tightening up the trainwreck lowend

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

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martin manning
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Re: tightening up the trainwreck lowend

Post by martin manning »

Try reducing C1 to 10uF or 5uF, and/or similarly C7. That will trim some of the low-end.
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Curranproducer
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Re: tightening up the trainwreck lowend

Post by Curranproducer »

cool! thank you for the tip! :shock:
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Littlewyan
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Re: tightening up the trainwreck lowend

Post by Littlewyan »

Did you try running it stock? Slope resistor back to 100K, Cut control out of circuit and your master volume controls on full?
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Curranproducer
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Re: tightening up the trainwreck lowend

Post by Curranproducer »

I have built a few trainwrecks, and they are all pretty much the same for me. a little loose in the low-end. the cut control is on purpose, to get rid of the spike-y top end that is in the circuit. the adj NFB is for fun. and the variable slope as well. the marshall style MV and splawn solo boost are what they are. if I put them all the way up they go away with minimal impact on the tone. being a super metal distortion guy the low-end reacts like a great classic distorted tube amp. It is not reactive enough and clouds the pick attack a little bit. I just want to get the transient attack of the guitar to smack through across the entire spectrum. the low-end is where it is a little loose over all.
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Littlewyan
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Re: tightening up the trainwreck lowend

Post by Littlewyan »

Ah ok fair enough. Just wanted to make sure you'd tried it first :)

You have a few options.

1. Reduce the Cathode Bypass Caps on V1a and V1b like Martin suggested. Even if its just down to 10uF it'll help.

2. Reduce C8 from .0022uF to .001uF. Be careful here though as this cap will make a HUGE difference.

Also what pots did you use? Did you try running it stock with the settings I suggested? Don't forget the log taper is different on some pots.
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Ken Moon
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Re: tightening up the trainwreck lowend

Post by Ken Moon »

I've experimented with C1, and liked a 10uF film cap the best (this is a good mod on a whole bunch of amps), but some folks like a 1uF film cap here.

The Dayton series caps from Parts Express are good ones that aren't too huge in size, or terribly expensive:

https://www.parts-express.com/dayton-au ... r--027-410
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Curranproducer
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Re: tightening up the trainwreck lowend

Post by Curranproducer »

I love using the 1uf's on the high gain shredder stuff I build but it suckes out so much of the responsiveness. that is why I figured I would start here with you guys. Since most of you all are into the very true and touch sensitive types of distortion in tube amps! This is fun but odd territory for me to be in with this kind of tube distortion. I built a few TW's for people that wanted that kind of sound, BUT it always very limiting for ME as a player
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Rick
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Re: tightening up the trainwreck lowend

Post by Rick »

martin manning wrote:Try reducing C1 to 10uF or 5uF, and/or similarly C7. That will trim some of the low-end.
That is exactly what I would recommend. A 10 uF in V1 cathode bypass works wonders, I use one in 2nd stage as well and it removes flubbiness almost entirely. I use a 10 uF/2.2K bias resistor for EF86 cathode bypass too in my Match Wreck amps. Merlin Blencowe discusses this, which is where I found it, in his preamp design book.
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rooster
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Re: tightening up the trainwreck lowend

Post by rooster »

Jelle has the best idea, I agree and have a dual choke option switched into my Express, 1K and 180 ohms. You can hear an overall tightening of the bass and a volume boost.

Glenn has mentioned that the stock Ken built Express was seeing 420VDC on the plates. Really? How did I miss this? I always thought it was 400VDC. HOWEVER......this said, I built one using 435VDC on the plates and it was tighter than the ones I built at 400. :lol:

I also have to ask, what are your tube choices? Tubes are a big ingredient here. NOS Siemens are pretty good with the bass although Ken was apparently fond of the Mullard XF2s.
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2tone
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Re: tightening up the trainwreck lowend

Post by 2tone »

I have had 5 ken built Expresses, all around or just under 400 volts..
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David Root
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Re: tightening up the trainwreck lowend

Post by David Root »

Mullard XF 2 works very nicely in the Express, as it also does in old Marshalls. Double getters are considered better than single getters.
The Amperex brown base double getter EL34 is also very good indeed, but much less commonly seen, and even more expensive!

I have always wondered what an Express would sound like with EL37s - anyone ever try that?
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Colossal
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Re: tightening up the trainwreck lowend

Post by Colossal »

rooster wrote:Jelle has the best idea, I agree and have a dual choke option switched into my Express, 1K and 180 ohms. You can hear an overall tightening of the bass and a volume boost.
Rooster, what do you mean by "dual choke option"? Are you able switch between the stock 1k/25W resistor and a choke measuring 180R at DC or do you mean a 1k resistor in series with a choke measuring 180R?
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rooster
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Re: tightening up the trainwreck lowend

Post by rooster »

Ha, my tube reference source is from a knowledgable friend of Ken's. Regarding the single getter xf2s, I have 3 pairs and they sound fantastic but in fairness I have never heard the dual getter xf2.

2tone, this is good info, thank you.

Colossus, I have the stock 1K resistor and a parallel 25 watt resistor (do the math for it's value) that is attached to a SPST 5A switch, a typical Fender power switch. The bias goes up slightly (2ma) and downstream my preamp tubes see an increase in voltage, yes, but it hangs together very well. What you have is a tighter, louder Express, more Marshall territory. A lot of players who stop by say they prefer the tighter louder version, but typically they are NOT players who really understand the touch response and guitar volume pot control of the stock Express.
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martin manning
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Re: tightening up the trainwreck lowend

Post by martin manning »

rooster wrote:...I agree and have a dual choke option switched into my Express, 1K and 180 ohms... ...I have the stock 1K resistor and a parallel 25 watt resistor (do the math for it's value) that is attached to a SPST 5A switch, a typical Fender power switch.
So you have a 1k resistor and a 180 ohm resistor that can be switched in parallel (reducing the net value to 153 ohms), no choke involved at all. This will raise all the voltages from the screen node on down, and reduce the dynamic effect of increasing screen current with signal level.
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rooster
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Re: tightening up the trainwreck lowend

Post by rooster »

Hm. Actually, Martin, I said do the math? What would you parallel with a 1K resistor to make it 180 ohms? 153 ohms does not occur in my amp. Funny, too, I don't make the distinction that says the 1K resistor does not perform as a choke - which you seem to be saying. ..Or are you saying it is not a literal choke? Anyway, I do appreciate it is not a coil of wire on a steel core, but it is still a coil of wire with an air core and both are considered inductors. So let me say that I have two inductor values in my amp taking the place of a traditional choke.

My power situation downstream, yes, it changes wth inductor value. However when you say that it will 'reduce the dynamic effect of screen current with signal level' (stating the obvious) it's does not say that the amp will still experience the dynamic effect of screen current reduction with signal level. See what you did there? A Marshall Plexi uses a 100 ohm steel core inductor and it is very dynamic in the hands of a great guitar player. (And keep in mind these amps did not use 1K screen resistors, these would come later.)

Ah, but if you were just pointing out that changing the inductor value would change the feel of the Express, then, of course, it would, and that would be the point of the mod in this case.
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