yes.... I Know....I'm starting a #183 build!

[Reeltarded]

you two get a room...

Or a Lab!

These are the things I would like to see harmonically modeled.

Pass the popcorn I am done too. Agree Good discussion!

Tony

I didn't say a motel room!

My experiments with thru-hole tube boards and using elevations to break planes like a uranium storage facility tell me there is a lot more to be understood about the choices we make in the even the simplest of circuits.

[norburybrook]

One thing I noticed is the PAB doesn't seem to be actually boosting much, more like a bass cut if anything. Could I have wired it wrong or is this how the #183 PAB is?

183's PAB is like the others, so I'd say you have a wiring error. Check the resistance from the top of the bass pot to its wiper, and the bottom of the treble pot to the top of the bass pot, with and without PAB engaged (Rock mode).

Ok PAB off I get 156k from top of bass pot to wiper. and 450k from treble to bass pot

PAB on 156k bas pot to wiper and 730k treble to bass.

all wiring checks out fine.

M

[erwin_ve]

The 22m resistors: are they measured 22m?

[martin manning]

I think both of those resistances should be zero in normal mode, and some bigger number in PAB.

[norburybrook]

I think both of those resistances should be zero in normal mode, and some bigger number in PAB.

let's make sure we're on the same page then. Top of pot is the first pin on the right as I'm looking at the back? bottom the third pin?


M

[martin manning]

Yes, looking from the back, lugs up, top is right, bottom is left. Refer also to this schematic:

[norburybrook]

resistors are def 22M I've just lifted a leg and checked.

soldering it back in place seems to have done the trick. It's now working, actually it sounds great, it's a nice boost and doesn't seem to be thin like my #102 PAB result. it was tricky soldering the resistors as the PCB holes for the relays would only take one wire, so I had to get creative!

right waiting for the post man with my pots...




M

[Max]

...allot of myths and opinions floating around amp building communities with regard to harmonic content?

Just to avoid misunderstandings "... because some sources give the reader the impression that, once one knows the proportions of the different frequency components, one knows the timbre.* ":

When tweaking the design of a guitar amp in order to move the perception of its timbre by a player/listener into a specific direction (less sharp, less boomy etc.) IMO it's important to remember, that the harmonic content of a perceived sound isnt't the only factor influencing the perception of timbre. So when tweaking the design of a guitar amp with some specific perception of timbre in mind IMO the designer will have to take care of all the design specs affecting envelope and starting (and sometimes finishing) transients, too.

Here's a sound file with "A demonstration of the importance of envelope to timbre": http://www.animations.physics.unsw.edu. ... velope.htm

(" *Note, however, that the spectrum of the entire sound sample (including both amplitude and phase) does contain all the time information and so does contain the envelope, just as the time recording V(t) contains all frequency information.")

Cheers,

Max

[norburybrook]

thanks Max.

It's a complex issue for sure and that's what makes it interesting as it's not black and white. I'm sure people who do amplifier/circuit modelling use these calculations when trying to accurately model a complete circuit. Also as we all know most of what we like about a certain persons tone comes from their hands and that's the infinite variable that cannot be ignored. When Larry Carlton used my amp/cab it sounded lust like classic Carlton/Dumble, I didn't sound anything like that when I played the exact amp/cab with the same settings.


For an amp maker/designer knowing the technical aspects of what affects the tone and how is really important if you're making amps for specific people, so like HAD did he could subtly tweak things to suit the person buying the particular amp and I think this was a big part of why great players came to him at the time. This isn't most large non boutique amp manufacturers however as it's time consuming and therefore expensive.

_____________________________________________________________________________

Yesterday, after messing with the PAB, I realised I'd been playing with the amp in Jazz mode (the amp was facing away from me so I couldn't see the front) and the PAB was a really nice full boost, hence my post. Back in Rock mode the PAB was a lot less in boost but still OK. I don't use Jazz mode very often so have never compared the PAB in both modes. Is this normal behaviour? I must say, I was enjoying using the amp in Jazz modes, the OD and PAB were very nice and the lack of gain really worked for me.

will be interesting when I eventually get these 250k pots in to see how that changes things. apparently they'll be here today or tomorrow so I'll be able to report back by the end of the week at least


Marcus

[martin manning]

Marcus you are going from 300k to 250k on the drive and level? The difference there will of course be much less than the 250k to 100k example I showed above. I don't think you will perceive any great difference in harmonic content (or timbre, which is a much better word than "gainyness"), but we will see. At least you will have the actuation torque that you prefer.

[norburybrook]

Marcus you are going from 300k to 250k on the drive and level? The difference there will of course be much less than the 250k to 100k example I showed above. I don't think you will perceive any great difference in harmonic content (or timbre, which is a much better word than "gainyness"), but we will see. At least you will have the actuation torque that you prefer.

Actuation torque I Like that phrase


I think I measured my pots and they were about 325k, both above the 300k anyway. If the drive especially is the voltage divider with the OD resistor then wont the difference of 50-60k make a difference in gain? I Know when I messed around with the voltage divider on one of the gain stages in the wonderland build I did, it made quite a big difference. I can't remember what the magnitude of resistance differences was however ;D


M

[martin manning]

Max available gain (as in voltage gain) will be a bit lower, since with the pot all the way up the lower leg of the voltage divider formed by the series resistor and the pot is smaller. Vout/Vin = Rlower/Rtotal, so now with 100k series resistor you have 300/400 = 0.75, and after you will have 250/350 = 0.714.

[talbany]

Marcus you are going from 300k to 250k on the drive and level? The difference there will of course be much less than the 250k to 100k example I showed above. I don't think you will perceive any great difference in harmonic content (or timbre, which is a much better word than "gainyness"), but we will see. At least you will have the actuation torque that you prefer.

I agree!
50-60K will not be that noticeable. (Especially with respect to gain) I thought he was going down to 100K


Tony

[norburybrook]

Ah, yes I can see it's hardly worth bothering with. If I drop down to 100k then yes, there would be more of a difference but then I'm heading back into #102 territory , where I'm already covered.

thanks guy's , sorry for the misunderstanding on this


i'm going to crack on with the cabinet. it's cold here but it's dry so I'm going to 'make hay while the sun shines' as we say here.

m

[norburybrook]

Ok time for the big reveal

Spent the last two days making a cabinet. Went with the original #183 colouring

need to keep playing to get a good feel for what it does.

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Marcus