A hello and a question.

[Kobaia]

Hello all,

I live in Edinburgh, Scotland and I'm 24. I've played guitar since I was ~13 or so. I've always had SS amps of various types. At the moment I have a vintage HH VS Musician 212 combo at my parents' house which I've done some work on.

When looking for a smaller amp, I chanced upon a Vox Pathfinder 15R in a pawnbrokers. Having liberated it, I've enjoyed the tones from it ever since. I've done the common LED mod, though I'm not 100% sold on it.

What I would really like to do is mod the tonestack. I would like to make the amp overall less bassy, and more tight sounding. I would also like to maybe reduce the brittle high treble content a smidge. I understand this can be done through the tonestack. I found a thread on here regarding the Pathfinder 10, but it seems that the circuits don't directly translate.

Using the commonly found schematic, I presume that VR3 and VR4 control bass and treble. However these are not near each other, topologically, which makes me wonder how this circuit works. Can anybody shed any light on this area?

It looks like C12, C13, C14 comprise something that looks, to my untrained eyes, like the Vox diagram in the Duncan tonestack calculator. However the bass control is located near C20, if I'm reading the circuit correctly.

Any help would be appreciated. I realise I cannot expect anything too great here, but I feel the tonestack is slightly less than optimal in the 15R, especially given that it is a 2-band EQ. I feel that the bass has become 'flubby' since I removed the LEDs.

[J M Fahey]

Please post the schematic here.

"Common found" doesn't cut much ice ..... unless you want answers similar to "oh!!, the Pathfinder !! .... apply some of the common found soutions !!! "  :lmao:

[Enzo]

Hi Kobaia, we are glad you came, but please to link us to whatever schematic you are using.

[Kobaia]

Fair shout!

The link is here;

http://www.fenderforum.com/userphotos/index.html?recid=69518

Its a big image, probably exceeds bandwidth rules on here at a guess.

I've modded my Pathfinder to have a louder reverb as well. Anybody interested in these mods?

[phatt]

Hi Kobaia,

VR2 is Treble and VR3 is Bass.
R18 is Midrange,  which you can replace with a ~5k pot for mid control.

R17 is called the slope resistor and larger values will increase the treble.

As to the brittle top end that's much harder to nail down and others here maybe better qualified to comment on that But I'd guess a change of speaker may help a lot.
Phil.

[J M Fahey]

^^^^^^^^^^ FULLY agree  :dbtu:

The schematic by itself is not bad, nor special either, follows the blueprint of 1000 other entry level amps.

The tone stack is what Phatt said, adding that EQ values are quite closely the classic Fender ones, so there's basically nothing wrong there.

Most you can do is decrease R17 a little, say to 22K, or C14 from the .1uF it has now to, say, .047uF.
Both will raise low mids and make sound a little warmer.

If shrill treble bothers you, you can raise C12 from present 1200pF to 1600 / 1800 / or 2200pF , which will let more high mids through.

Although I guess what plagues you is the curse of *all* entry level amps: a real cheap speaker in a very small shoebox size open cabinet.

Post a couple amp pictures with measurements, *maybe* you can cut a new front baffle and miunt a larger/better speaker there.

Or leave it as is, add a speaker out jack (we can help, but pull the chassis out and post a couple pictures, to see what space you have available) and make an external speaker cabinet, using yours only as a "head".

Good luck.

EDIT: I just listened to a demo:

http://youtu.be/VBpWK8tmmBs

Ouch!!, buzzier than h*ll !!!!

Now I understand your concern  xP

*Clearly* a speaker problem, maybe the designer thought they needed a tweeter.

Mind you, *killer* spanky sound for chickenpickin' or any Country sound with a Tele or Strat, the Dire Straits song was sublime ... but absolutely useless for distorted sounds, so I strongly encourage you to check whether you can remove that front baffle (it might be *glued* in, for all I know), and either cut a 10" hole or make a new one (you'll have to pull that nice front cloth anyway) and mount a Jensen MOD10-50 there or a Celestion G10L35 / Rocket 50 .

Both speakers are smooth sounding, and will tame the beast.

Or maybe you can get a used HH (Invader) 10" 35W speaker , pulled from a Laney .

All 3 speakers I mention have the same "formula" , under different brands, and should be available in the UK.

In Scotland also

[Kobaia]

Thanks for the advice guys! That Youtube video highlights some of my grief, just in micro detail. If nothing else, that is not how you play The Wind Cries Mary. Life in the Fast Lane is a bit rough as well.  :trouble I think the Les Paul tones especially reveal the 'skuzz' I'm trying to remove.

I'm surprised that VR2 and VR3 are the treble and bass controls because I was counting knobs left to right, and figured they would be VR 3 and VR4. Thanks for setting that straight!

Any ideas how to shift the bass control up a little as well? It is boosting bass in an area I don't need the bass boosted. I ran this amp into an 8 ohm Ashdown bass cab I have here, and ran my bass into it, and it works quite well as a bass amp. Too much bass!

[J M Fahey]

Any ideas how to shift the bass control up a little as well? It is boosting bass in an area I don't need the bass boosted. I ran this amp into an 8 ohm Ashdown bass cab I have here, and ran my bass into it, and it works quite well as a bass amp. Too much bass!

What you write sounds like a contradiction.

[joecool85]

Any ideas how to shift the bass control up a little as well? It is boosting bass in an area I don't need the bass boosted. I ran this amp into an 8 ohm Ashdown bass cab I have here, and ran my bass into it, and it works quite well as a bass amp. Too much bass!

What you write sounds like a contradiction.

I think he meant how to shift it up in the frequency spectrum, therefore decreases bass output.

[Kobaia]

Any ideas how to shift the bass control up a little as well? It is boosting bass in an area I don't need the bass boosted. I ran this amp into an 8 ohm Ashdown bass cab I have here, and ran my bass into it, and it works quite well as a bass amp. Too much bass!

What you write sounds like a contradiction.

As it stands I can use my Pathfinder 15R as a usuable bass amp if I run it into a bass cabinet.

As it is meant to be a guitar amp it seems to have too much bass on tap. I haven't had any luck modelling the tone stack in the SD tonestack calculator yet, but it seems that the bass control on the Pathfinder currently boosts bass around too low a frequency for 1) guitars in general and 2) a wee practice amp with an 8' speaker.

In my head, I think the amp would be better if the bass control boosted higher frequencies, roughly what bassists would call 'low mids' (though guitarists still call them bass frequencies). I guess around 300 Hz or so. I don't want to lose the fundamental note of the lowest string of my guitar, but I don't want the farty flubby mess that the Pathfinder currently produces. In my mind they should have brought the treble and bass controls closer in terms of frequency cut and boost, and used a bit more aggressive LPF and HPF to keep things within the confines of what such a speaker (and cab) can realistically reproduce without sounding bad.

[Roly]

You aren't going to have a lot of luck with TSC because the Vox tonestack model is for an AC30 style and there's a slightly different arrangement in the Pathfinder.

Here's a suggestion you could try playing around with.  On the circuit you will find an 0.47uF polarised cap in the tonestack, C13.  You could try experimentally changing that for a 0.1uF cap (doesn't need to be polarised, a greencap will do, they've just done that for the small physical size).

This should move the control hinge frequency up a bit, perhaps a couple of hundred hertz, and at the same time reduce the amount of bass boost somewhat.  That may be too much, but at least we will get an idea if it is going in the right direction, then you can play around with the exact value.

[joecool85]

You aren't going to have a lot of luck with TSC because the Vox tonestack model is for an AC30 style and there's a slightly different arrangement in the Pathfinder.

Here's a suggestion you could try playing around with.  On the circuit you will find an 0.47uF polarised cap in the tonestack, C13.  You could try experimentally changing that for a 0.1uF cap (doesn't need to be polarised, a greencap will do, they've just done that for the small physical size).

This should move the control hinge frequency up a bit, perhaps a couple of hundred hertz, and at the same time reduce the amount of bass boost somewhat.  That may be too much, but at least we will get an idea if it is going in the right direction, then you can play around with the exact value.

Agreed.  If you want to really dial it in I would consider soldering in some single/inline socket pins so that you can swap the cap out in seconds.  Then you can try as many values as you want and don't need to fire up the soldering iron every time (also means a LOT less likely chance of wrecking your PCB by reheating too many times).

[Kobaia]

Well now...

I chanced C14 to 0.047uF, C12 to 2200pF and C13 to 0.1uF (or 0.094uF as I had to put two 473 caps in parallel). This works!

The shrillness is gone. In a weird way I slightly miss it. As somebody pointed out, the stock amp is good for 'country clean', and this is probably why they love it on TDPRI. With these mods, I can turn up the treble without it getting shrill, and I can turn up the bass without it flubbing out. It sounds more Marshally, though I'm not going to kid anybody with that really. The good thing is I can swap between humbuckers and singlecoils now without getting harsh single coils or muddy doubles. Great!

Thanks everybody for the help. I urge at least one other Pathfinder owner to do these mods!  :dbtu:

[phatt]

Good to hear you got it working the way you wanted. :tu:

Just be aware that tweaking is very addictive
Phil.

[Roly]

 :dbtu: