night train mods...

[JimiJames]

ehh... so when can we all heard this ?
Are there any samples around...?
Would like to do this to roommates NT... that I will be using ofcourse
Seems like the first thing to go is that bright cap, though...
_______________________________
-Jimmie

[Rs16iandy]

Followed by 22uf in c21 and c7 gives it the missing low end

[sickman82]

Just registered as I came across the thread with a Google search. I am involved in a similar thread at Music Electronics Forum, mainly to do with the issues the NT has such as the fizzy decay and poor interaction with pedals. I won't link to the thread as I'm not sure I can, but it isn't hard to find.. it's the top thread in the amp section 'mods & tweaks'.

I just thought I should let you guys know that the schematic you are working from is incorrect in at least one place. Here is a link to the correct schematic that was very kindly traced by somebody.. http://s590.photobucket.com/albums/ss34 ... ght_Train/" onclick="window.open(this.href);return false;

That schematic has so far been exactly right when I have been doing my tinkering, whereas the link to the schematic from the OP has caught me out once.. note the value and placement of R25. Go measure it, it is indeed 1M.. not 1k5.

[Rs16iandy]

i came a crossed the same problems with the schematic

couldn't be happier with the mods so far

[sickman82]

Wow.. that's a fair amount of mods you have done there. What are the main improvements? Care to do a step by step of what has changed, any problems ironed out etc etc?

[tjnugent]

I had a thought about the Night Train and your posting is one of the very few detailed NIght Train mod threads out there.

Here is my idea. Get the schematic and a turret board and recreate the board via hand wiring and premium components. You could use quite a bit of everything else, like the overbuilt transformers and all the switches, knobs, power and things like that. You would essentially end up with a hand wired Night Train. I would like to do this. How hard would it be to do? I am not good with a hot iron, but if I could find someone who would do it, that may be interesting.

Any thoughts from those who have modded their Night Train?

Also, Sickman, have you got or heard any modded clips of the Night Train? Do you have any of your own? Wersman, I would be very interested in your thoughts on this subject.

TJ

PS. This is my first post. I found the thread and now I am excited. How much of an improvement have you guys had modding this amp?

[Rs16iandy]

i have changed the OT and added a choke as well had to make a few other changes if andy one wants updated mods list email me i have photos as well. very happy with it. it has good head room and i think it sounds as good as a £1000 amp now not the £300 i paid for it.

[Rs16iandy]

rs16iandy@yahoo.co.uk

[tjnugent]

Are there any sound clips of these mods to listen toi. You guys are torturing me. I am dying to find out how the modded version sounds. The Night Train sounds pretty good stock, but a little ice picky and the gain sounds a little synthetic, not as warm as I would like. But the good news is that it has lots of gain, so if it can be re-shaped, it would be a resonably priced amp with great tone. The form factor and overall look is fantastic.

Clips anyone?

TJ

[sickman82]

Also, Sickman, have you got or heard any modded clips of the Night Train? Do you have any of your own?

Unfortunately I don't have any clips, I don't have the means to record it at home.. it won't be until later in the year until I get back in the studio with my band either. Sorry man. As for building a hand wired version of the amp, go for it.. it is a fairly simple layout, but if you don't have much experience with electronics then I would suggest you find somebody who is willing to help you. It would be a pretty expensive project as well, so bear that in mind.

The Night Train sounds pretty good stock, but a little ice picky and the gain sounds a little synthetic, not as warm as I would like.

It does sound good stock, but it lacks low end.. that is one of the main problems with the amp. What cab are you using with it? If you have the stock 1x12, I would suggest investing in a decent 2x12 closed back cabinet.. that will help a great deal. The stock cabinet is far too small to handle any low end.. in my opinion it is a very poor cabinet. You can also swap out the cathode capacitors for higher values, which will allow more bottom end through. Don't attempt that unless you know how to drain the filter capacitors, it ain't worth your life man.

i have changed the OT and added a choke as well had to make a few other changes if andy one wants updated mods list email me i have photos as well. very happy with it. it has good head room and i think it sounds as good as a £1000 amp now not the £300 i paid for it.

Hey Andy, I hope you don't mind, but I'm going to email you with some questions - I'm really interested to hear if you got rid of that fizzy decay that the Night Train has. I have some more parts on order, I'm replacing most of the caps for high grade audio caps, I'm going to alter the voltages on the HT rail and experiment with the resistance on the anode of the preamp valves as well.. similar to what you have done, if I remember correctly.. i.e reducing them down from 220k to 150k or so. I'm hoping that will take care of the fizzy decay. But I'd like to hear your input, so check your inbox soon.

[Razorc195]

Hey Andy where do you stand on this so far...done? are they just the mods you listed at the bottom of the previous page of this post.... I would really like to hear your amp, could you post.... and what tubes did you settle on using.... Thanks!

[Ross Grey]

Found the source of the buzz -- but look at my later post on PI changes.

This is apparently caused by pumping a very treble-biased signal through the second preamp stage and then leveling this out with a treble bleed before the signal went into the phase inverter.

With this thread and other on-line resource as I guide, I purchased a Night Train with the specific intent to modify an already good sounding amp and try to loft it into boutique amp territory. It has take a couple of months, tons of reading and many mods to get to a point worth mentioning in this forum.

The short version is that while I had many good improvements by following recommendations in this thread like, adding a choke (10 henry) and Sozo caps, clipping C27, JJ output tubes, metal film resistors were useful to reduce noise, I still had the 'fuzzy' distortion complaint that seems to follow this amplifier around. As soon as the drive was turned up, it didn't get crunchy, it got buzzy. To fix this, I needed to re-voice both preamp stages and remove the pre-PI treble bleed formed by C25 and R34.

Admittedly, this amp with these mods has a great clean sound -- great definition, good sustain, swirling harmonics where each note in a chord sounds like it's own instrument. While I do play some jazz, I play more rock and blues. Unfortunately this amp starts to sound like a cheap fuzz box when it gets cranking.

My last strategy was to voice the preamp stages like a Fender amp by modifying the plate resistors to 100K carbon comp, and change the cathode (bias) resistor bypass caps to something more Fender like -- Fender would use 22uf, I used 33uf with good results -- but only on the second stage (after the tone stack). As soon as I changed the cap in the first stage, the amp sounded way too fat and tubby. I put 1uf back in with better results. It sounded like a Fender/Vox hybrid - somewhat better, but still had plenty of buzz when pushed into distortion.

Then I recognized that C25 and R34 formed a 'treble bleed' after the second pre-amp stage. What the heck is this? I don't see in in the other, similar 18 watt amps I have been studying. I wondered if this was why the amp sounded so tubby when I put 33uf in C21 to voice the first preamp like a Fender, so I put 33uf in C21 and removed C25.

Viola! No buzz, and much smoother transition from clean to overdrive, with any pickup on my strat, even with the funky 1-12 Vox cab.

Now the amp sounds like a Fender with very good overdrive. I may re-voice the tone stack and the treble bleed (C28, R36) that gets switched in for 'thick' mode. But even without these mods, the sound is mighty darn good for rock and blues and is starting to rival my favorite low-power boutique amps. The really clean, shimmering Vox sound has been replaced by a clean Fender sound, but it is not the same as the Vox sound.

[Ross Grey]

My last (perhaps overly enthusiastic) post on this thread has not cleared the moderators yet, but I have had time to do more critical listening to the changes described earlier. I really like my current configuration for a good balance of clean, crunch and OD capability.

I would say that frizz has been reduced about 80%, since it was heard easily from my typical playing location on a stool next to the amp before these mods and not noticeable afterward from this same perch.

When listening to the amp directly in front of the speaker at 10 feet, the frizzy sound is still somewhat apparent at many settings when the amp starts to break up, but it happens at a level that better defines 'break up' rather than 'annoying'. I may stop making mods right here. The clean tone is still very nice.

=== more detailed observations about the changes

Defeating the pre-PI treble bleed (if this is what is going on) would probably be better done by removing R34 rather than by removing C25 so that C25 would still be run to ground when the guitar cord is removed from the jack. This was apparently designed to reduce the noise of the amp when the cord is unplugged and the amp is still 'on'. It looks like some of you found it unnecessary to do this when increasing pre-amp gain for low and mid frequencies, but this strategy did not work well in my testing.

The treble control now seems a bit 'shallow' with this pre-amp voicing. I'm not an expert at designing a tone stack, but I may implement component values that are more like the amps that I am imitating with the changes so far.

With these changes, there is more gain in the preamps and consequently more noise at idle. Wire routing may also be responsible for a little more hum now.

=== disclosure on the current configuration

JJ EL84's
Mullard 12AX7 preamp - seems to warm things up a bit
original Sovtek for the phase inverter
remove C27 to remove ice pick highs
remove C25 (suggest removing R34 instead) to defeat what looks like a pre-PI treble bleed
R9 and R26 - replace 220k with 100k (I used carbon comp)
C21 and C7 - replace with 33uf - 50V - this must be done with the changes to R9 and R26
Sozo caps in the signal chain (same as original values) C10, C16, C26, C22, C31, C32
remove and jumpered C15 and C30
replace R1 with a 10 henry choke (Hammond 158M)
change C29 to 250pF/500V silver mica
change R7, R8, to 470R 3W metal film - original values, metal oxide film may reduce noise

=== after all this, I believe that the essential changes for less frizz and better crunch are

remove C27 to remove ice pick highs
R9 and R26 - replace 220k with 100k (I used carbon comp)
C21 and C7 - replace with 33uf - 50V - this must be done with the changes to R9 and R26
remove C25 (suggest removing R34 instead, but haven't done this) to defeat the pre-PI treble bleed

=== what I may be temped to try next...

I'll probably work with this configuration for awhile with simple changes to further de-emphasize treble in the preamp stages to see if the crunch sound can be smoothed out a bit further. As others have pointed out, there are limits to what can be done with so few gain stages.

If I were to attempt significant new changes, I would consider trying to de-emphasize treble a bit further in the pre-amp stages for a warmer overdrive sound and use a Fender-like presence circuit to provide feed back from the output of the OT back into the phase inverter to re-emphasize the highs before the signal hits the output stage. This looks like the approach used in the DRZ Carmon Ghia.

I would love to post some clips and could use advice on effective recording techniques.

[Ross Grey]

May have really found the source of the frizzy decay rather than mask it with preamp voicing...

Ok, I have done enough experimentation with preamp voicing to know that frizzy decay can be somewhat masked but now think that this is not the source of the frizzy decay.

Yesterday I turned my attention to the bias settings for all stages as a possible source of harsh overdrive. Both preamp stages are biased at 1.1v, which should border on 'warm biasing' based on what I have learned from wizard Merlin Blencowe. At these voltages, preamp biasing is probably not the source of frizz.

Then I noticed that the 'bright - thick' switch was modifying a relative ground (my terminology) for the phase inverter and suspected that the PI was being cold biased, especially in the 'thick' mode to add an aggressive character to the overdrive.

Working on the assumption that the PI may be cold biased even in the bright mode, I removed R38 so that only R28 sets the relative ground for the initial (inverted) PI stage biasing. I suspected that this would warm up the PI when it is overdriven.

Removing R38 brought the bias voltages for the inverted PI stages to 1.25v. This is a pretty good match for the bias on the non-inverted stage which was measured at 1.33v. This may be closer to center biasing that warm biasing, but I don't have access to an oscilloscope at this time to see if this stage is clipping first or not.

By simply removing R38, I believe that the source of the frizzy decay has been cleaned up to a large extent and my tests confirmed this, even after I returned C21 and C7 back to values closer to factory specs (2.2uF).

Now I feel like this is getting somewhere - the clean tone is a bit warmer than stock, and then breakup starts to kick in when the gain is increased, it is warmer and frizzy decay is mostly eliminated. Extreme gain settings will still get fuzzy and pretty radical.

It may be interesting to warm up the bias in the PI a bit further to see that this does, but I suspect that those of you who find the frizzy decay annoying will get welcome relief from simply removing R38.

After I can figure out the mods needed to bring PI bias voltages to around 1.1v and evaluate the impact of this, I'll post again.

[Ross Grey]

I don't have access to a good mic right now, but I did enough testing to convince myself that the built-in mic in my MacBook is sufficient to demonstrate that frizzy decay has been largely eliminated until extreme gain settings after my latest mods which include changes to R28 and R31 in attempt to reduce the gain in the PI and warm up the biasing.

MODIFICATIONS now being evaluated for removing 'frizzy decay'

R38 removed to eliminate first preamp input to the phase inverter
R28 changed from 2.7k to 4.7k
R31 changed from 56k to 100k

My recording setup is an unmodified strat directly into the amp (no effects), bridge pickup, volume and tone on the guitar all the way up (10). With the current amp voicing, tone controls at 11-o'clock are a nice balanced tone for clean, but I'll leave these here for all of these clips even though this gets a little tubby as the gain goes higher.

I'll try to use the same riffs at key gain settings so a comparison can be made. I used a very heavy pick and there is some fret buzz if I really dig in.

At different settings I will open with some adjacent string harmonics because this has always been a way to easily evoke the dreaded frizzy decay.

The mic position will be about 30 degrees off-axis and 18 inches in from of the speaker cab, which is the fairly inadequate Vox 1-12 cab. This drives the mic pretty hard so master volume is pretty low.

It looks like there is a limit of 3 attachments per post. There is one more with more gain in my next post.