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Post subject: Fender 75 Reverb Problem??
Posted: Wed Dec 23, 2015 2:11 pm
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I've had an old Fender 75 head with a 4x12 cabinet for many years. I love this amp and it sounds great. I recently took it in for repair when it started sounding weird. The guy cleaned it up and said it works great. I agree, I tested it and it sounds awesome, except for one thing and I don't know if this is a real problem or not but I've never noticed it before in 10 years. When I have the volume turned all the way up, on amp and guitar, I notice that I still hear some reverb coming through even though it is switched off. I may have never noticed it before considering I don't turn it up that loud very often, but I think if it was there I would have noticed considering I noticed right away this time. When I switch the reverb on via the footswitch, it sounds great but when I switch it off, I can still here some faint reverb, even when I turn the volume down a bit. Also, when I pull out one of the reverb plugs on the back, the reverb goes away completely. Is this normal on these types of amps? It seems like the reverb is not being totally bypassed when it's switched off. I called the repair guy and he said this is pretty typical of some older fender amps. If it's normal then that's fine but I want to take it back in if this is a new problem. Any help is appreciated.


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Wed Dec 23, 2015 3:02 pm
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I can't say definitively about Fender's 75 but years ago I played with a guy who owned a 140 (a close relative to the 75) and his reverb circuit behaved in exactly the same manner. However, since he wasn't prone to diming the amp very often, it wasn't really a priority issue. I suspect your amp may be similar in that respect.

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Post subject: Re: Fender 75 Reverb Problem??
Posted: Wed Dec 23, 2015 3:32 pm
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Ok thanks for the info. I like the reverb so I don't want to keep the plugs out, but hearing it when I don't want to is kind of bothering me. Maybe I just never had it loud enough to hear it before.


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Wed Dec 23, 2015 4:15 pm
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You might try cleaning the contacts of the footswitch, its jack and plug, and the reverb control pot on the front panel. Use a quality electronic spray cleaner such as Caig's De-Oxit and spin that control shaft rapidly several times from stop to stop.

I think there's an inherent design flaw but such measures may help.

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Post subject: Re: Fender 75 Reverb Problem??
Posted: Wed Dec 23, 2015 6:24 pm
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I'll give it a try, thanks again! I'm afraid you're right though.


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Wed Dec 23, 2015 7:03 pm
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The Fender 75 seems to have only one tone stack for one input (whether reverb is on or not). Unlike earlier Bf and SF that have two inputs (Normal and Vibrato). My guess, is that if the ground-out switch (foot pedal) isn't completely grounding out the reverb portion of the circuit, you will get some bleed through.

http://bmamps.com/Schematics/fender/75_schem.pdf


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Wed Dec 23, 2015 7:09 pm
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That's a good suggestion. Do you mean to check the switch on the footswitch itself or the jack in the amp for the pedal? I made the footswitch myself so it's definitely possible something came loose, but it does switch the reverb on and off properly, just still can here some when it's off.


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Wed Dec 23, 2015 7:41 pm
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I think I got it!! Thanks for the suggestion BMW. I took a look at my footswitch and it looks like there were some loose connections and the ground wires weren't totally connected to a grounding spot. I soldered some better connections and that seems to have done the trick. I can't hear any reverb when it is off. I'm not playing it too loud, kids are sleeping, but I definitely hear a big difference. Thanks again to all the comments!


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Wed Dec 23, 2015 9:15 pm
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And once again, another satisfied Fender Forum member.

:wink:

Rawk on!

8)

Arjay

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Post subject: Re: Fender 75 Reverb Problem??
Posted: Thu Dec 24, 2015 2:31 am
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Retroverbial wrote:
And once again, another satisfied Fender Forum member.

:wink:

Rawk on!

8)

Arjay


+1


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Thu Dec 24, 2015 6:53 am
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Well I spoke a little too soon. I just tried it out again and I can still hear faint reverb turned all the way up. I'm guessing at this point that it was always there and I just never noticed it. It still sounds good but it's kind of bugging me in case I want a perfectly clean tone without reverb and I don't want to have to pull the reverb plug out. Oh well, I guess I'll have to live with it but it still sounds great. If this is typical then so be it. I suppose the high volume is causing vibration in the springs and that's what I'm hearing, unless there is something else I can do. Otherwise, I'll just deal with it.


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Thu Dec 24, 2015 6:58 am
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Are your switches and solder are OK ? You said you fixed them , are you sure about the job you do ?


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Thu Dec 24, 2015 7:21 am
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Not totally sure, I bet I could clean it up more but it works fine turning the reverb and lead channels on and off, so would fixing the solder joints fix the reverb problem? I'm not to knowledgeable on this stuff so I don't know if all it does is just turn the channels on and off or if they do affect the problem I'm seeing. If it does, I would gladly redo the whole thing.


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Thu Dec 24, 2015 8:46 am
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Harris Norton wrote:
Well I spoke a little too soon. I just tried it out again and I can still hear faint reverb turned all the way up. I'm guessing at this point that it was always there and I just never noticed it. It still sounds good but it's kind of bugging me in case I want a perfectly clean tone without reverb and I don't want to have to pull the reverb plug out. Oh well, I guess I'll have to live with it but it still sounds great. If this is typical then so be it. I suppose the high volume is causing vibration in the springs and that's what I'm hearing, unless there is something else I can do. Otherwise, I'll just deal with it.


I think, because how the circuit is laid out, it will be near impossible to have absolutely zero reverb, with amp turned to "10." The foot switch "off" position just can't give you zero potential (no resistance) across the long connection. You'll need to pull the RCA lines in the back of the amp that connect the reverb tank. Or pull the 12AT7 reverb driver tube & 12AX7 recovery tubes... to get the reverb to go completely quiet.

http://i.ebayimg.com/images/g/hoQAAOSw3 ... -l1600.jpg

Most Fender amps have a little bleed from the reverb part of the circuit to the Normal or non-reverb side. You can hear it with amp very loud and you tap the amp's cab.

I wouldn't worry about it. Esp if you regularly use the reverb. Which most guitarists do...


:)


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Post subject: Re: Fender 75 Reverb Problem??
Posted: Thu Dec 24, 2015 9:02 am
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BMW2002Ti wrote:
Harris Norton wrote:
Well I spoke a little too soon. I just tried it out again and I can still hear faint reverb turned all the way up. I'm guessing at this point that it was always there and I just never noticed it. It still sounds good but it's kind of bugging me in case I want a perfectly clean tone without reverb and I don't want to have to pull the reverb plug out. Oh well, I guess I'll have to live with it but it still sounds great. If this is typical then so be it. I suppose the high volume is causing vibration in the springs and that's what I'm hearing, unless there is something else I can do. Otherwise, I'll just deal with it.


I think, because how the circuit is laid out, it will be near impossible to have absolutely zero reverb, with amp turned to "10." The foot switch "off" position just can't give you zero potential (no resistance) across the long connection. You'll need to pull the RCA lines in the back of the amp that connect the reverb tank. Or pull the 12AT7 reverb driver tube & 12AX7 recovery tubes... to get the reverb to go completely quiet.

http://i.ebayimg.com/images/g/hoQAAOSw3 ... -l1600.jpg

Most Fender amps have a little bleed from the reverb part of the circuit to the Normal or non-reverb side. You can hear it with amp very loud and you tap the amp's cab.

I wouldn't worry about it. Esp if you regularly use the reverb. Which most guitarists do...


:)


This is what I figured. Thanks for that good explanation. I bet I just never noticed it before cause I never turned it up that much. I'm fine with leaving it the way it is. Thanks again for everyone's help!


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