Low Budget Trainwreck Express Clone Build Problems

[bluesky636]

I've been working on a low budget TW Express clone based on the Weber JAVA kit.

[img1500]https://taweber.powweb.com/store/java_schem.jpg[/img]

[img1047]https://taweber.powweb.com/store/java_layout.jpg[/img]

I am not using the cathode follower of the basic kit.

In order to get the noise level down, besides the using wire dressing tricks, I have used shielded cable from the input jack to a 68K grid stopper attached directly to pin 2 of V1, shielded cable from the volume control to the 1K grid resistor for V2 (the 1K is on the board and the cable goes to the resistor on the board), shielded cable between the treble pot wiper and volume control, and shielded cable between the 8 ohm position of the impedance selector to the feedback resistor (56K feedback resistor is about as large as I can go).

The amp is very quiet, almost hum and hiss free at all normal playing levels and sounds reall good with a Strat or humbucker equipped guitar. The primary problem I am having is if I turn the volume all the way up, if I advance the treble control (I used a 250K audio pot with a 250pf cap, it was too bright for me otherwise), at about 3:00 on the treble pot there is a burst of hiss and when turned up all the way the sound is noisy and distorted. Turned back below 3:00 (with the volume dimed) and everything is fine.

The secondary problem is not being able to go higher than 56K on the feedback resistor (which actually sounds good).

The last problem is getting the presence pot to work. It too breaks into noise above 3:00, like the treble. It is currently not installed.

I have read the Ron Worley's Exprees build guide from cover to cover and followed many of his suggestions for building and troubleshooting. Although the JAVA is not physically like an Express, I have made it electrically similar. I am only using a single 100pf bright cap, added a switch to disconnect the V1 cathode bypass cap to drop the gain, and made a few changes to the treble tone control (amp was too bright for my taste).

I'd like to get the treble pot problem fixed first. The other two issues I am less worried about. Any suggestions? I have tons of photos taken during the build if they will help. Thanks in advance.

[bluesky636]

Reading a little more. I'm think I should take the 1K V2 grid resistor off the board and mount it directly to pin 2 of V2 and run the shielded cable from the volume control directly to the resistor on V2. Does that sound reasonable?

[Colossal]

Reading a little more. I'm think I should take the 1K V2 grid resistor off the board and mount it directly to pin 2 of V2 and run the shielded cable from the volume control directly to the resistor on V2. Does that sound reasonable?

Yes, a good idea to get your grid resistors right on the sockets on both stages.

You probably know this but the Java layout may not be conducive to getting an oscillation free amp in the Express format. You are definitely suffering from high frequency oscillation given the instability in the feedback circuit. The presence control is a known trouble spot with Expresses. Wire your amp as close to the Worley layout as possible. You should be able to use a 100k feedback resistor on the 8R tap and pull it off if you get the lead dress right. Oscillation is there but very prevalent at high gain settings and will manifest as an ugly hash riding on your distortion. Not much for it unless you get that worked out. The Express, as has been said many times, can be a cruel and unforgiving mistress. The ultimate test is if you can dime everything, including the presence control and all you hear is hiss at idle/no signal.

Good luck!

[M Fowler]

Or change the presence knob to a treble cut control and call it a Komet instead.

[bluesky636]

Well, I connected the 1K grid resistor for V2 directly to pin 2 and connected it to the volume pot with shielded cable. Didn't really help much. In fact, I must have inadvertantly moved some wires as when I put the chassis back in the cabinet to try it out, EVERY control was now microphonic. I pulled the chassis back out and threw it on my workbench and rearranged the wires on the tone stack and when I put the chassis back in the cab, the microphonics were gone. But the hiss breakdown with the volume control dimed and the treble control past 3:00 was still there.

Tomorrow I'm going to try and relocate the feedback resistor with a longer shielded cable. Need to get more heat shrink tube.

Any other thoughts or suggestions?

[Colossal]

Well, I connected the 1K grid resistor for V2 directly to pin 2 and connected it to the volume pot with shielded cable. Didn't really help much. In fact, I must have inadvertantly moved some wires as when I put the chassis back in the cabinet to try it out, EVERY control was now microphonic. I pulled the chassis back out and threw it on my workbench and rearranged the wires on the tone stack and when I put the chassis back in the cab, the microphonics were gone. But the hiss breakdown with the volume control dimed and the treble control past 3:00 was still there.

As you have seen, getting stability in the circuit can be challenging. There are volumes written here on the matter. They are very sensitive to lead dress. You will have hiss no matter what, that is the nature of a high gain amp. Tube choices can change that to some degree but not eliminate it. Do a search and read everything by Geetarpicker. Glenn owns real Trainwrecks and has posted at length on their behavior and characteristics. Many others here have successfully built clones but in every case, be advised, that deviating from the original layout can and often results in stability problems. The test of your layout will be that diming everything, including presence should result in hiss at idle, but not whistling or a tinny, microphonic quality. If you have oscillation, it will clutter the otherwise beautiful musical distortion and dampen or even kill the blooming sustain and feedback.

Tomorrow I'm going to try and relocate the feedback resistor with a longer shielded cable. Need to get more heat shrink tube.

Just another point, also posted in the past (hint hint..search is your friend), you should not need shielded wire in an Express, except maybe at the input. However with the Java layout, if that's what your using, some exceptions may be required. In other words...yer on yer own

Keep those grid resistors right on the tube sockets. Don't think that because they did not solve your problem that they are not helping. Your problem lies elsewhere.

[bluesky636]

Well, I connected the 1K grid resistor for V2 directly to pin 2 and connected it to the volume pot with shielded cable. Didn't really help much. In fact, I must have inadvertantly moved some wires as when I put the chassis back in the cabinet to try it out, EVERY control was now microphonic. I pulled the chassis back out and threw it on my workbench and rearranged the wires on the tone stack and when I put the chassis back in the cab, the microphonics were gone. But the hiss breakdown with the volume control dimed and the treble control past 3:00 was still there.

As you have seen, getting stability in the circuit can be challenging. There are volumes written here on the matter. They are very sensitive to lead dress. You will have hiss no matter what, that is the nature of a high gain amp. Tube choices can change that to some degree but not eliminate it. Do a search and read everything by Geetarpicker. Glenn owns real Trainwrecks and has posted at length on their behavior and characteristics. Many others here have successfully built clones but in every case, be advised, that deviating from the original layout can and often results in stability problems. The test of your layout will be that diming everything, including presence should result in hiss at idle, but not whistling or a tinny, microphonic quality. If you have oscillation, it will clutter the otherwise beautiful musical distortion and dampen or even kill the blooming sustain and feedback.

Tomorrow I'm going to try and relocate the feedback resistor with a longer shielded cable. Need to get more heat shrink tube.

Just another point, also posted in the past (hint hint..search is your friend), you should not need shielded wire in an Express, except maybe at the input. However with the Java layout, if that's what your using, some exceptions may be required. In other words...yer on yer own

Keep those grid resistors right on the tube sockets. Don't think that because they did not solve your problem that they are not helping. Your problem lies elsewhere.

Trust me. I have searched and read all the relevant threads here that I could find, including the ones by Geetarpicker. I'm a EE by degree and systems engineer by profession. I've built and/or extensively modified several amps in the past, but they have all been low gain, vintage type amps. This is my first really high gain amp and I did a lot of research before starting on it.

I am going to back off a couple of the shielded cables and just keep the ones on the two grid resistors as they are the longest cable runs. It seems that before I added the shielded cable between the treble pot and volume pot and to the feedback resistor, I had slightly more hiss, but was not having the problem with the oscillation when the volume and treble pots were dimed. I'm going to try and get back to that state.

[Firestorm]

One of the most sensitive areas in a Trainwreck (any amp, really) is the tone stack, especially the leads connecting the treble pot. Compare the length of those leads in the Express layout versus the Java. Consider swappping the locations of the treble and bass pots; you can reduce the length of the treble connections. The lead from the treble cap should be exceedingly short and sit right against a ground; leads from mid and bass caps should get tucked into the bend at the inside edge of the chassis.

[romberg]

The test of your layout will be that diming everything, including presence should result in hiss at idle, but not whistling or a tinny, microphonic quality.

I don't have any specific suggestion to make. But I can offer that the java layout can do this (I think). I can dime everything and get hiss and no whistling. I'm not exactly sure what a tinny microphonic quality sounds like. So, I may or may not have that.

It will feed back like a mother dimed if I turn the guitar volume up. But I was standing right next to a 4x12 cabinet in a small unfinished basement armed with a gibson 333. So, I kinda expect that.

I more or less used the stock layout (including the heretical cathode follower). The master volume also differs from "stock". Otherwise, pretty much the layout from weber:

http://home.comcast.net/~mike.romberg/a ... index.html

Mike

[bluesky636]

Well, it appears that I have done it. I took Firestorm's suggestion and swapped the bass and treble pots and rewired the tone stack per Ron Worley's Express layout. I was also able to get the presence pot working and upped the feedback resistor to 100K. All pots dimed and no whistling or other bad noises beyond a fair amount of hiss. Throwing the bright switch on tends to start to push the amp over the edge, but that certainly isn't a normal operating condition. I want to thank everyone that weighed in on my problem. Ya'll were a great help. Here's a few photos of the amp guts.

Overall wiring:
[img:800:532]http://farm9.staticflickr.com/8542/8691 ... 7429_c.jpg[/img]

Tone stack/bright switch/gain switch wiring:
[img:800:355]http://farm8.staticflickr.com/7053/8690 ... 7a3f_c.jpg[/img]

Presence pot wiring:
[img:800:532]http://farm8.staticflickr.com/7043/8691 ... d4c8_c.jpg[/img]

PI tail resistor (raised resistor on the board):
[img:800:532]http://farm8.staticflickr.com/7047/8690 ... 9d0d_c.jpg[/img]

V1 and V2 shielded input cables:
[img:800:532]http://farm8.staticflickr.com/7056/8691 ... 8c9d_c.jpg[/img]

[bluesky636]

Here are some final assembly photos:

[img:800:441]http://farm9.staticflickr.com/8257/8691 ... d16b_c.jpg[/img]

[img:800:586]http://farm9.staticflickr.com/8253/8690 ... b587_c.jpg[/img]

[img:800:592]http://farm9.staticflickr.com/8394/8690 ... 0a25_c.jpg[/img]

[img:771:800]http://farm9.staticflickr.com/8118/8691 ... 9887_c.jpg[/img]

[img:800:446]http://farm9.staticflickr.com/8406/8690 ... 30d2_c.jpg[/img]

[img:800:498]http://farm9.staticflickr.com/8254/8664 ... 4e58_c.jpg[/img]

[img:800:532]http://farm9.staticflickr.com/8121/8691 ... 4297_c.jpg[/img]

[img:800:532]http://farm9.staticflickr.com/8243/8663 ... 7474_c.jpg[/img]

Debbie is my wife of 37 years.