To choke or not to choke

[duke of earl]

I've been studying power supplies and working on a Fenderish (2)6l6 build. I know that chokes have been used in Fender circuits to smooth out current ripple since filter caps smooth out voltage ripple. I was wondering how critical the choke is and how many Henrys will yield good performance for this particular amp.

[jojokeo]

I generally use them more often than not. As for Henries too much can "choke" your tone & feel. The rule of thumb is the more the better but over 10H isn't necessary. Fender's actually use less at only 3 to 4 henries but up to about 9 or 10 is fine if you're buying Hammond types for example (rather than Fender types). Most often they are used after the resevoir cap & plates so only the screens, pi, & preamp tubes are getting the benefits (and only what's needed). This saves $$$ since it can be smaller in the 40 to 50 mA range for el84 & 6v6 amps for example.
As for sound...when I installed a choke and the standard resistor on a switch for real time testing between filter nodes, I noticed only slight and subtle differences w/ a SE amp at the time. But the distortion seemed smoother and more refined & is what sticks out in my head of the experience. I can't remember any noticeable noise floor change, stiffening of the power supply, or anything else from doing it. But it could & likely should help these in higher powered amps where the differences may be greater and more easily heard or felt.

[tubeswell]

Chokes make more difference in SE amps than they do in PP amps in terms of ripple cancellation/smoothing when used in CLC filters as 'whole-of-supply' filters.  In PP amps, any residual ripple riding on the signal tends to get cancelled out in the opposing sides of the OT primary anyhow (whereas SE OTs don't have that feature, so you otherwise get to hear the ripple). Bear in mind that you need a choke rated above the maximum DC current draw of the amp if use in a 'whole-of-supply' filter.

But chokes do have their uses in CLC filters in PP amps between the plate and screen supply nodes, not only because they achieve excellent ripple cancellation, but because they do it without hardly any drop in voltage, so you can have your screens idling at, or even slightly (i.e.: 1-2V) above, plate voltages for maximum gain.

You can also use chokes as 'whole of supply' filters in LC filters as well - but why bother? You don't get nearly as much B+ that way (and its arguably an extravagant waste of money to use one just for the purpose of losing B+ voltage when there are other cheaper ways of lowering B+ voltage) and its more of a hassle setting the circuit up to ensure that the choke in an LC filter gets a continuous current supply during operation. JM2CW

[Fresh_Start]

I used a 5 Henrie choke from Hammond in a 5F2-A build (single-ended), and it was much quieter than just a C-R-C filter before the plate node of the power rail.  No loss of tone or feel in that application.

However, a C-L-C filter for the entire power amp is darned expensive even for a 6V6 push-pull amp because of the current rating needed.  It is surprising how much ripple rejection you can get out of an extra C-R-C filter in front of the plate node of a push-pull amp, but it doesn't noticeably reduce noise in my limited experiments.  Adding a choke between the plate & screen grid nodes of the power rail does reduce noise levels.

IMHO it's worth playing around with Duncan's PSU model to get a feel for the impact of C-L-C vs. C-R-C filters, relative values of resistors and filter caps, etc.

Cheers,

Chip

[bluesbear]

I always use them except for low power single ended amps. The other guitar player and amp builder in my band never does. Both our amps sound great. Of course, he always uses SS rectifiers. and, except for bass amps and single ended amps, I always use a tube. My point is, don't get too hung up on "rules". I can't really see that my amps sound any better than his. Different, maybe, but that's just a matter of preference. I'll guarantee you couldn't listen in a blind test and tell which of ours is made one way and which the other.
"It's an art, not a science."
Dave

[jojokeo]

IMHO it's worth playing around with Duncan's PSU model to get a feel for the impact of C-L-C vs. C-R-C filters, relative values of resistors and filter caps, etc.

I've just been trying to get a feel of the .psu program over the last month or so and w/ a new build underway. But, I'm having some issues w/ interpreting the results in the same way one has to learn how to interpret the results when first using an oscilloscope. Any ideas or places you can point me to as I don't know anyone near me that I can speak with and go over this stuff in person. Thanks Chip (tinman). 

[jjasilli]

I'm a choke fan, but I like vintage tone.  I think they slow an amp down and open up the tone.  But a tighter, faster amp is better for heavy metal and shredding.   So I think it depends on the application.  There's some info, I think in the champ or 6v6 amp info section, at www.angela.com and at the advanced tech page at http://www.aikenamps.com/

[38Super]

I'm a choke fan, but I like vintage tone. I think they slow an amp down and open up the tone

Can you explain this?  I don't understand how PS ripple filtering affects the speed of an amp.


cheers,

rob

[Dave]

It adds just a little weight to the overall load the casters have to bear. More weight, more strain on the ball bearings and more drag. All that works to "slow the amp down".
I mean, come on man, that's amp physics 101.

Dave

[jjasilli]

I'm a choke fan, but I like vintage tone. I think they slow an amp down and open up the tone

Can you explain this?  I don't understand how PS ripple filtering affects the speed of an amp. cheers, rob

Chokes can give an additional spongey feel to the amp, and a subtle change in tone.  This will be most evident at high signal levels.  The screens draw more current through the choke causing a voltage drop (sag).  Unlike a resistor, the induction of the choke is dynamic and works by the build-up of a magnetic field.  I.e., the energy required to create the magnetic field gets "robbed" from the amp, which is a good thing if you like chokes.  It takes time for the magnetic field to build-up; and then it persists and lasts a bit longer than it “should”.  The result is sag with delay, which forms behind in time from the note being picked on the guitar.  This adds soul to a long-held bluesey note, but can be annoying if you’re playing 16th notes.

“Responsiveness” of an amp means very different things to a blues player than to a shredder.  Analogy to cars: vintage carburetor vs. ultra-modern, fuel injected, multi-valve engine.

[duke of earl]

Thanks guys! I believe I will choke 

[jeff]

Is putting a choke/resistor switch a bad idea? I seem to remember something about how coils can store voltage and something bad about discharge. Maybe that had something to do with relays. Not exactally sure. Anyone?

[jojokeo]

Neither a choke or a resistor can store a charge, only a capacitor does that.

[duke of earl]

Right! Chokes only resist a change in current which smoothes out the ripple in the current.