Why's it called a "coupling" cap?

TelZilla · August 16th, 2007, 12:17 PM

Just because it's between two tubes (sometimes with some pots or other components inbetween)?

Also, anybody know a good on line glossary for all the various tube amp terms (filter cap, coupling cap, center tap, cathode, etc. and so on)?

sjhusting · August 16th, 2007, 01:09 PM

http://www.aikenamps.com/AmpTerms.html

"Coupling capacitors - capacitors which are used between stages in a guitar amplifier. They block the DC plate voltage of the previous stage, while passing the AC guitar signal on through."

They "couple" two amplifier stages together. Also called "blocking" caps because they "block" DC voltage.

steven

TelZilla · August 16th, 2007, 01:43 PM

Quote:

Originally Posted by sjhusting

http://www.aikenamps.com/AmpTerms.html

Thanks for the link. I knew I'd seen this before but couldn't remember where.

Here's my favorite definition:

Modeling amp - a computer that is passed off as a guitar amplifier. See "solid-state".

sjhusting · August 16th, 2007, 01:59 PM

I like 'solid state'

Solid-state - a component that has been specifically designed to make a guitar amplifier sound bad. Compared to tubes, these devices can have a very long lifespan, which guarantees that your amplifier will retain it's thin, lifeless, and buzzy sound for a long time to come.

11 Gauge · August 16th, 2007, 03:24 PM

Actually, there is a variation on the coupling cap design, that allows for "signal coring," which (if done right) is supposed to result in a superior interstage signal versus traditional coupling cap (allows for more DC driving of the stages).

The problem with 'coring' is that you can end up with too big of a 'core' in the middle of the waveform. When this happens, you end up with crossover distortion (this is what occurs when the power section is biased way too cold).

While I love really old amp designs, the coupling cap value choices often leave a lot to be desired. 99% of the time it's one of 3 values: .022, .047, or .1 uF. Oftentimes, if you take the time to really tweak the interstage couplers either up or down, you can end up with a much more lively amp. Just changing 1 or 2 caps can be really dramatic. I've personally had this happen with a .01 or .0047 in just the right spot.

Another problem with coupling caps - leakage. When they leak, they no longer block the DC 100%. The tonal results can be horrible, and I hate tracking down the culprit(s). As a matter of typical maintenance, the couplers are not changed out, like electrolytics are. Therefore, it's easy to dismiss them altogether, and typically blame symptoms on other parts of the circuit, that occaisionally the couplers are responsible for.

Tremo · August 16th, 2007, 09:32 PM

Because it "couples" the signal from one stage to the next, while blocking the DC.

August 16th, 2007, 12:17 PM	#1 (permalink)
TelZilla Tele-Afflicted Join Date: Jan 2007 Location: Cleveburg, USA Age: 38 Posts: 1,842 6 Photos	Why's it called a "coupling" cap? Just because it's between two tubes (sometimes with some pots or other components inbetween)? Also, anybody know a good on line glossary for all the various tube amp terms (filter cap, coupling cap, center tap, cathode, etc. and so on)? __________________ Thanks,Nick Nec Aspera Terrent

August 16th, 2007, 03:24 PM	#5 (permalink)
11 Gauge Friend of Leo's Join Date: Mar 2003 Location: The East Coast Posts: 2,898 10 Photos	Actually, there is a variation on the coupling cap design, that allows for "signal coring," which (if done right) is supposed to result in a superior interstage signal versus traditional coupling cap (allows for more DC driving of the stages). The problem with 'coring' is that you can end up with too big of a 'core' in the middle of the waveform. When this happens, you end up with crossover distortion (this is what occurs when the power section is biased way too cold). While I love really old amp designs, the coupling cap value choices often leave a lot to be desired. 99% of the time it's one of 3 values: .022, .047, or .1 uF. Oftentimes, if you take the time to really tweak the interstage couplers either up or down, you can end up with a much more lively amp. Just changing 1 or 2 caps can be really dramatic. I've personally had this happen with a .01 or .0047 in just the right spot. Another problem with coupling caps - leakage. When they leak, they no longer block the DC 100%. The tonal results can be horrible, and I hate tracking down the culprit(s). As a matter of typical maintenance, the couplers are not changed out, like electrolytics are. Therefore, it's easy to dismiss them altogether, and typically blame symptoms on other parts of the circuit, that occaisionally the couplers are responsible for. __________________

August 16th, 2007, 09:32 PM	#6 (permalink)
Tremo Friend of Leo's Join Date: Mar 2003 Location: Silicon Valley, CA, USA Posts: 3,684	Because it "couples" the signal from one stage to the next, while blocking the DC. __________________ Exposing the CONs. www.myspace.com/59tremolux

August 16th, 2007, 01:09 PM	#2 (permalink)
sjhusting Tele-Holic Join Date: Jul 2003 Location: Germany Posts: 621 14 Photos	http://www.aikenamps.com/AmpTerms.html "Coupling capacitors - capacitors which are used between stages in a guitar amplifier. They block the DC plate voltage of the previous stage, while passing the AC guitar signal on through." They "couple" two amplifier stages together. Also called "blocking" caps because they "block" DC voltage. steven

August 16th, 2007, 01:59 PM	#4 (permalink)
sjhusting Tele-Holic Join Date: Jul 2003 Location: Germany Posts: 621 14 Photos	I like 'solid state' Solid-state - a component that has been specifically designed to make a guitar amplifier sound bad. Compared to tubes, these devices can have a very long lifespan, which guarantees that your amplifier will retain it's thin, lifeless, and buzzy sound for a long time to come.