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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Sun Apr 14, 2013 11:59 am
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Well, I was up till 3:00 am this morning doing some more wire redressing.

I combined the power grounds into a single star ground.

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I did some more rerounting of the control wires to get them further away from the circuit board. I also replaced the "modern" presence pot configuration with the original configuration.

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Finally, I pulled the shielded input wire out from under the eyelet board and left it hovering above the board.

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The net result of all this is that the amp is still humming quite badly. However, when turning the presence pot counterclockwise from the max setting, the squeal does not appear until about 11:00 O'clock vs 1:00 O'clock as previously. I also tried plugging in a guitar and there is very little volume. Clearly there is something not right in the circuit. Time to start tracing the signal path. I am open to any suggestions. :(

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Sun Apr 14, 2013 1:29 pm
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Ok. I solved the volume problem. I neglected to run the plate supply for V1 from the 100K resistor to the power supply. I redid the wiring and the amp is loud but still with a bad hum and squeal from the presence control. I also noticed that although the treble control works (but with a lot of noise), neither the bass nor midrange controls have any effect. Looks like that is the next stop.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Sun Apr 14, 2013 10:41 pm
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Things have not gone well today.

I lined the bottom of the head cabinet with aluminum tape to seal the open bottom of the chassis when installed. That seems to have reduced the hum a little bit but it does not seem to be consistant.

I eliminated the 68K grid resistor for V1 per the Trainwreck schematic and ran a shielded cable from the input jack directly to the input pin on V1. That has helped a little.

I also removed the 1K resistor between the volume control and the input to V2 per the Trainwreck schematic. Not much difference. I'm considering adding a DC blocking cap where the 1K resistor was (and where a wire jumper is now) as the only thing between V1 and V2 to block DC is the tone stack.

I cannot seem to get rid of the squeal when turning down the presence control. From the change in tone when turning counter clockwise, it almost seems like the control is wired backwards. I am going to try a bit more feedback (using a 56K feedback resistor instead of the Trainwreck 100K resistor) in the hopes of making the amp a little more stable

I replaced the Trainwreck 1M treble pot with the stock JAVA 250K pot as that seems to give more control over tone. Still doesn't seem like the tone controls are working right, even though I cannot find any wiring errors.

I had to rewire the bright switch from a DPDT w/center off to a SPDT w/center off configuration as the way I had it did not work at all. The new scheme still seems to have a few problem.

Flipping the gain switch to remove the cathode bypass cap is causing a noise that didn't occur before.

The amp does now make sound since I wired the power to V1 correctly. But all the problems don't make it practical to play yet.

This amp has TONS of gain. I have rerouted many wires and regrounded the power grounds. I still can't seem to get rid of all of the noise.

I'm getting a little frustrated. :(

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 15, 2013 4:29 am
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Just a thought, maybe nothing, but the shielded cable should only have the shield tied to ground on one end and the other end of the shield left unconnected. Or is it only a two wire cable with shield as negative? :idea:

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 15, 2013 10:23 am
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shimmilou wrote:
Just a thought, maybe nothing, but the shielded cable should only have the shield tied to ground on one end and the other end of the shield left unconnected. Or is it only a two wire cable with shield as negative? :idea:


Yup. The shield is grounded at the input jack. Heat shrink over the other end where the shield is trimmed back. Ground is solid.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 15, 2013 5:49 pm
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Just thinking out loud here Bill, but what if you moved those components you mounted on the underside of the eyelet board and moved them up top to bring the eyelet board down closer to the chassis? Also, how difficult would it be to go back to the original schematic, and after you've got that circuit going then maybe start applying your mods one by one?

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 15, 2013 9:41 pm
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IT'S ALIVE!!!!!!!

There are still a couple of quirks I have to figure out, but the amp is working at about 95% of what it should be. Here is what I found out.

After making the changes I did last night, I was two tired to test things out so I went to bed. This evening when I flipped the amp on I was greeted with a very loud and unpleasant oscillation. I quickly turned the amp off and wanted to cry. I sat down and stared at the schematic for some time. Then it struck me. I decided to swap the two primary wires on the OT that connect to the output tube plates. There wasn't much room and I had to lengthen one of the wires a bit. But after swapping them I flipped on the power and the oscillation was gone!

Next I started rotating the controls:

No more squeal from the presence control.

Tone controls seemed to operate normally.

The volume control, however, made a loud "pop" when turned to about 9:00. Back on the bench where I decided to replace the 1K resistor that is in the JAVA schematic but not in the Trainwreck schematic. Result: no more pop.

I was still getting a lot of noise from the bright switch, so once again I rerouted the wires to the volume control, this time running them above the input jack (looking at the chassis upside down) getting them well away from the jack. Result: Much less noise.

I moved the ground for the switchable V1 cathode bypass cap from the input jack to the same ground that the cathode resistor uses. Result: No more popping and odd noises.

Time to plug in the guitar.

One thing I have noticed is that after turning the main power switch on, then waiting about a minute and turning the standby to operate, the amp makes a pop with some hum that gradually fades out after a few seconds. Not sure what is causing this or how to fix it.

With the presence and tone controls set to 12 noon, bright switch off, and gain switch set with the cap in circuit, I turned the amp volume to 9:00 and began advancing the volume on the guitar (Epiphone Les Paul Jr with a GFS Alnico 5 pickup in the bridge). The amp became quite loud as the guitar volume was advanced (I didn't go too far as it was about 11:30 pm). The bass and mid control operated properly and quietly. The treble and presence acted oddly. When advanced fully clockwise, the treble became very distorted and started to oscillate. When advanced fully clockwise, the presence seemed to drop out of the circuit and cause noise (I tried two different pots, one wired the old way, the other the modern way, so it's not the pots). I'll have to investigate that more.

Flipping the bright switch to the 100 pf position resulted in a nice brightening of the pickup without a lot of noise. Flipping to the 500 pf position resulted in too much noise in the midrange. I think I am just going to go with a switchable 100 pf bright cap and remove the 500.

Flipping the gain switch to disconnect the V1 cathode bypass cap resulted in a slight but noticable reduction in gain and a change in tone. This sounded good.

There are still a few random pops, but nothing like before. Noise level is greatly reduced, though when you turn the volume above 10:00, the hiss becomes more noticable, but that is to be expected with as much gain as this amp has.

That's about it. Time for bed. I'll investigate the presence and treble pot issues over the next few days, change the bright switch to a single bright cap, and do a final bias on the amp. The little bit I played the amp tonight sounded good . Things are looking up. :D

Oh. Before I forget, my cast came off today. I have a gauze and elastic bandage to wear to the end of the week (after which I can wear a sock) and have to wear a heavy surgical boot. I can start gradually putting weight on the foot while using the walker. Hopefully by the time of my next appointment in two weeks I'll be walking and driving. 8)

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 16, 2013 4:55 am
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Very encouraging! I know how disheartening it can be when you aren't making progress on troubleshooting, so I'm glad for you. Good to hear that you are healing up nicely. Thanks for the warning about being back on the road in a couple of weeks. :lol: I hope to take a vacation to VA sometime in the near future to visit family and I'd really like to look you up, hopefully you'll have a working amp and foot. :)

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 16, 2013 6:44 am
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shimmilou wrote:
Very encouraging! I know how disheartening it can be when you aren't making progress on troubleshooting, so I'm glad for you. Good to hear that you are healing up nicely. Thanks for the warning about being back on the road in a couple of weeks. :lol: I hope to take a vacation to VA sometime in the near future to visit family and I'd really like to look you up, hopefully you'll have a working amp and foot. :)


Thanks. :D

I have some ideas I'll try tonight. The amp is really pretty bright, even with everything set to noon. I'm gonna tone the treble down a bit which should reduce the noise more and hopefully get rid of the distortion at max treble. Probably get rid of the 500 pf bright cap. It really accents the upper mids and makes things really noisey. The 100 pf bright cap sounds good. I might try putting in a 250 pf cap or even a 50 pf bright cap to just give a little bit of a boost with, say a Tele bridge pickup.

Need to troubleshoot the presence circuit and figure out why it is acting funny at max. I have the same configuration presence control in both my 5F6A clone and BDRI and neither of them act like this.

Finally, anyone have any thoughts on the burst of noise I get when powering up? It disappears after a few seconds but is very annoying. I'm thinking of adding a thermister like in the BDRI to slow down the high voltage in rush current a bit since it is a solid state rectifier. What do you guys think?

Shimmi, let me know when you are coming to NOVA and I'll give you my phone number and home address. I would love to meet you.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 16, 2013 10:08 am
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Will do. :)

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 16, 2013 2:01 pm
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Bill, glad things are moving along. I also glad to hear your foot is doing better.
I'm sure you'll sort it all out and have a fine sounding amp. I don't have the balls to take on a project like that. I need the instructions as well as diagrams. :oops:
I can read an measure parts and voltages, but where I lack is the knowledge of what cap values change the tone to what degree.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 16, 2013 5:03 pm
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Bill...Glad the foot is coming along...not sure how I missed the whole Walker Thing...as I would have had many jokes for ya...but since its time is nearly over, I'll let those go.

Keep troubleshooting, you'll get it all figured out as you always do. You have great patience so just keep at it, you will get this amp sounding perfect soon!

T2

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 16, 2013 9:11 pm
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63supro wrote:
Bill, glad things are moving along. I also glad to hear your foot is doing better.
I'm sure you'll sort it all out and have a fine sounding amp. I don't have the balls to take on a project like that. I need the instructions as well as diagrams. :oops:
I can read an measure parts and voltages, but where I lack is the knowledge of what cap values change the tone to what degree.


There are a number of amp calculators that Ihave talked about befoe that I use all of the time. One of the most useful is the tone stack calculator:

http://www.duncanamps.com/tsc/index.html

Then there are a number of calculators on the Amp Books site that do everything from cathode bypass caps to long tail pair gain balance and negative feedback values:

http://ampbooks.com/home/amplifier-calc ... capacitor/

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 16, 2013 9:12 pm
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T2Stratman wrote:
Bill...Glad the foot is coming along...not sure how I missed the whole Walker Thing...as I would have had many jokes for ya...but since its time is nearly over, I'll let those go.

Keep troubleshooting, you'll get it all figured out as you always do. You have great patience so just keep at it, you will get this amp sounding perfect soon!

T2


Oh, there's still time for walker jokes. I'll be hobbling around for another few weeks. :lol:

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 16, 2013 9:43 pm
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Made some more progress tonight.

I removed the 500 pf cap from the bright switch and replaced it with a 50 pf (kept the 100 pf on the other pole). This reduces the hiss significantly and adds a little less brightness than the 100 pf, but still noticable. I have had to play around with wire dress as a hard hit on the higher notes can start the amp oscillating. I was reading a writeup from the Amp Garage forum on building a TW clone and it stated that you should stick the two caps to the switch body with silicone RTV to prevent vibrations which can cause parasitic oscillations. I will try that, but I'll also get just a simple SPST switch and use a single 100 pf cap if I can't get the double cap version to work.

I replaced the 500 pf cap on the treble control with a 250 pf cap which has cut the noise but still gives good range to the treble control. With the treble control full clockwise, the sound is still a bit distorted but no bad noises. I'm beginning to think that since the tone stack is early in the preamp stage and there is so much gain in the preamp, with the volume control coming right off the treble pot, max treble is just overdriving things a lot.

Still having problems with the presence pot when full clockwise. It still seems to cut out. Looking at the layout drawing, I'm wondering if I need to ground it better. The pot mounts to the same brass plate that the other controls do, but I notice that in the layout diagram, the 0.1 mf cap is grounded directly to the brass plate and not to the back of the pot like I have it (although that is how I have it in my 5F6A clone and it works fine, the 5F6A does not have as much gain as this amp does). I will try adding a ground wire tomorrow.

Finally, I replaced the 10k tail resistor that the TW uses with the 22k tail that the JAVA uses and also dropped the negative feedback resistor down to 47k (started at 100k, then 56k). I tied the 47k feedback resistor to the 8 ohm output vice the 16 ohm output as shown in the JAVA schematic. This gives a bit less feedback and slightly more loop gain, but not as much gain as with the 100k feedback resistor. I found a TW clone schematic with this same configuration so I figured "what the heck".

I've only had a chance to play the amp just a little and not cranked. With the amp volume at 9:00 and the guitar volume on 6 (still the single humbucker Epiphone Les Paul Jr), the amp is loud. Crank the guitar volume towrd 10 and the amp starts to get nice and gritty. The gain switch that removes the cathode bypass cap from V1 works very nicely now.

It is hard to realize how important component selection and wire dress is in a very high gain amp. Even though the circuit I am building is a clone of the Trainwreck Express, the layout is very different. I'm not surprised, therefore, that things that work in a true Tainwreck may not work with this clone, but it is getting there. :D

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