Single-Ended Rocket

[sst4270]

Thought you guys would be interested in this...

I built this amp for customer in Canada.
I call it the Torn Sun Dark Star Mk II.
He posted a clip on YouTube of his son playing the amp.
It's a Rocket front end with dual inputs where the second simply parallels V1. Then into a 6L6GC. Operating in Class A.
About 20W at idle... 12~15 during use.
OT is Weber 25W SE.

Enjoy.

Here the video: http://www.youtube.com/user/GuitarJacks ... Kq71g0LTGs

I'm attaching the schematic and some photos I shot of the amp. Gut shots will be forthcoming.

Although not in the video it's got very similar break-up to a Rocket when turned up.

Steve

[M Fowler]

V1a/b is what the Matchless Spitfire does.

Nice looking amp will have to wait until I get off work to take a listen.

[Structo]

Cool!

I remember this amp!

http://www.youtube.com/watch?v=S5h5jfRH ... re=related

[sst4270]

Sorry Structo. Different amp. I just finished this one a couple of months ago.

[breakfastbuddy]

this was thin and sqicky sounding , so when you make it you have to bevare of that

[RJ Guitars]

Steve,

Nice looking build. I always like anything that is based upon the Rocket, it just seems like a very forgiving platform.

Can you say whether it has any of the typical Rocket vibe to it? It seems the video has been pulled so I wasn't able to actually listen to it.

The one schematic question I have is that there is usually a little bit of gain coming off of the phase inverter in a typical push pull long tail pair circuit. In your single ended implementation this doesn't exist so I might expect this thing to have more headroom and a cleaner sound? Any thoughts about it being better or worse or just different without that gain stage?

thanks,

rj

[sst4270]

RJ,

The owner of the video moved it to a different location. I've updated the link above and posted a gutshot. (ignore the diode. That was an failed experiment that I left on the board unattached to anything.)

I certainly believe it has a lot of that Rocket "3-D" sound. Especially on the cleans, but combined with the Single-ended platform. That gives it a unique tone all its own. It does break up really nice at full volume very much like the Rockets break up around 12.
And most importantly at full volume you can use the guitar volume to control break-up without sacrificing tone or loudness a feature which I think is key to a great playable amp.

One drawback apparent in the video IMHO is that the original owner put in an old low wattage alnico driver of some kind that lacks the bottom end that would be available with a different speaker rated with higher power . i.e. scumnico, tone tubby, celestion blue, etc...

Enjoy.

Thanks to all the advice and information here at TAG for making possible another happy guitar player.

Steve

[fayser]

Hey Steve... relative newbie here.. I have been thinking about putting my toes in the water with a build and rather than jump straight in to a Francesca build I was wondering if you wouldn't mind my trying my hand at your design.. It seems quite different to all the other single ended designs out there (fenders etc).. If you prefer this not to be used I can well understand.
Cheers
Thanks

[M Fowler]

I don't know I have a whole section on my CPU with circuits just like this one, nothing sticks out that is that extraordinary. What am I missing?

[RJ Guitars]

Thought you guys would be interested in this...

Here the video: http://www.youtube.com/user/GuitarJacks ... Kq71g0LTGs

Although not in the video it's got very similar break-up to a Rocket when turned up.

Steve

That is too sick when a kid can play like that.

Can we assume that the recording is overly bright and the real deal has more low end?

rj

[sst4270]

RJ,

Yes the recorder's mic has no bottom end, but also the speaker is to blame.

Mark,
I agree there are many many similar circuits out there, but very few Single Ended 6L6 guitar amps. And not any that I could find with the configuration that I chose.



-ST

[Structo]

Can you describe how loud this amp gets?

Do you think it is around 10-12 watts?

[dave g]

I've found single ended 6L6 amps to sound remarkably good; much better than single ended EL34 amps. I think the reason is due to the fact that 6L6s, when running in a single ended class A configuration (with no negative feedback), typically reach THD levels of ~10% at maximum unclipped output. That's compared to like 1% when you run them in push-pull (with negative feedback). EL34s, on the other hand, are in the 3-4% THD range when put in a similar single ended configuration.

To my ears, single ended 6L6s have a lot in common sonically with push-pull EL84s. Lots of chime. For the record, AC30s usually fall into the 10% THD range.

I think the circuit looks pretty good, Steve. If it were me, I might up the first coupler to a .005 or .01.

[RJ Guitars]

... If it were me, I might up the first coupler to a .005 or .01.

Do you mean the 500pF?

If you don't mind, tell me what you expect from that change?

thanks,

rj

[dave g]

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