what do you guys think of this?? (guitar player article)

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swt
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what do you guys think of this?? (guitar player article)

Post by swt »

http://www.guitarplayer.com/miscellaneo ... cXKSG.dpuf

i know it's a conjuctive filter, but looks wrong whatever you wanna read about it...at least according to the formula i know...and waht about those 1watt 8.2meg resistors??
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romberg
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Re: what do you guys think of this?? (guitar player article)

Post by romberg »

The 8M resistors just balance voltages across the caps. You need to stack two caps to not go over their max voltage ratings.

You'd hope that if they sell this as a kit they would also sell you some sane way to mount these parts. Those pictures look scary.
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M Fowler
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Re: what do you guys think of this?? (guitar player article)

Post by M Fowler »

Those are sold as a kit and they do not have special mounting just stick straight up. I have never used this product, just saw them for sale.

Mark
R.G.
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Re: what do you guys think of this?? (guitar player article)

Post by R.G. »

It is unfortunate that the article is under/mis-informed about transformer saturation. While a primary-side snubber may be desirable, and may protect the OT from some failure modes, OT saturation does not happen the way the article alludes to, nor does it necessarily have the effect the article says.

Magnetic cores saturate from having too much magnetic field intensity in the core. the core literally is filled as much as it can be with magnetic field, and quits acting like a ferromagnetic material, beginning instead to act like non-magnetic materials.

Field intensity is a result of the magneto-motive force, which can be measured as the ampere-turns of current through the windings. However, it's only the UNBALANCED ampere turns that cause field in the core. Letting current "escape" through transformer action sucks some of the ampere turns away. Since the core is an inductor, current can only increase according to the inductor equation, V = L*di/dt. Rearranging that a little, di (that is, the change in current in some time interval) is equal to V*dt/L, or the voltage times the change in time. For non-DC signals, what matters is the sum of the voltage-time applied to the primary.

If you have a given voltage*time sum, for shorter times, you can withstand proportionately more voltage. So if you halve the time the voltage is applied, you can apply double the voltage before saturation happens.

>>That means that the core saturates most easily at lower frequencies. <<

This is why switching power supplies can be so much tinier than AC mains frequency supplies: the switching frequency is so much higher that the ferromagnetic core can be proportionately smaller.

Saturation of an OT with signal happens first at the lowest signal frequencies. Double the frequency, double the signal voltage needed to saturate. As a practical matter, you can't saturate an OT with any signal the rest of a guitar amp can produce at anything except the most bass of bass frequencies. The circuits saturate first, and the signal quits getting bigger.

This is a fairly subtle point of magnetics that only transformer designers really understand. The stuff on the internet about an amp's sound coming from saturating the OT core is bulls... er, I mean, misinformed. Yeah, that's it. Misinformed. :D
swt
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Re: what do you guys think of this?? (guitar player article)

Post by swt »

i remember asking you R.G, 8 or 10 years ago about saturation, and gave me some nice explanation. That's why i brought this after reading it. And the conjuctive filter formula states that the resistor should be something like 1.3 times the impedance of the primary. So an 8k primary for 2xel84s will get a 10k resistor. I remember asking this at old amp forums, and the guy from Drz amps pointed me to the right formulas and way of implementing it. I've used it succesfully in a lot of old amps built in my country with sloppy ots, and it did improve the sound. It was a long time ago, so i don't remember now the values and formulas...but can check if i got them in some hdd.
Still...the saturation part is also messed...which can be acceptable from an unreliable internet source, but not from a respectable magazine...i think
R.G.
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Re: what do you guys think of this?? (guitar player article)

Post by R.G. »

It's not that conjunctive filters or snubbers can't make a decent sound, they can. It's just that it's not saturation that does the work.

These things work by being an added resistive load on the primary side of the transformer above the frequency where the capacitive reactance is less than the resistor's resistance, and by adding a capacitive reactance to the unavoidable leakage inductance that is hiding just inside the transformer's primary leads, where you can never get at it. You can get extra phase margin on an amplifier that's otherwise unstable or only marginally stable, or reduce ringing on transients, etc., so they're in general good things, if properly applied. That "properly applied" is a highly technical term, though.

For amps not near oscillation or ringing, the filter/snubbers work by wiping off some treble response. This can be a good thing, and as long as it doesn't offend you by making the sound too dull, that's pleasant too.

So this >may< be a decent thing to do, but the basis as explained is flawed. The thing about a respectable magazine is that they're journalists and guitar players, not engineers, so the magazine probably has no way to know about the subtler points of their articles.
Firestorm
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Re: what do you guys think of this?? (guitar player article)

Post by Firestorm »

This is the problem I've always had with Mr. Keen: I know that he knows what he is talking about, but I have no idea what he's talking about. Love you RG. 8)
R.G.
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Re: what do you guys think of this?? (guitar player article)

Post by R.G. »

I learned everything I know by studying the turbo encabulator. For students of technology of all kinds, it's worth while to watch the several youtube versions of the turbo encabulator video. It really puts things in perspective.

https://www.youtube.com/watch?v=rLDgQg6bq7o
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pompeiisneaks
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Re: what do you guys think of this?? (guitar player article)

Post by pompeiisneaks »

Magneto reluctance!!! :) lol I've seen that one a long time ago but forgot how funny it is!

~Phil
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swt
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Re: what do you guys think of this?? (guitar player article)

Post by swt »

:shock: :D :lol: :lol:
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