Two Rock Custom Sig

[Robert]

I found this link on Gear page tonight. http://www.online-discussion.com/Tonequ ... .php?t=130 An interesting read. The TR guys (~2/3 of the way down) talk about component selection as being the critical aspect of building an outstanding amp. Surprisingly they allowed a couple pics of their Custom Sig chassis. I have seen in their amps, and Dumbles (I think) caps with the polarity marked. I have been wondering about this and would finally like to ask someone more knowledgeable than I to comment. How does one determine a caps polarity, and which direction would you ideally want to install it in? I thought initially caps had to be formed to acquire a polarity? Anyway an interesting article everyone should enjoy!

[Darkbluemurder]

Electrolytic caps are polarized by design, i.e. they have a positive and a negative pole. Observing the polarity with these is critical. Put 'em in wrong and the amp doesn't work or in the worst case blow up.

Coupling caps (= caps coming off a tube plate - pin 1 or pin 6 of a 9 pin tube) are not polarized in the same way, i.e. they will work either way. Yet they have a polarity. Gerald Weber discusses this in his third book in detail. Wrap a tin or aluminum foil around the cap and measure with a digital cap meter the capacitance between either wire and the foil. One wire will give a higher reading. This is the outermost wire, and this - pursuant to Mr. Weber - should be connected to the grid of the next tube or volume/gain whatever control. The other wire should be connected to the preceding tube's plate. The idea behind this is that the higher capacitance on the grid wire shall prevent oscillations.

My personal measurements never showed more than 1 pf difference. Therefore I do not believe that it makes an audible difference whether you put the cap this way or that way. If it is audible then it certainly won't make or break an amp.

Cheers Stephan

[dogears]

The reason is not due to capacitance, it is explained here by Aiken....

http://aikenamps.com/OutsideFoil.htm


"While it it true that polarity on a non-electrolytic capacitor doesn't matter, signal-wise, the outer foil is marked because it can be used as a shield against electric field coupling into the capacitor. In order to take advantage of the shielding properties of the outside foil, the capacitor must be connected in the circuit in a particular orientation. "

You determine which leg is the shield by using a scope. I have been doing this for a couple of years. Gary Johnson has been doing this as well in all of his builds, predating the Tonequest article. It is good practice IMO.

[Darkbluemurder]

That is very interesting indeed as it is exactly the opposite of what is in the Weber book. I'll check the orientation of my caps but if they aren't marked I won't bother since I don't have a scope.

[pamaz67]

Coming myself from several years of diy in hi end tubes and solid state experience, where sometimes attention to details is more similar to magic than to objective facts, i'm a little bit surprised that a big importance is given to these aspects ( cap polarity in foil caps) , while in the meantime other aspects are completely left out of any attention.
Think as an example at the connectors we use in our guitar amps. At their best the quality of the contacts they can assure is crappy, also if you use the best brands and manufacture models. It's the basic design that is poor.
Have you ever tried to substitute all the jacks of your amps with a soldered connection? ( i know it' not a practical thing for sure...)
If you have not experienced this, give it a try, especially at higher listening volumes. You'll be amazed.
All of this just to say that there is a lot of room for immediate improvement in our guitar amps, and most of the times it's something you can do for free (or on the cheap).....

Bye

Paolo

[Bob-I]

Think as an example at the connectors we use in our guitar amps. At their best the quality of the contacts they can assure is crappy, also if you use the best brands and manufacture models. It's the basic design that is poor.

Interesting. I've found some dramatic tone loss with poor cables so it makes since that the jack would be as critical.

Another point is that some folks will tack solder components to test different values. This can give false results as a poor solder joint can add quite a bit of resistance. I've taken to soldering an aligator clip on the turrett and clipping in different caps/resistors to test. Seems to give a nice connection.

[glasman]

That is very interesting indeed as it is exactly the opposite of what is in the Weber book. I'll check the orientation of my caps but if they aren't marked I won't bother since I don't have a scope.

I would tend to go with Aikens analogy, a low impedance on the outside is less likely to pick up noise. I always connect the outside foil to the low impedance side of the circuit. ie plates.

Gary

FWIW, I always found the Weber column in Vintage Guitar entertaining reading.

[BobW]

Someone mentioned a while back, maybe on the old Ampage site, that Gerald Weber has about a 40% baloney factor, as does Dan Torres. I couldn't agree more. Aiken is correct stating the outside foil is for shielding purposes. I have tried Weber's and Aikens methods to determine the outside foil. Gerald's is more difficult to determine, but Randy's scope method is a lot easier to determine especially with the flourescent lights in my shop.

[Robert]

Thanks for the great answers and the Aiken article. I always forget to recheck his site and then someone goes and points out another one of his excellent articles on a fundamental aspect of amplifiers I failed to realize the significance of the first time I read it. I'm surprised no one has commented on the Custom Sig yet and the other voodoo factors they refer to. I thought that would be most entertaining.

[glasman]

40% baloney factor.....

This is going in my quotable quotes....

[skyboltone]

I've taken to soldering an aligator clip on the turrett and clipping in different caps/resistors to test. Seems to give a nice connection.

Good tip. Thanks
Dan