with this method and I could not discern a difference with NOS 70s Mustard caps.
NOW the only audible difference in your comparison is when you physically touch the cap with your hand. Both orientations exhibit the same noise level when not touched and amplified in circuit.
I am uncertain orientation has any impact in a amp.
The point is if the capacitor is susceptible to noise, picks it up and is orientated the wrong way then it will pass the noise towards the next gain stage which is unwanted.
Please refer to the quote below stickyfinger
The noise only happened when it was being physically touched not fingers close or near while in circuit.
The question is are capacitors susceptible to noise? Is the "shielded" side really shielding? A piece of plastic is sill separating both sides of the foil in any orientation.
The purpose of the fingers was to inject a decent amount of noise to do the test.
Capacitors are susceptible to noise, no question.
Its technically not shielding but rather the same foil used throughout the capacitor but in some capacitors there is an outer most foil/layer that connects to one side's lead. That outermost foil readily passes any noise to that lead.
Honestly it depends on the capacitor design and makeup but the concept of proper orientation and connection is basically common sense to an electronics engineer/technician type I would think.
It is the same concept as shielding of a signal carrying wire/cable being connected at only one end, the right end, to channel noise towards AC ground.
In order to keep this in perspective there are other actual amp tech’s, builders, modder’s & hobbyists that agree and disagree.
As for me I build my circuits to minimize noise to signal ratio’s. This includes proper cap orientation, grounding scheme and avoiding coplanar layouts in addition to proper lead dress.
So I for one will continue doing what I do the way I do it and respect all other builders as long as safety is practiced.
Another example is wanted or unwanted capacitance. For example a guitarist will get less added capacitance with a 10’ guitar cable than a 20’ guitar cable.
When asked how to make the modded amp sound like it does with a 20’ cable while using a wireless, John Suhr stated the guitarist would need to roll up the 20’ cable and stick it inside the amp lol. Smart man.
Not that Ken Fisher (RIP) wasn’t awesome but he in my opinion did indeed go off the rails claiming that purple shielded wire sounded better. I of course can not go there. I have nearly memorized the Trainwreck Pages.
In high gain amplification .002uf caps certainly need to be oriented correctly. But that is my opinion a contributing factor in the construct of my circuitry. To each their own.
Respectfully, David Hopkins
a.k.a. New Religion
Why would anyone want the sound of a higher capacitance 20' instrument cord?
That is what I would like to know.
Same reason some guys prefer OD pedals or stiff spiky speakers etc...
Cool I’ll bet it aids in their rig that may suffer from other shortfalls to suit their ears.
I have noticed a couple of my favorite players changes speakers over the last 25 years to those with more high frequencies. My observation? I believe they as professionals are suffering serious hearing impairment.
Likely a plethora of reasons to which I could not assume.
Why do some guys prefer certain physical attributes in a mate over others?
I just referenced Merlin Blencowe's Designing Tube Preamps for Guitar book knowing he would mention this as he likes to bring up cork sniffery subjects (page 39). Sure enough the subject only lasted a few sentences simply saying it can be connected to the lower impedance side acting as a shield around the cap. Finishing with its not critical in guitar amps.
I will experiment on my next build, sadly I just finished a turret board and it may be a few months.
Congratulations on your build. Nothing sad about that.
I will never claim to know more than Merlin or anyone else. I know what works for me on my 4 stage all tube high gain builds. Cathode Follower or not.
If it helps a guy great. If it makes no difference to them great. I am not affected either way.
Certainly is something worth being aware of.
Another example with high gain amps. I do not care for DC heaters as IMO it may reduce noise but only if the grounding scheme sucks to start with. It is a great way to aid with the issue in mass production. But my collected and self built AC heater amps pound the DC heater amps I have.
Try it sometime. Just lift the DC filaments and tap into the AC off of the PI or Power Tube. Boom. Every little tweak makes the amp in its entirety.
Okay. Enough debating for me. I just wanted to pitch in my $.02 for what it is worth. Speaking of worth. One of my mentors, Mark Cameron disagree’s with me about foil orientation but he has his own ears as I have mine. I would think Mark has more to offer in the high gain experience than any of the great masters of the Clean guitar amp development etc...
I have heard amps built by some electrical & electronic engineers with less than stellar results IMO. In this area of electronics what looks great on paper may lack total character and harmonics.
Again. I don’t care as I know what works for me.
No it is not critical to most. The amplifier will still work. The option is a practice if known to the technician.
It is like using a crescent wrench. You will see a crescent wrench in most layman's hands when doing mechanic work. You will never see a crescent wrench in a seasoned professional mechanic's hand.
A crescent wrench is more of a plumber's tool.
I have mentioned this before. Film capacitor orientation is not a topic of general discussion in advanced learning centers. No you will not find it in text books.
But you may and can find it in capacitor manufactures descriptions and notes. I have never seen mention of any of this in specification data sheets.
This characteristic is associated with certain film capacitors that have an outer foil layer. All film capacitors are NOT manufactured the same.
"All film capacitors are manufactured the same...."
No they are not.
Some high end caps are manufactured to reject external magnetic noise, no matter which direction they are installed.
No matter which direction, the noise is equally low.
Test it you will see.
"No it is not critical to most. "
In high gain circuits (which are actually high sensitivity circuits), it can be extremely critical.
"High gain" is a term which is often misused and confused with high sensitivity.