[dukeamps]

Hallo Leute,
 
hier ist ein Amp, den ich modifiziert habe. Original war es ein Trainwreck Express Amp. Hier sind ein paar Clips, wie der Amp klingt.
 

http://soundclick.com/share.cfm?id=9934173

http://soundclick.com/share.cfm?id=9646821

http://soundclick.com/share.cfm?id=9937439
Falls Ihr Lust habt den Mod auszuprobieren, folgt der folgenden Beschreibung:
 
Als erstes modifiziert den Amp zu einem 2203 oder 2204
 
Der input resistor ist  33k, wendet den shield Trick am input an, das shield geht zur Anode anstelle zur Erde. Dann setzt einen 500pf cap über den zweiten plate resistor, .1uf über den 10k, .68uf über den 820r, 1000pf bright cap, 500pf klingt auch gut, der tone stack ist 33k/500pf. Das Wichtigste ist, b+ auf 390v herunterzubringen, dann den Bias für die el34 auf  31.5ma - so bekommt man den brown sound in den Mix.
NFB ist 47k/.1uf/.68uf (was immer am besten gefällt), 4ohm tap. Fizz cap ist 100pf
 
Die Transformer sind original vom Trainwreck Amp, gekauft von Marstran, der PT hat schon den niedrigeren b+ daher braucht man keine zener dioden um ihn herunterzubringen. Ich habe den Choke auch dort gekauft, aber man kann das an jedem Amp ausprobieren und sehen, wie es klingt, man mus nur sicherstellen, dass man das b+  bei einem 50W jmp Amp von 440v auf 390v herunterbringt, bei einem 100W  jmp Amp von 480v auf 430v.    
 
Cheers
Nigel
 
PS: Versucht dies nur, wenn Ihr wisst was Ihr tut. Oder ich kann es auch für Euch machen.

Sorry, da meine Muttersprache englisch ist, habe ich ein paar englische Begriffe im Text gelassen, ich hoffe, Ihr könnt meiner Beschreibung trotzdem folgen. Ansonsten fragt mich einfach.

[Stone]

Hallo Nigel

Sounds pretty good - the "ain't talking" clip is my personal favorite.

Der input resistor ist  33k, wendet den shield Trick am input an, das shield geht zur Anode anstelle zur Erde.

I am not sure about this, but read this quite often last time - what does it do exactly? I think it is kind of capacitor effect and therefore I would use a cap ... or is it kind of negative feedback, because of interference?

Dann setzt einen 500pf cap über den zweiten plate resistor,

I think this is to limit harsh sounding highs and upper mids and to give the tone more crunch.

.1uf über den 10k,

I would lower it 3k3 ;-) This will make the crunch a little bit harder sounding.

.68uf über den 820r, 1000pf bright cap, 500pf klingt auch gut,

Actually - while working on a similar project - I altered the values of the cathode, but this depends on personal taste; in order to "copy" the "brown sound" a lil' more, I would recommend using 1k || 330µF or at least 100µF.

The bright caps could be choosen using a multiple switch with multiple values connected I think 1nF is the highest value to use.

der tone stack ist 33k/500pf.

The "original one" is 56k and 250pF according to the schem of an '68 100 watter ...

Das Wichtigste ist, b+ auf 390v herunterzubringen,

Referring to a Marshall 2204 schem you should have 365 volts at the plates of the power tubes.

dann den Bias für die el34 auf  31.5ma - so bekommt man den brown sound in den Mix.
NFB ist 47k/.1uf/.68uf (was immer am besten gefällt), 4ohm tap. Fizz cap ist 100pf

The 100pF will make the sound a little bit darker (at least so it sounds to me) - some people state, that compression increases, too.
 

Sorry, da meine Muttersprache englisch ist, habe ich ein paar englische Begriffe im Text gelassen, ich hoffe, Ihr könnt meiner Beschreibung trotzdem folgen.

My native language is German, but I see this as a good chance to trainee my English once more.

Regards, Dietmar

[dukeamps]

Hi Dietmar thanks for your feedback.

So like I said before the amp was a trainwreck express amp, and the idea behind this amp was a sort of mix between a brown sound and #34 mod amp.

When you use the anode as shield it takes a lot of noise and oscillation & fizz away its a neat trick, on the #39 amp it had it on the first three stages or so I believe, it also gives the amp that nice sound. I have tried a lot of different values, but that’s just where I thought it sounded best, but if you or anyone else wants to try this mod of course mess about a bit and see what comes out, my values are just guide lines. On the jcm 800 sche I have seen its 33k/470pf, but I could be wrong. With the b+ I was just going with my jmp 50w which has 440v, didn't know that the jcm 800s had so a low b+ 365v.

It’s nice that we can use English here also.

Cheers

Nigel     

[mac-alex_2003]

Hi,

I am not sure about this, but read this quite often last time - what does it do exactly? I think it is kind of capacitor effect and therefore I would use a cap ...  

because of the amplification of the stage the capacity of the shielded cable is multiplied by the amplification factor. An easier and safer way is to use a small cap from grid to ground. I am not a fan of anode-grid caps. Why? What will happen in case of failure?...

The combination of these mods (500pF || ra; input-c; fizz cap, lower voltage) will reduce the highs a lot. So on the one hand you will reduce treble with these mods, on the other hand you will get your highs back in the power amp when using a 100k at the 4 Ohm tap in the feedback circuit in combination with the 100nF parallel to the 10k. This smoothens the sound a bit, but the small feedback voltage still gives you a harsher sound.

Another way is to let the highs "flow" through the amp with as few (bypass-)caps as possible and make it smooth with a higher feedback. This will give you a more shimmering sound. It is just upon you!

100pF as a fizz cap reduces these shimmering highs a lot, for my taste it is too big. 50pF is good, 68pF will also work.

and: nice sounding amp

Yours,
Marc

[Stone]

Hi Nigel

So like I said before the amp was a trainwreck express amp, and the idea behind this amp was a sort of mix between a brown sound and #34 mod amp.

Seems as if we share the same ideas at the same time

I am not sure about the #34 values - at least I have got three different schems, which are based on a mv circuit; I think all of them come very close to VH-I and -II sound and also to Slash' "use your illusion".

When you use the anode as shield it takes a lot of noise and oscillation & fizz away its a neat trick,

Ok, then it is a capacitance - I would beg there is a small amount of negative feedback because of the interference of shield and wire.

on the #39 amp it had it on the first three stages or so I believe, it also gives the amp that nice sound.

Hm ... I think it will smoothen the amp a bit, yes.

I have tried a lot of different values, but that’s just where I thought it sounded best, but if you or anyone else wants to try this mod of course mess about a bit and see what comes out, my values are just guide lines.

As we are dealing with electronic parts which are belonging to the dinosaurs age, you will have enough drift within the values of the parts, so everybody will tweak them to his personal taste and hearing.

On the jcm 800 sche I have seen its 33k/470pf, but I could be wrong.

No, you are right. I think Marshall changed them values from 56k / 250pF to 33k / 470pF very early but not on all models. As Eds amp is stated as an '68 plexi, the values could have been 56k / 250pF, if they have not been changed.

With the b+ I was just going with my jmp 50w which has 440v, didn't know that the jcm 800s had so a low b+ 365v.

I think during the JMP era Marshall used the same PTs for 100 and 50 watter - I have never measured the voltages of my JCM800 2204, but the schem shows that low voltage and it is sounding completely different to an JCM800 2203.

It’s nice that we can use English here also.

So, why not?

I am glad that you 've understood me ...

Regards, Stone

[Stone]

Hi Marc

because of the amplification of the stage the capacity of the shielded cable is multiplied by the amplification factor. An easier and safer way is to use a small cap from grid to ground. I am not a fan of anode-grid caps. Why? What will happen in case of failure?...

That 's what I have in mind, but to be honest, I do not care much about anode-grid caps ... on the other hand side, you are right, grid-cathode caps seem to be much safer.

Regards, Dietmar

EDIT: sorry, mixed it up ... I am using anode caps most of the time - anode-grid caps will result in negative feedback, which is different to effect of anode caps

[dukeamps]

Hi,

because of the amplification of the stage the capacity of the shielded cable is multiplied by the amplification factor. An easier and safer way is to use a small cap from grid to ground. I am not a fan of anode-grid caps. Why? What will happen in case of failure?...

The combination of these mods (500pF || ra; input-c; fizz cap, lower voltage) will reduce the highs a lot. So on the one hand you will reduce treble with these mods, on the other hand you will get your highs back in the power amp when using a 100k at the 4 Ohm tap in the feedback circuit in combination with the 100nF parallel to the 10k. This smoothens the sound a bit, but the small feedback voltage still gives you a harsher sound.

Another way is to let the highs "flow" through the amp with as few (bypass-)caps as possible and make it smooth with a higher feedback. This will give you a more shimmering sound. It is just upon you!

100pF as a fizz cap reduces these shimmering highs a lot, for my taste it is too big. 50pF is good, 68pF will also work.

and: nice sounding amp

Yours,
Marc

Hi Marc, thanks for the feedback

Nigel

[dukeamps]

Hi stone, Here's what i know about the #34 mod. First mod to a 2203. Over the 10k put a.1uf, over the 820r/1k put .47uf or.68uf, over the second plate resistor put a 470pf cap & on the gain pot, put a 150k from the wiper to ground. I also believe there was a 1000pf on the gain pot.
The Nfb 47k or 100k/ .1uf or .68uf on the 4ohm tap.

Try and see what you think

Cheers

Nigel

Ps your English is very good  

[custom]

Hi
die Sounds hören sich Klasse an. Wie hast Du denn die Aufnahmen gemacht?

Gruß, Bernd

[dukeamps]

Hi
die Sounds hören sich Klasse an. Wie hast Du denn die Aufnahmen gemacht?

Gruß, Bernd

Hi Bernd,

Vielen Dank für das schöne feedback.
Für die Aufnahme habe ich ein Sennheiser E606 verwendet und es genau zwischen Außen- und Innenrand vom Lautsprecher platziert, ungefähr 10cm weg vom Lautsprecher.
Die Lautsprecher sind vom Typ Celestion G12H30 Heritage.

Gruß Nigel

[Stone]

Hi Nigel

Thanks for the compliment

As I have little time until evening, one question in between: would you please be so kind to measure voltage at anode of very first triode?

The rumours about #34 are from having every stage lowered to 2k7 || .68µF up to the things you mentioned - as I am not that much in Slash tones, I do not care about them really, but they are a very good starting point for Eds sound.

BTW: my favorite one is "1984" sound, esp "girl gone bad" and "panama" - I think there is a major / big change in Eds sound from pre-1984 albums to 1984.

Regards, Dietmar

[dukeamps]

Hi Nigel

Thanks for the compliment

As I have little time until evening, one question in between: would you please be so kind to measure voltage at anode of very first triode?

The rumours about #34 are from having every stage lowered to 2k7 || .68µF up to the things you mentioned - as I am not that much in Slash tones, I do not care about them really, but they are a very good starting point for Eds sound.

BTW: my favorite one is "1984" sound, esp "girl gone bad" and "panama" - I think there is a major / big change in Eds sound from pre-1984 albums to 1984.

Regards, Dietmar

Hi Dietmar, so the first triode anode measured 169v.

Cheers

Nigel

[Stone]

Hi Nigel

Tried to lower them, too, but average voltage is stated as 192v on anode of the 2k7 system and I got 202 volts - wondering, why this / my 2204 has that much, but it is built in 1980 / 81, so the transformer might be quiet the same as on the 2203 models.

Hm ... I will try to come close to 170 volts tomorrow - maybe I am able to make some sound files, too.

Regards, Stone

[dukeamps]

Hi Nigel

Tried to lower them, too, but average voltage is stated as 192v on anode of the 2k7 system and I got 202 volts - wondering, why this / my 2204 has that much, but it is built in 1980 / 81, so the transformer might be quiet the same as on the 2203 models.

Hm ... I will try to come close to 170 volts tomorrow - maybe I am able to make some sound files, too.

Regards, Stone

Hi stone, maybe you have to use some zener diodes to bring the voltage down. I have ordered some of these here, http://cgi.----.de/ws/----ISAPI.dll?ViewItem&item=250474373375&ssPageName=STRK:MEWNX:IT

To try them in my 100w amp.

Cheers

Nigel 

[Stone]

Hi

I am using resistors ... did you place the diodes between center tap of the PT and ground (so CT gets "removed" from ground)? Or do you place them - as some people advice - between B+ and anodes?

Regards, Dietmar