5E3 farting out sound and VVR

[FosterW]

Can someone post a video or link of a 5E3 playing with a "farting out" sound, and maybe one with a demo of a VVR?

I'm asking because I built a 5E3 from scratch, and I'm having a weird volume dropout when playing it with a humbucker guitar. I'm thinking this must be the farting out, but it sounds like someone is turning the volume down and then back up, rather than a flubbing sound like I imagined. I've never played a real 5E3, so I'm not sure what the farting out sounds like.

The circuit started out mostly stock, but for SS recto. I used Classictone 5E3 iron, also added a home built VVR, just because I was curious. The speaker is a emi cannabis rex, because that's what I had on hand.

So, what I'm hearing is when I hit it hard with a low note, the volume drops out. There is no "sag" resistor or choke. I upped the reservoir cap network to 40uF (doubled and paralleled 20's with bleeders). Still the dropping out. I thought it might be some kind of weird blocking distortion, so I smallered the coupling caps (.01 on input stages and .022 on PI. I'm really liking the sounds of the changed coupling caps.)

Even with the changes, I'm still having the issue with the sound drop out. I'm not sure if this is the flubbing, or if there is an issue with the VVR. I have found that I have to turn the VVR all the way up when I power the amp on, then dial it back after it is all warmed up. I figured that had something to do with the tube warmup/current flow and maybe the cap network fully charging, but I've never seen anyone talk about this in forums or online.

So I'm reaching out to the community. I'm pretty experienced in other builds (higher gain, dual channel rocker amps) but I was always curious about the 5E3. If I can get this solved, it will probably give me some new direction in my custom builds.

Anyway. Much appreciation for any replies.

Thanks!

FosterW

[d95err]

Technically, I believe "farting out" is when you have to much bass going into a distorting stage (try playing palm muted heavy riffs with a fuzz pedal...).

From your description, it sounds like extreme sag. The 5k dropper to the screen supply should cause significant sag, regardless of rectifier type. Try lowering it to something like 1k.

[pdf64]

Maybe excessive squish http://www.aikenamps.com/index.php/what-is-sag
What happens to the cathode voltage, eg what's the cathode voltage under static and 'dropped out' conditions?
It may be that the bias voltage (Vg-k) is being increased to the point of cut off.

What's the power tube static dissipation at full VB+?

It would be helpful to monitor the plate and screen B+ nodes, and the cathode voltage, under static, max clean(ish) and max overdriven outputs.

Try lowering it to something like 1k

I think that may further increase the static plate current, which may not be a good thing.

It would be helpful to provide a sketch of the schematic; once the mods begin piling up, the 5E3 reference loses relevance.

[John_P_WI]

Sounds to me like there is a missing grid leak or ground reference...

[JazzGuitarGimp]

Did you build the amp with the VVR from the get-go, or did you add the VVR after the amp was built and functional? If you added it after the amp was working, did it exhibit this same problem before you added the VVR?

[The Ballzz]

FosterW,
A few questions for ya:

A) Whose schematic did you use for the build? Some folks do the phase inverter quite differently from each other.

B) Does the VVR regulate the whole amp or just the power amp section?

C) If just regulating the power section, does this include the PI? And again, begging the question of which PI version did you choose?

I'm in much the same boat you described that you were in prior to your build.

Many folks talk of some "improvements" that should be done automatically, but I would prefer to start with as bone stock build as possible and then witness, first hand, any step by step improvements and their results to make my own judgement call.
Just Curious,
Gene

[FosterW]

Thanks for the replies. This is my first post and its nice to see such helpful folks. For the schematic I used the "5E3 with VVR" attached below. I used the schem of the vvr from the 18 watt lite. It drops voltage for the whole amp, ala the 5e3 schem. I used a STP9NK9OZ for the MOSFET, mica insulated on a heat sink, and built it in the circuit from the get go.

I felt like the stock circuit was too muddy, probably due to my speaker choice, and the nature of the deluxe. I do like the overall brighter tone of the smaller coupling caps.

The problem sound is not a nasty blatty sound like typical blocking distortion. I'm pretty sure these no missing grid leak. I'll double check that all grid leaks are installed. I've done dumber things.

It does seem to be related to the setting of the vvr, higher settings lessen the effect. But like I said, the overall operation of the vvr is different than I expected with the turning it all the way up while it warms up, slight delay in the reponse from making an adjustment. Curiouser and curiouser.

Thanks everyone!

FW