More headroom in a 5e3?

[markmalin]

Hey guys!

I built a 5e3 with a master volume a while back, which has amazing tone both for jazz and blues.  I've been playing more jazz lately and if I play a venue that's large enough to turn it up a bit, it starts to break up, especially with humbuckers.  I'm trying to understand if there's a way to give it more headroom?  It's already using a 12AY7 in the pre-amp, which is very low gain.  If I turn the master down and the volume up, it breaks up earlier, obviously.  I'm guessing the pre-amp is overdriving...can I adjust plate voltages on the 12AY7 to get it to go further before breaking up?


Any ideas or thoughts would be appreciated.


Humbly,
Mark

[sluckey]

Higher preamp voltage should help. Temporarily solder a 6.8K resistor across the 22K between the filter caps. This will reduce the 22K to about 5K and increase preamp voltages. Any better?
 

[markmalin]

Higher preamp voltage should help. Temporarily solder a 6.8K resistor across the 22K between the filter caps. This will reduce the 22K to about 5K and increase preamp voltages. Any better?

Thanks, Sluckey!  I will give that a try later this week :)
Mark

[sluckey]

Maybe use a switch so you can easily get a sound comparison.

[markmalin]

Maybe use a switch so you can easily get a sound comparison.

Yah, I was thinking of that.  :)  Jazz and Blues mode!

[pdf64]

...I'm guessing the pre-amp is overdriving...can I adjust plate voltages on the 12AY7 to get it to go further before breaking up?...

I think it rather more likely that the power stage is overdriving; as the signal level is increased from zero, given sensible control settings that's how it works. Otherwise, if the preamp hit overdrive first, the amp could never reach its intended max power output.
To achieve a cleanish tone at a higher sound pressure level, a beefier amp / more sensitive speaker cab, is necessary. (Or just mic it up )
A beefier amp would need beefier transformers and maybe a bigger chassis, so a more sensitive speaker / micing up seems simpler.

[markmalin]

Thanks for the input, pdf64


What I've noticed is playing live (mic'd) with the master about 3/4 and the volume set about 1/3, whereas my jazzmaster will remain clean but too thin, the humbuckers on the 335 make it muddy/overdriven.  What I didn't try was setting the master to 10 and backing down the volume... I know, I know, it's a 5e3 and by nature will break up early.


I realize i haven't published a circuit or anything - it's more of a general question.  I'm curious to see if adjusting the plate voltage on the pre-amp tubes does anything different.  Just for my own curiosity's sake.


How's that for non-scientific hack mentality! :P


Incidentally, the next day with a 50w Dumble clone the clean jazz tone was amazing!  Thing is, I prefer the 5e3's clean tone when it's set to livingroom volumes.


Whatever...I appreciate the discussion.

...I'm guessing the pre-amp is overdriving...can I adjust plate voltages on the 12AY7 to get it to go further before breaking up?...

I think it rather more likely that the power stage is overdriving; as the signal level is increased from zero, given sensible control settings that's how it works. Otherwise, if the preamp hit overdrive first, the amp could never reach its intended max power output.
To achieve a cleanish tone at a higher sound pressure level, a beefier amp / more sensitive speaker cab, is necessary. (Or just mic it up )
A beefier amp would need beefier transformers and maybe a bigger chassis, so a more sensitive speaker / micing up seems simpler.

[92Volts]

I think it rather more likely that the power stage is overdriving; as the signal level is increased from zero, given sensible control settings that's how it works. Otherwise, if the preamp hit overdrive first, the amp could never reach its intended max power output.

You'd expect that, but it's not safe to assume every design is "sensible" or assume what the designers aimed for. Fenders are known as clean amps, but they offered options like the Twin for max clean volume. It may have taken a back seat to other goals in a 5E3. Big filtering resistors lower voltage (maybe below what's ideal), but they could have been chosen to reduce noise with the low size/high cost caps the designers were dealing with.

The 6V6s could need over 30v clean signal and the cathodyne phase inverter in could definitely struggle. The 56k plate/cathode resistors are fairly low for a 12AX7 so I might actually suggest trying a 12AT7 in the second position, if anywhere. But more voltage will be a pretty direct way to increase headroom.

[92Volts]

What I've noticed is playing live (mic'd) with the master about 3/4 and the volume set about 1/3, whereas my jazzmaster will remain clean but too thin, the humbuckers on the 335 make it muddy/overdriven. 

You could try reducing cathode bypass capacitors to cut bass (technically to boost treble, while stock 25uF caps in the 5E3 boost everything) or using an EQ pedal to cut bass.

Too much bass can make for unpleasant distortion which is why high-gain designs cut lots of it. It also takes lots of power to produce loud bass, and it could be limited by your OT, speaker, or the design's expected power output.

[Willabe]

Have you tried a different rectifier tube?

Try a 5AR4/GZ34 in place of the 5Y3.

Try alone 1st, then try it together with what Sluckey suggested.

[chocopower]

Dumble version of 5e3

[Leevi]

Modifiy the power amp like in 5D3


http://el34world.com/charts/Schematics/files/fender/Fender_deluxe_5d3_schem.pdf


/Leevi

[pdf64]

Modifiy the power amp like in 5D3


http://el34world.com/charts/Schematics/files/fender/Fender_deluxe_5d3_schem.pdf


/Leevi

I think that the 5D3's 10k HT dropper for the g2 node will act counter to markmalin's goal

[dscottguitars]

I have found that by increasing the value of the preamp cathode resistors helps, to 3.3K to4.7K. Also eliminate the bypass cap on the second stage all while increasing plate voltage too.

[92Volts]

I have found that by increasing the value of the preamp cathode resistors helps, to 3.3K to4.7K. Also eliminate the bypass cap on the second stage all while increasing plate voltage too.

That sounds real high for a 12AX7. It would reduce gain/volume which might prevent distortion, but I'm not sure it would increase clean signal handling

Worth a try though, cathode resistors are easy enough to test

[dscottguitars]

I’ve seen higher values used on later preamp stages. It is to cut gain. I guess it depends on how many stage there are. It helps to cut preamp distortion.

[dscottguitars]

I have found that by increasing the value of the preamp cathode resistors helps, to 3.3K to4.7K. Also eliminate the bypass cap on the second stage all while increasing plate voltage too.

That sounds real high for a 12AX7. It would reduce gain/volume which might prevent distortion, but I'm not sure it would increase clean signal handling

Worth a try though, cathode resistors are easy enough to test

What’s the difference between distortion and clean signal handling?

[SILVERGUN]

See if this helps:
https://vimeo.com/33244955

One concept that isn't covered is the fact that using a larger cathode resistor will result in a higher negative bias voltage  (we are expected to know that)

And they don't talk about what happens when you raise the plate voltage either, but it should be fairly obvious.

[markmalin]

I sure appreciate all the discussion, guys. :)


So with changing the cathode resistor, it's going to change the tone, isn't it? 


I've messed around with cathode resistors before to get more/less bass.  I like the tone...but maybe I can find a value that will make it a little "rounder".  I built this am for myself to use for both jazz and blues, and tend to play more jazz these days so the rounder/fatter the better :)


Hope to get some time on my bench in the next week or so

[SILVERGUN]

I sure appreciate all the discussion, guys. :)


So with changing the cathode resistor, it's going to change the tone, isn't it? 


I've messed around with cathode resistors before to get more/less bass.  I like the tone...but maybe I can find a value that will make it a little "rounder".  I built this am for myself to use for both jazz and blues, and tend to play more jazz these days so the rounder/fatter the better :)


Hope to get some time on my bench in the next week or so

In your case, since you're looking for more clean headroom, I'd follow sluckey's advice first and then if you like that you could also apply that same logic to the 5K dropper between the plate and screen supply (in line with pdf64's reply #12). Replace with a choke if you have one laying around or just strap/switch a 1K across it.

You're essentially trying to maximize signal swing from stage to stage and the best/simple way to do that is to increase plate voltages because the signal can only swing up to the plate voltage at each stage before it gets clipped. The further along in the signal chain you get, the more critical it is to have higher plate V if you're trying to keep it clean.

[markmalin]

In your case, since you're looking for more clean headroom, I'd follow sluckey's advice first and then if you like that you could also apply that same logic to the 5K dropper between the plate and screen supply (in line with pdf64's reply #12). Replace with a choke if you have one laying around or just strap/switch a 1K across it.

You're essentially trying to maximize signal swing from stage to stage and the best/simple way to do that is to increase plate voltages because the signal can only swing up to the plate voltage at each stage before it gets clipped. The further along in the signal chain you get, the more critical it is to have higher plate V if you're trying to keep it clean.

Help me understand how a choke would affect things?  I may have one or two laying around, now that you mention it.


Mark

[SILVERGUN]

In your case, since you're looking for more clean headroom, I'd follow sluckey's advice first and then if you like that you could also apply that same logic to the 5K dropper between the plate and screen supply (in line with pdf64's reply #12). Replace with a choke if you have one laying around or just strap/switch a 1K across it.

You're essentially trying to maximize signal swing from stage to stage and the best/simple way to do that is to increase plate voltages because the signal can only swing up to the plate voltage at each stage before it gets clipped. The further along in the signal chain you get, the more critical it is to have higher plate V if you're trying to keep it clean.

Help me understand how a choke would affect things?  I may have one or two laying around, now that you mention it.


Mark

It will drop less voltage than the 5K that is currently there, so it would result in higher voltages downstream

It will also have the inherent effect of raising the max. output power slightly, so you are getting further away from what makes a 5E3, but you are gaining the increased headroom you were looking for. It could also be made switchable.

[pdf64]

I have found that by increasing the value of the preamp cathode resistors helps, to 3.3K to4.7K. Also eliminate the bypass cap on the second stage all while increasing plate voltage too.

Are you sure that you haven't merely reduced gain?
I really can't see how that change would increase the amp's max clean SPL.
I suspect that by reducing gain, the volume control needs to be set higher in order to achieve the max clean SPL, but the max clean SPL hasn't changed.

Help me understand how a choke would affect things?  I may have one or two laying around, now that you mention it.

The amp's max plate current (and hence power output) is related to the g2 voltage.
A choke has much less resistance than a 5k resistor, hence the g2 voltage will be higher and stiffer.
The problem with this approach is that the idle plate dissipation will increase. I think that the amp is probably already configured to get the most power output in cathode bias with p-p 6V6. Of course higher power output is feasible if the designer ignores the constraints of the tube's limiting values.
If moving to a choke supplying the g2 node, then I think it would be very beneficial to switch to fixed bias. But then the amp would likely put out too much power for the OT to accommodate.

[92Volts]

What’s the difference between distortion and clean signal handling?

Distortion happens if you exceed the amp's clean signal handling.

You can avoid distortion by raising that limit... or by keeping the signal size below that limit in other words, "just" turning down the volume.

Reducing gain with these mods might make the amp much easier to use with settings/equipment that tend to push it past its limits. But if you need more total volume, it's not exactly offering more headroom/bigger clean signal.

[2deaf]

Before the 6V6's, the cathodyne is way far and away the limiting factor.  You only need around 0.6Vp or so going into the gain side of the 12AX7 to clip the cathodyne side at the DC voltage running in a typical 5E3.  As long as the cathodyne is swinging enough signal to clip the 6V6's, there is nothing you can do to the pre-amp to increase headroom.  It looks as though the cathodyne may be coming up a little short in this amp, but raising the DC on the cathodyne node will cure that.  Sluckey already has that covered.