Friday, January 8, 2010

Upgrading the Fender Silver Face Champ

I decided my Fender silver face Champ needed a line out, so I took it to Bruce Collins at Mission Amps. Well… one thing led to another and the Champ is no longer Champ-like at all. It roars and growls and moans and grunts. This ain’t yer daddy’s Champ.

Bruce had a few ideas to improve the tone, so we kept trying this - then playing the amp - then trying that, and playing the amp again. We ended up replacing all the caps and other components as well. The Champ now has NOS Paper in Oil tone caps!

The little amp already sounded good. Regular readers will know it has a 10-inch Weber 10A125-O alnco speaker and a NOS 5V4 rectifier tube. The preamp tube is an NOS 5751. The power tube is an NOS RCA blackplate 6V6. It was the best-sounding Champ I’d ever heard, but now it doesn’t sound like a Champ. It sounds like a beast.

Here are the changes Bruce made to the circuit of the amp:

2 .068uF/400v Paper in Oil K40y caps
1 .047uF/40ov Paper in Oil K40y cap
2 22uF-50v Electrolytic cathode bypass caps
1 100uF-50v Electrolytic cathode bypass cap
1 .001uF-500v CM Ceramic cap
1 .001uF-630v Mallory 150 cap
1 .0015uF-630v Mallory 150 cap
1 250pF-300v Silver Mica cap
1 150pF-300v Silver Mica cap
1 470 Ohm 5 Watt 6V6GT tube cathode bias resistor
1 47K 1w carbon comp B+ power supply resistor
1 56K 1/2w carbon comp NFB reduction mod resistor
1 220K1/2w CF Line Out mod resistor
1 47K 1/2w CF Line Out mod resistor
1 Mono Jack non-switching Line Out Jack

Now we are looking for a 10-watt transformer with a 4-ohm tap…

The amp sounds incredible. I plan to gig it this weekend and next. Check this out: It weighs in at only 21 pounds! I just need a coiled up cable in my harp kit to line it out to the PA, and Look Out Mama.

Email bruce at missionamps dot com

UPDATE: Here's a link to a sound clip. I'm using a bullet mic with Shure CM element. No effects or editing at all. This was recorded using a Zoom H4 digital recorder about 4 feet from the amp.


peter Moore said...

My Super Sonny will crush that little thing!

Rick Davis said...

No doubt! It weighs about four times as much.

Anonymous said...

It looks a clean little amp Rick. Amazing what va little love and care can do when things are valued. Thanks for the post.My friend John O' Brien has one similar.I'll pass this on.

Mike said...

I can't wait to hear it!!!!! I owe you a DT review and will have one for you yet this month...just waiting for rough mixes from the studio.

Heck, I'll even give your blog a free download from the album...give me until Feb.

Unknown said...

Hi Rick- Which changes were alterations in component values or circuit design versus upgrades in component quality?

I also have a modified SF Champ. A very useful change is to add a mid pot as in a Fender with three control tone stack. It involves swapping a pot for one resistor. The pot can replace the input 2 if a small body pot is used, so a new faceplate hole is not needed.


Rick Davis said...

Hey Jim, great to hear from you. The vintage Masco ME-18P you crafted for me is still beautiful amp, and a workhorse.

To answer your question: I'm not sure. As Bruce was making every change in the amp he carefully explained to me the impact it would have on the tone. Some of the changes we re-did with different value components after listening tests.

The problem was, I was not taking notes. But my impression is that almost everything he did to the amp was to benefit the tone. The tone stack became darker. The grid plate voltage came down a bit. My favorite K40Y PIO tone caps were installed. The line out was created and modeled after the line out in my 5F2H amp.

Some of the original resistors remain, but others were changed to more heat-resistant components.

I'll pass this question along to Bruce and get you a more definitive answer.

peter Moore said...

how different is the sound of a line out compared to micing the amp?

Rick Davis said...

Peter, there is little difference in sound with the line out. The line out makes the amp so convenient (and loud) that any small differences in tone don't mean much. I like the tone either way.

A Bassman amp puts our about 45 watts. This little Champ can manage only about 4 or 5 watts, but I line it out to our PA that has many thousands of watts. it sounds very, very good that way.

peter Moore said...

I have an old tweed fender, a deluxe
I hate the idea of poking a hole in it, but can that have a line out added? I'd love to use it on gigs, but it doesn't carry the room like my SJr.

Anonymous said...

Just purchased a nice Champ, & wondering if you can give me more info about how to disconnect the negative feedback circut in the champ
Thank you for your help

Bruce Mission Amps said...

Remove the thinner wire from the output jack that goes to the resistor on the eyelet board.
You can email me directly if you want...
Mission Amps

Rick Davis said...

Anon, if it is a Silverface Champ, I have photos of the NFB wire in an earlier article on this topic here.

As Bruce said, it is a wire that runs from the speaker tap to a resistor on the circuit board. Just clip it, insulate the end of the wire, and tie it off out of the way.

Rick Davis said...

Peter, I thought Gary Onofrio put a line out on all his "Sonny Jr." amps...

One thing you might consider with your vintage Tweed Deluxe is the H&K Red Box DI, which I reviewed here.

Anonymous said...

Thanks for the NFB info
I'm new to the Harp/Amp scene & this site is providing super info & interest
As a "tinkerer" can you suggest a book out there that might explain tube amp basics
Thanks again & keep up the great work

Dave said...

Hi Rick,

I have a SF Twin Reverb with BF circuiting that is acting as my main amp for my guitar (52 Reissue tele with Joe Barden T-Style pickups if that means anything to you). I just bought the Shure 520 DX bullet mic and want to run it through this amp. Do you have any suggestions as far as EQ/volume settings to get that beautiful dirty tone you get here.

Also, if you could give me suggestions as to something close to what's in this video below, that would be great too since that's what i'm trying to achieve at points as well for the lo-fi vocal sound.


Ray Dodd said...

Hi Rick,
I've been following this with interest as I have a silverface champ myself. Can you tell me where to take a line out from?
I understand that this quest for tone has been a progressive project, but it seems to me now that there is very little left of the original amp. Do you think with hindsight that you may have been better building an amp from scratch?
Best regards, Ray Dodd

Rick Davis said...

Hi Ray-

The line out is taken from the speaker tap, with a resistor inserted to bring it down closer to line level.

Yes, as I progressed on the SF Champ project I lost more and more of the desire to keep the amp original. You are right that that amp now is much different than the original. But along the way I learned a LOT about harp amps.

Would it have been better to just build an amp from scratch? Well, I don't really have the skill for that. But you are right. I have LESS invested in my 5F2H, which is a much better sounding amp. But I have an emotional attachment to the Champ, and its big raspy tone is outstanding. At this point it is the best sounding Champ I've ever heard for harp.

Bruce Mission Amps said...

On an amp such as a Champ, what you want is to make up a voltage divider the when used, samples the voltage delivered to the speaker but sends only about 1/10 to 1/15 of it to your line out jack.
To reduce the speaker voltage you can use any pair of 1/2 watt to 1 watt resistors that when added together has a resistance that is VERY high when compared to the speaker load.
By very high, I mean insanely high!! Like many many hundreds or thousands of ohms higher.
You do not want any real current to flow across these resistors, just some solid audio voltage to use as pure signal to another preamp, the PA or mixer.
A really hot Champ might be able develop about 6-7 volts of AC audio to an 8 ohm load (some are 4 ohms of course so the voltage would be lower).
The two 1/2 watt resistors are across the output of the speaker jack... one end is grounded and the signal for the line out is taking at the two resistor's junction.
All these simple line outs need to be tweaked for a tone you like, but a good safe place to start would be a 220K to 360K resistor at the jack and a 22K to 36K resistor to ground with a wire at their center over to your line out jack.
For a small 2w to 5w amp and an 8 ohm speaker, a 1/10 voltage divider would give you about +300mvac to +600mvac signal to a PA input and still have high impedance to the PA mixer or board.
If you want a hotter signal, you would reduce the value of the larger resistor but don't go crazy.

Mike said...

Hi Rick,

Long time lurker, 1st time commentor. Thank you for sharing your vast knowledge of amplified harp and the associated gear. I find it an invaluble resource.

I recently obtained a 69 Champ. I took it to an amp tech who brought it back to spec. I also had a line out installed. I put a 12AU in the preamp socket which smoothed it out but the volume has suffered. I am going to try a 5751 on your advice. It has the stock 8" Oxford speaker which I am thinking of upgrading with either a Weber Sig or Vintage series ceramic or an Eminence 8" Alpha. I love the tone of the modded VHT you just posted as a reference of what I am seeking. Namely, Chicago with a bit more bass and volume without sounding like I am ripping the speaker in two when I lean into it. Would appreicate your thoughts and any suggestions.

Rick Davis said...

Hey Mike, thanks for visiting my blog and for commenting.

Yeah, the 12AU7 is too much of a tone suck for a 5-watt amp. The 5751 is a better way to go. Tube Depot has a really good NOS JAN Philips 5751 but the've raised the price from $20 to $30.

For the 8-inch speaker I'd stay away from the Jensen (ice-pick tone) and the Weber vintage alnico (low efficiency).

I have not tried the Eminence 8A speaker. It is rated at 125 watts (!) which is awfully high for a little 5-watt amp. I'd try the Weber Sig ceramic first. Get the smooth cone 4-ohm version. Only $24.

Try disconnecting the negative feedback loop. If you want the smooth tone of the VHT stay with the 5Y3 rectifier.

A Champ with an 8-inch speaker will never sound as big as the VHT Special 6, but Champs have a VERY cool tone. You will have fun with this project.