Vox Pathfinder mods

[Rob Denton]

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?

[voxrules!]

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

[Rob Denton]

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.

[Jaybird]

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.
http://harmony.demont.net/myharmonies/Jaybird/voxguts5F1.jpg
http://harmony.demont.net/myharmonies/Jaybird/voxnewgrill.jpg

[Rob Denton]

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

[voxrules!]

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

[Rob Denton]

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?

[voxrules!]

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

[Rob Denton]

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.

[voxrules!]

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