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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Fri Sep 13, 2013 5:13 pm
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the gold pin JJ 12AT7s arrived today, but I was concentrating on setting up the BDRI with the E-H 6V6GTs. I'll get back to this amp later this weekend. :D

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Sep 17, 2013 7:17 pm
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Well, it seems that Trainwreck Express-type circuits don't like 12AT7s in the PI. :(

I tried the gold pin JJs and had the same results as with the regular JJs, an odd sort of buzz/rattle that dies out quickly. It does not occur with a 12AX7 in the PI. The gold pin JJ 12AX7 is definitely louder than the gold pin 12AT7 in the PI. There is nothing in the room that would seem to be causing this noise since the louder 12AX7 would excite it more and it doesn't seem to do that. Oh, well. It was an interesting experiment. I didn't try a 5751 in V2, only V1 (which I did not like). Maybe I'll try that later this week.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Oct 07, 2013 5:05 pm
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Tried some more tube rolling in the Wrecking Ball tonight with some very interesting results.

If you look back at my last few posts, you will see my tests using both a regular and gold pin JJ 12AT7 and one of my NOS JAN GE 5751. To say that I was underwhelmed by the performance of those tubes in this amp is putting it mildly. I was flat out disappointed. :cry:

Tonight I tried a new JJ Gold Pin 5751 (two of which arrived today). The results were quite surprising and unexpected.

Test 1
V1 = JJ Gold Pin 5751; V2 = JJ Gold Pin 12AX7; V3 = JJ Gold Pin 12AX7 - The results with this test were very disappointing. The overall sound was very dark and muddy. Highs were non-existent. I almost pulled the 5751 and trashed it .... but I didn't.

Test 2
V1 = JJ Gold Pin 12AX7; V2 = JJ Gold Pin 5751; V3 = JJ Gold Pin 12AX7 - Interestingly enough, this combination was a noticeable improvement over Test 1. The highs were back (it seemed almost too much so) and the mud was gone. But the overdrive just did not sound right. I can't explain it, but it sounded kinda raspy. So, on to ...

Test 3
V1 = JJ Gold Pin 12AX7; V2 = JJ Gold Pin 12AX7; V3 = JJ Gold Pin 5751 - Holy crap! This was like night and day! The highs and lows were nicely balanced (unlike a 12AT7 in this position which showed too much bass) with tight lows and smoother treble (I actually turned the treble on the amp up a notch to check). The overdrive decreased just slightly but was much tighter and smoother sounding. This was especially noticeable with humbuckers, but my Strat still had a good crunch to it. Even more important, I didn't have as much of a feedback problem with humbuckers like I do with 12AX7s in all three positions. The overall gain seemed to be just slightly lower (I'll try and post comparison graphs later this evening) and it was the quietest of the three tests. This combination will definitely be investigated further.

It is interesting the difference in the performance for the three positions of the 5751. Test 1 really baffles me and I have no explanation for the results. I don't think I accidentally turned the tone controls down on the guitar, but it sounded muddy regardless if I was using the neck or bridge positions. The bridge and middle together sounded downright nasty. Very strange.

So I will play this combination for a while and see how it wears. I know that Dr Z uses a 5751 as a PI in some of their amps, amp it seems like a good choice in this one.

I have some audio taper pots on their way from Amplified parts to try in place of the linear taper pots in the bass and treble controls. I'll be reporting on that in another week or so. Stay tuned.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Wed Oct 09, 2013 3:22 pm
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Location: Natural Bridge, Virginia
Here are the gain calculators for the phase inverter using a 12AX7 and 5751.

12AX7
Image

5751
Image

Just about a 3 dB difference in gain. Interestingly enough, the PI with the 5751 is better balanced than with the 12AX7.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Oct 14, 2013 7:07 pm
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stratele52 wrote:
Look to be a great kit , Cab look very nice. Hours of fun and you'll forget you pain .

This remind me that I have few kits of plastic airplane and one in Balsa wood to built.


And I have an OCF dipole to construct! :lol: :lol:

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If it aint' broke,...don't fix it! I like to keep my amps and guitars factory original,...no mods necessary,...don't want them,...don't need them!

My gear as of now;
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Hot Rod Deluxe III amp
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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Oct 17, 2013 5:30 pm
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Location: Natural Bridge, Virginia
The day after I last played the amp with the 5751 in the PI position, a very strange thing happened. It had been raining in NOVA for several days and was cool and damp in the house. The amp suddenly began feeding back with the guitar while just sitting and holding the guitar in my lap, unplayed. The amp controls were at "6" and the guitar volume wide open. I sit 10 feet from the amp. The amp would start to howl as soon as I unmuted the strings and was effectively unplayable. I noticed that certain strings were actually vibrating. It was almost immediate with humbuckers and pretty quick with the SCNs in my Strat. It had never done this before.

I did all the usual things: tried different guitars (howl); different cables (howl); different tubes (howl). Everything I tried, the amp would howl. Yet I could tap the tubes, chassis, and controls and there was no evidence of microphonics. The amp was rock stable with no guitar plugged in and all controls dimed and I could switch the bright switch in and out with no effect. It was hissy as hell, but completely stable with no hint of oscillations.

Over the next few days and with the help of Mike K (KCA NOS Tubes) I went through the entire amp. All lead dress was where I left it since I last worked on the amp and it exhibited no problems when tapped. The only thing I found were two solder joints (the s l o p e resistor) that looks a little dull which I reflowed. But even they were quiet when tapped.

By the time I completed all of my investigations, the rain had stopped and everything dried out. Interestingly enough, the feedback also stopped. I can still get the amp to feedback while playing but it is controllable. Just sitting and holding the guitar with the strings unmuted will result in slight feedback which stops immediately when I shift position. It is no where near the banshee howl that it was doing a few days before. As of now, the amp is back to the way it was and is operating in a way that I consider normal.

So what caused the howling? The dull solder joints on the s l o p e resistor? The dampness in the house? Was the dampness affecting my guitars (the amp howled with the four out of six guitars I tried) or the amp (oddly enough, I noticed my Weber 5F6A clone was exhibiting similar behavior though not to the same extent)? Will the howl return the next time it rains and the humidity goes up? To be honest, I don't have a clue. I guess I'll just have to wait and see. Until then, I'll enjoy playing all of my guitars through the amp. :D

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Oct 17, 2013 5:52 pm
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Bluesky, it sounds like you maybe getting an RF induced feedback or common mode type feedback from a slight ground loop in the wiring of your house's ground (potential between main circuit board) and the outlet that the guitar is pulled into. Esp if the AC line is carrying noise on top of the sine wave or on top of the grounding line. Potential differences between the main circuit's ground point and the grounding of your amp can induce hum, RFI, and even feedback.

The guitar's pups are acting like an antenna picking up this RFI or grounding potential and feeding this into the input stage of your amp. A slight potentil in the amp and guitar is enhancing the feedback noise and amplifying it.

When the earth is wet the "loop-circuit" is "tighter" due to the reduced DC resistance between the earth ground and the instrument/guitar grounding point. I've heard of this happening in high-power hi-fi amps (esp those that use high-mu gain stages). And with Ham Transmitters (usually a loop between antenna's ground and transmitter's ground).

You can test the theory by trying a "cheater plug" (one that adapts two prong devices to three-prong outlets). If the feedback is changes or is broken or reduced --- you've found the issue.

Rewiring the ground scheme of the outlets to the main box or strapping the offending outlet to a grounding pole may work.

BTW... this is how a lot of old amps pickup AM radio signals. The slight potential between the AM station's ground and the grounding of your outlets.


For your reading pleasure: :D

http://www.ti.com/lit/an/slla057/slla057.pdf


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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Oct 17, 2013 6:06 pm
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Once I got the howling problem taken care of, I decided to address the issues brought up by the owner of Action Music.

The first thing I tried was changing the bright switch from 100-off-250 to 50-off-100. The 100 sounded good, but the 50 pf really had no significant effect on the tone. I decided to keep the switch at 100-off-250.

I have already discussed my efforts at using lower gain tubes (12AT7 or 5751 at different positions in the amp). But I wanted a more permanent, circuit based solution, so I started investigating different ways to drop the gain. Since the amp sounded good with a 3 dB drop in gain from the 5751 in the PI, I started looking at the PI and the stage just before the PI.

While I was thinking about how to best drop the gain, I decided to mod the tone stack to get a little more flexibility out of it. I tried changing the 250K linear treble pot to a 250K audio taper pot but found it a little dull so I stayed with the linear pot. I also changed the 56K s l o p e resistor back to 100K. This mod dropped the overall gain (actually increased the tone stack insertion loss) by about 3 dB below 400 Hz (eliminating some muddiness in the bass through the upper mids with the new Celestion Greenback Reissues) as shown in the following plot.

The red curve is with the 56K s l o p e resistor. The green curve is with the 100K s l o p e resistor.

Image

This tone stack configuration doesn't really increase the overall range of the controls, but I think it smooths out their operation a bit more and makes the desired settings easier to achieve. Also, given that the gain is decreased by about 3 dB at the middle settings of the controls, I decided not to change anything else in the circuit and to stick with the three JJ gold pin ECC83s. The overall tone is changed enough that it cuts the bass slightly to eliminate boominess with the 4x12 Crate cab loaded with the Celestion G12M 25 watt Greenback Reissues. The bright switch (with the volume control below noon) sounds better now. Humbuckers using the 250 pF setting and the volume on 5 sound really nice and crunchy.

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Last edited by bluesky636 on Thu Nov 07, 2013 5:40 pm, edited 2 times in total.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Oct 17, 2013 6:06 pm
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Sorry. I had to break this post into two.

So the schematic now looks like this (also corrects an error in the power supply cap drain resistors from when I first drew it).

Image

The amp is still too loud (I prefer it that way. :lol: :lol: :lol: ), but is stable and sounds really good to me. When I get a chance, I'll take it back to Action Music.

With this post, I think I'll declare this thread at an end. I still have a very slight hum that I have been trying to get rid of (different grounding schemes have reduced but not eliminated it, so it may be as low as it can get). I am satisfied that there really is nothing else I can tweak to get the sound I want. It's now time to just play my guitar.

I'd like to thank those who participated in this thread and helped me through my several issues. I hope everyone enjoyed reading it, including those latecomers who chose to just lurk and monitor the thread (you know who you are :wink: ). If anything changes in the future, I'll be back (I still have to get my guitar instructor Vinny Roth to record a new demo for me. 8) ). Till then, if you have any questions or comments, feel free to post 'em here or PM me. See ya around the electrical outlet. :lol: :lol: :lol:

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Last edited by bluesky636 on Thu Nov 07, 2013 5:43 pm, edited 2 times in total.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Oct 17, 2013 6:16 pm
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Location: Natural Bridge, Virginia
BMW2002Ti wrote:
Bluesky, it sounds like you maybe getting an RF induced feedback or common mode type feedback from a slight ground loop in the wiring of your house's ground (potential between main circuit board) and the outlet that the guitar is pulled into. Esp if the AC line is carrying noise on top of the sine wave or on top of the grounding line. Potential differences between the main circuit's ground point and the grounding of your amp can induce hum, RFI, and even feedback.

The guitar's pups are acting like an antenna picking up this RFI or grounding potential and feeding this into the input stage of your amp. A slight potentil in the amp and guitar is enhancing the feedback noise and amplifying it.

When the earth is wet the "loop-circuit" is "tighter" due to the reduced DC resistance between the earth ground and the instrument/guitar grounding point. I've heard of this happening in high-power hi-fi amps (esp those that use high-mu gain stages). And with Ham Transmitters (usually a loop between antenna's ground and transmitter's ground).

You can test the theory by trying a "cheater plug" (one that adapts two prong devices to three-prong outlets). If the feedback is changes or is broken or reduced --- you've found the issue.

Rewiring the ground scheme of the outlets to the main box or strapping the offending outlet to a grounding pole may work.

BTW... this is how a lot of old amps pickup AM radio signals. The slight potential between the AM station's ground and the grounding of your outlets.


For your reading pleasure: :D

http://www.ti.com/lit/an/slla057/slla057.pdf


Thanks BMW.

This is the kind of out-of-the-box thinking I asked others to apply when considering my concerns. Instead of reading and understanding what I wrote (and asking questions if they didn't), I got a bunch of "suggestions" to do things that I had already tried or said I was going to try (that's the "reading" part) from a group of "experts" who insisted that my amp was now working the way it was supposed to work and that I was stupid to think that it working in any other manner was correct (the "understanding" part). I guess since I built my version of a clone of their "holy grail" amp, it had to sound and operate the way they said it should instead of the way I wanted it to. Foolish me. Guess they taught me my lesson, eh? But that's OK. I'm fine being stupid in other people's eyes as long as I am happy and not hurting anyone. :lol: :lol: :lol:

Anyway, I have a big stake that has been pounded deep into the ground behind the garage. I'll check to make sure the ground cable is connected tight the next time I'm out back picking up dog poop (which is almost every day :shock: ) from my two Goldens. My studio is an addition to the house from several years ago and all the wiring was done by a pro. I don't mess with house wiring. That $hit can kill you. :lol: :lol: :lol: :lol:

My high power amps have been plugged into a Furman power conditioner with isolated outputs since I finished this amp in April. I also play through a Radial Engineering Twin City Bones ABY switch which isolates the inputs to the two amps I switch between.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Oct 17, 2013 10:05 pm
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Bluesky, try that "cheater plug." If you have any loop in the grounding, this method is a quick-&-dirty way to tell earth and/or accessories loops.

You may have a couple of loops going-on. One between the grounding of the guitar's electrics and the amp. And one with the earth ground and the amp. I use a jumper with alligator clips on both ends to test for pup loops. Clip one end to bridge and one to good amp ground point.


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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Oct 17, 2013 10:15 pm
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BMW2002Ti wrote:
Bluesky, try that "cheater plug." If you have any loop in the grounding, this method is a quick-&-dirty way to tell earth and/or accessories loops.

You may have a couple of loops going-on. One between the grounding of the guitar's electrics and the amp. And one with the earth ground and the amp. I use a jumper with alligator clips on both ends to test for pup loops. Clip one end to bridge and one to good amp ground point.


BMW,

I guess I'm not sure about what you are calling a "cheater" plug. In your last post you described it as "one that adapts two prong devices to three-prong outlets". I thought it was the other way around, one that adapts a three-prong plug to a two-prong outlet and that they were a definite no-no from a safety standpoint. I do have one of those outlet checkers that are used to determine if an outlet is wired properly (it is) and I would have thought that since the Furman uses isolated filter banks that ground loops in the power system would not be a problem. Please clarify. Thanks.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Fri Oct 18, 2013 2:26 am
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Bluesky, yeah. I mean an adapter to plug your three-prong wire into a two-prong outlet. Effectively lifting the ground. This is only used to test whether you have a ground-loop issue with the wiring of your house and the amp. You can also flip the adapter to see if the problem is a hot-neutral polarity issue.

Sounds like a ground issue --- since rain enhances the problem. Are you close to any AM station antennas? I've heard of guitar pups acting as antenna that pick up RFI. Enhanced during certain atmospheric conditions.

You may also want to measure the DC resistance between the guitar's bridge and the grid-to-ground point of the input tubes.


Anyhow, good luck with finding the problem. :D


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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Fri Oct 18, 2013 4:37 am
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I thought the same thing, a poor or improper ground somewhere in your house, or two grounds (water pipes and ground rod), evidenced by the fact that it only happened when the ground was wet. I suspect that possibly the neutrals from your outlets are not connected properly in the circuit-breaker box, and/or the ground rod is not long enough or not connected properly. The neutrals and the grounds in the circuit-breaker box should be connected to separate bars/terminals , and only the ground bar connected to the ground rod, and the two bars bonded together. Any current in the ground circuit can cause some weird things to happen, such as noise or feedback.

I also agree that the two prong adapter (lifting the ground) is a big no-no, unless used properly. The way to properly use the two-prong adapter is to connect the little lug sticking out to the center screw in the outlet, which maintains the ground circuit. The only reason to have a ground is for safety. Lift the ground, lift the safety, at your own risk. :idea:

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Fri Oct 18, 2013 5:44 am
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Aspiring Musician
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BMW2002Ti wrote:
Bluesky, yeah. I mean an adapter to plug your three-prong wire into a two-prong outlet. Effectively lifting the ground. This is only used to test whether you have a ground-loop issue with the wiring of your house and the amp. You can also flip the adapter to see if the problem is a hot-neutral polarity issue.

Sounds like a ground issue --- since rain enhances the problem. Are you close to any AM station antennas? I've heard of guitar pups acting as antenna that pick up RFI. Enhanced during certain atmospheric conditions.

You may also want to measure the DC resistance between the guitar's bridge and the grid-to-ground point of the input tubes.


Anyhow, good luck with finding the problem. :D


I also wondered that since rain seems to enhance this howling situation if it was a grounding issue. You mention AM station antennas,...I also wonder about the possibility of nearby ham radio operator stations and his guitar pickups acting as an antenna and picking up some kind of RFI from those as well. Being a ham radio operator myself,I can see the possibility!

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If it aint' broke,...don't fix it! I like to keep my amps and guitars factory original,...no mods necessary,...don't want them,...don't need them!

My gear as of now;
Standard Strat
Hot Rod Deluxe III amp
Champion 20 amp
'59 Bassman LTD Reissue


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