VOX Powered Rocket with VVR2

[RJ Guitars]

Hello Forum,

I have completed another iteration of the Rocket amp. This time using all VOX transformers and additionally I've added Dana's VVR2 module.

It is all working and it sounds really good... maybe not a surprise but it seems to sound very much like the Heyboer powered Rocket I built earlier this year.

I'll post some voltages and other info dependent upon the interest that is shown.

I used the VOX transformers for several reasons. but among the good reasons to do this is that they have a 120/230 option for the primary.

More tests and playing with things has to be done to get a good evaluation of what I like and don't like about it, but generally speaking I'd say I'm pleased with it.

rj

[RJ Guitars]

In the event anyone is curious, here is the data I took last night from the 5 B+ nodes on this Rocket amp with VVR2 control. I'll have a further evaluation on the VVR as well as the Rocket performance as soon as time allows me to play with it.

rj

[UR12]

Congrats! I see you also went for the cap cans.

[Zippy]

What does 100/75/50/25% relate to? Is that measured output power or what?

I'm curious to compare SOUND and RESPONSE at the "half power" range. Then we can start wrapping our heads around what makes the difference between a Two-Hole Rocket vs a Four-Hole Rocket running VVR.

Given my experience with Fenders of the different eras, I would expect to feel and hear a drastic change as preamp voltages get ever lower and the character of each stage's response changes. Eventually, the gain structure is going to fall out of the Trainwreck paradigm and you'll just get "something else". Then it becomes an issue of whether this "something else" is still as versatile a player's tone tool.

Cool stuff, RJ. Keep at it!

[UR12]

What does 100/75/50/25% relate to? Is that measured output power or what?

I'm curious to compare SOUND and RESPONSE at the "half power" range. Then we can start wrapping our heads around what makes the difference between a Two-Hole Rocket vs a Four-Hole Rocket running VVR.

Given my experience with Fenders of the different eras, I would expect to feel and hear a drastic change as preamp voltages get ever lower and the character of each stage's response changes. Eventually, the gain structure is going to fall out of the Trainwreck paradigm and you'll just get "something else". Then it becomes an issue of whether this "something else" is still as versatile a player's tone tool.

Cool stuff, RJ. Keep at it!

Zippy

I think the Graph percentages are for B+ voltage at different percentages of full Voltage. That is different than actual power.

In response to your expectations, I think you will be surprised if you actually try a VVR. Since everything in the Rocket is self biased, (Both Power amp and preamp tubes) Their bias also changes in response to the change in B+ voltage and everything stays on a linear portion of the tubes curve charts. In laymans's terms you will keep the same sound and gain structure all of the way down. You will notice a change in the sound of the amp once you get to apoint that you aren't providing enough power to drive your speakers hard enough to move any air. The response and Feel of the amp will also remain the same as a cranked amp at a reduce vol until you reach the point again where the speakers aren't moving enough air.

There is a BIG difference in removing 2 of your 4 output tubes (1/2 power) and the VVR ( 4 tubes 1/2 B+). Just my 2 cents YMMV

[Zippy]

There is a BIG difference in removing 2 of your 4 output tubes (1/2 power) and the VVR ( 4 tubes 1/2 B+). Just my 2 cents YMMV

I agree that there should be a big difference - I would expect more compression in the 1/2 B+ version, more dynamic response in the 2-tube version running the preamp at full power.

Given the difference in signal coming out of the PI in the two cases, at what % of B+ does one get half the output power? Has anyone measured output power and looked at the corresponding B+?

I really want to be able to quantify some of this and understand it. I can accept that it works but don't yet understand HOW VVR can work at low voltages and yet maintain the characteristic response. I think I need to get a 'scope on a VVR Rocket and watch the response of each stage. I'm recalling that someone did a similar study on an Express where they evaluated where the drive starts happening. Something like that would be compelling to me.

Thanks for the response to my note.

[RJ Guitars]

Zippy / Dana,

you guys are on a cool track for exploration here. I have a little bit to add about the amps behavior. Primarily the way it sounds with different guitars.

These amps always seem to sound great with a Strat - great clean and Blues tones especially for power chords. At max voltage this is true for this amp, but when I dial it down, it's not as sweet and full and the distortion gets a bit fizzy.

With my ES-339 it seems to really like the dialed down settings and the distortion is sweet and downright pleasant.

I don't know what that is telling us, but it's interesting at the least.

The amp is still really loud until I get the voltage knob below 1/4 power. Then it starts to get a lot quieter and breaks up real easy.

I've also noticed that at settings of 1/4 voltage or less, the VVR puts out a lot of heat. I don't know if it is working abnormally hard but I will need to be careful about dialing it down for a long gig at very low voltage. Above 1/4 it doesn't really seem to generate much heat.

rj

[Zippy]

Zippy / Dana,

you guys are on a cool track for exploration here. I have a little bit to add about the amps behavior. Primarily the way it sounds with different guitars.

These amps always seem to sound great with a Strat - great clean and Blues tones especially for power chords. At max voltage this is true for this amp, but when I dial it down, it's not as sweet and full and the distortion gets a bit fizzy.

With my ES-339 it seems to really like the dialed down settings and the distortion is sweet and downright pleasant.

I don't know what that is telling us, but it's interesting at the least

That's telling me that it's on the edge of being starved for signal at the first stage. Prime excuse for moving that "spare" 1/2 12AX7 to the first position and switching in an extra 3dB by going parallel on the first gain stage. Call it the "Low Power Strat-Happy switch".

I've also noticed that at settings of 1/4 voltage or less, the VVR puts out a lot of heat.

If people are using this for bedroom SPLs, that may be a concern with the wood face plate. How hot is "hot"? Maybe it would be better suited to mounting it on the outside of the chassis bottom with a heat sink and insulation between the sink and chassis. Of course, then you'd get people that burn their fingers wondering if the heat sink is getting hot...

[UR12]

Zippy / Dana,

you guys are on a cool track for exploration here. I have a little bit to add about the amps behavior. Primarily the way it sounds with different guitars.

These amps always seem to sound great with a Strat - great clean and Blues tones especially for power chords. At max voltage this is true for this amp, but when I dial it down, it's not as sweet and full and the distortion gets a bit fizzy.

With my ES-339 it seems to really like the dialed down settings and the distortion is sweet and downright pleasant.

I don't know what that is telling us, but it's interesting at the least

That's telling me that it's on the edge of being starved for signal at the first stage. Prime excuse for moving that "spare" 1/2 12AX7 to the first position and switching in an extra 3dB by going parallel on the first gain stage. Call it the "Low Power Strat-Happy switch".

I've also noticed that at settings of 1/4 voltage or less, the VVR puts out a lot of heat.

If people are using this for bedroom SPLs, that may be a concern with the wood face plate. How hot is "hot"? Maybe it would be better suited to mounting it on the outside of the chassis bottom with a heat sink and insulation between the sink and chassis. Of course, then you'd get people that burn their fingers wondering if the heat sink is getting hot...

From what you have described you are regulating the whole amp. It doesn't make any difference how much of the amp you regulate, just the Power tubes, Power tubes and PI or the whole amp. If you do just the power tubes you can overdrive the power tubes running at reduced voltages with a preamp running at normal voltages. This is why you need to install a PPIMV. If you regulate the whole amp then it is possible for the signal from your guitar to overdrive the first preamp stage running at reduced voltages. Different guitars have different output levels from their pickups. If you roll the guitar vol back a little you should be able to get the same tone you had at the louder power levels. It is exactly the opposite of "being starved for signal". It is sounding different for different guitars because of the pickups in those guitars are all different when it comes to signal levels. Some pups are just a lot hotter than others.

The heat should be at the greatest between 3/4 and 1/2 on the control. Once you reduce the voltages down to a point the tubes aren't drawing enough current through the mosfet the heat should be less not more, so the heat should be less at 1/4 voltage than it is at 1/2 voltage. There is a great post by PRR on just this subject if you do a search on this forum. If heat becomes a problem then you may need an external heat sink. I personally have a VVR installed on a few 36 watt amps using a quad of EL84s without external heat sinks and they all have been running fine for years.

[RJ Guitars]

From what you have described you are regulating the whole amp

Some pups are just a lot hotter than others.

The heat should be at the greatest between 3/4 and 1/2 on the control. Once you reduce the voltages down to a point the tubes aren't drawing enough current through the mosfet the heat should be less not more, so the heat should be less at 1/4 voltage than it is at 1/2 voltage.

I personally have a VVR installed on a few 36 watt amps using a quad of EL84s without external heat sinks and they all have been running fine for years.

Dana, thanks for the info. I am regulating the whole amp and I am really enjoying this option.

The pups on the 339 are quite a bit hotter than my Strat pickups. The 339 really seems to like the amp at all voltages. The Strat requires a bit more finesse at lower voltages.

I made several videos but I just can't quite capture the real sound with the mic on my camera... I'll try to get a more sophisticated AV setup because I really want to add some clips of all these Rocket amps to the info on AGF.

I was curious about how robust the VVR is... I was assuming heat means that it is working hard and I didn't know if I was pushing it or not.

I think it's really interesting how the amp really stays loud and even somewhat clean (with a lighter touch) all the way down to 25% of full voltage (of the knob rotation). Looking at my voltage data, that means that these tubes are actually functioning pretty well with only a hundred volts on the power tubes and even less on the preamp tubes.

If the amp retains it's general character (I'm not arguing that it does or does not) as you uniformly drop the voltage, then you should be able to take a transformer that produces a much smaller B+ and create an amp with a similar character... does that sound reasonable?

rj

[UR12]

Dana, thanks for the info. I am regulating the whole amp and I am really enjoying this option.

The pups on the 339 are quite a bit hotter than my Strat pickups. The 339 really seems to like the amp at all voltages. The Strat requires a bit more finesse at lower voltages.

I made several videos but I just can't quite capture the real sound with the mic on my camera... I'll try to get a more sophisticated AV setup because I really want to add some clips of all these Rocket amps to the info on AGF.

I was curious about how robust the VVR is... I was assuming heat means that it is working hard and I didn't know if I was pushing it or not.

I think it's really interesting how the amp really stays loud and even somewhat clean (with a lighter touch) all the way down to 25% of full voltage (of the knob rotation). Looking at my voltage data, that means that these tubes are actually functioning pretty well with only a hundred volts on the power tubes and even less on the preamp tubes.

If the amp retains it's general character (I'm not arguing that it does or does not) as you uniformly drop the voltage, then you should be able to take a transformer that produces a much smaller B+ and create an amp with a similar character... does that sound reasonable?

rj

I guess it all boils down to what it is you are trying to achieve with your sound. Reduced power levels deals with more than just different B+ voltages. If you think about the whole power supply in the Rocket you have a pretty stiff unit with 80 -100uf cap on the plates, a 40 or larger on the screens with a choke, a tube recto capable of 250ma and a tranny capable of 300ma. It is designed to supply enough power to run the Rocket at a given power level. As long as you keep enough of these component values in a range and get a tranny that produces much lower B+, I guess it would work or have similar character. But why would you want to build a Rocket with 4 power tubes and run it at a fixed low voltage? If your amp with the VVR installed keeps it's character when you lower it's voltage then you have the answer to your own question.

[Zippy]

Excellent, Dana. Thanks.

[RJ Guitars]

I guess it all boils down to what it is you are trying to achieve with your sound. Reduced power levels deals with more than just different B+ voltages. If you think about the whole power supply in the Rocket you have a pretty stiff unit with 80 -100uf cap on the plates, a 40 or larger on the screens with a choke, a tube recto capable of 250ma and a tranny capable of 300ma. It is designed to supply enough power to run the Rocket at a given power level. As long as you keep enough of these component values in a range and get a tranny that produces much lower B+, I guess it would work or have similar character. But why would you want to build a Rocket with 4 power tubes and run it at a fixed low voltage? If your amp with the VVR installed keeps it's character when you lower it's voltage then you have the answer to your own question.

Yes Dana,

Zippy is right Excellent!!

My interest in both the Trainwreck and Dumble amps has been to learn where that "Holy Grail" tone comes from. In a previous life as an amp builder I only made very small low wattage amps. So, great tone and power scaling really return me to that original amp building interest with several new tools and ideas... I am really working toward convincing myself that a lower voltage Rocket would indeed still sound like Rocket... and/or what might have to be changed or left alone to preserve what I've got tonally.

There are a couple things the VVR Rocket doesn't do... but I'll have to say it's mostly a matter of mass and weight between what I might hope to build and what the Rocket is. I'm not sure if the theory holds water or not, but it seems that if I could put the Rocket tone in a smaller lighter package, it would be altogether cool... albeit less useful when that outdoor gig comes around.

Anyway thanks. The VVR Rocket has inspired me toward a couple more builds.

rj

[Curbdog]

RJ, my thoughts exactly after building the Rocket ! Based on my satisfaction with the tone of my Rocket-inspired amp at half-power, I was thinking about building an amp with the Rocket pre-amp and power supply, 2 tube power section and smaller transformers. Is this an AC-15? Also considering solid state rectification. I know this starts to become quite a different amp at this point, but I am thinking I woud like to give it a try. I just happen to have a small chassis laying around that would be perfect...

[RJ Guitars]

...I was thinking about building an amp with the Rocket pre-amp and power supply, 2 tube power section and smaller transformers. Is this an AC-15? Also considering solid state rectification. I know this starts to become quite a different amp ...

Curb always good to have your thoughts... I see you are also looking at Rocket #3. I guess a guy just can't have too many of those things around.

I kinda believe that KF used the GZ34 rectifier in the Rockets because it was so stiff... so stiff in fact that it really acts something like a SS rectifier. This also allowed him to follow the VOX tube layout and accomplish his stated intention of making the AC-30... only better. I think you loose 17 volts with the GZ34 so I'm thinking SS rectifier and less voltage will probably still sound Rocketish... only the build will really tell.

There are a couple good data points out there. In the old "Pre-group-build" Rocket archives, Paul Ruby built one that is supposed to sound just amazing. I know he ditched the choke and maybe the GZ34 too, I can't recall off the top of my head. I'm sure he'd tell us a few good things if we ping him about it.

I think of the AC-15 as a different amp because they use much more voltage for the B+. I had the thought of using that PT for a scaled down Rocket but then I saw the AC voltage was 330-0-330. I'll attach a wiring diagram on them. I really don't know a any more about the AC-15 but it's kinda going the wrong way as far as scaling the power down.

Edcor has a 190-0-190 that supplies 250mA... maybe just right for Rocket # 3? As far as an output transformer I'm still not quite sure about that, Maybe the AC-15 OT will be right for that, assuming you go with a 2 tube output section.

rj