Help Building a Champ??

[Jaicen]

What is going on here?! I've typed this reply THREE TIMES!! and it keeps disappearing?!

Right, first off thanks for the history lesson, who says musicians are dumb?!

I guess I should have picked a better thread title really, as it is a bit misleading. I want to build an amp that's pretty much a champ, but not necessarily a vintage replica. Something with the tone and feel is all I really want. Headroom is not an issue, I want something quiet, so if it's breaking up at 50% that's just fine! With this in mind, would I be ok using the 240v secondaries? I'll (almost) definitely be using silicon rectifiers, because they're cheap and easy and also very reliable. Would this result in an amp that breaks up earlier with less output?
My plan is to have the tonestack with a bypass option, and also a rear-mounted NFB on/defeat, so I can clean things up when needed. I've considered moving the tonestack after the pre-amp for a more pronounced effect, what are your thoughts on that???
Can anyone record me a sample of a champ made with the same voltages I'm planning to use??

[steve]

I'll probably get crucified for this but here goes:

5W can be very loud in a small room.

For recording I've had good luck using a power attenuator to knock down the SPL to a whisper. I've used the Behringer GI100 speaker cab simulator or the H&K Red Box with the power attenuator to good effect. Is this setup perfect? No. Does it sound like a real miked 4X12"? Not really, but the aforementioned setup makes it very convenient to record quietly.

As stated before, the Maplin PT will work and with SS rectifiers and you'll probably get about 310v or so. I like to use UF4007 diodes instead of the 1N4007s. The UF4007 is the ultrfast recovery version and cuts down on power supply noise.

I like lots of capacitance in champ type circuits. I've used up to 390uF, 450v snap in caps with good results. I first used the high capacitance caps as a band aid for hum in the amp. With 150uF to 390uF in parallel with a 47uF cap, the amp is dead silent. Later, I realized I actually liked the tone better.

You can't put that much capacitance on a tube rectifier, the recto will wear out very quickly.

I've tried defeatable negative feedback, and if you're recording it might be a nice feature to have.

I usually build the 5F2-A tweed Princeton circuit which has a tone control. I don't have any experience placing the tone control after the second gain stage.

HTH,

steve

What is going on here?! I've typed this reply THREE TIMES!! and it keeps disappearing?!

Right, first off thanks for the history lesson, who says musicians are dumb?!

I guess I should have picked a better thread title really, as it is a bit misleading. I want to build an amp that's pretty much a champ, but not necessarily a vintage replica. Something with the tone and feel is all I really want. Headroom is not an issue, I want something quiet, so if it's breaking up at 50% that's just fine! With this in mind, would I be ok using the 240v secondaries? I'll (almost) definitely be using silicon rectifiers, because they're cheap and easy and also very reliable. Would this result in an amp that breaks up earlier with less output?
My plan is to have the tonestack with a bypass option, and also a rear-mounted NFB on/defeat, so I can clean things up when needed. I've considered moving the tonestack after the pre-amp for a more pronounced effect, what are your thoughts on that???
Can anyone record me a sample of a champ made with the same voltages I'm planning to use??

[Jaicen]

This forum is driving me up the wall again! Where do my posts keep going?

Thanks for that Steve. I'm still not 100% decided what i'm going to do yet, but It's nice to know that transformer will work. Do you have any samples of the amp you made using those voltages?? I'd be very interested to hear them if so.
I won't be using any attenuation when recording, I can run a twin and an AC30 full up at the studio, it's more so I can use nicer mics and also use the amp at home. I got a Flextone, but it just doesn't do it for me.
With regards to those diodes, I heard that they cause spiking in the PSU, have you noticed anything like that?
I don't know about the champ, but in the AC30 custom we have at the studio, when the larger filter caps are engaged, the tone becomes slightly stiffer, which I don't really like. I guess that's because it sags less, which wouldn't be applicable. Either way, i'm going to start with more or less the stock values and work upwards till i'm happy.
I found this Click kit yesterday, which pretty much has everything needed to build a blackface, save for the tubes (and cab/speaker obviously!). Has anyone built one of these? I'm quite attracted to it, not least because it takes out all the guesswork. It also uses NOS stuff, which is cool. The only thing is, I'm not sure about the windings on the primary, the shop have not yet got back to me.
So yeah, if I get this kit i'll be happy as larry, assuming I don't get hit with mega shipping/import tax etc. If it's not suitable, i'm definitely going with a SS rectified PSU with big caps and no choke.

[steve]

Thanks for that Steve. I'm still not 100% decided what i'm going to do yet, but It's nice to know that transformer will work. Do you have any samples of the amp you made using those voltages?? I'd be very interested to hear them if so.

I don't have anything recorded with my lower voltage champs. I doubt you'd want to listen to my guitar playing, though

I won't be using any attenuation when recording, I can run a twin and an AC30 full up at the studio, it's more so I can use nicer mics and also use the amp at home. I got a Flextone, but it just doesn't do it for me.
With regards to those diodes, I heard that they cause spiking in the PSU, have you noticed anything like that?

I have not heard that. I do find the UF diodes to be quieter in the PS than the 1Ns. In the US, UF4007s are about $.25 each, so it is not expensive to experiment with them.

I don't know about the champ, but in the AC30 custom we have at the studio, when the larger filter caps are engaged, the tone becomes slightly stiffer, which I don't really like. I guess that's because it sags less, which wouldn't be applicable. Either way, i'm going to start with more or less the stock values and work upwards till i'm happy.

As I said before, using massive amounts of capacitance was pure laziness on my part to quiet an amp down using brute force. I use snap in caps in parallel with the filter caps on the board. I have this idea to make the snap in cap switchable, so I can see what the amp sounds like both with and without the massive filtering.

I found this Click kit yesterday, which pretty much has everything needed to build a blackface, save for the tubes (and cab/speaker obviously!). Has anyone built one of these? I'm quite attracted to it, not least because it takes out all the guesswork. It also uses NOS stuff, which is cool. The only thing is, I'm not sure about the windings on the primary, the shop have not yet got back to me.
So yeah, if I get this kit i'll be happy as larry, assuming I don't get hit with mega shipping/import tax etc. If it's not suitable, i'm definitely going with a SS rectified PSU with big caps and no choke.

Thanks for the link, I hadn't seen that before. With the 350-0-350 PT you'd definitely want to use a real 5Y3 tube rectifier. The Sovtek 5Y3 being sold isn't a real 5Y3, it has lower internal resistance and you'll get higher B+ voltages using it, just as a heads up. I doubt that PT has a 230/240 winding for European usage since it isn't listed, but you never know. I've looked at their OT before, and it seems kind of small.

As far as a choke goes, I generally don't use them as I like to build amps on the cheap. For studio use you may want to consider using the choke though. They can really cut down on the noise. With a choke you wouldn't need massive filter caps.

BTW, you may want to check out this website:

http://www.ampmaker.com/index.asp

Barry posts on a couple of the boards I read, and I've heard nothing but good things about him. His stuff is more Marshall oriented, but he has a nice 5w OT that might work for your project.

HTH,

steve

[Jaicen]

Yeah i've been there before. It's actually his fault i'm back here again!
I was just going to get one of his S5a kits for my birthday (in march), but I thought about it and it's not really what i'm looking for. He's also only selling kits for the next few months while he moves premises.
I heard back from TriodeElectronics and that's more bad news. The primaries on the PT they sell are just 110v, which sucks! Looks like i'm being pushed toward the 240v trannies!

EDIT: I just found the website for Danbury Electronics, who sell some very competitively priced transformers which appear to be just what I need. Center tapped heaters at 3.6v @ 5-7A and 350-0-350V secondaries at 200mA (Overkill much!). They also have a nice looking OT, and for the pair it's just £50, which is very reasonable. Not only that but they sell the HV caps and things, so i'm going to have a good look there and see what turns up.
So, if I were to use the 350V transformer, would I need the Tube rec to bring the voltages down a bit?? I'm stull unsure what should be what if i'm honest.

[Jaicen]

Ok i'm back again!
Having thought about this project day and night for some time, and done some sums I realise that this project is not going to be as cheap as I thought initially. Once the cabinet and speakers have been factored in, the amp is easily going to be as expensive as a real silverface champ.
So, for me to justify building it, the amp is going to have to be the ultimate recording/gigging amp for my needs. As such, i'd like to build two-channel pre-amp, one normal champ channel for clean/crunch and a second more modern voiced cascade style channel.
My plan right now is to have an extra 12AX7, and use both halves as a cascaded gain stage for preamp dirt, and run that into the second half of the first 12AX7 used for the normal champ channel via the Volume control. Both channels will be always on, I just plan to ground either input when not in use. What I need to know is, will this cause any noise problems??

[Jaicen]

No takers???
Is there any reason why I wouldn't want to have the two channels running into the second half of the champ's 12AX7? I see in the deluxe that the two channels run parallel, but that's a push pull so the NFB is connected to the PI, so this is the only way around it that I can see.

[Steve Conner]

If you have both channels feeding into the power stage all the time, there will be a lot of noise from the high gain channel when the clean channel is in use.

I did something similar with a Selmer Treble'N'Bass 50, but since this was a 2 channel amp to start with, it was just a case of turning down the volume for the unused channel. I actually bolted an EF86 onto the front of one channel to increase the gain, and left the other stock. Eventually I added two SPCO relays operated by a footswitch to change both the inputs and outputs over, and ground the unused ones. This turned it into a full channel switching amp. It was the real ugly aluminium fronted model, so I don't feel too bad about butchering it completely.

How many amps have you built? Are you ready to build your ultimate amp yet? If you're worried about money, did you consider picking up a Champ-style amp off eBay and modding it? I got a Selmer Corvette in a junk shop a while back for 70 quid. It's a 3 watt single ended amp using one EL84, and all 3 watt amps are as close to being Fender Champs as makes no odds This one even has vibrato and a freaky fake croc-skin cabinet.

[Jaicen]

Hmm, i'm not sure about any amp with an EL84 being close to a champ at all!
I really don't like El84's that are getting pushed to the max, they sound brittle and glassy to my ears. I much prefer the sound of a 6V6.
I'm sure you're right about the noise issue, i'd pretty much expected that myself. I was thinking that if I had the input of the channels grounded when not in use that would quiet them down a bit. As I said, the Deluxe has both channels feeding into the same triode stage, and that works just fine so I figured I could do the same.
This is my first amp, but I am experienced with electronics. I do some synth repair stuff an build stompboxes, so amps are pretty simple in comparison
I have considered getting a cheap amp like the Valve Junior or Harley Benton (£70 delivered!) and modding that, but the money i'd spend getting it how I want, I could easily build my own with higher spec components.

[Steve Conner]

Well, they're "close" in the sense that if you don't like EL84s, it's a half hour job to bodge a 6V6 in there instead. The EL84 is a very high gain tube and I guess that is what makes it sound brittle.

Doesn't the Deluxe have a volume control towards the end of each channel, so you can turn the unused one down?

[Jaicen]

The deluxe has the same pre-amp configuration as a normal champ, just two of them!
I've not had any trouble with noise from the Deluxe I use at the studio, but I do turn the unused channel down anyway even if it appears not to make a difference. The vibrato on the other hand does seem to bleed through when not in use, so I turn the depth and speed down on that too.
I really like the deluxe actually, but it has to be cranked quite hight to get the tone that I want, hence the champ output stage.

[Steve Conner]

OK, so you're just proposing to bolt the output stage of a Champ onto the front end of a Deluxe? That should work fine. Which Deluxe, the 5E3? http://www.ampwares.com/ffg/schem/deluxe_5e3_schem.gif