Single-Ended Rocket

[RJ Guitars]

Thanks Dave,

I keep a collection of good tweaks for the Rocket... I ran a thread on it once but I don't think there was anything about this that was added to that thread.

thanks again,

rj

[dave g]

I actually did post some of these tweaks in that thread

http://ampgarage.com/forum/viewtopic.ph ... ket+tweaks

Since then I've gone back on a few of the tweaks and added others. For example, I do like the sound of the stock PI when an extra 100k or 220k to ground is added at the PI entrance. What I posted yesterday, though, reflects my current recipe.

[dorrisant]

Just out of curiosity, how would this amp sound if it had a Rocket pre with the fake pi? Just wondering if you might have tried this already. If so, what is that like. If not, is there any reason why it wouldn't?

[sst4270]

Dorrisant,

I hadn't considered the addition of another gain stage (to simulate the PI) at the time I built the amp. I wanted a really clean chimey practice amp/small gig amp that would get a little bite when you dug in...

Ironically, the owner just recently contacted me to tell me that he put a Celestion Gold in the amp and it really opened the amp up quite a bit.

He sent me a couple of clips. I'm a little hesitant to post them because he was recorded them with a Zoom recorder he just got, and he was still getting used to using the recorder. The recording volume was really low and, I believe, a little too close to the amp to catch any of the room reflections. So the recordings are a little dry as well.

I'm hoping to get some more clips this weekend from a live gig. We'll see.

Anyhow, here you go. Hope you like 'em. Turn up your volume for these clips or more preferably listen with headphones.



Steve

[dorrisant]

The first clip has that clean sound that I've been looking for.... Makes me salivate just a bit. I am seriously considering building something similar... like an express with a fake pi mated to a 6L6 single ended pa. This thread has got me thinking that the rocket may be a better candidate. I love the sound from the first clip but I would want to be able to dial in a bunch more overdrive. I may have to implement some of the mods mentioned by dave g. I am experimenting with getting the pa stage to distort first (a la express). I know you are one to have experimented with this pre quite a bit and look forward to any advice. I did notice that the filter caps were a different value than those given in the schematic... just wondering what prompted the change.
All in all, that is a beautiful tone, even with a poor mic job. And who wouldn't be proud of that gorgeous cabinet? Awesome job man!

Tony

[Zippy]

Just out of curiosity, how would this amp sound if it had a Rocket pre with the fake pi? Just wondering if you might have tried this already. If so, what is that like. If not, is there any reason why it wouldn't?

How much gain do you think is added by the Rocket PI?

Is there an example of such a "fake PI"? I'm not familiar with this as applied to a SE amp.

[dorrisant]

Zippy,
To answer your question... I don't know exactly how much gain there is to a Rocket PI... but I do know there is some there. The example I'm typing of is a Trainwreck Express... Since you don't need the PI for a single ended amp, you can use just one half (the top half in this instance) of the PI to add a little more gain to the pre and use the unused half of one of your 12AX7s. Clear as mud right? I believe the first time I saw this was last summer on one of the stompbox sites... Steve drew up the schematic on it(don't be mad if I'm wrong about that).
Here it is...
[IMG380]http://i946.photobucket.com/albums/ad30 ... pwZw-1.jpg[/img]
I have tried this incarnation feeding into a hybrid amp as well as running it directly into a Peavey classic 30. Sounds awesome!
Now you know... What do you think?
Tony

[marcoloco961]

Yes, I mean the 500pF. A .005 would give the amp much better lower midrange and bass response by lowering the knee frequency of the first stage from 637 Hz to 64 Hz (which the amp needs, IMHO). If that's too much bass, a .002 would give a rolloff freq of 159 Hz.

That 500pF coupler is one of the things about the Rocket I simply don't like. I can somewhat understand it in the case of an EL84 power section since those tubes simply can't handle the bass as well as others, but 6L6 amps handle low frequencies better than just about anything else.

For the record, when I build a Rocket, I typically use a .001 or a .002 in place of the 500pF, a 120pF treble cap (rather than a 50pF), an extra 220k (sometimes a 100k depending on what I do to the second gain stage) to ground at the PI entrance (after the series 220k), and .01 or .022 couplers in the power section rather than .047s. I also like about 360 volts at B+1, with a shared 75 ohm bias resistor for the EL84s. Sometimes I will also kick up the 2nd stage cathode resistor to something like 2.2k - 4.7k and add a small bypass cap (.68 to 5uF). You can always add series resistance to the bypass cap if the boost is too dramatic.

That's my personal recipe, YMMV

I do think Dave is on to something with the 500pf coupler cap. That is a pretty high roll-off. A .0047 to a .0022 should add some mids and lows to the sound without making it too "muddy". You might have try a few different ones to find "your sweet spot". If it is still bright, a 500K treble pot in T.S. might help. A grid leak after the T.S might be nice also. Gives the TS a little more gain and control. Maybe a 100k to 470k? This is, assuming 12ax7's in the pre. and using a 250v HT for calcs.

[manamp]

Steve,
Is there a diode that is located between two resistance on the motherboard? I do not see it on schematic.

Age

[dorrisant]

Manamp,
Steve had stated earlier in the thread that it was a failed experiment that he had left on the board but not really attached to anything.
Tony

[manamp]

OK - Thanks for the reply

[Colossal]

A grid leak after the T.S might be nice also. Gives the TS a little more gain and control. Maybe a 100k to 470k? This is, assuming 12ax7's in the pre. and using a 250v HT for calcs.

Hi Marco,

Interesting idea. For an added grid leak, do you mean placing it *immediately* after the tone stack and *before* the volume pot or just after the volume pot, just before the second stage? I'm thinking you're not including the volume pot as part of the tone stack but just wanted to clarify.

Thanks.

[marcoloco961]

A grid leak after the T.S might be nice also. Gives the TS a little more gain and control. Maybe a 100k to 470k? This is, assuming 12ax7's in the pre. and using a 250v HT for calcs.

Hi Marco,

Interesting idea. For an added grid leak, do you mean placing it *immediately* after the tone stack and *before* the volume pot or just after the volume pot, just before the second stage? I'm thinking you're not including the volume pot as part of the tone stack but just wanted to clarify.

Thanks.

I think we are talking about two different schematics.

I was referring to the first schematic titled Torn Sun Dark Star MKII, not the second one. On the first one the treble wiper runs directly into the power tube. I have seen this done before, and I am not sure how much of a load the power tube puts on the TS if any, but a volume pot behind the TS is pretty common, and does act as a load.

I have had my best luck with a 500k - 1M volume pot or a grid leak directly after the TS. IMO, it seems that the TS is more user friendly with a load behind it, without it I feel as if the tone shaping of the stack is rather weak. If I don't have a volume pot right behind it, I always like to use at least a 220K. Punch the data for your favorite F/M/V TS into the Duncan TSC and try it with a few different load values behind the TS. You should see what I am trying to get at.

[Colossal]

I think we are talking about two different schematics. I was referring to the first schematic titled Torn Sun Dark Star MKII, not the second one.

Yes, I was referring to the Express schematic posted just above, not the SE Rocket/Dark Star. So, yes, adding the grid leak after the Dark Star's tonestack makes sense.

[ampbldr2]

I have a Heyboer 7k pri 25watt OT that needs a project. Would it work in this circuit?