Question for the professionals...

[SolderBoy]

This might be better off in the lounge or something, but...

I've noticed that the guitarist in my band is for ever tweaking the vol on his amp between and during songs.  I'd watch him, and he seems to just touch the top of the (chicken head) knob with two fingers.  I'm thinking - "that can't be doing anything! - the poor guy's got a nervous disorder or something!"...  Anyway, I asked him about it and he said that the vol controls are EXTREMELY sensitive.  I had a chance to mess with them the other day and I'm sure that they must be linear pots in there.  At 2-3 the amp is absolutely CRANKED, making the control essentially useless!  No designer in their right mind would do this on purpose, surely...?!

I'm thinking that the only reason that Fender (the amp is a deville) would do this is for some kinda showroom advantage, where you put the thing on 2 in the guitar shop and get blasted, so you think that its a really powerful amp or something.  Please correct me if there is some other reason they wouldn't be log pots.

So my question is; has anyone around here who has designed something for one of the big guys been asked to do something stupid like that just for some kinda silly showroom advantage?...

Or have I missed the point entirely, and there really is a good reason for the vol controls to be designed like this...

SB

[GibsonGM]

Hi Solder,

Until the 'pros' can answer that, just wanted to say go easy on your guitarist, LOL - poor guy.  I have a  Fender Hot Rod Deluxe..both that and the DeVille have a log volume pot;  a linear one wouldn't 'lose resistance' so fast, and would give the amps much more control.  Tell him there's a pretty straight-forward mod to put in a linear, if it's not under warranty anymore.   You could have a Fender tech guy do fairly cheap and keep the warranty, probably.  I got used to the way it is in about a month, I just leave it on 2.5 or 3, no big deal.  And yes, the consensus is that they did it to make it go loud quick in the showroom ("Hot Rod")...the controls even go to 12, ha ha ha.  Stupid.  But I guess I forgive them, it's a pretty decent amp when driven by an MXR Distortion + on the clean channel (which is a normal taper pot).   

[Mark Hammer]

Thanks for your hesitation about sticking your post here, rather than in the lounge.  Seriously.  This forum is getting cluttered with stuff that either belongs in the lounge or on other forums (e.g., pickup winding, amps, etc.), so your demonstration of at least some concern over proper placement is appreciated.  I hope it's contagious!   As it turns out, your question is really more one of pot taper than about amps in particular, so it has broader relevance to builders than maybe you intended, and especially beginner builders.

Volume controls are the textbook example of where one should use a logarithmic taper pot.  It is in the nature of human hearing (and indeed, the sensory systems of most mammalian species) that perceived intensity/loudness requires bigger and bigger actual changes in intensity/loudness to be detected (see Stevens' Power Law: http://en.wikipedia.org/wiki/Stevens'_power_law ). 

To reproduce this relationship, volume/log pots generally produce larger and larger changes in resistance as you rotate clockwise, instead of the equal changes in resistance produced in "linear" pots.  As it happens, unless you spend large sums of money on pots, the actual taper is often only in the neighourhood of the stated taper.  So, linear taper pots are quite different from log, but frequently not purely linear (i.e., 10 degrees of rotation = same resistance change anywhere on the pot), and conversely log taper pots are distinct from linear but not perfectly logarithmic in their taper.

It CAN happen that manufacturers aiming for the naive entry-level consumer will use linear taper where log should be used and the brunt of the volume changes take place in the first 60 degrees of rotation, leading the buyer to think "WOW!  If it's this loud on 4 it must be deadly on 10".  But this seems to happen less and less.  More likely it is simply the installation of a budget pot whose taper is off-spec, and not quite as logarithmic as it ought to be.  It can also be the case that the pot is either poor quality or simply dirty and twitchy as a result.

The other thing to consider is that gain is multiplicative.  So, if I have three cascaded stages, each with a gain of x10, the end product is an overall gain of 10 x 10 x 10 = 1000.  Changing the gain in any one of those stages can produce substantial overall difference in gain.  If I drop the gain of any of those stages by half (from 10 to 5), I go from x1000 to x500, which is a pretty big difference.  I mention this because, depending on the way in which even the most perfectly logarithmic volume pot is actually used in the design, it may produce non-logarithmic differences in gain and loudness.  Stick the same pot at different points in the amp or structure the gain in a different way, and the volume can go from smooth change to twitchy.

[Gilles C]

I have a Hot Rod Deluxe, and I would suggest you to read that...

http://studentweb.eku.edu/justin_holton/tooloud.html#mastervolume

I have the same problem, so I know how it feels.

Now for the Deville

http://www.diyguitarist.com/GuitarAmps/HRD-MV-Mod.htm

Gilles

[brett]

Wot?  Show(room) ponies?  Never.
Actually, there are many amps out there that promise things at 2 and 3, but don't live up to the promise at 7 and 8.
Did I say "late-model Marshall" anywhere there?

My MusicMan (made during Fender's time in limbo) is the reverse, and it's just as annoying - it delivers nothing tone-wise until a touch of distortion comes in at 6 or 7, and then it warms up.
cheers

[sta63bmx]

My cousin's HRD is the same way.  I think those amps just have way too much gain and get touchy as a result.

[Gilles C]

Still about my HRD, I didn't want to modify my amp, so I began to use this volume box at home a while ago to be able to use it at lower volumes.

http://www.fortunecity.com/marina/newland/2081/id3.htm

I even tried it on stage a few times, but found out that a footswitch controlled volume would be better.

I didn't use it live since a few years, but I always tell myself I should make one of these boxes anyway.

http://www.banzaieffects.com/support/index.php?_m=downloads&_a=viewdownload&downloaditemid=4&nav=0,1

(The volume pot is incorrectly pictured, lug 1 should be the ground, not lug 3)

But I would use 2 pots, one for the normal volume, one for more gain, and would always keep the preamp at the same volume, no matter the size of the place I would play.

I also used my Berhinger MIC200 preamp instead of the amp preamp once with good success.

Gilles

[Paul Marossy]

Yeah, that Hot Rod DeVille master volume is ridicuously touchy with the drive control maxed. By the time the knob is at 2, your ears are bleeding! That's why I had to do something with mine.

[Gilles C]

I just remembered that on one of the sites where I saw the lin2log pot mod explained, it was mentioned that it caused a mismatch between the Normal and Drive channels of the Hot Rod series amp. That's because the Drive/Overdrive channel is calibrated to match the volume of the Normal channel with the linear pot.

When the pot is changed to a log one, the difference between the channels becomes too much.

So that could make me choose a different solution if I had to do it...

Gilles

[QSQCaito]

Mark said it.. maybe it's offtopic.. but our ears are "logarithmic"..

just wanted to add that.. i was told that a week ago

bye bye

dac

[SolderBoy]

So I was right! - they ARE linear...

Thanks for the links, guys!

these turkeys had put a LINEAR taper pot in there where an AUDIO taper pot belonged.

A player walks into the music store, plugs in and turns up to "2." The amp wails like a banshee, and he/she immediately turns the volume down to about "1/2" so as not to be expelled from the store. The player thinks, "wow, if this thing is this loud at 2, it must have just gobs of volume in reserve. If I buy this amp, my drummer will never be able to drown me out again!" Cha-ching, another amp sold.

And it looks like I'm not alone in thinking that the only reason was for a showrom advantage!

How silly.


And thanks Mark, I can see that my 2nd Q would be better off in the lounge...

[Paul Marossy]

And it looks like I'm not alone in thinking that the only reason was for a showrom advantage!

I don't think that was the reasoning behind their design, but one thig for sure is most people seem to be annoyed by this feature of the Hot Rod series amps.

[SolderBoy]

I don't think that was the reasoning behind their design

What do you think the reasoning was for this design choice?

[Paul Marossy]

What do I think? Well, I'm not sure. Whatever their design intent was, it sure is counterintuitve! I really dont think that it's to impress people in a music store, although it seems to have that effect on people.

I remember reading about one guy who thought it was great that those amps go up to 12 instead of 10 like other amps. My first thought was "So? Big deal. I could build an amp that went up to 20. Would that make my amp better?" You could make it 100. It's all how you want to divide up the 270 deg. of pot rotation.

[Paul Perry (Frostwave)]

I remember reading about one guy who thought it was great that those amps go up to 12 instead of 10 like other amps. My first thought was "So? Big deal. I could build an amp that went up to 20. Would that make my amp better?" You could make it 100.

That's the wonderful thing about DIY, the only idiot you have to please, is yourself

[Paul Marossy]

That's the wonderful thing about DIY, the only idiot you have to please, is yourself

LOL! 

[Gilles C]

This thread made me realise a problem I had at some Blues jams where many times I would be too loud, and when the guy organising the Jams  (always the same one) would turn my volume down, I would then be not loud enough after that. It must be because he was adjusting as if it was one of his vintage Fenders.

So, instead of going to 12, maybe that the Volume should be labeled with this progression 0-2-4-6-7-8-9-10

Gilles

[Dai H.]

some people like a faster taper since it apparently allows them to control the nuances in the distortion range more effectively (the range they like takes up a bigger part of the physical rotation), but for others (as wittnessed) it can be annoyingly fast and not allow good control of the volume range. There are different audio tapers available such as 10%, 30%(10% of the resistance up at halfway rotation, 30%...), semi-log also apparently (seem to be uncommon).

[Paul Marossy]

Hmm... I bet a semi-log might work well in this case. 

[Dai H.]

oh yeah, tapering resistors might work to alter the taper to something more useful/pleasing. There is an article on RG's site, and some stuff at Elliot Sound Products (Oz), and some place (vendor?) had some old article on a page.