5e3 Volume Mod Question

[bradberry00]

Hello,

I am sure this has been discussed plenty, but....

I want to take away the interactive volume controls in a 5e3 circuit. I drew up a little diagram and want to see if it is correct before i go through with it. I also posted this in the mods and tweaks section.

is this right or do you have some suggestions?



thanks much,
-david

[pdf64]

Very close, but the 500pF is better fed from the 0.1uF cap/hot track end node, rather than the wiper. See the 6G3 schematic
http://www.ampwares.com/schematics/deluxe_6g3.pdf
However, note that the 6G3 is wire slightly differently, such that the 'cut' cap will be applied to the preceding plate circuit, whereas yours will be applied to the grid circuit. The 6G3 arrangement will give a more consistant cut response, whereas yours will vary according to the vol pot setting.
Also the 0.1uF caps are best replaced with smaller values (I like 0.022uF and 2n2), in order to limit an excessive subsonic response. Pete.

[bradberry00]

ok like this?



p.s. already changed the .1 to .022 (i just put .1 down to make it stock for the sake of the diagram)

is there a better way to do this?

[pdf64]

That's it.
Using that 6G3 arrangement, a 4n7 'cut' cap is rather subtle. 10n or 22n gives a better effect, though it's worth trying them all.
This is arguably the best '1 knob' tone control. Pete.

[bradberry00]

Thank you pdf64!

[bradberry00]

one more option....would this allow both channels to use the tone control (drawings are getting sloppier and sloppier)? any downsides to this if so?

[pdf64]

Yes, that will work fine. However, my preference is to not bother with a tone control with the 'normal' channel but to use it as a lead boost on an AB box - if I need a treble cut then the tone controls on the guitar work better for that.
Similarly for the dual pot tone control - unless a dual concentric pot is used with the funny knobs, you're stuck with the same setting for both channels. Again, it suited me better to leave the normal channel without a tone control, just to cut the low end a little with the 2n2 coupling cap.
Try it various ways and see which suits you better - there's no one right way to do it. Pete.

[catnine]

I have a question on the reason the 6G3 uses the 220k resisters between the vol pot wiper and the grid on the second gain stage V2 .
I built a 5E3 but since I used a 71 MM bass amp chassis and cab I only had two inputs and one vol and one tone so I just used one triode of the 12AY7 but didn't like the early breakup so I used the vol and tone set up of a 6G2 princeton which is like the 6G3 other than the tone cap values and the 220k resisters.

Are the 220k resisters used on the 6G3 to cut some of the gain since the 6G3 uses a 12AX7 as a preamp tube and a 5E3 uses a 12AY7 . I thought it must be the NFB loop the 6G2 has and the 6G2 has no bypass cap on the second gain stage so I made it switchable one way I have the bypass cap and no NFB (5E3) and the other no bypass cap and NFB and still the amp may not break up as soon using the 12AX7 preamp yet it bereaks up sooner than I like . I took out the cathode bias and installed an adjustable fixed bias and did this well before the switch was added thinking perhaps that will change the breakup . I never played a true 6G2 princeton so I don't know if they break up early like my build did but with the NFB that takes away the openess and make s the amp sound sterile so I just leave the switch for the 5E3 setting. I didn't install the tremlo either no room for it in this chassis.

I still like the adjustable fixed bias and the 6G2 tone stack and no NFB and use a 12AY7 preamp tube and I have the head room I wanted . The rest of the amp is still the PI and output section of a 5E3 only adjustable fixed bias . The main reason I installed the adj fixed bias was because with the tranny's from Allen Amps I used I can run 6V6GT's and 5Y3 or 6L6GC's and GZ-34 . It was all to get clean headroom and breakup past 7 on the vol and with the 6L6's more power and more headroon . the adj fixed bias was so I could install and bias either set of output tubes without screwing with cathode resisters and pulling the chassis plus I can use different 6V6's and set the bias I need for the different makes.

I thought after seeing this post that someone could tell me the reason the 6G3 uses the 220k resisters off the vol pot wiper to the grid of the second gain stage. I thought perhaps the 220k's were a way to get around using the 12AY7 .

[loudthud]

The 220Ks are what are called mix resistors. If you just hooked the wipers of the volume pots together, if one of the pots is turned all the way down, it will kill any signal coming from the other pot. The 5E3 gets around this by the way the volume controls are wired. With the mix resistors installed, there is 6dB of attenuation of one channel if the other channel is turned all the way down. In a single channel amp you don't need a mix resistor. It could act as a grid stopper to prevent blocking distortion, but it's not needed unless you are overdriving the first stage input of the amp with an overdrive pedal.

I think the 5E3 uses a 12AY7 because there is no feedback around the output stage to reduce gain so the higher gain of the 12AX7 is not needed or desired. The extra gain makes the amp breakup very early on the volume control.

[catnine]

The 220Ks are what are called mix resistors. If you just hooked the wipers of the volume pots together, if one of the pots is turned all the way down, it will kill any signal coming from the other pot. The 5E3 gets around this by the way the volume controls are wired. With the mix resistors installed, there is 6dB of attenuation of one channel if the other channel is turned all the way down. In a single channel amp you don't need a mix resistor. It could act as a grid stopper to prevent blocking distortion, but it's not needed unless you are overdriving the first stage input of the amp with an overdrive pedal.

I think the 5E3 uses a 12AY7 because there is no feedback around the output stage to reduce gain so the higher gain of the 12AX7 is not needed or desired. The extra gain makes the amp breakup very early on the volume control.

Thank you , now I understand the reason for the resisters.
Back to the 12AY7 in the 5E3 . In the build I have described in my previous post even when I added the 6G2 princetons NFB loop and removed the bypass cap on the second gain stage so the amp was at that point a 6G2 which shares the same power section of the 5E3and I installed an adjustable fixed bias and tried a 12AX7 it still broke up far to early and lacked headroom . If I leave the amp like a 6G2 and install a 12AY7 the amp is transformed with much more headroom yet with the NFB it looses the open sound , so basically without touching the vol control or tone control and I did add a switch so I can flip the switch and either have the NFB and no second gain bypass cap of flip the switch the other way and it's back to no NFB and with the second gain stage bypass cap the amp one say 3 on the vol with NFB is like I turned it down to 2 . As I said I never played 6G2 so perhaps this is the way they sound like the last step before the BF fenders came out where the tone stack and NFB of a BF made the amps real clean sounding by sterile as I would describe them. To me the tone stack the 6G2 used is one of the best out there for it's sound and control it's simple . I did try that same tone stack on a fender SF champ which is the typical BF stack and got more breakup yet the SF champ is SE so the 6g2 stack which is the same as a princeton 5F2A brought the SF champ to sound like a 5F2A . I never tried it but might try a 12AY7 in a 5F2A and life the NFB and see what I get since it's all about gain lose through a BF tone stack or the gain of the preamp section. There is one problem using a 12AY7 in a SF champ is I would need a second 9 pin socket so as not to alter the second gain stage and use 1 triode of the 12AY7 preamp and then the stack and then 1 triode of the 12AX7 second gain stage. The chassis I built my SF champ in has one extra 9 pin hole . It's a fender style narrow panel tweed chassis that Allen Amps used to sell so you could built anything from a SE with extra gain to a push/pull with a SS rect , it has two 9 pins and 2 octals and is printed and cut for the BF tone stack .

[loudthud]

Headroom in an amp with a single volume control is not a function of volume control position. It is a function of gain and clipping level of the stage(s) before the volume control and the clipping level of the power amp. If the guitar signal is too big, the first stage will distort it and turning down the volume control won't change that.

A 20dB log taper pot may start to distort at 50% rotation. A linear pot in the same amp will distort at 10% rotation. The headroom is the same in both cases. There are also 10dB audio pots. One of those in the amp will distort at about 20% rotation.

What is the taper of the pot in your amp? Disconnect all wires to the pot and adjust it to 50% rotation. Measure the resistance from the center lug to each end lug. Are the resistances about the same? That's a linear pot. One side twice the other? That's a 10dB audio pot. One side about 9 times the other? That's a 20dB log pot.
　
One way to change were distortion begins on your amp would be to add a resistor to limit the signal available to the volume pot. The 5D2 Princeton adds a 1 meg resistor in series with the volume pot to give 6dB of attenuation. It also allows the tone control more treble boost at 100% rotation of the volume pot.

Link: http://www.el34world.com/charts/Sche...NCETON_5D2.pdf