Rocket low end and midrange

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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Doxie man
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Rocket low end and midrange

Post by Doxie man »

I am thinking about changing the mid cap in my Rocket build to something less baddy. .01uf or maybe .0047uf. This circuit has soooo much bottom and low mods. I want to lean it out a bit and was curious to others experimentation and findings. Also....I am using the Classic Tone transformer set speced for the Trainwreck stuff.....using the 260v tap 👍 I have not heard anyone talking about the Classic Tone iron around here. I have always had great results using their transformers personally
Bob S
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Re: Rocket low end and midrange

Post by Bob S »

Lots of us have used ClassicTone iron - with good results.
I think it was RJ who named Rocket "Fat Bottomed Girl" Lots of low end. I've never had to dink with the stock circuit much.
Mark Fowler is the TAG Rocket Man so I'll let him comment on best methods for knocking some of the bottom end off.
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Re: Rocket low end and midrange

Post by brewdude »

At the risk of sounding like a dick, can you just turn the bass knob down?
Doxie man
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Re: Rocket low end and midrange

Post by Doxie man »

That's BRILLIANT ! .....can't wait to get home and give that a try 👌
Roe
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Re: Rocket low end and midrange

Post by Roe »

I'd mod the PI first. Try a 1nf or 750pf input cap and 10-15nf coupling caps
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M Fowler
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Re: Rocket low end and midrange

Post by M Fowler »

I use .022uf caps but if you increase the slope resistor that will lessen the bass and increase treble.

Use a trim pot and set to desired tone stack or add slope pot to front of amp where it is easy to get too.

The mid range is set by that 10k resistor of the bass pot increase the value to 25k.
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rp
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Re: Rocket low end and midrange

Post by rp »

The interactive tone controls are problematic on Voxes, if you have no Vox experience it’ll throw you off at first, pretty much any way you twiddle the tone knobs you scoop the mids and loose treble and the amps sounds bassy, you have to find your sound, guitar included, and live with it as is, as generations of Vox fans have done. Not sure why Fisher kept his version as original but I’m guessing he loved his Voxes as is quirks and all. I like it as is too is but then I had spent time around Voxes before learning to screw around inside amps, otherwise if you have no habits, it’s no big deal to fix what is really an annoying circuit error. Google ‘vox interactive tone controls’ I don’t recall if you ground or lift one end of the bass pot (think the later) but you do whatever the opposite of what it is, i.e. make it like a Fender. You can also add a 10K midrange pot or trimmer, or a 25K for a boost (off hand, I think copy the Express TS) you can then cut bass and not loose mids. Perception goes a long way to reality, move one part of the EQ and the whole thing seems to skew up or down, so this might solve your problem. It won’t change the circuit but it makes your Vox tone controls work proper like a Fender, better balanced and not affecting each other or the mids and highs. Again, it throws me off, it doesn’t take away your fave Vox tones just makes them hard to find them again, too much twiddling for me especially with a mid pot, but nothing some patience shouldn’t solve. Just a few minutes work to experiment.

Also, why not try SOP? Lower the 25mf bypass cap on V1 to 1-5mf. Lower the filtering, try Vox filtering. And then the various coupling caps like other suggested. But you are moving away from the Vox and KF thing here.
Doxie man
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Re: Rocket low end and midrange

Post by Doxie man »

Well....I tweaked the hell out of this thing and have drawn up my own opinions about this circuit:
1. IT will not and can not compete with a Plexi circuit when it comes to rock tones. The Marshall circuit delivers a much nicer rock tone IMO. That being said...the VOX tone is kinda cool for what it is. I have to admit I have VERY little time spent under the hood or playing VOX based circuits. The Fender Tweeds and
Marshalls have always kept me happy 👍
2.The CLEAN and "jangle" are what I really like about the Rocket and VOX circuits. They sound FANTASTIC 👌 So I definitely have respect and a use for them. I basically ended up building a Z-Wreck preamp in the end. The 220k to ground just ahead of the PI is crucial to getting this circuit to smooth out and play nice. I also lowered the PI input cap to .01uf to smooth things a bit. I changed the mid cap in series with the 10k down to .0022uf and increased the treble cap to 500pf as in Marshall. These changes made a nice difference. All that is left to do I think is remove all that unnecessary filtering in the power section. Remember....this amp started out as a Liverpool and I still have not changed the power section. The heavy filtering in these things is a little rediculous IMO. I wanted to stay true to the original as close as possible for my own education but none of these TW circuits need anywhere near the heavy filtering to function properly AND sound nice but I do understand Ken's theory as to why he did and respect that 👍 Anyway....it's been a fun project and once I trim the fat away on the filtering I think this circuit will be a keeper for clean and light overdrive Another nice tweak was to increase the coupler on V1 from 500pf to .001uf ala MATCHLESS Lightning 😉
Last edited by Doxie man on Thu Mar 23, 2017 12:07 am, edited 2 times in total.
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Guy77
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Re: Rocket low end and midrange

Post by Guy77 »

I have also just completed converting my stock Liverpool amp to a ZWRECK and I absolutely love it!
The amp has a much nicer sparkle to it now.
Here are my finding as I completed the conversion.

1. Completed the preamp first (with zwreck dropping string resistors, 27K,22k and 22K) and dropped the first filter cap to 40uf , kept all other filter caps stock Liverpool)
Sounded nice and I liked the fact that my Gibson SG guitar now sounded much better with this than with my Liverpool. My strat was very nice with the Liverpool and it was nice with my new Zwreck as well.

2. Added the choke in place of the 1K resitor, the amp sounded so much better (more sparkle)!

3. Changed the power tube resistors from 100R to 1K and the overdrive sounded a little smoother, I liked this and kept it!

4. Changed the choke to a Marshall JCM800 choke and I liked the overdriven tones a little better. More importantly the sparkle was still their.

I kept my output transformer stock Liverpool 6.6K and lowered B+ to 300v with Zener and mosfet.
It seems like the choke ads a lot to this zwreck amp.
Funny thing is when I added the choke to the Liverpool ( at an earlier date before the conversion) it did not suit the amp.

Cheers

Guy
Doxie man
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Re: Rocket low end and midrange

Post by Doxie man »

Yep 👍.....I just ordered a 15hy/410R/75ma choke from Hammond and will install that this weekend. I am going to also reduce that excessive filtering down to 47/47/16/16/16 . These changes should really open the tone up a little. I'm not going to go tube rect. though. No benefit in doing so. I prefer the SS rect. Better efficiency, one less tube to fool with . I like the higher voltages with no sag for myself. This circuit has plenty of breath and bounce anyway 👍

I always install 1K/5W wire-wounds on my screens on every build I do.......at 100R....why even bother 👎
Roe
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Re: Rocket low end and midrange

Post by Roe »

If you use 100R screen resistors try a high resistance choke like the AC30 chokes. 410R or more is recommended.
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Doxie man
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Re: Rocket low end and midrange

Post by Doxie man »

The choke Im using is the Hammond 158L which is the proper unit. I use 1k/5w screens on my builds .....ALWAYS 👌
Mark
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Re: Rocket low end and midrange

Post by Mark »

Roe why does the screen resistors effect your choice of choke. I've never seen a lot of voltage drop across the choke though I haven't measured across a choke in some time.

BTW I found the bass and mids in the Rocket to be good. It does appear to be sensitive to valve choices. A large plate GE 12AX7 made my Rocket clone sound bassier the more I turned it up. Amperex 12AX7's worked for me.

I have wondered what a different cathode follower valve would be like in this amp. Surely a 12AT7, a12AU7, etc could be used. The cathode follower doesn't provide gain, perhaps volume loss wouldn't be an issue?
Yours Sincerely

Mark Abbott
Roe
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Re: Rocket low end and midrange

Post by Roe »

Mark wrote: Sat Apr 15, 2017 11:55 am Roe why does the screen resistors effect your choice of choke. I've never seen a lot of voltage drop across the choke though I haven't measured across a choke in some time.
the ef84s need some considerable screen resistance if you run around 320v like vox did. Vox used a 420R choke in series with 100R screen resistors. I'm running a 470R shared resistor in series with 100R individual screen resistors myself (along with a CLC filter and a SS rectifier)
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pompeiisneaks
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Re: Rocket low end and midrange

Post by pompeiisneaks »

Mark wrote: Sat Apr 15, 2017 11:55 am Roe why does the screen resistors effect your choice of choke. I've never seen a lot of voltage drop across the choke though I haven't measured across a choke in some time.

BTW I found the bass and mids in the Rocket to be good. It does appear to be sensitive to valve choices. A large plate GE 12AX7 made my Rocket clone sound bassier the more I turned it up. Amperex 12AX7's worked for me.

I have wondered what a different cathode follower valve would be like in this amp. Surely a 12AT7, a12AU7, etc could be used. The cathode follower doesn't provide gain, perhaps volume loss wouldn't be an issue?
yeah most choke's tend to act like 500-1000 ohm resistance, not a lot of voltage drop there.

~Phil
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