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WREKNOTZ.TXT  Complied from threads at AMPAGE and other
sources. If your name/e-mail address is listed below and
you want it removed or edited, let me know!  Steve Ahola

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Name: Joel
E-Mail: 
Date: 10/13/99 6:57 PM
Subject: trainwrecked espreeso updates

I started this on a JTM45 reissue chasis. I have not had the time to play around with
values recently, but last night I tried to address the problem of the amp being overly
bright by doing the following:

On the schematic, I always thought that the amp would be very bright judging from the
.001uF cap feeding a 56k resistor to ground between the second and third gain stage.
Since I didn't have a .001uf cap I made one by connection two .0025uF caps in series.

Baseline: .0025//.0025=.00125uF + 56K : TOO Bright

Experiment #1: Shorted one of the .0025, leaving one .0025 feeding the 56K. This was
still iverly bright.

Experimet #2: .0025uf feeding a 100k resitor, still too bright, but getting better.

Experiment #3: .0025uF feeding a 160k resistor, this got beter, tight low end but still too
bright.

Experiment #4: I brute forced the cap using a .022uF feeding the 160k resistor. The cap
is now an order of magnitude larger and it was not overly bright, HOWEVER, the low
end went completely to mush as I think there is too much low frequecy gain through the
three gain stages. I should note that I am using a tube rectifier and this could be
contributing to the mushiness, but it only existed with the higher value cap.

Here are my conclusions. When I have more time I am going to try to increase the
capacitor value and or the resistor value. The last good place I left off was the
.0025uF/160K resistor. I will incrementally try to increase one or the other value.
Looking at the schematic, it seems like the cap should be incresed so as to have the
second stage driving a lower value resistor and potentially creating more harmonics from
the loading.The cap should fall somewhere between .0025 and .022uF to balance the
amp from having a tight low end but not overly bright high end.

One other thing that I have noticed is that the treble control does not have very much
range with the 47/50 pF treble cap. I am going to try to increase this value to see if I can
make the control more responsive.

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Name: Mook
E-Mail: 
Date: 10/14/99 1:19 PM
Subject: Re: trainwrecked espreeso updates

I'm going to 2nd your findings. Maybe I should have
written this a few months ago. I tried many of the
combinations you mentioned and I got EXACTLY the
same output. Of special note, the .022 has the perfect
high end, but turned the bottom to mush.

Mook 

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Name: Mystery Man
E-Mail:
Date: 10/14/99 2:37 PM
Subject: Re: trainwrecked espreeso updates

Keep your .02/150K before the third stage, and try lowering the value of the .1uF
coupling cap that goes from the plate of the third stage to the input of the PI. 

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Name: Joel
E-Mail: 
Date: 10/14/99 5:27 PM
Subject: Re: trainwrecked espreeso updates

Mystery Man,

I already have a .022uF from the third stage to the PI. I do hAVE 0.1uF caps
from the PI to the power tubes. I don't think this should make a huge difference as
a .022uF/220 bias resitor will give a high pass corner of 32Hz, a 0.1uF/220k
bias r will give 7Hz. The low "E" is 80 Hz.

I think the .022uF will not make a big difference between the third stage and the
phase invertor, BUT, I will try a 500pF - .001uF ala Fender Blackface. 

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Name: Sam
E-Mail:
Date: 10/18/99 1:57 AM
Subject: Re: trainwrecked espreeso updates

Joel,

I certainly hear what you are saying with the math, but I guarantee a huge
difference in bass response (with the amp at *full tilt*) with .1uF PI coupling
caps as opposed to .022uF. Have you tried keeping what you've done to the
pre-amp, but changing those coupling caps to .022uF?
What is the make and plate-to-plate impedance of your output transformer?
Express is 6K6.
Average plate voltage is ~400-410 volts.
Is your clone tube or ss rectified?
How is your power supply network set up?
Couple other notes:
1) treble cap 500pF, treble pot 250k audio taper
2) second pre-amp stage's cathode bypass cap to 25uF or 22uF
3) If after above, AND changing PI coupling caps to .022uF or .033uF, bass
response is still too overwhelming:

Try .002uF/150K RC network after second stage. Move .002uF value up
*gradually* if overall sound isn't full enough.
Still consider fiddling with PI input cap.
The schematic on Steve Ahola's site might very well be a reverse engineered
Express, but remember that Ken Fischer often tweeked his amps according to a
customer's style or specific request for a sound or sounds. There may very well
be two Express amps with identical component values, but I'm sure most are
slightly different from amp to amp. Good Luck!

Mystery Man 

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Name: Doc
E-Mail: 
Date: 10/14/99 5:29 PM
Subject: Re: trainwrecked espreeso updates

Try to reduce the excessive bass energy by lowering the value of the stage's
cathode bypass cap. Currently it's shown with a 220uf cap bypassing a 2.7k
resistor. I'd try 25uf to see how the balance is with the .022 stage output coupling
cap. Raise it a little at a time until the bass is adequate, but not mushy. 

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Name: Joel
E-Mail: 
Date: 10/14/99 5:53 PM
Subject: Re: trainwrecked espreeso updates

Doc, 

I think it may even need to be a lower value. If you look at it a 2.7K/220uF cap
would give a HP corner of 0.27Hz. A 2.7K/25uF cap is 2.3Hz. Since the low
"E" is 80Hz, I don't see how this cap would change things looking at it in this
way. I have heard/read that you can increase bass in Fenders by changing the
25uF to a 220uF but I never really understood why.

Joel 

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Name: Gil Ayan
E-Mail:
Date: 10/14/99 6:20 PM
Subject: A Little Note -- Re: trainwrecked espreeso updates

Guys, I see that you use the 1/(2PiRC) formula to calculate the frequency break
points wile tuning an amp. That works as an order of magnitude approximation
though, but it is hardly accurate. Especially on the plate side, you have the tube
internal resistence, the plate load, whatever comes after the coupling cap and any
feedback you may have. So if you think in pencil and paper 2Hz and 50Hz is the
same because they fall below the guitar's lowest fundamental, maybe give it a
shot anyway.

Also, reducing the cathode bypass cap VS reducing the coupling cap after a stage
may both brighten the sound, but they do so in a different way. I have heard some
people say that the cathode bypass cap should always be bandpass to ensure
there is a smooth sound... something to do with the electrolytic going crazy when
it gets close to the freqeuncy knee. Some people refuse to use electrolytics all
together there, and prefer the sound of metal film caps.

Lastly, you can reduce the bass content at the output of the tube by using a small
coupling cap, but sometimes a 1st order LPF works better (to my ears). So say
you have a .047uF couplig cap and the sound is way too mushy because you're
feeding too much bass into the next grid, causing it to go positive/clamping
whatever you want to call it. One idea would be to use say a .001 (or whatever)
coupling cap instead, but, I prefer to use a "PI" type arrangement, where you still
use a "normal" size coupling cap and through a resistor to ground, forming a
HPF.

For an example of the above idea, look at the Marshall 30 Anniversay schematic
(which Steve Ahola's site has), in the lead channel there is some of that going on.

Just some ideas. Hopefully you guys will soon have come up with a shcmeatic
for a "Trainwreck" (gotta cal it something) that doesn't sound too bright.

Cheers,

Gil 

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Name: Randall Aiken
E-Mail:
Date: 10/15/99 12:20 AM
Subject: Re: A Little Note -- Re: trainwrecked espreeso updates

Gil speaketh the truth!

If you just use the value of the cathode cap and cathode resistor to calulate the
lower -3dB corner frequency, you will be off by quite a bit, because this doesn't
take into account the impedance seen looking into the cathode, which is
effectively in parallel with the cathode resistor. You must use this parallel
combination resistance when calculating the corner frequency. 

In addition, the rolloff formed by the cathode cap is not a first order, continuous
-6dB/octave slope. It is actually a shelving filter. The max gain is the fully
bypassed gain, and the min gain is the fully unbypassed gain. The gain transitions
from one level to the other smoothly at the corner frequency. In contrast, the
rolloff formed by a series cap on the plate side, in conjunction with the grid
resistance of the next stage, does behave as a first order highpass filter with a
continuously decreasing gain with a slope of -6dB/octave. Each has a different
effect on the tone, and you have to know which to use to shape the response,
depending upon the desired effect.

For a better explanation of how to calculate these gains and frequency
breakpoints, as well as plate and cathode output impedances, check out the paper
on the tech pages at http://www.aikenamps.com entitled "How to calculate
triode gains and impedances". It shows a plot of the frequency response of a
partially bypassed cathode resistor as well.

Randall Aiken 

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Name: Doc
E-Mail: 
Date: 10/14/99 8:33 PM
Subject: Re: trainwrecked espreeso updates


I see your point, but all these turnover R-C networks are in series along the great
signal path. Their attenuative effects can be cumulative. The resultant pass band
is not dependent on one R-C constant. For instance, just because the cut is 3db@
80hz at this particular point isn't the whole story. (Hypothetical example:)3db cut
this stage, then another 6db cut the next stage, and 2db cut the next stage, ends up
being 11db cut after the signal has passed through all three stages. It's best to use
the "cut & try" method when changing a component value when modifying a
multi-stage amp, and listen to the actual sonic effect. 

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Name: Joel
E-Mail: 
Date: 10/18/99 5:58 PM
Subject: Re: trainwrecked espreeso updates

Mystery Man,

Thanks for the advice. Here is where I stand.

I have built this on a JTM45 reissue chassis. I have not measured the primary
impedance but I have read that the reissue is about 6K+. The data sheet in the
Doyle Marshall book shows a 6.6K impedance for the *Original* JTM45's. I
think this should be close. The 50W Marshall's have about 3.4K I think.

I am using a tube rectifier as this is how the amp is set up and it is delivering
400V to the plates. I realize that this could mush things up but I wanted to stay
below 400V initially, as I think there is some magic in having lower voltages
and a SS rectifier with this power transformer will raise things even further.

I have not paid close attention to the power supply network, (I still need to
"optimize" the preamp tube voltages), but I think there GZ34 feeding a 50uF cap
on B+ , through a choke to another 50uF feeding the screens,10K resistor and
50uF from the choke to the PI power supply, and 10K + 50uF feeding the three
gain stages.

I left the .0025uF/160K resistor I ended up with between the second and third
gain stages, and started experimenting with the tone controls as I have not been
comfortable with the 50pF cap. I changed the cap on the treble from 50pF to
250pF and then to 500pF and this improved the midrange significantly and
gives the amp a better tonal balance overall. The treble pot was 1Meg. A
1meg/500pF had more mids than a 250K/500pF so I am going to stick with the
1Meg/500pF on the treble control.

At this point, I think I can tweak the bass in by playing with .002/160k setup. I
think I also need to change the .022 cap at the PI input to 0.1uF as has been
suggested to bring up the low end.

Do you have any ideas for the power supply or what the real Express plate
voltage is?

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EXPRESSO MUSINGS (from an anonymous correspondent)

October 25, 1999

The schematic reference for what follows is the "Trainwrecked Expresso" on Steve Ahola's site. I'm sure most of us know that Mr. Fischer fine tunes his amps to each player's tastes and styles (types and values of caps, resistor values, tube types,etc.) so take what follows with a few shakes o' salt.

1. treble cap to 500pF, treble pot to 250k audio
2. RC network at second stage plate: .002uF/150K
3. 22K cathode resistor at PI should be 10K
4. second stage bypass cap to 22uF
5. NFB resistor: 47K, from 8ohm tap 
6. screen grid resistor to 1K


Output tranny plate-to-plate Z: 6K6
Not sure what make the OT is, but a Hammond P-T1650H will get you fairly close. 

Average plate voltage is ~410 volts

Set up to use 6V6s (PLEASE use NOS...not sure about the new Sovtek 6V6EH) or EL-34. You can use 6L6 variants if you want to of course (KT-66 sounds like a good candidate for experimentation). I don't know how they sound with the amp though. If you run a good quality EL-34, don't be afraid to run them somewhat hot. The amp will like that ;).  

Solid state rectified

Power supply layout:
80uF on plates -> 1K/25W resistor choke 
40uF on screens -> 18K2
20uF for the PI -> 9K1
20uF for the 3rd stage -> 9K1
20uF for the 1st and 2nd stages.

Experiment with different cap types in different places in the circuit (i.e. oil caps in tone circuit and/or PI bypass, mylar, polyester/paper, polystyrene, etc).

This amp's response, as with many simple designs, noticably changes with brand of pre-amp tube. Expect to do a lot of experimenting here as well. There may be a 'Wreck out there with some new production pre-amp tubes (as well as power tubes), but I don't know about it. That's not to say that new production pre's can't sound good. I'm sure there are some that will sound fine in specific places in the circuit. Hell, go crazy...make one with octal pre-amp tubes, Alessandro does.
 
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Name: Mook
E-Mail:
Date: 10/22/99 11:38 AM
Subject: Re: Trainwreck & Alessandro
         Transformers

I believe 'Wrecks use Pacific trannies. I just happen
to know that the manufacturer code for Pacific is 1052.

I was looking at an Allen amp last week and the codes on the
trannies were 1052, so I assume Allen uses Pacific trannies,
too.

I know Dr. Z uses Schumacher

I asked Callaham about his trannies......he was "tight-lipped"
and said they were wound by hand. There are no codes on his
trannies.

Mook

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Name: Mook
E-Mail:
Date: 10/25/99 12:30 PM
Subject: Well....the Story goes like this...


I did a bunch of research on 'Wrecks, Callaham, and
Allesandro. To my knowledge, Callaham and Allesandro
are about as close to a 'Wreck as any person (mere mortal?) is
going to get. Even if I could afford a 'Wreck (well over $10K),
I never see any for sale.....

Well in my research (web/newgroup readings and personal
contacts/interviews), I learned that Callaham got ahold of
a Trainwreck Express. He reverse engineered and "Blue
Printed" the Express. Aside from a few (minor) differences
(which I won't reveal because I don't want to get in "trouble"),
the Callaham is a "dead-ringer" for the Trainwrecked Expresso
schematic on Steve Ahola's site. 

Does it sound like a 'Wreck? I don't know, but it does give
me a sound I was looking for - about 80% Marshall and 20%
Vox. It crunches up more than a Plexi (if you want it to), but
can nail the plexi sound, cold. But since it's only about 25
watts, it's not as loud as my Plexi. I have the EL84R which is
(as you guessed it) 4xEL84. He also has a 2xEL34 (which is
really like the Express). The two amps use the exact same
pre-amp.

Does it do everything? No, but it's still a very nice amp.

The best part of the story is about the time I was ordering
the Callaham, I was putting the finishing touches on my own
Trainwrecked Expresso. I however, used only two EL84s and 
copied the Fender Deluxe Reverb B+ rail. 

My Expresso and the Callaham sound NOTHING alike. Both
are
good amps, but both are different. My Expresso sounds more
like a Dr. Z Prescription (compressed and Voxey).

Perhaps someday, I get around to ordering an Allesandro. If
Ken Fischer went back into business, I'd order one of those in
a Hearbeat.

As for Allen, he designs/builds amps that are Blackface based,
with only a few differences such as a Master Volume and a
"raw" switch. What can I say, his amps sound very
Blackfaced. It's also a very nice amp.

Mook 

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And here is what Ken Fischer had to say...
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Name: Mook
E-Mail:
Date: 11/12/99 5:24 PM
Subject: Re: What were the corrections Ken
         mentioned for the 'Wreck schematic?

1) He said the .1uf into the PI was correct. He
said the PI used .1uF throughout.

2) The treble cap is a 500pf, not 50pF.

3) He said his Express has a 3 position bright switch,
but is missing from the "Expresso".

4) Other than the 3-way bright switch, he said the
schem is VERY close.

Mook 

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Name: peter
E-Mail:
Date: 12/17/99 5:15 PM
Subject: trainwreck clone

Built one. Not happy with the sound. Played
around with the much-discussed 0.001 uF- 56kohm
network, can't get a sound I'm happy with.

It was previously posted that the 50 pF cap
in the tone stack should be 500 pF. 
Even with that change, if I program
the tone stack into the Duncan simulator,
it has a strange response, with the mid-dip
below 200 Hz.

Anybody built one of these, got any comments?

How confident are we that the tone circuit is 
correct?

thanks. 

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Name: Joel
E-Mail:
Date: 12/17/99 7:16 PM
Subject: Re: trainwreck clone

Peter,

I had better luck when I used a 1meg treble pot with a 500pF treble cap,
more mids and better low end.

I also have a 0.0025uF/160K between the second and third stage and the
low end improved as well, still not enough so ewhen I have time I am
going to try a 0.0047uF in this position. I also built the amp with a 0.022uF
input to the phase invertor, and I think I will get alow end improvement
when I change it to the correct 0.1uF. 

 
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Name: Matt D
E-Mail:
Date: 12/19/99 3:01 PM
Subject: Re: trainwreck clone


Peter,

My 'wreck clone has been my main amp for the last month or two. I have
found it to be a great match for my style and sound.

I've ended up bumping the pi coupling caps from .022 to .047.

I upped the cap across the 150k plate resistor to .003.

.001 coupling cap to .0015 (crucial spot for listening & tweaking. Hell for
that matter EVERY component is critical in this design due to its
simplicity).

Do you have a grid input resistor on the initial 12ax7? If removed the highs
increase signicantly.

Bias current toward the hot end?

Careful selection of pre tubes. The trainwreck web site shows many
Express owners use Mullard pre's. I swallowed hard and spent $50 bucks
on a Mullard CV4004. I THINK I can detect improved mid coloration...

I liked the girth and mid bite with Svet EL34's but Mazda 6V6's let me
crank the volume higher to take advantage of the output distortion at
slightly lower volume.

I'm using a Celestion Vint. 30 and a G12H30 wired in series. 

OP transformer primary of 8k ohms (as close to 6.6k as I can get with my
setup).

I found the amp rather brite initially. I took it to practice and found that at
band volume the freq. balance was awesome..output section begins to fill
in bass (never flabby) and highs begin to roll off somewhat. Also, because
the thing is so damn dynamic, its bright nature allows warm clear sounds
with guitar volume rolled off. When guitar is cranked full for leads the
bright edge allows the higher harmonics to sing.

You'll have to pardon my gushing but I'll tell you this- this amp is the most
dynamic design I've ever played. I can do without stompboxes because the
guitar volume knob can do it all...even the drummer is impressed!

Good luck! It works for me but of course YMMV!

Matt D 

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Name: peter
E-Mail:
Date: 12/19/99 7:11 PM
Subject: Re: coupling values?


Increasing the coupling caps lets more bottom end through.

I played around with the 0.001/56k and ended up 
replacing it with a marshall-like divider 
with 2 470k resistors and a 470p cap.

Matt I know what you mean that the thing has a kind 
of unique clarity... maybe I am just using the 
cabinet with it-- marshall 4x10. In a room that
doesn't have much absorbing material it is just too 
bright.

What was that about a 150k plate resistor? My circuit
doesn't have that, nor a cap across it!?

I tried various tubes but the subtle variations
between them are buried under the excess
brightness.

Yes, I have 68k grid resistor on stage 1.

thanks for you comments.
peter

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From: peter
Date: 4/13/2000 2:36 PM
Subject:
Re: Trainwreck amps


besides the schematic there is also some 
discussion of (1) corrections, and (2)
modifications. I built one and found it 
had an interesting and different sound, 
but was far too trebly for my taste.
Much of the discussion of modifications
involved taming the high end. Easy
enough to reduce the treble, but then it
loses the unique character that it had.
Still haven't got mine to a state that
I'm happy with.

YMMV,
peter 

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From: nathan
Date: 4/13/2000 3:21 PM
Subject:
Re: Trainwreck amps

What types of tubes did Ken Fischer use for his amps? Where did you find the
power amp schems? Did you model the power section after another amp?

Thanks,
Nathan 

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From: peter
Date: 4/13/2000 4:43 PM
Subject:
Re: Trainwreck amps

Hi,

I don't know what kind of tubes.

The schematic I have includes both preamp
and power amp. The power amp is nothing
unusual, typical marshall/fender type of
circuit.

The preamp has one stage before 
the tone controls and two after, so the distortion
comes AFTER the tone control, unlike e.g. a marshall.

Between stages 2 and 3 there is a 0.001 uF cap
loaded by a 56k resistor, forming a high-pass filter. Those 2 components have a
profound effect on the character of the amp.

peter 

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From: anonymous
Date: 4/14/2000 12:02 AM
Subject:
Re: Trainwreck amps

Peter - the correct values between the 2nd and 3rd stage are 2n/150k. Also the
2n is made up of 1n film and 1n ceramic. Try it out 

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From: Steve Ahola
Date: 6/??/2000 ??:?? ?M
Subject:
Re: Trainwreck amps


   ... But if someone had really good ears for building an amp, they could
hear how some combinations work really well and others don't. Like if you
have perfect pitch you can tell right away when something is out of tune; the
rest of us have to get our tuners out to check..."

    In any case, I believe that Ken Fischer's "magic touch" has nothing
to dowith the voodoo topics like pure silver wire and other audiophile-grade
components. I bet that if he was to work at any of our benches for a day
or two, he could come up with an absolutely killer amp using the same parts
that we have been using... (Or substitute whatever amp builder that you
respect a lot for the reference to Ken Fischer.)

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From: wreckboy
Date: 6/??/2000 ??:?? ?M
Subject:
Re: Trainwreck amps

Steve,

You're totally right. Ken can build a "Trainwreck" amp just using spare
parts that he had laying around his shop (the same parts any tech would have).
I own the first Trainwreck amp built. It's a 15 watt Class-A amp built on
a gutted Fender chassis. No aluminum chassis, no custom transformers,
parts from old Ampeg/ Marshall/Fender amp, using a stripped Fender circuit
board. He calls it a piece of "junk" made from "spare parts" that "blows
away any AC-15 or Marshall 18 watter" ( and he has worked on and played a
number of these classics). It was built to test out ideas ( ex. it had
features like switchable fixed/cathode bias ) before he built the full power (4
EL-84) model. Ken does have the "Magic Touch" but he also has the "Magic Ear"
to go along with it. It looks like just another Fender chassis that someone
had modded.....but when you hear it ....Wow, it's like from another world.
Hey,next time that Aron comes back home I'll let him play the the amp and he
can do a review for Ampage:-)

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