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May 16, 2021, 08:06:28 PM

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1
Amplifier Discussion / Re: FET Self Biasing Method
« Last post by GB on Today at 09:06:40 AM »
I have been fortunate to have got a supply of original 2SK and 2SJ FETs... like the 2SK30, 2SK369, 2SK170... etc... which has given me a wider choice of options to vary and optimise designs... still using (primarily) the Danuk process.
I have even developed a couple of XL spreadsheets which integrate the key formulas... and then expand the calculations to other areas e.g. Voltages, Currents, Gain, etc...  If you would like the xls file send me an email address(s) and I will send it that.
Graham
2
Amplifier Discussion / Re: FET Self Biasing Method
« Last post by willpirkle on May 15, 2021, 08:46:18 AM »
I buy J113’s a hundred at a time from Mouser ($0.13 a piece) and use a FET tester I built (the simple one from runoffgroove) then spend a rainy Saturday sorting them. It takes less time than you’d think (and I live in South Florida so we have many rainy days...). The J113 works great for Danyuk’s circuit.
3
Amplifier Discussion / Re: FET Self Biasing Method
« Last post by dimkasta on May 14, 2021, 11:20:16 AM »
Yep, as the guys said, fets can be all over the place. It's very common to buy largish batches and select/match parts with similar characteristics. Many parts also come in different grades, meaning that you might be able to buy parts closer to what you need in your design.
4
Amplifier Discussion / Re: Vox Pathfinder 10 as a modding platform
« Last post by dimkasta on May 14, 2021, 04:33:42 AM »
By the way, about R8, I just restored it and I will probably keep it as is

I also added another TODO point, to experiment with R27 and R28 to see if I can get a more usable volume and gain range
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Amplifier Discussion / Re: Vox Pathfinder 10 as a modding platform
« Last post by dimkasta on May 13, 2021, 09:03:47 PM »
My plan is to replace the 2030 with a 2040 and put in a larger transformer to drive a little more wattage.

As Phil said, it's not really worth it. The 2030A is already at its max with +-20V, being able to give around 18W. That's plenty loud for a guitar unless you are playing big venues, in which case the limit is the speaker.

The easiest and probably the most effective way to get more output is to add the output jack and hook it into a cab with a more sensitive speaker. Even a 2x12.



LM1875 could be a good candidate to get more power. But it will need a new PSU and probably a beefy heatsink. For now, this is probably "going too far" territory for me.

For bass, the preamp is too mid-focused. Perhaps the FX loop would be a solution for you so that you can bypass the preamp with its highpass filtering and drive the output directly with a bass preamp or pedal. But to be honest for bass I would just get a fender rumble and call it a day.

what's the difference between adding a 1/4" for driving an external cabinet v. the headphone/line out jack?

The headphone output has series 1W resistors that limit the power to levels adequate for headphones.
6
Amplifier Discussion / Re: Vox Pathfinder 10 as a modding platform
« Last post by joecool85 on May 12, 2021, 02:41:17 PM »
Great job!  I love modding these small amps, plus the Vox Pathfinder 10 looks mint!
7
Amplifier Discussion / Re: Vox Pathfinder 10 as a modding platform
« Last post by phatt on May 11, 2021, 06:12:22 PM »
The Difference between the 2 chips is not worth the effort.
Your ears would hardly be able to notice the Difference between 10 Watts and 15 Watts.
Those chips will now likely be hard to find anyway so *Just buy a bigger amp*.
Re the headphone out. Well it's exactly what it says,,
for driving headphones,,, different Z and Voltage.
If you plug in a speaker you won't hear much. :-[
Phil.
8
Amplifier Discussion / Re: Vox Pathfinder 10 as a modding platform
« Last post by mguzzo on May 11, 2021, 12:24:36 PM »
lots of good tips there. I haven't modded any of the circuit on mine yet. I did install a Celestion 8" in place of the 6.5" bulldog speaker. It fit quite well in the cabinet. My son has been using it with his string bass for small gigs (church, musical pit), the clean channel and speaker handle the string bass tone quite well in those small settings. My plan is to replace the 2030 with a 2040 and put in a larger transformer to drive a little more wattage.

what's the difference between adding a 1/4" for driving an external cabinet v. the headphone/line out jack?
9
Amplifier Discussion / Re: Vox Pathfinder 10 as a modding platform
« Last post by phatt on May 10, 2021, 07:18:18 AM »
If you can find space on the panel you can always replace R7 with a pot and re-solder the Leds.
That will give you much more control on how hard the leds (Or diodes if you prefer) activate.
I've never had this amp so just a thought.
Cheers, Phil.
10
Amplifier Discussion / Re: Power amp transistor choices??
« Last post by Enzo on May 09, 2021, 08:27:43 PM »
Never lose sight of the fact this is just a guitar amp, not lab equipment.   And a lot of those audio discussions are from hifi people whose goal is an amp flat from almost DC up to radio.  Totally not needed even for them and certainly not for guitar amps.
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