C*rr*m Mod?

[vanhalen5150]

so did you end up trying this on a 50?
thanx

Yeh, page back. Just a quick mp3. Not really going for articulation, just sound to see how it works.

[Dunkmop]

Impedance can be loosely described as resistance whose value depends on frequency.

Yeh, I was taught impedance was basically resistance for AC.

I have a speaker in the loft, but not to hand. Do you know how much, off the top of your head, that the speaker varies from 16ohm for instance? +/- ....%?

[mr.twistyneck]

I think that the soundclips of the 3k and 4k resistors are probably the best example of "dipping your feet into the water".

think of it this way. in normal state, there is nothing connecting the primaries, except air. nothing passess between them. So, the higher the value of the resistor (ie: the more it resists) the less "effect" you're going to see. The lower the resistance, the more crunchola and lower volume you will see. so theoretically, a resistor with a value of zero (ie, a wire) connecting the primaries would give you no volume. probably because it would blow up, i would assume.

try 1.5K on an amp that you are comfortable with taking the risk.

[jerrydyer]

so did you end up trying this on a 50?
thanx

Yeh, page back. Just a quick mp3. Not really going for articulation, just sound to see how it works.

[vh junkie]

I think that the soundclips of the 3k and 4k resistors are probably the best example of "dipping your feet into the water".

think of it this way. in normal state, there is nothing connecting the primaries, except air. nothing passess between them. So, the higher the value of the resistor (ie: the more it resists) the less "effect" you're going to see. The lower the resistance, the more crunchola and lower volume you will see. so theoretically, a resistor with a value of zero (ie, a wire) connecting the primaries would give you no volume. probably because it would blow up, i would assume.

try 1.5K on an amp that you are comfortable with taking the risk.

You did this with a 100w amp... Are the values your suggesting for a100 watt amps? Did you always do this w/o a variac? Bias set at normal levels (70%) for a given plate voltage?

[mr.twistyneck]

the values i'm suggesting are what i've used in the past, whether the super lead was using 6550's, EL34's or 6CA7's. initially, i thought that you couldn't do it with a 50watt, only because i've never had a 50 watt amp of this type in my life. when i was hanging out at the PPBB, i know somebody tried it with a 50 watt and had predictable results (distortion) but i seem to recall they didn't care for it all that much.

if i had the time and the gumption i would recommend running it with a variac for these reasons:
- my mind tells me lower voltage means less stress all around (i have no proof of this, and am not qualified to support it)
- variacs sound cool. "i have a marshall" Yawn. "i run my marshall on a VAR-EE-YAK" <wide eyes, mouth forms big O>

I have had three Marshall related epiphanies in my life, as follows:
1) a dimed super lead sounds extremely cool, and is fun to try and control.
2) all Marshalls, due partly to age and dotty repair/replacement part history sound different.
3) when I tried C erre m's Mod on a super lead i got big wide eyes and my mouth formed a big O.

each of these makes me go hmmmmm. There are so many really great mods out there that will give you safe, reliable noise-free awesomeness. Judging solely from soundclips (and in only two cases from personal experience) i just wasn't thrilled with what i heard (and to be fair, that makes me quite the hypocrite). when i tried this mod, it was like "whoa, now what the heck have we got here, this is nuts". and it is noisy, unreliable and unsafe (which I say mostly to be politically correct, but in practice don't give a flip).

[vanhalen5150]

I think that the soundclips of the 3k and 4k resistors are probably the best example of "dipping your feet into the water".

think of it this way. in normal state, there is nothing connecting the primaries, except air. nothing passess between them. So, the higher the value of the resistor (ie: the more it resists) the less "effect" you're going to see. The lower the resistance, the more crunchola and lower volume you will see. so theoretically, a resistor with a value of zero (ie, a wire) connecting the primaries would give you no volume. probably because it would blow up, i would assume.

try 1.5K on an amp that you are comfortable with taking the risk.

You did this with a 100w amp... Are the values your suggesting for a100 watt amps? Did you always do this w/o a variac? Bias set at normal levels (70%) for a given plate voltage?

Shut your pie hole and try something!

[leadguy]

think of it this way. in normal state, there is nothing connecting the primaries, except air. nothing passess between them. So, the higher the value of the resistor (ie: the more it resists) the less "effect" you're going to see. The lower the resistance, the more crunchola and lower volume you will see. so theoretically, a resistor with a value of zero (ie, a wire) connecting the primaries would give you no volume. probably because it would blow up, i would assume.

Basically that was what I was trying to say.

The more effect the primary resistor has, then the more the primary impedance variations are going to diminish.

Speaker impedance

http://www.churchsoundcheck.com/imp1.html" onclick="window.open(this.href);return false;

The thing is that the output transformer primary impedance goes up and down in sync with the speakers impedance variations and the primary resistor (depending on it's value) tends to restrict these primary impedance variations from happening as much, so the output tubes end up working into a more constant impedance for all frequencies and so more frequencies of equal strength end up being sent to the speaker ie more frequencies get a more equal go.
Also the output section is going to be more independent of the speaker load.
No matter what different speaker is connected as a load, the primary resistor is going to diminish any different speaker manufacturers impedance variations from affecting the primary impedance that the output tubes see.

That's why I said it ends up sounding like a giant EQ with the frequency boost bands near max, because there are more frequencies of the same sort of strength in the output.
The primary resistor alters the whole EQ of the amp/speaker.

The primary impedance variations in a usual amp->speaker setup cause some frequencies to be higher or lower in strength than others, so the strength of the frequencies being sent to the speaker are more variable ie some frequencies dominate over other ones.
Also the output tubes see a varying primary impedance in sync with the speakers impedance.

I thought twisty tried just about all the workable resistor values in his clips.

[vh junkie]

I think that the soundclips of the 3k and 4k resistors are probably the best example of "dipping your feet into the water".
...
try 1.5K on an amp that you are comfortable with taking the risk.

You did this with a 100w amp... Are the values your suggesting for a100 watt amps? Did you always do this w/o a variac? Bias set at normal levels (70%) for a given plate voltage?

Shut your pie hole and try something!

Me! Not try things! Half of my questions are to help you out!
Mostly I was trying to keep you from going to low!

I thought twisty tried just about all the workable resistor values in his clips.

A 50w is a different animal than a 100w.

I went down to 500 ohms with a 100w amp tonight.
No tubes going crazy! The most alarming thing is how hot the 50w 500 ohm resistor gets.
I will go lower, but I need to rewire the setup to I can put resistors in parallel to share the load.
The changes in volume are there, and some changes in frequency response.
I think the characterization of an EQ with all of the sliders pushed up is wrong.
Aikens take here is closer:
http://www.pleximods.com/cerremmod3.html

I think the sound is fuller (more low end)... with a different (but not ice picks!) high end component...

[leadguy]

"Also, adding a low parallel resistance across the primary of the OT makes the amp’s output source impedance look very low and very resistive, which changes the damping factor and flattens the frequency response, eliminating the natural bass and treble boost you get from the speaker’s impedance curve. The end result is a flatter, midrangey tone.

Randall Aiken"


That's what I've been saying but my EQ analogy should probably have been all sliders at the the same setting instead of maxed out.

All sliders at the same setting because the primary resistor is really letting more frequencies hit the speaker with more equal strength.

The speaker still rolls off the high and low ends according to it's frequency curves ie the classic Celestion curves but it still sounds like all the different frequencies coming out of the speaker are more even in strength.

To me it sounds nothing like any period Ed but if someone likes it then they like it.
It's really just an idea from C e r r e m and nothing more.

If you are running a 500 ohm resistor then that's taking most of the current because of it's low value and it's going to get hot and the 500 ohm resistor is basically setting the primary impedance which is very low for 50 or 100 watt output tubes to see.

[plexified]

Chris described this was an old ham radio application and very common . This is a circuit from the 40's actually .

When he described this mod he also told of the usage of the variac used as an attenuator in between the amp output
and speaker cabinet .

This halves power at the 90v setting and sounds very much like push comes shove . It has a shimmer that swells like a sweet feedback . The output signal is technically so far from the amp after it hits the speakers when it kicks back voltages to the amp the signals collide as usual , but now it introduces a delayed time signiture and alot of happenstance .

The resistor in between the two sides is playing a tug of war and needs to actually be tuned . Some values may need to be put together on a switcher so you can have a wide range . When you find the sweet spot its pretty much tweaked . I wouldn't use any type attenuation while tuning to find the right resistor you like . And keep in mind your amp should sound its best before a tweak like this , since you can make it switchable .

Just keep reminding yourself of the large voltages in their and DC will not let you go once your zapped , AC lets you get away with just a lesson and an accelerated heart rate .

I put the Variac instructions on page 5 of the ****** Mod thread in case your interested . I don't have time to paste it now , gotta go !

[vh junkie]

Here are some before and after clips.
I used a reamp clip supplied by a fellow forum member (should not be too hard to figure out who is playing!).
Both clips were recorded on the same night with the same settings.
Except: The ****** resistor required me to boost PowerBrake output level to compensate for the loss in volume.

Original recording:

reamped_dreamer.mp3

(609.56 KiB) Downloaded 477 times

About 2.5k across the plates:

reamped_dreamer_Cerrem_2k3k.mp3

(608.7 KiB) Downloaded 463 times

500 ohms across the plates:

reamped_dreamer_Cerrem_500ohm.mp3

(609.4 KiB) Downloaded 448 times

I think 500 ohms may be kind of extreme. 2k would probably be enough to let the sonic effect the mod makes come through.

[StuntDouble]

Wow, bigger, badder, fuller...Daddy like!

BTW, remember that time a forum member here proposed the idea that Ed's reamping might have been done post recording and not in a live setup. That is to say that it would have afforded him more flexibility with EQ'ing and would have allowed him to punch in his effects under a controlled setting for recordings. I can't remember off hand who brought up that idea, but I recall him getting flamed for it. These clips do kind of make you wonder though.

[vanhalen5150]

I stopped at 3K. Anything lower sounded like Nickleback.

[vh junkie]

Gotta keep in mind that your 50watter would have a 3.5k OT Primary, while the 100watter would have a 1.75k OT Primary... one might infer that a 100watter would sound the same with half the cross plate resistance... though I think there are other reasons the 100watter sound different...