Trainflex

[RossH]

I've drawn a schematic called a Trainflex with various mods and alternatives that can be applied to the basic Express. I will itemize them below:

http://theoctave.home.comcast.net/Trainflex1.jpg

1 - Because of an extra 1/2 of a 12AX7 Note 1 is utilizing it with a parallel option. The alternative is an Express/Komet input stage.
2- There are optional shielded wires to add (I had to add a shielded wire from the VOLUME pot to the second stage to eliminate parasitic oscillation)
3- Note 2 is an alternative mod replacing the traditional BRIGHT switch with a BRIGHT/THICK switch
4 - Note 3 is an alternative mod adding the split plate load resistors and the FAST/GRADUAL switch from the Komet.
5 - Before the 3rd stage there is a note pointing to the BASS TWEAK cap
6 - The resistor to ground is shifted to a pot named INTENSITY offering real-time modification of this stage
7 - After the 3rd stage is another pot labeled LIMIT offering the ability to pinch off the signal path from here for further flexibility
8 - The negative feedback loop has a pot on it to offer variability in the NFB voltage. It is labeled TIGHTNESS. Can you think of a better name?
9 - After the PI there is a CUT control across the plates to offer more high end wave shaping
10 - There is a cross-line master volume across the PI plates as another alternative.
11 - On the bottom side of the PI there is another pot called BODY. This offers the ability to cut or vary the bottom half of the wave hitting the output section altering the fullness of the sound
12 - Note 4 shows an alternative BIAS supply.

I am in the process of adding a Power Scaling circuit for 0-30W variability and a Sag circuit for variable power supply sag.

I know it is busy but if nothing else it can be a print of potential mods.

Or is it just heretical? What else can I add?

If anyone else can look it over for errors or anything else I would appreciate it.

Let me know your thoughts.

Thanks,
Ross

[MSS]

Great job.

Of course I know its almost a curse, but an efferts loop would be great for a little external reverb/delay. Of course an internal tube reverb add-on would really rock, if you got more room & power for extra tube filaments...

MSS

[snide]

Nice work Ross!

I like the idea of having most of the mods in one document. I have several of these in my Express because I wanted more of the Komet sound. My amp is slightly thin in the bass department...I'm gonna have to tweak some more My Fast/Gradual circuit is slightly different but it is sure nice to have.


Eric

[Chris G]

Hi Ross,
nice work!!!!,I would love to see some power scaleing circut for this type amp.
again.......very nice job
Chris

[RossH]

Of course I know its almost a curse, but an efferts loop would be great for a little external reverb/delay.
MSS

I suppose it really takes it out of the Express purity with an effects loop, but I agree...it would be cool and handy.

I added one in for version 1.1 This particular FX loop has a parallel/series option and a return loop gain switch to adapt to guitar or line levels. It also has an additional stage in the power supply to aid in decoupling to reduce noise.

http://theoctave.home.comcast.net/Trainflex1-1.jpg

Comments are encouraged.

Ross

[RossH]

My Fast/Gradual circuit is slightly different but it is sure nice to have.

What does yours look like?

Ross

[loverocker]

Great work You've answered a lot of questions on the Komet differences. I may put some into my next project which is an Express from an old Traynor. I've also been wondering about some of KOC's ideas in the Wreck.

Power Scaling works great (I have a London Power Studio). I've made up the kit for a cathode-biased amp - 18W clone - but I haven't seen a schematic that also scales the bias for fixed-bias amps. I'm too theory-lite to figure out how the bias needs to track B+... Is it tricky?

Question about the FX loop idea: isn't a significant part of the Wreck overdrive tone in the PI? If so, I can't help thinking that an FX loop'd only work well for pretty clean tones.

[MSS]

Of course, I consider a effects loop bypass switch mandatory, to ensure we can get back to the pure tone we built the amp for!

[RossH]

isn't a significant part of the Wreck overdrive tone in the PI? If so, I can't help thinking that an FX loop'd only work well for pretty clean tones.

I understand that it is an end-backward thing but the 3rd stage is where the gain mods occur. I don't know if this FX loop would work effectively or not in a wreck...and in this location. Maybe someone smarter than me can chime in. The effects loop is London Power's "The Best All Tube Effects Loop" from TUT1. I am going to put the reverb in there as well this weekend. I will post that when I am ready.

MSS, I will add the switch to pull it out of the loop. I agree...it is essential.

I'll post later this weekend with some changes.

Ross

[erigm]

If you plugged into the "parallel" input wouldn't your resistance to ground be cut in half (two 1M in parallel = 500k)? I would remove the 1M resistor on the "parallel" input. Only problem with that is then you are relying on a good contact at the switching input jack for your input resistance. You could also attach the bottom of the top 1M resistor to the point where the switch on the upper jack connects to the junction of the 1M and 68k on the bottom jack. On man, did that make any sense?

[erigm]

But then you are still relying on the itegrity of the switch contact on the bottom input jack. Anyone have a solution, or am I being anal?

[loverocker]

I don't know if this FX loop would work effectively or not in a wreck...and in this location.

Well, I'm guessing that the Wreck's PI is distorting, because it's quite similar to the 18Wer's PI and it's getting a hefty signal from stage 3, plus the favourite MV for this amp is the post-PI MV like the one you've added. So I guess the pre-PI FX loop should work as well as it does in (say) a reissue Marshall SuperLead - fine for clean and pedal-driven tones. For cranked amp tones, I'm assuming you'll get distorted reverb, instead of reverbed distortion? IYSWIM

I'll be interested in hearing about the results.

You're going to do all this over this weekend! Wow - you're a fast modder!

[neilium]

Omar,

This merits a post on the permanent collection. Great work, Ross.

-n

[snide]

My Fast/Gradual circuit is slightly different but it is sure nice to have.

What does yours look like?

Ross

[Moose]

But then you are still relying on the itegrity of the switch contact on the bottom input jack. Anyone have a solution, or am I being anal?

You're being anal. But that's not a bad thing! You make a valid point.

I don't have a good solution, but I will say I've used similar switching schemes, as have many marshalls and other vintage amps. The switch contact is actually pretty good. It's not carrying enough voltage or current for that to be an issue, and if those switches aren't good you end up with nasty noises at idle, so we're trusting them in any circumstance.

Personally, when switching matters I just use Neutrix or Cliff's jacks and NEVER go for cheap ones. Then I keep my fingers crossed.