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Post subject: Vibro-Champ XD Mods; New Tubes?
Posted: Sun May 30, 2010 12:19 pm
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While I think this is a great travel and practice amp with very nice mojo, I'm already thinking of ways I can get a little more out of this little punk.

So here's what I'm thinking:

-NOS Sovtek pre-amp tube to replace the Fender 12AX7
-NOS RCA power tube to replace the 6V6
-Jensen P8R to replace the stock Fender speaker

I've come to discover I almost never use most of the 15 other preamp settings (unless I want to play this amp as quiet as I can and still be able to get a cranked tone, in which case, I'll just turn the voice knob to 2).

If you milk this amp the old fashioned way, by turning the gain and master knobs up to 10 and ripping them off, the sound is a bit on the tinny side and much to bright to sound like a pushed tube amp (honestly, it's a bit too bright clean as well).

I'm thinking the P8R would add some traditional warmth back to the tone of this amp. As for the tube replacements ... they're just two ideas I'm throwing around in my head.

If you can suggest a set of tubes that will add a little more bottom end and warmth to my Vibro-Champ, drop me a line here.

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Posted: Sun May 30, 2010 1:32 pm
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For pre-amp: try ECC83 Telefunken (very difficult) or equivalent JJ E83CC for crystal sound

Recently I've tried SPAX7 with a very good sound (difficult to say the origine due to a huge ring but it sounds like EH)

For amp: try winged C 6L6GC with a hot bias (or equivalent for 6V6)

Let me know the difference u find

Tissan


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Posted: Mon May 31, 2010 9:18 am
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I'm going to check into those suggestions. Thanks!

Another modification I'm trying to look into would be adding bypass switching for the voicing knob, returning the 12AX7 to a pure preamp tube instead of adding tube gain to the SS preamp and then back to stock again. This is one feature this amp really, really needs so that it can be used as a pure tube Champ amp with SS effects on board.

EDIT: Maybe the above mod wouldn't be so simple, since everything is processed by the effing DSP and the DSP would have to be hacked/reprogrammed to accept the switching and it's function. There isn't even analog volume, gain, and EQ controls in this; it all runs through the DSP.

There might be a way, though. I'm seeing this amp as sort of an '80s Chevrolet 305 with the very first incarnation of computer controls; you can return the engine back to the "old school" way of running and still retain some of the basic necessary functionality (for SES lights, whatever) of the computer.

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Posted: Mon May 31, 2010 3:17 pm
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Is this a fixed bias amp??


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Posted: Mon May 31, 2010 4:13 pm
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I believe the Vibro Champ is cathode biased. Just plug and play.

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Posted: Mon May 31, 2010 6:15 pm
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thanks


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Posted: Mon May 31, 2010 7:56 pm
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Cathode biased hmmm? So you don't have to re-bias this amp?

I'll admit, this has been a fun amp to learn about.

Someone described this amp as a "cyborg," and that's a very accurate description honestly. Cyber technology meets "organic" tone and functionality.

Another set of tubes I'm going to look into might be NOS GE tubes. Or a combination of the tubes mentioned.

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Posted: Tue Jun 01, 2010 9:47 am
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It's class A, no need to bias.

The preamp valve just powers the DSP doesnt it? I've never noticed any change when swapping preamp valves in mine.

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Posted: Tue Jun 01, 2010 11:02 pm
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nikininja wrote:
It's class A, no need to bias.

The preamp valve just powers the DSP doesnt it? I've never noticed any change when swapping preamp valves in mine.


Actually, the preamp in the Vibro-Champ is a hybrid preamp. It's my understanding that the preamp tube works in connection with the DSP to provide true tube gain and help give the amp true tube tone, so that the amp doesn't sound like it's digitally programmed, etc. (This is where a Vox Valvetronix amp falls short to a VM amp.)

With this amp, think of the voicing switch not so much as to providing modeling, but as a way to manipulate the sort of distortion you can get with the preamp tube at low volumes in a various number of ways; sort of like a tube amp with a volume and master volume knob or a tube amp with an attenuator, but with far more potential.

Because the preamp tube works in connection with the solid state preamp to help prove tube tone and give true tube gain, you can still set the voicing knob at 1, a clean tone, and crank the gain and volume knobs and get the distortion and break up you would get with any other tube amp.

Changing the preamp tube would, indeed, alter the tone, especially when pushed to the edge in setting 1.

Owners of Super Champ XDs do note altered tones with their amps with NOS or higher quality tubes for the preamp and power stages. The Vibro-Champ wouldn't be any different -- in fact, the circuitry of the VCXD is slightly less complex than the SCXD.

The preamp tube of the SCXD has to serve double duty not only as a preamp tube, etc., but to serve as a phase inverter. The Vibro-Champ's preamp tube is only that, a preamp tube with only one function. I see this as the VCXD's advantage over the SCXD.

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Posted: Fri Nov 26, 2010 9:16 am
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phoenix-caster wrote:
nikininja wrote:
The preamp tube of the SCXD has to serve double duty not only as a preamp tube, etc., but to serve as a phase inverter. The Vibro-Champ's preamp tube is only that, a preamp tube with only one function. I see this as the VCXD's advantage over the SCXD.


There is no significant advantage with the SCXD. A 12AX7 is a twin triode, so all this means is that the VCXD is not using one half of the 12AX7.

Also, it is misleading a bit to say that the preamp 12AX7 in either of these amps is working in "conjunction" with the solid state parts. The signal from the solid state section leaves the output of one of the last solid state op amps and then goes to the input to one half of the 12AX7 for preamplificaation. the VCXB uses the second half of it's 12AX7 and the SCXB uses the first half of the 12AX7 for preamp and the second half for the PI. It's not really an advantage, because the SCXD uses two 6V6 finals.

SCXD Schematic

VCXD Schematic

The VCXD is cathode biased (non-adjustable)
The SCXD is fixed biased (adjustable)


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Post subject: Re: Vibro-Champ XD Mods; New Tubes?
Posted: Fri Nov 26, 2010 10:59 am
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phoenix-caster wrote:
While I think this is a great travel and practice amp with very nice mojo, I'm already thinking of ways I can get a little more out of this little punk.

So here's what I'm thinking:

-NOS Sovtek pre-amp tube to replace the Fender 12AX7
-NOS RCA power tube to replace the 6V6

If you can suggest a set of tubes that will add a little more bottom end and warmth to my Vibro-Champ, drop me a line here.


Sooner or later you'll plug in the JJ ECC83s and JJ 6V6s and wonder why you spent all that money on NOS tubes. Why not start with the less expensive stuff?

Here's some info you might find useful (on the SCXD, but might apply to the VCXD):

http://billmaudio.com/wp/?page_id=314

http://www.fender.com/community/forums/ ... 2&start=15


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Posted: Fri Nov 26, 2010 11:24 am
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Good suggestion dude. The JJ 6V6 are awesome, but some people very much prefer the EH 12AX7s.


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Posted: Tue Nov 30, 2010 7:08 am
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Are you using this amp for gigging, or just for home use?

I have one that I use for home use. I recently plugged in an Epiphone 1x12 cabinet, and I think it sounds much better. Now, the Epi cabinet has a 16 ohm speaker, and the Fender wants a 4 ohm load, so I will be changing the speaker in the Epi cabinet. I do not crank this amp, though.

The point is that using a larger speaker dramatically changes the sound of this, for the better.


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Posted: Sat Dec 04, 2010 2:07 am
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+1 for the JJs they are very articulate in sound.

And they sound good with single coils IMO. If you like a lot of gain and early breakup for your Fender VCXD try a power tube tested/measured for high gain. If you like clear tones I would avoid the high gain Tung-sol 12AX7, they make all my amps sound dark at low to moderate volumes. I think they sound best cranked up.

Another option is calling some of the online tube stores that specialize in tues for your Fender. They may be able to help.

The extreme option is; install a DIY handwired clone of the Fender Blackface Vibro Champ in your chassis and cabinet. That way you'll get options for vairous modifications and a rectifier tube to give you sag.


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Posted: Sun Dec 05, 2010 6:57 am
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JJ's are great tubes, but the Vibro Champ XD is a hybrid. I don't see a whole lot of benefit in the tone department because of the DSP effects.

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