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Thread: Vox Pathfinder mods

  1. #1
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    Vox Pathfinder mods

    Just used some spare change to buy a 15 Watt Vox Pathfinder. Great amp for the price. Certainly got my money's worth. I wanted an amp that I could unabashedly ravage without worrying about the consequences. Cheapest and easiest mod was to slap a 3/4" piece of pine on the back to close it up and give it some warm and compressed-sounding bass. Swapped the 4558s out for 5532s but that didn't help the noise floor problem. I want to clean up the final output and smooth the transition from hot -to-not; or balls-to-the-wall vs nothing-at-all, or simply round off the curve before clipping. Yes, I know this isn't a tube amp. Any ideas?

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    Hi Rob,
    I own a Pathfinder 15R, and I agree it's great value for the money, still, I couldn't keep myself from performing some mods.

    I replaced the original op-amps with 5532s ( and it did help in lowering the noise, are you sure your 5532s are not crappy chinese fakes? ) and added DIP sockets for a quick replacement, but as a matter of fact I did the major mods on the PS and PA sections.

    I replaced the original PT with a toroidal PT, with a slightly higher voltage and a better current rating, then I changed the rectifier to a 4 Amp bridge, this allowed me to increase the filter capacitors' value ( to improve the dynamic range ). I also added voltage regulators for the preamp section ( to avoid early clipping on the op-amps due to voltage drops when the amp is driven hard ).

    I substituted the output chip - seems to me it was a TDA 2030 - with a TDA2040 and changed the original 8" speaker, putting in a 10" Celestion I salvaged from a wrecked Cambridge 30.

    Hope this helps

    Best regards

    Bob
    Last edited by Robert M. Martinelli; 11-12-2008 at 07:17 AM.

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    Thanks Bob,

    THe 5532s I used were Texas Instruments. I couldn't get the hand picked "A" series, that might make a bit of a difference. I didn't put in sockets as I thought that might add to the problem. Frankly, I thought the new Op Amps cleaned things up a little but not a lot. I have some TL072s on order and some OP227s I'll try those as well.

    I'll definitely try your PS and PT tips next. I've also been sniffing around for better power amp chips, the one in there looks like it's had a questionable background. I've been looking at things in the LM series (LM3875, 47XX). It really sounds to me like the noise comes from the final amp stage.

    The VRs on the IC's is a great idea to smooth things out. I'll let you know how it goes.

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    I had a Pathfinder that went up in smoke, so I remade it into a 5F1 in a Vox cab. It sounds great and still has that nice Voxish look.


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    Nice Pic

    Impressive logo. I think I might end up doing something similar combining the Vox with a Blackheart Killer Ant.

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    Quote Originally Posted by Rob Denton View Post
    Thanks Bob,

    THe 5532s I used were Texas Instruments. I couldn't get the hand picked "A" series, that might make a bit of a difference. I didn't put in sockets as I thought that might add to the problem. Frankly, I thought the new Op Amps cleaned things up a little but not a lot. I have some TL072s on order and some OP227s I'll try those as well.

    I'll definitely try your PS and PT tips next. I've also been sniffing around for better power amp chips, the one in there looks like it's had a questionable background. I've been looking at things in the LM series (LM3875, 47XX). It really sounds to me like the noise comes from the final amp stage.

    The VRs on the IC's is a great idea to smooth things out. I'll let you know how it goes.
    Hi Again Rob,
    The 5532s I used were indeed "5532AN" - as to the power amp section the LM3875 and 3876 are probably too much for the cabinet and speaker, you would also need much bigger a transformer, as the 3876 is rated at 56 W....
    I would suggest you to go ahead with a TDA2050 which is rated at 28W and is pin to pin compatible with the original.
    Let me know how the mods work
    Best regards
    Bob

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    Oooops

    Hi Bob,

    Can you think of any reason why simply switching the 2030ah for a 2050v would cause the fuse to blow and the transformer to rumble?

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    Hi Rob,
    well, as I told you in my first post, I upgraded the PT ( because the 2040 and the 2050 obviously need more current ). The 2030 yields 15W RMS, the 2040 22 and the 2050 28 W, so I think it's normal for the fuse to blow and for the PT to "complain" and (g)rumble.

    Once you decide whether to install a 2040 or a 2050 you' ll have to choose a new PT ( I installed a toroidal one ) according to their voltage/current demand.
    I would go with a 40W PT for the 2040 and a 50W PT for the 2050. I would replace the speaker too, as the original is not capable to cope with the output power.

    Hope this helps
    Best regards
    Bob

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    Dumbo!

    Well, Bob, I obviously need to go back to a re-learn some stuff that I thought I already knew. Thanks for the guidance and suggestions. I've decided to close the amp up before I do any real damage and open my textbooks for some basic refreshers.

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    Well Rob,
    I wouldn't be too hard on yourself...
    from time to time we all make mistakes, and often that's the only way to learn, I'm not immune from making mistakes either; time ago I wrote a post with good advice but unfortunately wrong values ( because I was trying to do more than one thing at a time and I didn't put much attention on what I was doing ) and misled a member...nothing serious, but it gave me a chance to think very thoroughly about it...

    Should you decide to go on with the mods on your Pathfinder I' ll gladly try to help.

    Best regards

    Bob

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    Hey guys,

    I know this is a somewhat of an older post, but googling for a nice mod of my pathfinder came up with actually only this post.

    i got mine almost 10 years ago while wanting to start playing guitar. and now that ive moved came across it again and felt it had to have more to it.
    ive already modded my squier fat strat via guitarnuts.com, great mods on there. you should check it out. put shielding in there, fender 4 wire humbucker with series/parallel push pull pod. and other capacitors.
    sounds awesome now.

    my question is if you could give me a somewhat more of a noobie discription of what and how to change and more importantly, specs of the parts needed.
    this because im dutch and there could be some diferences in techtalk.
    don't want to be lost in translation .

    second of all. ive noticed that the cirquitry where the headphone out is located has more possibilities. i think that vox uses the same board there for other amps. i'd like to add a send/return or line out for recording. something like that. and and maybe also add a jack for the speaker out.

    i hope you guys could help me out.
    im on a learning curve here, so feel free to mail me.

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    Update on Vox P15R mods (op amps)

    I just wanted to update this thread for those that get a Pathfinder. I have a 9168 model made in Korea (not Vietnam) and the op amps are not all 4558's like in the schematic I found online. It's a different circuit. The online schematic shows 6 of the 4558's in use, but the amp I have uses 4, but only the one for the Reverb was a 4558. I replaced that with a 5532 and there was no noticeable benefit, especially regarding the buzz that so many report with this amp (reverb and master vol).

    The others I recall were a 072D for the gain/volume in combination with some FETs that I can see, a CA30805 for the tremelo depth and a 062D for the tremelo speed.

    So if you get a modern Vox P15, save yourself the trouble of trying to upgrade these opamps unless you really have time on your hands. For lay folks like me, it wasn't hard to get a low power solder iron and grounding wriststrap to do the job. But it seemed like a lot of trouble for nothing, other than a good chance to spray the pots, since I bought mine used.

    These P15R's have that Vox sound, but some people can't seem to get past the noise that's worse in some rooms than others. Cool amp, but can be noisy compared to most small amps, especially if you want to record with them.

    I may try placing some foil along the back top panel to see if some shielding will help. Hopefully won't make it worse with a loop.

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    Quote Originally Posted by thirstyghost View Post
    .....I replaced that with a 5532 and there was no noticeable benefit, especially regarding the buzz that so many report with this amp (reverb and master vol).....

    .....So if you get a modern Vox P15, save yourself the trouble of trying to upgrade these opamps unless you really have time on your hands.....

    I may try placing some foil along the back top panel to see if some shielding will help. Hopefully won't make it worse with a loop.
    Hi,
    If the problem is hum/buzz related, then you just can't expect swapping the op-amps to be a solution.

    5532s have a lower En ( equivalent input noise voltage ) so they improve the overall "noise figure" of the amp; it's worth noting though, that we're talking about white/thermal/shot noise and NOT about buzz/hum/ripple, which is caused by other factors ( poor voltage regulation/poor shielding/poor decoupling/ground loops etc. ) and thus needs other actions to be taken.

    I started modifying my PF by replacing the output IC with a TDA 2050, then I changed the PT and threw in a ( bigger ) toroidal one, ( fixing it to the chassis by means of a nylon bolt and nut ) I also threw in voltage regulators, put in bigger filter caps and a bigger rectifier bridge to better cope with the TDA2050 current demand. I also replaced all the 4558s with 5532s for the above reasons, and, last, but not least, I glued a "cut-to-measure" brass foil on the amp's back cover, to completely shield the circuitry from external noise sources.

    The result is a hiss/hum/buzz free 28 W RMS Pathfinder with a tighter low end and a better dynamic response ( increased headroom ). The next step will be to replace the speaker, since the original one just can't cope with the increased output power. ( I'm thinking about throwing in a 10" in place of the original 8" ).

    Cheers

    Bob
    Last edited by Robert M. Martinelli; 11-10-2009 at 06:04 AM.
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    URL for schematics PF15R?

    Hi all, i am a new member here, and owner of PF15R since today.

    Your thread is very informative, thank you for this, could you point me to a download link for schematics for the PF15R eventually?

    Can't find this on the Vox web site.

    Thanx very much in advance, and greetings from Berlin

    jrp

  15. #15
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    Hi,
    check this:

    Links to Vox schematics

    One of the links is about the PF15.

    Cheers

    Bob
    Hoc unum scio: me nihil scire.

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    Help

    Quote Originally Posted by Robert M. Martinelli View Post
    Hi Rob,
    I own a Pathfinder 15R, and I agree it's great value for the money, still, I couldn't keep myself from performing some mods.

    I replaced the original op-amps with 5532s ( and it did help in lowering the noise, are you sure your 5532s are not crappy chinese fakes? ) and added DIP sockets for a quick replacement, but as a matter of fact I did the major mods on the PS and PA sections.

    I replaced the original PT with a toroidal PT, with a slightly higher voltage and a better current rating, then I changed the rectifier to a 4 Amp bridge, this allowed me to increase the filter capacitors' value ( to improve the dynamic range ). I also added voltage regulators for the preamp section ( to avoid early clipping on the op-amps due to voltage drops when the amp is driven hard ).

    I substituted the output chip - seems to me it was a TDA 2030 - with a TDA2040 and changed the original 8" speaker, putting in a 10" Celestion I salvaged from a wrecked Cambridge 30.

    Hope this helps

    Best regards

    Bob
    Bob
    Do you have a part # for the PT. I 'm gonna use the 2050 but was unsure about the appropriate Pt i know you suggest 50W any advice appreciated. I'm kinda/ somewhat new to the Mod thing my dad has an electro/mechanical degree and helps alot if i get in trouble. It's sad for a 28 year old to have to call dad when a circuit keeps faulting lol...I also was wondering did the OP amps help smooth the "breakup" out, or just reduce some minor noise? thanks
    Ryan

    PS did this do anything to the sound, or just amplify it?
    Last edited by role_65; 12-18-2009 at 08:56 PM.

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    hmm

    Is it Toroidal # 707.062 a 56 watt PT. Also is there any other brands?
    Ryan

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    Quote Originally Posted by role_65 View Post
    Bob
    Do you have a part # for the PT. I 'm gonna use the 2050 but was unsure about the appropriate Pt i know you suggest 50W any advice appreciated. I'm kinda/ somewhat new to the Mod thing my dad has an electro/mechanical degree and helps alot if i get in trouble. It's sad for a 28 year old to have to call dad when a circuit keeps faulting lol...I also was wondering did the OP amps help smooth the "breakup" out, or just reduce some minor noise? thanks
    Ryan

    PS did this do anything to the sound, or just amplify it?
    Hi Ryan,
    I used an Italian-made transformer, so I don't think its P/N could be of any use.

    The original output IC (TDA2030) calls for a +/- 18V supply, and therefore a 13-0-13 VAC (25/30VA) transformer is adequate.

    If you move to a TDA2040, you need +/- 20 V, so a 14-0-14 VAC (40VA) transformer will be OK.

    If you plan to use a TDA2050 instead, it calls for a +/- 25V supply, so you will need a 17.5-0-17.5 VAC (50VA) transformer (18-0-18 is still OK).

    The main improvement I had using different op-amps (5532s) was about noise reduction, while the sound was not affected.

    The improved bridge rectifier/filter cap section helped a lot with dynamics IMHO, as I noticed that, before modding the thing, while playing power chords at higher volumes the amp seemed to "squash" the sound somewhat....now the power chords are more "open" and the notes' attack seems no longer "squashed". The added power changed the amp from a home/studio thing into a rehearsal/small gigs/club amp, not bad for an amp of this physical size (and weight).

    If you go for a 2040, you can leave the original speaker in place, but, should you opt for a 2050, I strongly suggest to move to a better (and bigger) speaker (you'll need to put the soldering iron aside for a while and use a saw, a rasp plus some sandpaper instead).

    Hope this helps

    Best regards

    Bob
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    Looks like i might stick with modding the bridge and the Caps, what flavor of caps did you use? sorry to be a pest just starting my modding frenzy recently, I will be using this in a studio. depending on noise i might swap OP amps. Honestly i don't really love the sound a little harsh sounding to me so maybe some different value caps can change the tonality of the thing, but my first mod is to enclose the back. I thought about just getting an alinco speaker and closing it up to see what that does. sorry for all the questions and THANKS!
    Ryan

  20. #20
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    Hi again Ryan,
    since you're going to use the amp for studio work, I'd change all the op-amps and move to 5532s; only, be sure to buy them from a reputable parts seller because there are a lot of fakes around. Adding DIP sockets is always a good idea as it allows an easier replacement.
    I also glued a brass plate on the inner part of the electronics' back cover, this makes for an almost perfect Faraday cage, reducing the change for the amp to pick up unwanted noise.

    As to the PS filter caps, I used standard electrolytic capacitors.

    If you're going to tinker with caps along the signal path, poly capacitors will do just fine. Be aware though, that, in order to obtain a mellower sound, it could be enough to alter the feedback capacitor(s) in the preamp section (C7 for IC1B and C19 for IC2A). Those caps should be ceramic ones if memory serves me well, and by increasing their value(s) you will reduce the amp's highs content. Try a 330 or 390 pF (C7) for starters.

    As to the speaker, remember that, with a properly sized PT and PS section (I threw in a 4 amps rectifier bridge ad 2x4700 uF filter caps), your TDA2050 will put out 28 W RMS, and the amp's ability to respond to loud transients will be improved, so it's advisable to use an over-sized (40-50 W) speaker.

    Hope this helps

    Best regards

    Bob
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    Robert quick question and I should add I'm a complete noob to ss amp design,

    I haven't looked inside, but the TDA2030 is rated at 8W at 8 Ohms which appears to be the stock speaker rating. Is the amp using 2 chips bridged to achieve the advertised 15 watts? It would seem a TDA2040 would be necessary to achieve around 15 watts at 8 ohms? Or maybe the 15 watt advertised rating is simply optimistic?

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    Hi and welcome to the forum!

    Maybe the rating is optimistic, anyway, the 2030 inside the Pathfinder 15 is supplied at its maximum permissible voltage, and the 8 W figure is the "worst case" one. I'd say the "stock" power is something in between 11 and 14 W, it doesn't make much of a difference though, because to "hear a difference" you need a +3dB increase ( the minimum audible difference the human ear can perceive ), which can be achieved only by doubling the output power.
    FWIW I find the stock Pathfinder is pretty loud for home use, it needs a power increase only if you plan to use it on rehearsals or small gigs.

    (JM2CW)

    Cheers

    Bob
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    Quote Originally Posted by Robert M. Martinelli View Post
    Hi and welcome to the forum!

    Maybe the rating is optimistic, anyway, the 2030 inside the Pathfinder 15 is supplied at its maximum permissible voltage, and the 8 W figure is the "worst case" one. I'd say the "stock" power is something in between 11 and 14 W, it doesn't make much of a difference though, because to "hear a difference" you need a +3dB increase ( the minimum audible difference the human ear can perceive ), which can be achieved only by doubling the output power.
    FWIW I find the stock Pathfinder is pretty loud for home use, it needs a power increase only if you plan to use it on rehearsals or small gigs.

    (JM2CW)

    Cheers

    Bob
    Thanks for the response! Agreed the amp is more than sufficient for home usage. My goal with the amp is really to experiment and hopefully learn something beefing this puppy into a giggable amp and potentially converting it into a head unit. Based on your above statement, to get a significantly more juice it seems an upgrade to the 2050 (~32W, double the 2030) is the best route as the 2040 (~20W) would be a fairly subtle increase in output. In the second post you stated an upgrade to a 2040 but you also state swapping in a 2050. Did you try both?

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    Yup,
    I first subbed in a 2040, then moved to a 2050 ( modifying the PS section because of the 2050's greater current demand ).

    As already stated, if moving to a 2050 a speaker upgrade would also be advisable.

    Good luck with the mods, I really hope you'll have fun in the process and I also hope the results will be satisfactory.

    Cheers

    Bob
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    please help

    hallo guys. Im new in here and i have a little question for you. you all seem experts in the subject of Vox Pathfinder . I have my pathfinder 15 R since 3 years with no problem, until today. I just wired the pathfinder to a 2x12 cab thru the external cab out in the rear panel of the amp. the thing is that te amp sounded but something inside started to smell like freid circuits and then the amp just died.... well, not compleatly, the led in the amp says that the amp is still alive, but no sound comes from the speaker, nor signal fron the headphones plug or anything else. i think it can be that the problem could be the the power amp chip, the tda2030. what do you think guys? please some one help meee!

    (im so sorry for my english)

  26. #26
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    Hi and Welcome!

    According to the symptoms you described, yes, it's possible that you fried the 2030.
    My guess is that the cab's impedance was too low (4 Ohms? Did you check it before connecting the cab to the "ext speaker socket"?) and the 2030 has been forced to operate well above its ratings (The internal speaker is an 8 Ohms one). If you've been lucky you'll find only the 2030 has gone south....

    Cheers

    Bob

    P.S. - To help keeping the forum well organized, and to make the "search" function more effective, I suggest you to start a new thread instead of "hijacking" an existing one - this will make life easier for all the people needing help on similar problems.
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    tda2040 or tda2040a or tda 2040v

    Dear all,

    I realize this is an old thread, but I hope someone can clear things up for me.

    I am not a tech and have thus far only ever modded guitars and replaced speakers in amps - well I built an extension cab - that's the limit of my experience. I am curious to make the next step- and apart from trying the led mod on the Pathfinder 15r I am also curious to try to replace the tda2030a with a tda2040,

    In following the above posts it seems to me that I can just drop in replace one for the other?

    Also is there a difference between tda2040 and say tda2040a - and tda2040v? If so what should I (but a musician) keep in mind?

    I may be changing the stock speaker later as well - but as far as I can guess the stock speaker will not blow unless I drive it full throttle (I like the headroom and better dynamics of a higher wattage amp) - Or will the stock speaker blow?

    I thank any and all who are willing to help me out.

    Best regards,

    Jaka

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    Hello everyone, I've been enjoying all of the Pathfinder mods listed here for awhile. Thank You to every one that has listed their input. One mod I'd like to do is to drop the amount of boost when the "boost" botton is ingaged. Either by changing the voice or amount of gain. As is I find the switch unuseable as a lead/ boost option. Anyone have any ideas?

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    I was looking at a pathfinder schematic & wonder if changing the value of resister R10 from 4.7K to a larger value would help tame the Boost any or maybe changing the input resister R13 from 150K to +/- 300K. Any one have an opinion?

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    With help from the folks at the ssguitar forum I was able to put a boost volume pot in

    pathfinder15r-boost-variable-frankentone.gif

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