Page 1 of 2
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#1
Has anyone tried working on or modding a Fender Champ 600? disregarding speaker and tube swaps, has anyone tinkered with differnt valued resistors anywhere on it? I've read that the lifting/lowering the value of r19 increases output, at risk of the OT. Anything else? Thanks.
mr_hankey
also available in 3D
Join date: Jan 2005
834 IQ
#2
It's a Champ. Look for Champ mods.

You could add more filtering, add a tonestack, change the biasing of the tubes etc.
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#3
Quote by mr_hankey
It's a Champ. Look for Champ mods.

You could add more filtering, add a tonestack, change the biasing of the tubes etc.

Looked! Searched through a few pages of google. I was hoping to meet someone who had opened one themselves.

It's auto biasing anyway. Poo.
SomeoneYouKnew
UG God
Join date: Feb 2007
2,503 IQ
#5
Quote by mr_hankey
It's a Champ. Look for Champ mods.

You could add more filtering, add a tonestack, change the biasing of the tubes etc.
It's not exactly a Champ.

1 - It uses a smaller PT and a solidstate rectifier instead of a 5Y3 tube.

2 - It has an 8 ohm speaker and secondary on the OT, instead of a 4 ohm.

3 - The NFB resistor in the Champion 600 is 2.7k, not 2.2k 2.2k, not 2.7k.

4 - It has grid-stopper resistors (15k on the preamp sections, 1.5k on the 6V6) that don't exist on the Champ.

5 - It HAS a tonestack. But it has all fixed value resistors, instead of pots.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
Last edited by SomeoneYouKnew at Feb 10, 2008,
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#6
SYK, could you tell me which resistors make up the tonestack, other than the one Kurt mentioned, so I could experiment with putting pots at those locations?

Thanks, Kurt.
SomeoneYouKnew
UG God
Join date: Feb 2007
2,503 IQ
#7
Picture, thousand words, blah, blah, blah ...

First pic is a schematic of the Champion 600 tone shaping
and components on the circuit board.
I don't have a pic of the foil pattern,
so I can't tell which ends of the resistors are connected to what.
Not a big deal, you should be able to figure that out.

The second drawing is a couple of Fender schematics with tonestacks.

To make things a bit easier for you, I put things in colour according to the following:

Treble
Bass
Middle



Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
kurtlives91
Let The Pretend Take Over
Join date: Jun 2007
2,732 IQ
#9
WHo they are using a 15K for mids....whatever you can still add pots to all of them. You might want to change C8 to 0.15mF for better clearer bass response. Also on vintage Fenders C1 was 270pF....change from 250pF to 270pF you will probbly not hear a thing but Im juts putting it out there.

SYK how would you add a NFB switch?
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#10
Quote by forsaknazrael
SYK ftw.

A pretty good idea is just to run the Champion to a bigger cab.
Solves its boxiness.

Ah, definitely. I'd buy him a beer...if I were 21. Shame.

And I'm also thinking about getting a 2x12" cab built. I'll probably use it with the speaker in my Palomino V16 until the cab is built. Is there any chance of upgrading the speaker? I know a cab would be better, but it would be nice to be able get some nice tone out of it without dragging a cab around.

Thanks again, everyone. I'll be tearing it open as soon as I get back home.
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#13
Quote by kurtlives91
I think before you do anythng to the amp internally you should try this amp with a 212.

Well, I can try it with a Marshall 1960, a Peavey 4x12", and the speakers in a couple 1x12" Fender and Palomino combos. I'll be sure to do that tommorow.

forsaknazrael, thanks for the info. I hadn't found any 6" speakers anywhere! I heard scuttlebut about some guys stuffing 8" speakers in it, but I really don't want to even pretend that I'm making this into anything but a small quiet practice/recording amp.
MrCarrot
Sup.
Join date: Aug 2006
1,542 IQ
#14
Yeah, Weber reckons their Alnico Sig 6 is pretty good. Hence their (humorous) advert.
The Laney Thread are big and clever. No exceptions.
sunnysayshi
Banned
Join date: Feb 2007
784 IQ
#15
Mesa Boogie mark something?

Sorry wrong amp, got mixed up with the princeton
SomeoneYouKnew
UG God
Join date: Feb 2007
2,503 IQ
#16
Quote by kurtlives91
SYK how would you add a NFB switch?
Either of two methods will work.

You can short the node that the red arrow points to,

OR you can put a switch between that node and the 2700 ohm resistor, to disconnect it.


Quote by the.spine.surfs
Well, I can try it with a Marshall 1960, a Peavey 4x12", and the speakers in a couple 1x12" Fender and Palomino combos. I'll be sure to do that tommorow.

forsaknazrael, thanks for the info. I hadn't found any 6" speakers anywhere! I heard scuttlebut about some guys stuffing 8" speakers in it, but I really don't want to even pretend that I'm making this into anything but a small quiet practice/recording amp.
It always gets a bit dicey when you try to increase the size of a speaker.
Sometimes you can shoehorn one in, other times you just need a bigger shoe.

That said, there's a big difference between the cone area of a 6 and an 8.
(about twice as much)
Other things being equal, that will get you a ton more low end.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
mr_hankey
also available in 3D
Join date: Jan 2005
834 IQ
#17
Quote by SomeoneYouKnew

3 - The NFB resistor is 2.7k, not 2.2k

5 - It HAS a tonestack. But it has all fixed value resistors, instead of pots.


Well, I didn't know about that.

I suggest disconnecting the NFB loop, and bypassing the tonestack with a small cap, like .02uF. It'll get you much closer to the tweed Champ sound, and will give you more gain.
mr_hankey
also available in 3D
Join date: Jan 2005
834 IQ
#19
Here's another one (one I would definitely do): rip the pcb out, and rewire everything on an eyelet/turretboard. It's a very simple amp and you can just go by old Champ layout, so it shouldn't be very hard. It'll improve the reliability quite a bit, and further mods will be much easier.
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#20
Quote by mr_hankey
Here's another one (one I would definitely do): rip the pcb out, and rewire everything on an eyelet/turretboard. It's a very simple amp and you can just go by old Champ layout, so it shouldn't be very hard. It'll improve the reliability quite a bit, and further mods will be much easier.

That's quite tempting. Could I still use some of the original components (tube sockets, transformer, etc.), or would they need to go?
mr_hankey
also available in 3D
Join date: Jan 2005
834 IQ
#21
Quote by the.spine.surfs
That's quite tempting. Could I still use some of the original components (tube sockets, transformer, etc.), or would they need to go?

I'm fairly sure that the only thing you wouldn't be able to use are pcb mounted tube sockets. You might have to get some new components with longer leads, but those are cheap anyway.

How's your strat, btw? I've never even seen one in shop.
MrCarrot
Sup.
Join date: Aug 2006
1,542 IQ
#22
^ You could use the tube sockets (which I think are chassis mount, transformers etc. The PCB-mount Rs and Cs won't have very long leads though so you'd probably need new ones.
The Laney Thread are big and clever. No exceptions.
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#23
Quote by mr_hankey
I'm fairly sure that the only thing you wouldn't be able to use are pcb mounted tube sockets. You might have to get some new components with longer leads, but those are cheap anyway.

How's your strat, btw? I've never even seen one in shop.

Alright, I'll definitally look into it. Thanks.

My Jap Aerodyne? It's the nicest non-American Strat I've ever played. I'm usually not for blacked-out guitars, but the carved top, and cream binding are beautiful. It's worth noting that it's the Aerodyne made for the Japanese market (with a pickguard)), not the export Aerodyne.
SomeoneYouKnew
UG God
Join date: Feb 2007
2,503 IQ
#24
Quote by kurtlives91
What's this node?
Node is just a term for where components or wires are joined together.
The node I was talking about is at the top of the 47 ohm resistor.
Break the line going to the right from that point and install a switch,
going to the 2700 ohm resistor.

Quote by mr_hankey
Well, I didn't know about that.

I suggest disconnecting the NFB loop, and bypassing the tonestack with a small cap, like .02uF. It'll get you much closer to the tweed Champ sound, and will give you more gain.
There were production changes during the tweed era. The 5C1 circuit didn't have NFB, but used a single pentode (6SJ7) for the preamp, rather than a dual triode (12AX7)
The 5E1 circuit used a 12AX7 and had NFB.
They both used a .02 uF coupling cap.
You're right about the increase in gain.
The insertion loss of the tone-shaping circuit is about -10dB on the treble and bass ends.
Another -10dB on the mids.
That would make a huge difference in gain.
Quote by MrCarrot
^ You could use the tube sockets (which I think are chassis mount, transformers etc. The PCB-mount Rs and Cs won't have very long leads though so you'd probably need new ones.
You're thinking Epi VJ here.
The Champion 600 has the tube sockets mounted right onto the printed board.
The 9-pin socket doesn't have a mounting flange,
so that socket would have to be replaced.
Probably better to replace both of them with good quality ceramic sockets,
if you're going to the effort of reworking this with a turret board, anyway.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#25
So I tried to today with both the speaker in my Palomino V16 and a 4x12", and was suprised. There really wasn't much difference in tone, just projection and a touch of volume. I'm going to guess that since my Champ is used, and the speaker probably broken in rather well, that I don't need to overthink amp-cab relations while modding this.
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#26
Update - I lifted R19, the mid resistor from the tone circut, and picked up both gain and an unpleasent hum. Oops? Also, I have moderate fear that I'll trash the OT running the amp wide open like this; there's definitally about twice as much overall output.

So now, i think I'll try to bypas the entire tonestack, and install a NFB toggle. So I'll need a .02uF Cap to bypass the tonestack...where? Can I just look at the foil pattern, and trace around to find where to make the jump to/from?

For the NFB switch, just to clarify, I put a toggle between the red arrow and the cap to the right, to either short that connection, or complete it, correct?

mr_hankey
also available in 3D
Join date: Jan 2005
834 IQ
#27
Find that 2700ohm resistor, and put a SPST switch in series with that. Doesn't really matter where on trace/wire. You need those other components, like the 47ohm and the 1500ohm resistors, connected.

You could pop in a 6L6 for more headroom. No mods necessary.

Btw, I'm in the middle of modding my Champ as well. I'm turning the preamp into the clean channel of a Dumble ODS. So far, so good.
Last edited by mr_hankey at Feb 11, 2008,
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#28
Quote by mr_hankey
Find that 2700ohm resistor, and put a SPST switch in series with that. Doesn't really matter where on trace/wire. You need those other components, like the 47ohm and the 1500ohm resistors, connected.

You could pop in a 6L6 for more headroom. No mods necessary.

Btw, I'm in the middle of modding my Champ as well. I'm turning the preamp into the clean channel of a Dumble ODS. So far, so good.


Excellent, thanks. I'll start drawing up a list of stuff to order. Mouser, for in the US?

Thanks again. I think a moderate bit of my dad's dyslxia prevents me from remembering the difference between a 6V6 and a 6L6. I'll start thinking about an order from thetubedepot.com, too. I want a new 12AX7 for this, to replace the unbranded one it came with, and some new 12AX7's, and mabye a 12AY7, for my V16, which I think has microphonic preamp tubes.

So it'll have two discrete channels, or you're using the clean channel of the Dumble as a template?

Any advice on where the .02uF cap goes?
mr_hankey
also available in 3D
Join date: Jan 2005
834 IQ
#29
Quote by the.spine.surfs
So it'll have two discrete channels, or you're using the clean channel of the Dumble as a template?


No, just the clean channel. It is a vintage amp after all, so I don't want to start making holes in it for more tubes (I'd need another 12ax7 for the OD channel). Everything I'm doing is perfectly reversible.
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#30
Quote by mr_hankey
No, just the clean channel. It is a vintage amp after all, so I don't want to start making holes in it for more tubes (I'd need another 12ax7 for the OD channel). Everything I'm doing is perfectly reversible.

Ah, since it's vintage. Smart. Let us/me know once you've got it finished.
ECistheBest
Makes Pedals for YOU!
Join date: Jul 2006
1,824 IQ
#32
^no. if it's just switching the 2.7k in/out of the circuit, either side.
Call me "Shot".

ShotRod Guitar Works

Custom Hand-wired Amplifiers and Effect Pedals.

Est. 2007


Source to everything I say about Guitars, Pedals, and Amplifiers: I make them.


UG's Best DIY PedalBoard
kurtlives91
Let The Pretend Take Over
Join date: Jun 2007
2,732 IQ
#33
Great...does anyone know how effective this mod is in this circut...? Cause I remember hearing that the NFB mod on the VJ was kinda crappy.
SomeoneYouKnew
UG God
Join date: Feb 2007
2,503 IQ
#34
It will dirty up the clean, and allow the output section to be more distorted when you crank it.

Removing the NFB is more useful in a push-pull output stage than in a single ended type,
like the Champ or VJ. Removing the NFB also makes the overall gain higher. ie: the amp will be dirtier and louder.

I installed a variable NFB on a friend's silverface super reverb.
He labeled the control ... "Balls".
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
MrCarrot
Sup.
Join date: Aug 2006
1,542 IQ
#35
Quote by SomeoneYouKnew
Node is just a term for where components or wires are joined together.
The node I was talking about is at the top of the 47 ohm resistor.
Break the line going to the right from that point and install a switch,
going to the 2700 ohm resistor.

There were production changes during the tweed era. The 5C1 circuit didn't have NFB, but used a single pentode (6SJ7) for the preamp, rather than a dual triode (12AX7)
The 5E1 circuit used a 12AX7 and had NFB.
They both used a .02 uF coupling cap.
You're right about the increase in gain.
The insertion loss of the tone-shaping circuit is about -10dB on the treble and bass ends.
Another -10dB on the mids.
That would make a huge difference in gain.
You're thinking Epi VJ here.
The Champion 600 has the tube sockets mounted right onto the printed board.
The 9-pin socket doesn't have a mounting flange,
so that socket would have to be replaced.
Probably better to replace both of them with good quality ceramic sockets,
if you're going to the effort of reworking this with a turret board, anyway.
Ahhh, I heard the Champ 600 had chassis mount sockets. Point taken
The Laney Thread are big and clever. No exceptions.
the.spine.surfs
UG Spammer
Join date: Aug 2006
1,277 IQ
#36
Quote by MrCarrot
Ahhh, I heard the Champ 600 had chassis mount sockets. Point taken

Having opened up mine already...I think they are. At least, there's two small bolts/screws holding the preamp tube socket to the metal chassis that everything else is bolted on. I don't remember about the socket for the 6L6.
mr_hankey
also available in 3D
Join date: Jan 2005
834 IQ
#39
Quote by kurtlives91
^thanks

For the NFB switch will a 125 VDC switch be fine?


Yup.