freestompboxes.org

First off, I'm usin the AB763 schematic here http://www.ampwares.com/schematics/supe ... _ab763.pdf

What I'm trying to figure out, is how to eliminate the Normal Channel altogether and also take out the reverb while I'm at it. I'm thinking I can just take out the Normal channel's tube and that circuit and also remove the reverb tube and circuit. I'm getting hung up on what to connect the plate of the Vibrato's 12AX7 to. do I run it to second half of the 7025/12ax7? I assume I still have to run it through that 7025/12ax7 because it's the gain stage, however would I leave the other half dissconnected? I think I may be just making to too complicated.

Would it look like this: The components with the grey squares around them were ones I wasn't sure about. The 100k resistors look like they stay in the circuit between the transformer line and the plates of the tubes. However, I thought they might also be part of a mixing circuit for the Normal and Vibrato channels.

OR, should I run it through both halves of that 2nd 7025/12ax7 like this: Thanks for any help

jupagblkxten wrote:http://www.ampwares.com/schematics/bandmaster_ab763.pdf

Sweet, I didn't even consider checking out the other similar circuits. So, all I would do was remove that whole normal channel circuit. Do I have to remove that 220K resistor?

Since the bandmaster is basically the circuit I posted except I added that other 12ax7 in there after the EQ stage. I'll check them closer here in a bit to make sure they're as similar as I think. HOWEVER, if I wanted to add the belton brick reverb circuit, would I just remove the reverb driver tube and recovery tube and add the Belton circuit in there? Or would it be more complicated than that?

Turnerguitar wrote:Since the bandmaster is basically the circuit I posted except I added that other 12ax7 in there after the EQ stage. I'll check them closer here in a bit to make sure they're as similar as I think. HOWEVER, if I wanted to add the belton brick reverb circuit, would I just remove the reverb driver tube and recovery tube and add the Belton circuit in there? Or would it be more complicated than that?

All good until you said "just throw in a belton reverb" (I'll assume you mean the digi type?)

Go get a stand alone reverb, Hint.

A lot of guys used to pull the rev circuit and just use out board rev anyway as it's the extra triode in the rev channel makes the design OD in a wondeful way.
Driven hard on that Channel original reverbs used to clap out to much,, so just pull the reverb and fixed.
trying to shoehorn a SS rev circuit in here would likely kill the magic of the design,,, unless you adore Deville crappy reverb stuff.
My 2 cents, Phil.

phatt wrote:

Turnerguitar wrote:Since the bandmaster is basically the circuit I posted except I added that other 12ax7 in there after the EQ stage. I'll check them closer here in a bit to make sure they're as similar as I think. HOWEVER, if I wanted to add the belton brick reverb circuit, would I just remove the reverb driver tube and recovery tube and add the Belton circuit in there? Or would it be more complicated than that?

All good until you said "just throw in a belton reverb" (I'll assume you mean the digi type?)

Go get a stand alone reverb, Hint.

A lot of guys used to pull the rev circuit and just use out board rev anyway as it's the extra triode in the rev channel makes the design OD in a wondeful way.
Driven hard on that Channel original reverbs used to clap out to much,, so just pull the reverb and fixed.
trying to shoehorn a SS rev circuit in here would likely kill the magic of the design,,, unless you adore Deville crappy reverb stuff.
My 2 cents, Phil.

Thanks for the input. So, you're saying that swappin in a digital reverb would change the tone of the amp with reverb off? Or that the reverb will just suck? I've kind of decided against the reverb anyway because I'd have to bother with Voltage regulators and possibly charge pumps which I don't want to deal with. I'll just make a digital reverb pedal most likely.

Hi turnerguit,

I quote;
"So, you're saying that swappin in a digital reverb would change the tone of the amp with reverb off?"

>Well that depends a lot on how you intend to setup the reverb side chain.
In a real Super Rev Amp you just don't use the rev or you disconnect it.
In that case it matters little as it was all HiZ Valve stuff.
The rev circuit adds one extra triode in the preamp which makes the signal a little bit bigger and sounds fabulous when cranked. Just adds that little extra boost before power tubes. Nice until you want lots of rev at the same time as full
distortion.

Consider that point (after V3) in the signal path of a REAL Valve Amp circuit might exceed 100 VAC!
So to run SS Rev at that point in the circuit something has to give;

Now you have to squeese that big signal into a SS device that only runs on a 30VDC supply,, hum something has to give.
So you tend to loose the magical interface between the preamp section and the power tubes.

With most SS Rev circuits inside Valve amps you have to clamp the swing so those opamps can work. (good example to be found in Deville Amps where the signal can never exceed 30ish volts swing)

In that case (Reverb on or off) the signal is *ALWAYS Clamped* and that just kills the dynamics of what would otherwise be a very good Valve circuit.

Far better to keep the magic of Valves intact and just use an out-board reverb setup. HINT.

A word of avice;
Don't ever break the magic bond between preamp and power section of a Valve Amp,,
**unless you know exactly what you are doing**
Half the problems started because the masses wanted efx loops and reverbs and it just kills the magic and you will spend forever trying to curcumvent the issues you create by doing such. I've not yet found anything good about efx loops?

They give you these tricks to sell more units but fail to tell you it's all SS slammed right in the middle of a Valve circuit.(Then claim all Valve Amp.)
Phil.

phatt wrote: Consider that point (after V3) in the signal path of a REAL Valve Amp circuit might exceed 100 VAC!
So to run SS Rev at that point in the circuit something has to give;

Now you have to squeese that big signal into a SS device that only runs on a 30VDC supply,, hum something has to give.
So you tend to loose the magical interface between the preamp section and the power tubes.

I'm starting to learn this lesson myself. I modified my PV Windsor into a JCM800. It has an fx loop and sometimes the fx in the loop sound kind of weird. The original PV preamp clamped the signal pretty severely with a 5150-like stage with the 39k Rk. I converted that to a cathode follower and the preamp signal is much hotter- great- for driving the PI and power amp. However, now I believe the signal is too hot for the fx loop, which has a transistor buffer running on 24V (!). I believe the loop is fairly useless at this point.

But I'm philosophical about it. I view "loop" fx as being "production" fx anyway. I mostly record anymore, and add delays, reverbs etc in the "mix" (DAW). For clean stuff it doesn't matter. You can stick them anywhere you want. For dirty it usually sounds better after the distortion. In a band, have the sound man add delays etc in the mix. The amps I build are all low wattage power amp distorters. I don't even bother with fx loops on them. I think the amp fx-loop has kind of smeared the idea of the production effect with the guitar effect pedal in people's minds. But they are really apples & oranges.

phatt wrote:Hi turnerguit,

I quote;
"So, you're saying that swappin in a digital reverb would change the tone of the amp with reverb off?"

>Well that depends a lot on how you intend to setup the reverb side chain.
In a real Super Rev Amp you just don't use the rev or you disconnect it.
In that case it matters little as it was all HiZ Valve stuff.
The rev circuit adds one extra triode in the preamp which makes the signal a little bit bigger and sounds fabulous when cranked. Just adds that little extra boost before power tubes. Nice until you want lots of rev at the same time as full
distortion.

Consider that point (after V3) in the signal path of a REAL Valve Amp circuit might exceed 100 VAC!
So to run SS Rev at that point in the circuit something has to give;

Now you have to squeese that big signal into a SS device that only runs on a 30VDC supply,, hum something has to give.
So you tend to loose the magical interface between the preamp section and the power tubes.

With most SS Rev circuits inside Valve amps you have to clamp the swing so those opamps can work. (good example to be found in Deville Amps where the signal can never exceed 30ish volts swing)

In that case (Reverb on or off) the signal is *ALWAYS Clamped* and that just kills the dynamics of what would otherwise be a very good Valve circuit.

Far better to keep the magic of Valves intact and just use an out-board reverb setup. HINT.

A word of avice;
Don't ever break the magic bond between preamp and power section of a Valve Amp,,
**unless you know exactly what you are doing**
Half the problems started because the masses wanted efx loops and reverbs and it just kills the magic and you will spend forever trying to curcumvent the issues you create by doing such. I've not yet found anything good about efx loops?

They give you these tricks to sell more units but fail to tell you it's all SS slammed right in the middle of a Valve circuit.(Then claim all Valve Amp.)
Phil.

thanks for the advice. I've definitely decided against having the reverb in the circuit. However, if I understand your point, let me ask you another question: if I take out the reverb 12at7 and the recovery 12ax7 (as such in the bandmaster circuit), will I lose a bit of sparkle and high end? Can I just make up for this in the filtering of the EQ section?

Hi TG,
Not sure I follow but no matter here's what the circuit would look like if you remove the rev.
This should not alter tone in any dramatic way, though you may wish to alter the extra PI cap value or delete it altogether.

Pay close attention to all those old fender schematics....
A lot of those schematics are the same basic circuit but just alter one part.
the PI cap is often changed which of course alters the tone of the amp and the way it responds. (as do many other things)

You can of course add the 10pF bypass cap across the 3m3 resistor going to V3 but for my sounds I've always pulled it out.
(Depends how bright or dark the power stage and speakers are)

Also you can add or remove cathode caps on any of the stages. Raise R8 and or R12 to 1k or more to turn it up or down.
My bet is that a lot of amp tweakers way back also pulled or raised the FB resistor which makes the power stage drive a lot harder.

Heck as you are building it from scratch you can tweak away till you hearts content.

All up your on the right track that 3meg series before the 3rd triode does wonders for those amps,,even the Mesa Vtwin pedal impliments that trick in the clean section of their pedal.
Have fun, Phil.

phatt wrote:Hi TG,
Not sure I follow but no matter here's what the circuit would look like if you remove the rev.
This should not alter tone in any dramatic way, though you may wish to alter the extra PI cap value or delete it altogether.

Pay close attention to all those old fender schematics....
A lot of those schematics are the same basic circuit but just alter one part.
the PI cap is often changed which of course alters the tone of the amp and the way it responds. (as do many other things)

You can of course add the 10pF bypass cap across the 3m3 resistor going to V3 but for my sounds I've always pulled it out.
(Depends how bright or dark the power stage and speakers are)

Also you can add or remove cathode caps on any of the stages. Raise R8 and or R12 to 1k or more to turn it up or down.
My bet is that a lot of amp tweakers way back also pulled or raised the FB resistor which makes the power stage drive a lot harder.

Heck as you are building it from scratch you can tweak away till you hearts content.

All up your on the right track that 3meg series before the 3rd triode does wonders for those amps,,even the Mesa Vtwin pedal impliments that trick in the clean section of their pedal.
Have fun, Phil.

So I should add that extra 12ax7 that the bandmaster doesn't have? What do you think about transformers? I was gonna find one with the center tapped V in between the Bandmaster's and Super's. What do you think?

If I have calculated it right, having the 2nd 12ax7 right after the 3M will increase the voltage going into the phase inverter by 125 volts inverted which would be nearly 42 dB difference which makes me think I messed up somewhere. Could the preamp stage of the super reverb really be 41 dB higher than the Bandmaster? Or does it all kind of level out once it gets to the PI and 6L6s (kind of the way no matter how hard you push an overdrive pedal, it'll only get so loud--just adds more dirt)? Ands should I only run the signal through half of that tube or is there a way to take advantage of the other half?

If you mount triple carburetors on a lawn mower it will still work (use more petrol) and will still bog in tall grass.

Just as you can mount 10 AX?'s in front of a 30 Watt amp and it will still be a 30 Watt Amp. Sadly it will never be as loud as a 200Watt Marshall that only has 1 and 1/2 triodes in the preamp.

Preamp gain is a no brainer,, it just makes the preamp hit the roof earlier but does not really make the SPL much louder.
rows of AX&'s in the back of an Amp just makes the ignorant masses fell good.

A Fender hotrod Deluxe/Deville (can't remember exacts) has 90ish dB from the hot preamp,, but they still sound like crap because it's all triode distortion which is also Zener clamped,, Yukko pukass!

Don't get yourself lost with math’s,, just build it and tweak it as you go.

The preamp as I posted will be up about 60Db at 3kHZ. You will have around 60 volts swing entering the PI.
Plenty to get the power stage to sustain /sag/compress in a much nicer way than all those Master volume Amps where the whole thing is just preamp fizz bottle distortion and very little power section compression.

As to the spare preamp in that Ax7?
Well it does not get used,,,, learn to just accept that 3 is enough. at some point it starts to go backwards.

But then some car freaks will still try to tune 24 carbys.

It's a human Ego based disease, not based on scientific evidence.
Psychologically the bloke with a triple rectum-fryer is at an advantage over the chap with only has a dual Rectrofryer even if there is no sonic improvement to be heard.
That's just the sad simple fact of the way the masses tend to think.

Phil.

Okay, I understand now. And trust me, I don't buy into tube hype. I'm gettin rid of my twin because with it's stock tubes and speakers, my peavey solid state Steel amp sounded better. I think if people weren't so focused on tube amps, solid state technology would be developed more and refined for audio and amp technology and pretty soon we would have solid state that sounds as good or better as tubes. However, no one has really spent a lot of money and time developing the solid state components to do that. oh well. I ordered parts and all and now I'm makin the layout. Thanks for all the help. Really helped me.

Hey, one last question. If I wanna remove the Ext. Speaker Jack, do I leave that 820k resistor, or do I need to change that value at all?

Do you mean the *820 Ohm Feedback Resistor* coming from the output?

Thats just the FB R has nothing to do with how many speakers you have.

As I mentioned before AFAIK some hot rodders just pulled it out which runs the output fullpelt and unbalances the output which just creates a lot more distortion.

There is some debate about this upsetting the bias but as long as your HT voltages are not stupidly high it will likely be ok.
If you are not sure just look at old fender circuits for ideas.

Understand this simple rule, From mass power stage distortion to SS clean it works like this;
1/single ended output No FB (class A)
2/as above add bypass cap No FB
3/ as above but with parralelled output tubes (more power) No FB
4/pushpull output (PP), cathode biased (AB1) (think Vox AC15/30) No FB

5/ PP *Fixed bias* with lots of FB (much more power but also generally much cleaner running).
6/ PP UL (ultralinier) With FB Now the power stage is so clean it's getting much closer to SS clean.

at this point it starts to go backwards as the big ultra clean amps have very little power stage sag/ compression/distortion so the only choise is to add lots of fizzy triodes to get the signal to fatten up a bit ,, Oh and now that the darn thing is so loud you will need a master volume and of course if you desire the sweet singing Brian May styled power tube No Feedback sound then you will be swapping NOS triodes for the rest of your life but the magic will never happen because that has more to do with NO FB and simple Cathode biased Amp design.

Also note this very simple rule that the novice will miss;
TC (Transconductance) (Valve gain for the novice)
TC for common Guitar Valves;
6V6 = 3,800
6L6 = 8,000
EL84 = 11,200
EL34 = 11,200

Power in wattage has little to do with the way they work,, the TC dictates how the incoming signal gets treated.

Should be now rather obvious as to why Fenders sound very different to Marshalls Wink.

These days with so much focus on preamp (triode) distortion you may hardly notice this TC difference because the whole signal is just so full of crappy fizz you will never hear the power tubes natuarl dynamics as it's lost is shit.
So for a lot of modern Amps anything will work.
Phil.

Let me see if I'm digesting this correctly. Basically, you're saying we started focusing so much on preamp, we're neglecting the power amp tubes and missing out on the possibilities of what they have to offer tonally? And Marshalls sound different because you have to run the EL34s and EL84s hotter to sort of unlock their tonality? Or that those tubes add more tonality naturally because of their TC? And the super reverb would be number 5 as far as PP with FB? Why would amp builders keep wanting to move farther toward SS clean power stages? Sorry if this is all very basic. Like most young people now, tube technology is COMPLETELY foreign to me--research for this amp is the first time I've ever even known the basic function of a tube at all. I get the basics of tube function, however, TC and how they act in a circuit is still completely foreign. Hopefully it hits me soon and starts making sense. Thanks for the help. I love learning about this stuff, luckily for me, there's guys willing to share info

I quote;
""Let me see if I'm digesting this correctly. Basically, you're saying we started focusing so much on preamp, we're neglecting the power amp tubes and missing out on the possibilities of what they have to offer tonally?""

YES!!!!!!

Go find an *original* Bassman with 6L6.

Now just do 2 things,, Change the power tubes to EL34 and change the OT (output transformer) to some cheap crappy (totally wrong match for EL34 pentodes) badly made transformer.
and you will fall off your Soldarno at the differnce in tone/dynamics/fattness

When someone invents a triode trick that can do that,, then I'll listen.
Meanwhile it's all preamp fizz bottle tecknobabble to my ears.

If You want a great Guitar Valve Amp ? Then go read lots of HiFi pages until you learn every little trick.

Now go and build the *direct opposite* of what you learn about HiFi.
Phil.

/thirty second thread jack

Turnerguitar wrote:Okay, I understand now. And trust me, I don't buy into tube hype. I'm gettin rid of my twin because with it's stock tubes and speakers, my peavey solid state Steel amp sounded better. I think if people weren't so focused on tube amps, solid state technology would be developed more and refined for audio and amp technology and pretty soon we would have solid state that sounds as good or better as tubes. However, no one has really spent a lot of money and time developing the solid state components to do that. oh well. I ordered parts and all and now I'm makin the layout. Thanks for all the help. Really helped me.

Eh.. I just recently ran across this amp. Not trying to hijack a thread, just inform

http://lancekeltner.com/?page_id=18

Sounds pretty good, right?! And there have been other solid state amps that sound pretty good (Lab Series being the only one that comes to mind), but this one just kinda takes the cake..

disabling thread jack/

jwpartain1 wrote:/thirty second thread jack

Turnerguitar wrote:Okay, I understand now. And trust me, I don't buy into tube hype. I'm gettin rid of my twin because with it's stock tubes and speakers, my peavey solid state Steel amp sounded better. I think if people weren't so focused on tube amps, solid state technology would be developed more and refined for audio and amp technology and pretty soon we would have solid state that sounds as good or better as tubes. However, no one has really spent a lot of money and time developing the solid state components to do that. oh well. I ordered parts and all and now I'm makin the layout. Thanks for all the help. Really helped me.

Eh.. I just recently ran across this amp. Not trying to hijack a thread, just inform

http://lancekeltner.com/?page_id=18

Sounds pretty good, right?! And there have been other solid state amps that sound pretty good (Lab Series being the only one that comes to mind), but this one just kinda takes the cake..

disabling thread jack/

Well, I'll tell you, solid state EQing can really blow tube amps EQ out of the water. What I noticed when comparing my solid state to my twin or a super reverb was that little bit of sag and compression and sparkle the tubes give it. However, I don't believe that couldn't somehow be achieved with solid state technology. That amp definitely sounds great though.