tone vs. inductance

[pine]

What happens to the tone, both clean and OD in D style amps as the inductance of the choke increases? What sort of change in the feel of the amp?

[Tonegeek]

What happens to the tone, both clean and OD in D style amps as the inductance of the choke increases? What sort of change in the feel of the amp?

Good question. I only have experience with comparing using a high wattage resistor against using a choke. The choke makes the power supply stiffer (more filtered) so the sound is sligtly less compressed. Also ripple will be less with a choke. Personally I like no choke as the resistor simulates using a tube rectifier in that is sags somewhat on demand. I would think there is a range of choke values that would work, limited only by the voltage requirments of downstream circuits.

[roberto]

yes, there's a best range in which chokes sounds usually better to my taste.
Resistor has a different feel: muddier bass, less articulated mids, highs a bit suffocated. This is more evident when you raise with volume.

A right value choke (it depends, but with 100W I usually use 100/220uF - 5H 200ohm choke - 50/100uF) you have a more constant sound on every volume, more midrange focus, punch on low-mids, and transparent highs.

Choke with high values can be used with less supply cap filter, but they becomes huge and heavy.

It's interesting to put different resistors in series with a standard choke, so you have both worlds together and you can mix.

[butwhatif]

At hi volume w/o a choke, there is usually a superimposed frequency along with whatever is being played, most likely due to the resultant intermodulation distortion with the increased sawtooth ripple that comes thru the power supply.

[pine]

So you are saying that a low inductance choke will get rid of less of the sawtooth ripple than the higher inductance choke? That certainly makes sense, but what I am after is more along the lines of a tonal difference between the two, is a 10H choke darker sounding or less open sounding than a 5H choke? What are you losing besides the power supply ripple when you filter it more and more with the use of different chokes?

[talbany]

As for the inductance value, this depends on how much filtering you want. The inductance, in conjunction with the filter capacitance, forms a lowpass filter. The larger the inductor, the lower the cutoff frequency of the filter, and the better the rejection of the 120Hz (if full wave rectified) or 60Hz (if half wave rectified) AC component of the rectified DC. In general, the larger the better, within reason (larger inductance's at low DC resistances mean larger chokes, which cost more money). Typically, 5-20 Henries is a good choice with the standard 32-50uF electrolytic capacitors. The inductance and capacitance values also determine the transient response of the supply, which means the tendency for the supply to overshoot or "ring"(Ghost noteing) with damped oscillations whenever a current transient is applied (such as at startup or on a heavy current surge, such as a hard "E" chord at full power!).
Your not going to really notice any differance in tone and feel between a 5H-10-H choke with a 50 watt amp set on 5...Now a 100 watt cranked pretty good maybe a slight difference in pick attack and a smoother lowend responce... Clean or overdrive take your pick... Not much in the way of Feel or Tone mojo going on with chokes clean or OD..IMHO

I highly suggest going to Duncan Munro's website (http://www.duncanamps.com/) to download his power supply calculator program.


Tony VVT

[butwhatif]

So you are saying that a low inductance choke will get rid of less of the sawtooth ripple than the higher inductance choke? That certainly makes sense, but what I am after is more along the lines of a tonal difference between the two, is a 10H choke darker sounding or less open sounding than a 5H choke? What are you losing besides the power supply ripple when you filter it more and more with the use of different chokes?

As u know, a choke -because of it's inductance,tries to get rid of some of the quantity of a-c in the B+ supply, while leaving the dc to pass w/o much hindrance. I couldn't weigh in on the differences in added noise relative from no choke to two choke values, it's not that easy, but if u ever played an amp w/ old filter caps, and experienced the ghost tone that comes along with what u play at higher volume, then u might get the idea. Some actually like to replace the choke with a resistor, to get sag, but it's a balancing act. An amp with too much saggy dynamics is not fun to play live imo. I want to supply the dynamics, and there are better places to modify tone than the choke.
A choke with a small core also can easily saturate on peaks, if you like less headroom before added noise, use that. I equate 'open' sounding with clean headroom, especially in the bottom end, free of buzz, hum, and wierd IMD, and that's what you can get from a B+ free of a-c. If the low end of an amp's sound is mitigated by the intrusion of other created artifacts, it seems to lose it's openness--

[pine]

I finally bit the bullet and tried an experiment myself. I have an ODS style amp that has been tweaked to perfection by our own Heisthl, so I was understandably reluctant to even touch it, but my curiosity got the better of me and I put a choke in (temporarily) with a higher value of inductance, leaving everything else except for bias exactly the same. The resistance of the two chokes was pretty close as well, so I don't think it was a factor. The result was a similar, although not as rich, tone, maybe a smidge tighter on the low end. but the most glaring difference was a lot more hash riding on the notes in both clean and OD channels. I don't pretend to understand why, but I thought I'd report my findings and see if anyone could use them to help cure the "hash" problem.

[butwhatif]

I'm still trying to figure out what 'hash' is-- send me/post a clip of it---

[pine]

I'm still trying to figure out what 'hash' is-- send me/post a clip of it---

I don't have the equipment for recording clips, and I'm too embarrassed to post one in front of the calibre of players that frequent this forum, but it sounds like static riding on top of the note, a too-harsh crunch sound, or someone hawking before they spit (pleasant, huh?) In any case, I have already switched the choke back out and the amp is back to it's non-fizzy configuration

[butwhatif]

Somethings definitely wrong there---some parasitics, or interaction, something's not right, -if you have a scope u should be able to see what it is and track it down, if not, it would be difficult

[pine]

There's the rub, I have no scope. I am not experiencing any problems now because I have the original choke in there, I only tried the other hash-producing choke for an experiment, but it would be nice to know if the inductance change was what caused the distortion

[butwhatif]

so how do you know that it's not still there in some way, my guess it is --find a friend who might look at it

[Structo]

Yeah, I've used the hash word as a descriptor before.

To me it is a kind of harsh hiss, or lower frequency hiss that rides the note until it decays.

Seems kind of weird that the choke would add that.

How did you have the choke situated on the chassis?
Unless it was oriented for the lowest noise and bolted down with the frame grounded to the chassis, it probably wasn't a very valid test.

Your amp sound like it has the same issue as mine.
Although I have given up for now.

I don't think anybody could hear it in a band setting.

Unless it goes into cutoff when cranked...........

[talbany]

The only thing that comes to mind right off is a voltage issue there.. Resistors will drop more voltage than a choke will.. Generally around 10-15 volts....300-500 ohm's.... Did you check your voltages after you installed the choke?...


Tony VVT