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Fender NORMAL as distortion "pedal" ?

1/19/2000 3:18 AM
jeff	Fender NORMAL as distortion "pedal" ? does anyone have any schemas' etc .. of a actual working overdrive/distortion mod that ONLY utilizes the nearly useless 12AX7 in the Normal ch of a Fender amp? I have tried playing around with O'Conners ideas (like two diodes for clipping the signal), I have tried running the signal thru both triodes in the 12AX7 then thru various 'contours' and limiters like a 470K resistor and a 560pf cap etc .. but none of that sounded worth a damn . I guess I have in mind something like that nice tube sounding overdrive/singing sustain/warm distortion that Mesa Mark I's and Mesa SOB's can produce. thanks in advance for any ideas.

1/19/2000 3:18 AM

jeff

Fender NORMAL as distortion "pedal" ?

does anyone have any schemas' etc .. of a actual working overdrive/distortion mod that ONLY utilizes the nearly useless 12AX7 in the Normal ch of a Fender amp? I have tried playing around with O'Conners ideas (like two diodes for clipping the signal), I have tried running the signal thru both triodes in the 12AX7 then thru various 'contours' and limiters like a 470K resistor and a 560pf cap etc .. but none of that sounded worth a damn . I guess I have in mind something like that nice tube sounding overdrive/singing sustain/warm distortion that Mesa Mark I's and Mesa SOB's can produce.
thanks in advance for any ideas.

1/19/2000 2:12 PM
Lou	I've gotten one of those "MENDER" for my Twin Reverb and it fits in the tube sockets and the tubes fit in it. It has a gain control and a input jack for a foot switch to change from normal (gain)ch. to tremlo ch. Reverb and tremlo on both ch. too. The normal (gain) ch. is very saturated tube overdrive at low setting to heavy distortion at high setting. Pretty cool mode without pulling out the soldering iron! Hope this helps . Cheers Lou

1/19/2000 2:12 PM

Lou

I've gotten one of those "MENDER" for my Twin Reverb and it fits in the tube sockets and the tubes fit in it. It has a gain control and a input jack for a foot switch to change from normal (gain)ch. to tremlo ch. Reverb and tremlo on both ch. too. The normal (gain) ch. is very saturated tube overdrive at low setting to heavy distortion at high setting. Pretty cool mode without pulling out the soldering iron!
Hope this helps .
Cheers
Lou

1/20/2000 11:59 AM
jackson	That sounds promising. Where can I get more information on the "Mender"? thanks, jackson

1/19/2000 9:35 PM
Doc	I once played around with a twin reverb. I disabled the #2 jack of the normal channel and rewired it as a circuit break. When a cord was plugged in, the normal preamp signal (after the 2nd section of V1) came out. The cord was jumpered over to the input of the virato/reverb channel. Gain was outrageous, and unusable. I proceded to experiment with resistor pairs as voltage dividers, and installed a pair inside one plug of my special jumper cord. (That way, there wasn't any permanent voltage divider wired inside the amp.) Without the cord plugged in, the amp's operation was normal (except that #2N jack could not be used as an input). I messed around with this setup, using an A/B footswitch backwards, guitar cable into the "output" jack, and a pair of cords from the "input" jacks. One cord went to the vibrato channel, the other went to the normal channel amp input jacks. I had footswitchable gain-boost. The novelty wore off, and I eventually went inside and rerwired the jacks back to stock, and made both channels "reverb" channels. That's my story, and I'm stickin' to it.

1/19/2000 9:35 PM

Doc

I once played around with a twin reverb. I disabled the #2 jack of the normal channel and rewired it as a circuit break. When a cord was plugged in, the normal preamp signal (after the 2nd section of V1) came out. The cord was jumpered over to the input of the virato/reverb channel. Gain was outrageous, and unusable. I proceded to experiment with resistor pairs as voltage dividers, and installed a pair inside one plug of my special jumper cord. (That way, there wasn't any permanent voltage divider wired inside the amp.) Without the cord plugged in, the amp's operation was normal (except that #2N jack could not be used as an input). I messed around with this setup, using an A/B footswitch backwards, guitar cable into the "output" jack, and a pair of cords from the "input" jacks. One cord went to the vibrato channel, the other went to the normal channel amp input jacks. I had footswitchable gain-boost. The novelty wore off, and I eventually went inside and rerwired the jacks back to stock, and made both channels "reverb" channels. That's my story, and I'm stickin' to it.

1/19/2000 10:58 PM
Scott Swartz	The basic concept of the Boogie Mark I was an additional gain stage in front of the normal Fender blackface circuit, similar to what Doc describes above - cascaded preamp gain stages with careful component selection to provide good voicing. Just using the two stages probably isn't enough; You need to have at least three stages and a master volume, maybe a way to switch it in and out, etc. In Dan Torres book he shows a circuit for an extra gain stage that is selected by which input jack you plug into. You probably need a master volume to go along with the extra gain stage. Here's an option to think about. In between the first triode of the "Vibrato" preamp and the tone controls have a switch - one position as normal, the other routes the signal to the wasted tube. The wasted tube can be voiced for overdrive and the "Normal" channel tone controls can also be optimized for overdrive. There would be no reverb on the distortion channel. The switch could be a relay or done with LDRs. How far are you willing to mod the amp? This is a lot of work and ruins the resale value.

1/19/2000 10:58 PM

Scott Swartz

The basic concept of the Boogie Mark I was an additional gain stage in front of the normal Fender blackface circuit, similar to what Doc describes above - cascaded preamp gain stages with careful component selection to provide good voicing. Just using the two stages probably isn't enough; You need to have at least three stages and a master volume, maybe a way to switch it in and out, etc.

In Dan Torres book he shows a circuit for an extra gain stage that is selected by which input jack you plug into. You probably need a master volume to go along with the extra gain stage.

Here's an option to think about. In between the first triode of the "Vibrato" preamp and the tone controls have a switch - one position as normal, the other routes the signal to the wasted tube. The wasted tube can be voiced for overdrive and the "Normal" channel tone controls can also be optimized for overdrive. There would be no reverb on the distortion channel. The switch could be a relay or done with LDRs.

How far are you willing to mod the amp? This is a lot of work and ruins the resale value.

1/22/2000 6:32 AM
jeff	thanks Scott, this amp will never be sold, I have built several amps from scratch so the work is not a problem. Since the vibrato ch is a gain stage, tone stack, gain stage, mixer stage for reverb signal after recovery and heavily attenuated (3.3M - 10pf)original signal, then to PI etc ... and the unsed Normal ch is gain stage, tone stack, gain stage it seems that it should be possible to go from say the output from the vibrato ch thru the 2 Norm ch gain stages and use a master volume. The trick is what exact component values will actually work and sound decent .. make sense?

1/22/2000 6:32 AM

jeff

thanks Scott,
this amp will never be sold, I have built several amps from scratch so the work is not a problem. Since the vibrato ch is a gain stage, tone stack, gain stage, mixer stage for reverb signal after recovery and heavily attenuated (3.3M - 10pf)original signal, then to PI etc ... and the unsed Normal ch is gain stage, tone stack, gain stage it seems that it should be possible to go from say the output from the vibrato ch thru the 2 Norm ch gain stages and use a master volume. The trick is what exact component values will actually work and sound decent .. make sense?

1/22/2000 4:14 PM
Scott Swartz	You could get the signal that will be sent to the wasted tube after the reverb but I'm not sure you will get the sound you're after because: 1. The signal will already have the reverb on it. It usually works better to distort the dry signal. This is why I suggested getting the signal after the first triode of vibrato channel. 2. The signal path would be very long and I think noise will be a problem. With respect to component choices, you will have to experiment because your tubes,speakers,etc. will impact it greatly. A couple of classic Boogie tricks are bypassing the plate resistor with a cap to roll off highs and use small coupling capacitors to control the bass. Check out the Boogie schems on the net and use that as a starting point.

1/22/2000 4:14 PM

Scott Swartz

You could get the signal that will be sent to the wasted tube after the reverb but I'm not sure you will get the sound you're after because:

1. The signal will already have the reverb on it. It usually works better to distort the dry signal. This is why I suggested getting the signal after the first triode of vibrato channel.

2. The signal path would be very long and I think noise will be a problem.

With respect to component choices, you will have to experiment because your tubes,speakers,etc. will impact it greatly.

A couple of classic Boogie tricks are bypassing the plate resistor with a cap to roll off highs and use small coupling capacitors to control the bass.

Check out the Boogie schems on the net and use that as a starting point.

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