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Fender PR 241 repair (Frontman amp made in Mexico, high pitch sound)
Fender PR 241 repair (Frontman amp made in Mexico, high pitch sound)
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Old 11th October 2019, 02:32 AM   #11
PRR is offline PRR  United States
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Location: Maine USA
> leave the two switching pins always disconnected (input always on: it may produce the same noise if the guitar cable gets unplugged

No. There is a standard Switchcraft jack with a shorting switch, which was used on ALL guitar amps until that plastic PCB style came into favor. The one you want has 3 wire-lugs but only one plug-finger. Under that finger is a short leaf which touches the plug finger when no plug is installed. Wire the short leaf to ground.

You can also use the "Marshall" style plastic jacks. These usually have a lug which touches the plug-finger when no plug is installed.

A amp which SCREAMS if unplugged is Dangerous. As you dog will tell you.
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Old 11th October 2019, 02:35 AM   #12
ptaf is offline ptaf  Greece
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Quote:
Originally Posted by Gnobuddy View Post
Congratulations!

Thanks to Enzo providing that manual, adding reverb looks straightforward. All you need is one double op-amp, a few passive components, and the actual spring reverb unit (the only slightly tricky part!)


-Gnobuddy
You all gave me great info and advice! Service manual is always priceless, like any kind of technical or safety info.
Again, thank you all!!!

The reverb circuit seems easy now. I have to check the components for availability and total cost, to consider if it is worth the money. Else i will just build a reverb pedal .

Still need to figure out where i could add FX loop (send-receive) in the amp circuit . I suppose it is easy and simple, but i am not totaly sure atm. I am trying to learn from other amp schematics that have FX loop sockets implemented from factory. Could you provide any FX loop circuit that would be OK for my PCB and purposes? Alternatevely a simply designed amp model that in your experience has a simple FX loop circuit, will also do the job after i locate and read it's schematics.

Last edited by ptaf; 11th October 2019 at 02:56 AM. Reason: quote to Gnobuddy was missing
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Old 11th October 2019, 02:44 AM   #13
ptaf is offline ptaf  Greece
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Join Date: Oct 2019
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Quote:
Originally Posted by PRR View Post
> leave the two switching pins always disconnected (input always on: it may produce the same noise if the guitar cable gets unplugged

No. There is a standard Switchcraft jack with a shorting switch, which was used on ALL guitar amps until that plastic PCB style came into favor. The one you want has 3 wire-lugs but only one plug-finger. Under that finger is a short leaf which touches the plug finger when no plug is installed. Wire the short leaf to ground.

You can also use the "Marshall" style plastic jacks. These usually have a lug which touches the plug-finger when no plug is installed.

A amp which SCREAMS if unplugged is Dangerous. As you dog will tell you.
You have spoken wisely. Thanks! I don't want to risk my ears, or my dogs ears, my friends ears, etc. Marshall amps are sold everywhere here, but i have no clue for their parts.
This "auto-switch" has a good reason of being.
When my temporary fix dies, i will spend the 7.5 euros for the original Fender part.
The Marshall part i suppose will be at the same price or even more. Fender part is plastic too. The only metallic on this is the nut-washer and the contacts.
Also i have easy access to Fender parts, but i am not sure who imports Marshall parts here.

Last edited by ptaf; 11th October 2019 at 03:11 AM. Reason: corrections
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Old 11th October 2019, 03:59 PM   #14
shanx is online now shanx  Canada
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If you are going to install the reverb circuit, then either ordering up a spare reverb tank from Fender is an option, also consider Mod/Ruby tanks. Either way it's a tank with high input impedance designed to be driven by op-amps, not the low impedance version which is usually for valve/transformer drivers.
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Old 11th October 2019, 04:03 PM   #15
shanx is online now shanx  Canada
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The replacement tank for Fender 15R is going to be tiny, and I don't like the sound of them much. You could go for a medium size tank and mount in bottom of amplifier cabinet, if you want. The Blues Jr has op-amp driven reverb despite being a valve amp, and uses the medium size tank.
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Old 11th October 2019, 08:41 PM   #16
Enzo is offline Enzo  United States
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Electrically the size doesn't matter. The crappy little reverb in this amp is used for its size, it fits in the amp. The small pan in the BLues Junior fits in its cabinet. But if you have the room, a full size pan is fine. The circuits won't care.

4EB2C1B is typical of full size. 8EB2C1B for small pan.
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Old 11th October 2019, 08:59 PM   #17
shanx is online now shanx  Canada
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Enzo, I realized that the amp cabinet on this particular 15G model may not even fit anything but the tiny spring reverb. For a 25G cab would likely fit. The 25R used the same tiny reverb mounted in the chassis, probably a cost choice, as these amps are built that way.
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Old 11th October 2019, 09:18 PM   #18
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by shanx View Post
...The 25R used the same tiny reverb...
I owned a 25R briefly. The reverb wasn't bad if you kept the level low.

But turn it up a bit, and it would make this bizarre hyperactive-metallic-woodpecker-sliding-down-the-inside-of-a-drainpipe noise. Pick a note on the guitar, hear the mad woodpecker.

-Gnobuddy
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Old 11th October 2019, 09:24 PM   #19
shanx is online now shanx  Canada
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Quote:
I owned a 25R briefly. The reverb wasn't bad if you kept the level low.
Yes it was passable at quite low levels, from what I remember.. but the mad woodpecker sound is a good description!
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Old 12th October 2019, 05:44 AM   #20
ptaf is offline ptaf  Greece
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In the next month i will have an appropriate 1X12 inch cabinet to connect.
The 8inch speaker will be removed and i am planning to cut the amp combo in half so it looks like an amp head. So no problem to fit a bigger than factory spring reverb in there.
BUT the only problem i see is the cost. I can find even bigger/better amp combos with spring reverb for like 50-80 euro used (like Randal RG80 for 80 euros, Dean Markley K65 for 80, Ibanez 50 for 60euro, Fender Rock pro 1000 combo for 100euro, etc). An aftermarket reverb tank costs like 30-40 euros plus shipping/fees. A Frontman R costs like 50 euros max, used. I suppose that Fender will not sell for less than 30-50 euros their reverb tank as a part (Monday i will know).
What i am trying to say: i see that it is possible to add reverb on my amp, but does not worth the money, cause sping tank is not cheap and i have better alternatives.
Also i already have a GFX-5 guitar effects processor and some pedal effects including Digitech polara and Boss reverb, so the most value for money is to add an FX loop on my Frontman amp to make good use of my effects gear.
In the end it is much better to build my custom spring reverb external module/pedal and use it in FX loop anywhere i like, full of pride .
So coming back to the question: is it possible to add a proper FX loop on my amp? Is it possible to use the reverb circuit except of the reverb tank, using the reverb send and receive as FX loop send/receive? How many watts and what Ohms is my amps circuit rated to send and receive from the reverb tank? How do i calculate from Fender reverb circuit, how many Ohms it sends and how many is it supposed to receive? Is it possible with minor adjustments to the resistors or caps, to modify this and work as FX loop? Check my attached image to understand what i am talking about.
Attached Images
File Type: jpg schematics- mod reverb to FX loop.jpg (385.6 KB, 9 views)

Last edited by ptaf; 12th October 2019 at 06:12 AM.
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