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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 23, 2013 7:01 am
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stratele52 wrote:
bluesky636 wrote:


Yes, I used a shielded cable. Its all covered in gory detail in the thread.



I did not see them on photos , just at the jack input. Probably "first " version of the amp ?


It is important to read all of a thread, not just bits and pieces if one expects to get the entire picture of what is going on.

Shielded cable is only required at the intial low level input (to grid of V1), and not even then if the signal path is kept short or gain is low, or if a low level signal path is in close proximity to and cannot be separated sufficiently from a high level signal. Proper wire dress will handle most situations. I have already stated that I plan on experimenting with using shielded cable in the feedback and presence loops.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 23, 2013 7:28 am
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bluesky636 wrote:

Shielded cable is only required at the intial low level input (to grid of V1), and not even then if the signal path is kept short or gain is low, or if a low level signal path is in close proximity to and cannot be separated sufficiently from a high level signal. Proper wire dress will handle most situations. I have already stated that I plan on experimenting with using shielded cable in the feedback and presence loops.


I just say if you have some noise you can use more shielded cable . If you don't have noise everything is fine.

Shielded wire is not require at the initial low input ( to grid of V1 ) more than other place I write if proper ground are made and proper lead dress and if you have no noise.
But it is not easy to built like that I know .

Just look at any Fender Blackface to name few ; no shield and very quiet amp


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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 23, 2013 7:40 am
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stratele52 wrote:
Just look at any Fender Blackface to name few ; no shield and very quiet amp


Blackface Fenders have no where near the amount of gain that these amps do. Blackface and other vintage amps may have one or two preamp gain stages and are operating with loop gains in the neighborhood of 50% to 55%. Amps like Trainwrecks and other high gain amps use three or more preamp gain stages with loop gains pushing 70% and operate at the edge of stability.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 23, 2013 9:40 am
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You could be right I don't know Trainwreck amp.


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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 23, 2013 11:21 am
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stratele52 wrote:
You could be right I don't know Trainwreck amp.


Take a look at the links in my very first post in this thread. :D

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Apr 25, 2013 11:40 am
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Bill, have you tried the spiral-wound heater filament 7025, 12AX7A, or a selected Sovtek 12AX7LPS in the first gain stage?

Just a thought.


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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Apr 25, 2013 12:07 pm
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BMW2002Ti wrote:
Bill, have you tried the spiral-wound heater filament 7025, 12AX7A, or a selected Sovtek 12AX7LPS in the first gain stage?

Just a thought.


No. Just my standard JJs. Hum has been greatly reduced. Hiss is only a problem above 1:00 or 2:00 o'clock and you can't stay in the room for long with the amp at that level without ear plugs. :shock:

Once I see if I can get the B+ down a bit, I'm going to go back and try getting the presence control and a larger value feedback resistor (more loop gain) to work. I have some ideas for rerouting signal lines and maybe using shielded cable.

I'm also going to change the treble pot from 250K to 1M. Interestingly, that levels out the overall frequency response quite a bit and cuts the bass. With four 12's, there is so much bass, especially with humbuckers, that I have to turn the bass almost all the way down to keep the speakers in the cabinet. :lol:

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Sun Apr 28, 2013 10:38 pm
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Part 1

Well, I spent almost this entire weekend installing the 30 volt zener diode to drop my B+ voltage (easy) and troubleshooting the problems that were causing the parasitic oscillation when the treble and volume controls were dimed, getting the Presence control to work, and being able to use a larger feedback resistor than 56K (all hard).

I'm pleased to report that I was successful on all counts.

Installing the zener diode was easy. All parts came in the kit including the diode, filter cap, mounting bracket, and heat transfer goop. All I had to do as find a place to mount the diode and run the power transformer center tap wire to the diode instead of to ground. Weber recommended installing a thermister to deal with current surges through the zener when power is turned on and off so I did as well as add one to the AC input on teh primary side of the power transfer. Weber did not specify how much the current surge could be, so I decided to bypass the 1/2 amp slo-blo fuse that was installed in the PT center tap circuit. Here are the photos of the installation.

Input AC thermister:

Image

Three views of the zener installation showing the zener, mounting bracket, filter cap (0.1 mf, 1000 V cap), and thermister:

Image

Image

Image

Before the installation, my bias set point was 35 mA plate current and 475 VDC for a bias setting on 66% max plate dissipation. After the installation the bias set point is 37 mA plate current at a plate voltage of 452 VDC for a bias setting of 68% max plate dissipation. I could have gone with the 40 volt drop zener (a real Express B+ is around 400 VDC +/- 10 VDC), but I am happy with the settings and 452 is better than 475. :lol:

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Last edited by bluesky636 on Sun Apr 28, 2013 10:41 pm, edited 1 time in total.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Sun Apr 28, 2013 10:39 pm
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Part 2

Next I spent a lot of time trying to figure out why the amp made really horrible noises when both the treble and volume control were dimed. Granted, that is not a normal operating condition, but it goes a long way toward having a stable amp that doesn’t break into oscillations.

I tried all different things: redressing the wires for about the 6th time (no help), using shielded cable between the treble pot output and volume pot input (no help), using shielded cable to the grid resistors of both V1 and V2 (helped with overall noise level, but not the specific problem), and shielded cable between the impedance selector and the feedback resistor (no help). Finally, I decided to post in the Trainwreck forum on http://www.ampgarage.com.

I got the usual things (that I already tried), and then finally someone suggested that I swap the bass and treble control positions on the amp. In a real Express, the treble control is right next to the volume pot and the wires are very short. In the JAVA, the treble pot is the furthest tone pot from the vlume control with long wires.

Stock JAVA tone pot wiring (treble pot on far left, bass pot next to volume pot):

Image

I swapped the treble and bass pots (both are 250K linear, so all I had to do was change the wiring). I also rewired the tone stack per one of the Express configurations where both the bass and mid controls are wired as variable resistors. After rewiring, I found tht the control had become microphonic when you tapped on them. I found that the top two wires in the tone stack had to be laid against the inside front panel to couple with ground rather than being left floating in space. After making this change, the controls were no longer microphonic and best of all, I could dime all the controls with no nasty noises, just a lot of hiss (as expected). I also relocated the bright switch wiring so it did not cross the volume control wiring.

Express tone stack wiring (bass pot far left, treble pot next to volume control):

Image

Next I installed the presence pot. Since I had previously removed the presence pot, I installed the 4.7K PI tail resistor directly at the PI tail. I was going to use the "modern" presence pot, so I had to remove the 4.7K tail resistor installed on the pot.

PI tail resistor with presence pot connection:

Image

Presence pot with tail resistor removed:

Image

Now the presence pot worked without any odd noises when everything was dimed (just more hiss).

Finally, since I had run a shielded cable from the impedance switch to the feedback resistor, I decided to replace the 56K resistor with a 100K resistor. It worked also.

Shielded cable from impedance selector to feedback resistor:

Image

Shielded cable to feedback resistor (old 56K resistor still in place):

Image
Finally, everything was working as it should be. The overdrive at 11:00 using my SCN equipped MIM Standard Strat is great. I'll try a humbucker guitar tomorrow. Hiss level below 12:00 noon is less than before. Above 1:00 it gets louder. When dimed the hiss is very loud, but the amp would punch holes through the wall with a heavy power chord. :lol: :lol: :lol:

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Sun Apr 28, 2013 10:40 pm
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Part 3

At last, some final assembly photos.

Amp from rear showing zener diode:

Image

Amp from front showing all controls:

Image

Close up of power switches and pilot light:

Image

Close up of presence, tone, and volume controls:

Image

Close up of bright and gain switches:

Image

And finally, my logo:

Image

I'm gonna spend the rest of the week just playing different guitars through the amp and making sure everything is solid. next weekend I'll do a lessons learned, followed by some sound clips of the amp. See you all then. 8)

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 29, 2013 3:03 am
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Good job Bill. Moved the Letters as well, I see.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 29, 2013 6:07 am
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Art1 wrote:
Good job Bill. Moved the Letters as well, I see.

Art


Thanks Art.

This amp had me tearing out what little hair I have left. :lol: :lol: :lol: :lol:

When I first tested the amp out with the new tone stack configuration, I couldn't figure out why the bass and treble controls weren't behaving like I thought they should. Then I realized I still had the old names on the front panel. :lol: :lol: :lol:

Once I confirmed everything was working, I put the correct names under each one and added the presence name. :D

Oh, in case anyone was wondering, I had to break last night's post into three parts because it was over the posting size limit.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 29, 2013 10:15 am
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Bill,

Nice detective work! These kinda issues seem more prevalent in amps 30 watts & above. For many parasitic type oscillations in big amps (80-100 watts), I've used ferret beads for the PI and output stages. It's an old Ham Radio trick. I've seen some Ampeg SVT and V4 with wires wrapped in beads.

http://www.diyaudio.com/forums/tubes-va ... neral.html

Anyhow, good lucj with your amp. I've never owned or repaired a Trainwreck. Have played on a few. Great amps!


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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 29, 2013 12:15 pm
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Nice Bill, real nice, Congrats! Now you really gave me the itch. I decided I'm going to build the Build Your Own Clone Royal Tweed. It's supposed to have the circuits from the 5F1 Champ, 5F2a Princeton, 5F10 Harvard and the 5E3 Deluxe all in one amp. This thing has a cut switch for the negative feedback loop and a switch to take out the tone stack foe the 5F1. I know I already have a 5e3, but the circuit in the BYOC unit is 11 watts where the circuit in my current 5e3 is a little more juiced to the 15-18 watt range. I just want the head to save a little space because I already have a few speaker cabs. We'll see. I have to get past the expense of my second eye surgery for Glaucoma. Nothing to mess with since I make my living as a professional photographer. My insurance covers most of it but I still have my deductibles. :cry:

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 29, 2013 1:37 pm
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63supro wrote:
Nice Bill, real nice, Congrats! Now you really gave me the itch. I decided I'm going to build the Build Your Own Clone Royal Tweed. It's supposed to have the circuits from the 5F1 Champ, 5F2a Princeton, 5F10 Harvard and the 5E3 Deluxe all in one amp. This thing has a cut switch for the negative feedback loop and a switch to take out the tone stack foe the 5F1. I know I already have a 5e3, but the circuit in the BYOC unit is 11 watts where the circuit in my current 5e3 is a little more juiced to the 15-18 watt range. I just want the head to save a little space because I already have a few speaker cabs. We'll see. I have to get past the expense of my second eye surgery for Glaucoma. Nothing to mess with since I make my living as a professional photographer. My insurance covers most of it but I still have my deductibles. :cry:


Thanks. :D

No, no, no. You've already built your quota of easy amps. You need to build a hard one now. Since I did a Trainwreck Express, you need to do something like a Dumble Overdrive Special clone. :lol: :lol: :lol: :lol:

Hope everything goes well with your eye.

I went to my doc today. He wants me to be able to support 100% of my weight in two weeks while wearing the soft cast/boot and just using the walker for stability. I can start driving this weekend (obviously will have to switch between a loose fitting shoe to drive and the boot to walk) and return to my physical office on May 6 instead of working from home. Should be interesting.

My doc screwed up one of the diagnoses codes to insurance, so there is a $1500 claim insurance refuses to cover. I have to call my doc's billing person tomorrow and tell them to fix it.

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