5E3 Tweed Deluxe model with all 3 knobs, and the resulting channel interactions

Joe Bfstplk

Joe Bfstplk

Legend!
Hi--
It appears the current "Deluxe Tweed" 5E3 model is ignoring the "unused" channel, which is what is so incredibly awesome about that circuit.

The shared cathode resistor and bypass cap and the "backwards" wired volume pots (input to wiper, output from ungrounded end of resistance track) combine with the tone control to make a hugely interactive and very musical trio of controls.

Plugged into the unpadded jack of the "Bright" or "Instrument" channel (the labeling changed at some point in production on the Tweed Deluxe), with the volume about half up and the tone set to taste, if you turn up the unused "Normal" or "Mic" channel's volume past 3 o'clock you get a nice decrease in gain and low-mid response that mins out when the Normal/Mic channel is turned up all the way.

Switch your plug to the unpadded jack of the Normal/Mic channel, and instead of a mid dip, you get a nice mid boost with a little of the highs rolled off due to the tone control wiring and how it interacts with the two channels' volume controls. This makes a killer lead tone.

An A/B switch that grounds the unused output allows you to switch between the two channels and get a super, better than Blackface clean tone and a gnarly, raucous mid-heavy lead tone out of the little beastie.

Reference: - Post #1 on this thread:
http://www.trinityamps.com/phpbb/viewtopic.php?p=9773

Can we get the "Deluxe Tweed" model updated with the extra knob, and an "A/B" switch to put the guitar in the "Bright/Instrument" channel or the "Normal/Mic" channel?
 
favance said:
Why not just boost the Mid on the modeled amp?
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It's not quite the same thing. Try a 5E3 Tweed Deluxe reissue at your local guitar emporium that has one.

The mid cut/boost is the result of the out-of-phase relationship of the two input channels due to the lows below the shared cathode coupling resistor & cap's corner frequency nulling out the signal a bit at the frequencies where the cathodes' RC highpass in the channel you are plugged into is roughly equal to the RC lowpass of the channel you are not plugged into. The unused channel is driven by the cathode of the channel you are using, effectively turning the unused channel's triode into a common-grid triode stage that is out-of-phase with the channel you are using. The lows, provided by the channel you aren't using, are out-of-phase with the highs on the other side of the mid dip. When plugged into the bright channel, the treble peaking cap lets highs around the volume control to boost highs, but when plugged into the other channel, that same cap, due to the way the two volumes and tone are wired, gives a little top end rolloff and mid boost.

Verrrrrry interestink little complicatedly-simple circuit....
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Basically, as modeled, the "Deluxe Tweed" is really more of a "Prince Tone Tweed preamp into a Deluxe Tweed output section"
 
It's got nothing to do with the shared cathode. The corner frequency of the cathode network is 8 Hz. Nothing down there.

The unused channel influences the channel in use by changing the load.

Don't believe everything you read on the internet. Most of the self-proclaimed tube amp gurus don't know what they're talking about.
 
FractalAudio said:
It's got nothing to do with the shared cathode. The corner frequency of the cathode network is 8 Hz. Nothing down there.

The unused channel influences the channel in use by changing the load.

Don't believe everything you read on the internet. Most of the self-proclaimed tube amp gurus don't know what they're talking about.
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Have you tried operating one of these amps using all 3 knobs as described?
 
Joe Bfstplk said:
Have you tried operating one of these amps using all 3 knobs as described?
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I have. I'm not saying the unused channels knobs don't have an influence. I'm saying the reason has nothing to do with the cathode network. Furthermore you can replicate any of this with the input EQ and do things you could never do with three knobs.

Don't be stuck in the past. There are tools at your disposal to go far beyond the limitations of those old amps.
 
Actually, the 3dB down point WRT the common cathode stage, as set by Rk and Ck is not the same corner frequency as the LPF formed by the Rk and Ck as seen by the undriven side's cathode as an input. The driven side's cathode output impedance and the Rk||Ck form a low pass filter that drives the "unused" triode. Common grid gain is just a tiny bit higher than common cathode gain, but the input impedance is low, so it loses a bit when not driven by an extremely low impedance. Common grid output is in-phase with input, so OOP with common-cathode output.

Basically, the two input channels form a poor quality differential amplifier when only one input is fed a signal, with the "unused" stage being driven by the other's cathode, and the cathode bypass cap acting as a LPF at the "unused" triode's cathode input. It's similar to the way a long-tail pair ohase inverter works - the input stage is driven by the preamp while the "other" stage's grid is grounded and receives input signal via its cathode. So, the signal frequencies that are not well-bypassed bt Ck are amplified with a gain of roughly 31 (appx. 29.8dB), so not a lot of signal input is needed to be significant, and the LPF + the gain makes the corner frequency where there is significant signal there extend up into the lower mids. Can reply later with all the math step by step after work. Typing all this on my phone while on my lunch break currently.

I was not quoting "self-proclaimed tube amp gurus", nor do I claim that title for myself, but I do have 30+ years experience building with tubes and a good working knowledge of common circuits.

If your answer is, "We are disinclined to acquiesce to your request.", that's fine, but please don't impugn my knowledge....
 
Bottom line, I bought your product because it is generally excellent, and I suggest things to make it "excellent-er". Please take my commentary in that mindset.
 
I have one. Actually both a Painter 5E3 head and Axe 3. Try using the Fat switch and messing around with it. I use the 5e3 with a jumper and go into the bright input. Volumes could range from 4 to 6 to 9 variations. I was playing around with some different things to try and get that girth that happens with the jumper. I'm not saying it will do everything you may seek, but I could feel and hear a little more of what the jumper introduces so maybe it gets you close enough. I use it as a main amp and for the heavier channel on the Axe setting the fat channels does it for me. FWIW...



Side note - This could be an opportunity to use tone match... I may try that and see what the difference is.
 
I have a 5E3 channel in the VZA Simone amp I built 11 or so years ago. The other channel combines Orange's FAC idea (with different cap values) and an EF86 stage to land somewhere near the EF86 channel of the DC30 Matchless, but I digress.

The thing has two inputs and three knobs. It does the trick. Well, actually, both of the tricks. You get both a mid boost/top rolloff and a mid scoop/treble boost, depending on which input you use, if you set the 3 knobs right. To do either with EQ would be somewhat complicated and only get you close. To switch between them would be another whole level of complication to do what 3 knobs and an A/B switch can easily do. I have poked around extensively with the model, and tried to get it to do what the real thing does, and have been left wanting.

I suggest this mainly because the AxeFX seems to be all about accurate models, and I feel that this seminal amp's model does not include the most magical bit of its whole vibe, and I'd like to see that changed, as it is one of my favorite amps....
 
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Joe Bfstplk said:
I have a 5E3 channel in the VZA Simone amp I built 11 or so years ago. The other channel cobines Orange's FAC idea (with different cap valuea) and an EF86 stage to land somewhere near the EF86 channel of the DC30 Matchless, but I digress
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If you make some tonematch presets - remember me and send them my way. I like everything you mentioned. The Dr Z 66 and DC30 with the EF86 tube are favorites of mine, and I started out playing Orange Tube amps.

Fractal would need your amp to make the accurate representation. The tone match is a way to get there without mapping all the amps.
 
bshaw92 said:
If you make some tonematch presets - remember me and send them my way. I like everything you mentioned. The Dr Z 66 and DC30 with the EF86 tube are favorites of mine, and I started out playing Orange Tube amps.
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I added a +1 on someone else's existing DC30 EF86 channel request, with the additional request that the 6 way switch cap values be tweakable, though I doubt there is room in the UI for that depth of tweak.
 
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bshaw92 said:
I have one. Actually both a Painter 5E3 head and Axe 3. Try using the Fat switch and messing around with it. I use the 5e3 with a jumper and go into the bright input. Volumes could range from 4 to 6 to 9 variations. I was playing around with some different things to try and get that girth that happens with the jumper.
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Jumpered is yet another variation, which negates the cathode coupling wierdness that makes the other two tricks work. It is a valid 3rd choice for "how to use this amp". Try an A/B switch some time with the knobs set as described. It's almost as good as (and in some ways, better than) channel switching in later amps like MESA. The amp switches from a clean-to-cleanish sound that is easily as good as, if not better than, BF due to the squishy power amp, to a nice, smoky mid-heavy low-gain, compress-y, 6V6 grind, with not much volume difference. The guitar volume knob is your best friend, and you could do a whole gig with just the amp if you aren't doing metal....

bshaw92 said:
Side note - This could be an opportunity to use tone match... I may try that and see what the difference is.
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I may investigate that if I can glom onto all the recording equipment needed to get an accurate pic of what it's doing while eliminating the speaker differences and output section differences between my inaccurate 5E3 variation (6CA7s and a Weber Grey Wolf speaker in a Deluxe Reverb style chassis) and the model. I built Simone to give me a more powerful 5E3 style amp and improved, and more powerful AC15-ish amp all in one, that didn't need to be mic'ed up unless playing alongside a really heavy-hitting drummer.
 
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The output of the unused channel rolls off at 20 dB decade and starts at 20 dB down relative to the used channel. The corner frequency is around 11 Hz. The impact of summing the unused channel with the used channel is negligible.

Here's a plot of the used channel plus the unused channel if they were summed equally:
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The maximum difference is less than 0.6 dB rapidly diminishing to zero as the frequency increases.

What causes the difference is not summing the out-of-phase signal as it is very small in relation to the in-phase signal. What changes things is that the load on the summing junction changes. With the unused channel volume control at zero there's a 1M load. As the volume is increased that load decreases due to the low plate output impedance. With the unused channel volume at max the load is roughly 60K, quite a difference.

Yes the input stage looks like a (very poor) differential stage but the cathode cap shunts most of the signal to ground before it can be amplified. The finite cathode output impedance of the used channel actually exacerbates this. If it's impedance were zero there would be more signal at the plate but the output impedance creates a voltage divider. Differential stages need a large cathode resistance to work properly.
 
FractalAudio said:
The output of the unused channel rolls off at 20 dB decade and starts at 20 dB down relative to the used channel. The corner frequency is around 11 Hz. The impact of summing the unused channel with the used channel is negligible.

Here's a plot of the used channel plus the unused channel if they were summed equally:
View attachment 56206

The maximum difference is less than 0.6 dB rapidly diminishing to zero as the frequency increases.

What causes the difference is not summing the out-of-phase signal as it is very small in relation to the in-phase signal. What changes things is that the load on the summing junction changes. With the unused channel volume control at zero there's a 1M load. As the volume is increased that load decreases due to the low plate output impedance. With the unused channel volume at max the load is roughly 60K, quite a difference.

Yes the input stage looks like a (very poor) differential stage but the cathode cap shunts most of the signal to ground before it can be amplified. The finite cathode output impedance of the used channel actually exacerbates this. If it's impedance were zero there would be more signal at the plate but the output impedance creates a voltage divider. Differential stages need a large cathode resistance to work properly.
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That's what I was gonna say... ;)
 


This video illustrates what I am referring to. I dialed the guitar volume back so that the amp and the cell phone mic did not distort, to illustrate the relative magnitude of the signals.

The bright input cathode couples a small, but significant amount of lows and low mids to the normal channel's triode, which acts as a grounded-grid amplifier stage, and amplifies the signal without phase inversion. When mixed with the bright input's signal, it subtracts those lows and low mids. Note the knob positions - this works most with the normal volume at or above the 3 o'clock position (though you can start to hear it a little past noon).

At the 30 second mark, after I had dialed the normal channel's volume back to about where I like it, I roll off the bright volume, and the amp plays on with just the normal channel's volume up. The only way that volume knob got any signal to work with was via coupling across from the bright channel's cathode, with the cathode resistor and bypass cap setting a low pass filter (as I stated earlier) that leaves a small, muddy, and, most importantly out of phase with the driven channel so that it subracts the sound you hear from the overall mix instead of adding it. This small amount of signal coupling is amplified by the normal channel's triode, which is why what one normally would consider insignificant has a clearly audible result.

I can do a better recording with a professional mic and Logic Pro X if this doesn't convince you.

I can also dig out all the formulae from the RCA Radiotron Designer's Handbook to prove it to you with math, too.

http://www.tubebooks.org/Books/RDH4.pdf
 
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FractalAudio said:
What causes the difference is not summing the out-of-phase signal as it is very small in relation to the in-phase signal. What changes things is that the load on the summing junction changes. With the unused channel volume control at zero there's a 1M load. As the volume is increased that load decreases due to the low plate output impedance. With the unused channel volume at max the load is roughly 60K, quite a difference.
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Hi Cliff, do you think is doable to make a "load" parameter? It could be useful to add a "flavour" to current amp? (I'm talking not only for 53E, but for example for any input stage... or last stage...).
 
Smilzo said:
...do you think is doable to make a "load" parameter? It could be useful to add a "flavour" to current amp? (I'm talking not only for 53E, but for example for any input stage... or last stage...).
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We pretty much have that now with the Impedance selections in the In1 block.
 
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