shanester
501 posts
Feb 19, 2012
1:40 PM
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Calling all vintage tube amp gurus, I've got some questions.
I've got an old Champ amp: Silverface with the aluminum drip edge, so it must be a '69 at the oldest. It has the AA764 circuit.
Googling around I found some info saying that you could output to another amp from input #2. I tried it to a little solid state I have and it worked.
Can I output like this to a PA? Would there be any signal loss?
The other thing I discovered is I get a lot more range of adjustment before feedback from input 2, so I've been playing with that. Could I plug my sm57 into #2 and output from #1 to a pa?,
Also, if you can output that way, why are people retroing line outs on old champs?
When I play jams I've always used PA or the house harper's rig, and they almost always set them up muddier than I like.
I'd love to use my rig with my sound and be able to be heard over a loud-ass band!
Also if you know any other Champ tricks, please let me know!
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Shane,
"The Possum Whisperer"
Shane's Cloud
1shanester
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chromaticblues
1189 posts
Feb 19, 2012
6:10 PM
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@ The Possom Whisperer
Yes I have a list of stuff you can do to your amp to make it more harp friendly.
I'll look at my notes tomarrow and I'll get back.
Can you solder?
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shanester
505 posts
Feb 19, 2012
7:02 PM
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Thanks chromatic, I appreciate that! I can do simple soldering and I am an all around craftsman, so I'm not afraid to get in there.
I have a little electrical experience but not much electronic experience, so if you could clue me into what is dangerous in the amp I would appreciate that as well!
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Shane,
"The Possum Whisperer"
Shane's Cloud
1shanester
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bharper
150 posts
Feb 19, 2012
9:23 PM
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Rick Davis has an article about this at his blog:
http://www.bluesharpamps.blogspot.com/2008/03/harp-amp-project-fender-silver-face.html
Last Edited by on Feb 19, 2012 9:24 PM
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5F6H
1076 posts
Feb 20, 2012
1:03 AM
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Running a cord from #2 input (whilst plugged into #1) just splits the mic signal, you can do this no problem but it is not a "line out" and you are not sending any champ tone to the next device.
"Could I plug my sm57 into #2 and output from #1 to a pa?,
Also, if you can output that way, why are people retroing line outs on old champs?"
It really makes little difference which input you plug the mic into & which you daisy chain to the PA as when both #1 & #2 inputs are used they both are paralled into the #1 - neither is really the #2 input anymore, this is now switched out of the circuit. Be aware that if you plug the daisy chain cord into another device, that this will affect the impedance load of the champ & both champ & PA inputs will be averaged out to a similar impedance.
A "line out" takes the amp's output signal & character from a voltage divider at the speaker, after all the amp's circuitry, and sends this to a slave amp/PA. Daisy chaining the inputs just splits the mic signal between 2 devices inputs.
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www.myspace.com/markburness
Last Edited by on Feb 20, 2012 3:29 AM
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chromaticblues
1190 posts
Feb 20, 2012
6:37 AM
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Yeah shane like 5F6H said. That's not the same as a line out at all. IMHO the best way to line out is off the speaker.
I'm going to check out Rick Davis's article and just add my two cents if there is anything that I did different.
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chromaticblues
1191 posts
Feb 20, 2012
7:22 AM
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Shane Rick Dais's blog is pretty good. Check it out. He has a picture of the amp head.
I would just remove the negative feed back yellow on the speaker output jack that goes to the middle of the circuit.
Next your going to move the white capacitor (connected to pin 3 on the 12ax7) and coonect to the 470 ohm resister connected to pin 8 on the 6v6. This resister has the same capacitor connected paralell to. Just put it on the other side. You have to install it in same direction it was in. Negative (-) goes to ground. So the positive (+) is pointing toward the tubes.
Next your going to remove the capacitor that connects to pin 8 of the 12ax7. Just through it over your shoulder!
Next replace the 10K 1 watt power resister connected to pin 4 of the 6v6 with a 22K 1 watt and replace the 1K 1 watt connected to pin 8 of the 5y3 with 10K you just removed.
I would just stay with a 5y3. The voltage is high enough. It's actually very high for a 6v6 so stay with the 5y3.
Speakers I usually try to find old speakers on Ebay that are in good shape. I have had mixed results with this, but I do have a couple amps with great old speakers that I got off Ebay!
Putting a good low powered 10 inch speaker in it makes a big difference!!!
You have to be careful because not all speakers will fit! Then there is taking the grill cloth off and putting it back on. It's a pain in the butt, but it will be worth it when it's done.
If you have any questions you can Email me at: sbaker60@cox.net
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shanester
506 posts
Feb 20, 2012
5:05 PM
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Thank you for the link bharper!
5F6H, I did a little more experimenting and your right, no champ tone coming out of the input. Are you saying the more you daisy chain the weaker the signal overall?
Thanks for the info chromaticblues, sounds like I better do that line out to get what I want. Then I could get a champ sound out of the PA?
Also will that 10" speaker add a significant boost in volume? What's the deal with low powered speakers?
I appreciate your responses!
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Shane,
"The Possum Whisperer"
Shane's Cloud
1shanester
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Joe_L
1745 posts
Feb 20, 2012
8:04 PM
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"Also will that 10" speaker add a significant boost in volume?"
I suppose it depends on what you consider significant. Personally, I don't think the difference in volume is substantial or significant. You may like the tonal change.
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The Blues Photo Gallery
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shanester
509 posts
Feb 20, 2012
8:42 PM
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Thank you for your insight Joe, that actually sheds light on the question that I was unable to articulate at that time, which was is it a volume difference, or tonal, or both?
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Shane,
"The Possum Whisperer"
Shane's Cloud
1shanester
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Kingley
1816 posts
Feb 20, 2012
10:24 PM
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It seems fairly easy to add a line out (even for a thick git like me). Here's a link to a site about Kalamazoo amps that talks about how to add a line out. I'm sure you could use the same principal on a SF Champ. The line out bit is on the "modifications" page under "Easy line out jack".
Amp line out
Last Edited by on Feb 20, 2012 10:24 PM
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5F6H
1078 posts
Feb 21, 2012
1:31 AM
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@ Shanester "5F6H, I did a little more experimenting and your right, no champ tone coming out of the input. Are you saying the more you daisy chain the weaker the signal overall?"
If you daisy chain into the #1 of another Fender amp your signal will be cut a little, perhaps not so much that you will notice (signal will be split between 2x1Meg inputs & some PAs do have 1Meg hi-impedance "instrument" jacks for guitars & basses which will work fine).
But if you daisy chain to a lower impedance input, perhaps a 10Kilo-ohm unbalanced jack, then the overall load will be around that 10K...still possibly workable if you correct at the amp's volume control, but I should think it will soften the sound of the amp, making it less dynamic. PA will just sound like it would if you plugged the mic straight in.
If the only 1/4" input available on the PA is hundreds of ohms lo-impedance, then it will neuter the amp, possibly making the excercise a futile one.
This is why a line-out is often seen as preferable, it drops the speaker signal to a level that will work in a typical unbalanced jack input, with just a few Ks of load. You can also "match" the line-out signal to a low impedance PA input by using an "in-line impedance transformer", or DI box, if the PA only has lo-impedance inputs.
The line out does not affect the input load of the Champ, which continues to work as intended. It's not a perfect method, there may still be some teething troubles/experimentation, but with a bit of patience it can work a treat.
I often find when lining out that you don't need to set the amp to as high a volume as you would when just using the on-board speaker, otherwise sound from the PA may be overly fuzzy. Turn the amp low, PA high.
Also a lower gain preamp tube can sweeten the lined out sound, but this will also affect the champ's tone through it's own speaker, so a compromise might be needed here?
Typical values for the champ (5-6W into a 4ohm speaker) line out are a 2.2K dropping resistor and a 470ohm load resistor. These can both be 1/2W resistors.
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www.myspace.com/markburness
Last Edited by on Feb 21, 2012 3:35 AM
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shanester
510 posts
Feb 21, 2012
11:48 AM
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Thank you Kingley, lots of great information on that site!
Thank you too 5F6H for all the info. Looks like a DIY line out is the path I need to take.
Looks like I will be popping into RadioShack as soon as I reunite with my soldering iron back in Austin!
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Shane,
"The Possum Whisperer"
Shane's Cloud
1shanester
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