PhAbb NowWatt

[phatt]

Hi all,
Yet another circuit for you to play with.

This is the first part of what is basically an elcheapo Guytron GT100 inspired concept.

For those that don't understand this idea, it's basically a dual Amp setup where the first Valve  Amplifier is driving a load (Not a speaker) and the signal is tapped off and Re-Amplified via a Second Main Amp.

This gives *ABsolute Loudness Control* no matter how hard the first amp is driven.
You now have the ability to dial the Valve rig to the sweet spot and not have to ever worry about playing too loud.

This lifts the dreaded restriction of setting SPL levels in smaller venues or just playing at home. You can now play full up without annoying the folks next door.  A great asset for practicing those fast high gain licks.

The Guytron is a *2 Valve Amps in one Box trick* which would be fantastic but the cost is a little scary for the average player.  I've gone down the *Modular path* which allows me to swap things around if need be and because I'm using cheap S/hand bits I've kept my costs to a bare minimum.

The floor pedal is a mix of Mesa Vtwin ideas and my HiWatt inspired PhAbbTone. Sadly the Vtwin like most valve powered preamps tries to do the OD/Distortion all in the preamp stages but anyone who understands valve teck well would know that **Triodes can't do square wave like Pentodes** and although these circuits can produce copious amounts of crunch/ distortion they tend to lack the richness of a pair of output pentodes driving through a transformer.

*Pentodes where actually invented to overcome the sevre shortcomings of triodes,, hum.*
One wonders at the wisdom of rows of fizz bottle triodes??? :loco

As will be obvious to those who know the Vtwin circuit, I've only used the *Clean section* as the crunch channel is basically useless for the sound I wanted and was just wasting space.
**The main Valve Amp does the magic endless sustain and touch dynamic ODrive**

So don't build this floor unit thinking it will be a monster crunch pedal as this produces a very clean signal but with greater voltage swing than an all SS unit.
Although it does do a very nice rock (half wave) triode rattle when driven hard on the Clean channel. <3)

If you desire the *Mid scooped Metal sounds* you will need a Graphic in the final Loop before main SS power Amp and most will want a bigger main Amp and speaker setup as small amps struggle with low freq.

For the small gigs I do this little Laney is just so damn convenient.

A quick post of the first schematic section.
(I will Update this if there is some interest and give more details of the finer points of building such a rig.).

Enjoy, Phil J A.

[Zappacat]

Thanks for posting that.  I'm very interested in building something like that. 

Can you recommend a power supply to start with?  I'd like to make it fit in a 2U rack mount space without external wall wart type transformer.

Would it be possible to drive a Behringer Eurolive 1520http://www.behringer.com/EN/Products/E1520.aspx with the setup?

[phatt]

Hi Zappa,
              Sorry chum but I doubt that any guitar preamp signal will sound convincing through PA speakers but you could try. xP
Just go wire up a high freq horn to the back of any guitar rig and try to get rid of the NOW insane treble response.

Maybe Do the maths work out the highest possible frequency of your guitar then x2 that number then again for all that harmonic content. you final number will be under 5,000 cps.

To much bandwidth is a tone killer,, it's the last thing you want.

Yes you could rack it up but keep in mind any switching then becomes a lot more work as you will need relays and a foot controller anyway to change channels.
That was one of the main reasons I floor mounted it as any switching is purely mechanical.
(I have not drawn the 2 switching systems on the schematic but there is a Boost switch and an A/B switch)
I refuse to complicate things when there is no need.
IME, switching circuitry is what tends to break first,, often you find the audio circuit still works but the fancy relay system is shot.

I'll try and up load some pic's of the unit, might give you ideas.

Phil.

[phatt]

 
Just thought I should try to present some kind of Audio Demo on this otherwise all talk will probably mean little to those with  1,000 options and wondering which one to blow money on is often a big head scratch for those starting out.

This is taken from the preamp out of the Laney KB Amp so no cab sims just the raw sound so take that into account.

Recorded straight into Cakewalk on my nothing special laptop.
Track is then normalized and converted to low quality MP3.

Using the onboard Laney tank Reverb and my cheap DD Behringer.

Hope you enjoy, Phil.

[phatt]

Hey Zappa,
Whoops forgot, you asked about the supply.

http://diyaudioprojects.com/Tubes/12AX7_Preamp/

That is what I used to supply the pedal but the kit is no longer available.
You may wish to search for *nixie supplies* they can apparently deliver enough to drive at least 2 triodes.

You may even be able to get by with only 100 Volt HT as neither triode stage swings massive voltage.

Even with a 300mv input signal the triode's are only swinging about 30 VAC at full gain.
The supply I used has 250VDC HT and could deliver 40mA.

One word of advice when using these switching supplies;
*Watch your grounding layout* you can easy end up with a very noisy circuit.

**Any ground loops will wreak havoc on the unsuspecting builder.**

The Jaycar kit has an LM7812 which drives the heaters and runs the Auto transformer SMpU.
Oh and don't bother trying to build the Audio board Jaycar kit as it's for hifi,, so it's useless for guitar. :duh

Here's a pic of the Floor unit, Note that no expense was spared in making it look home made? Heck at least no one will steal it unless they first knew it's worth.

Also note the SMPU is still mounted on testing board.

Phil.

[J M Fahey]

Hi Phatt, liked the Demo, but I think you should re-record it miking the speaker, to hear the real thing.
Of course, if your KB amp has tweeters, as many do, disconnect it or at least stick the mic in the middle of the woofer cone.
Thanks.

[phatt]

Thanks JMF ,, glad it works.
As to Recording live... I would if I could
My dear wife hates Electric Guitar :grr especially played loud.

SPL level in my house is also the Divorce meter gauge,, if you catch my drift,, 

FWIW,
I record direct from the line out of the Laney Amp > Direct to laptop which has a half duplex modem /sound gizmo.

I Record with Cake 9 > Normalize the signal > convert to low quality MP3.
Finished.

Now played back through the laptop speakers it sounds rather cheap,,,,
BUT take the audio back into the Laney Amp and only Gods ears could tell the difference.
So take the mp3 and run it through any guitar amps efx return input (or similar setup) and you would have a fair representation of the sound I get live.

The only real diff is going to come from speakers used.

The Laney DID Have a FANE 12 inch driver but it was horrendously sharp and I swapped it for a no name driver which by luck is as close to the older Celestions,, which I love so much. <3)
(I know you love those eminance drivers but I just can't cop them, they are just way to harsh for me.)

I have messed with quite a few different drivers but I keep coming back to this setup.

So in reality by the time I setup mics and frig around with speaker compensations I'm actually going backwards.

The Laney is about as uncolored as one could make a SS Amp. The tone controls are always left at mid settings as they really don't add much for guitar anyway.

The Laney EFX loop has been changed from series to a parallel setup,, other than that it's stock. If you want the Laney circuit, google *Laney KB 80* (My Amp says KD 50 on the front but it's almost identical schematic)

Anyway here is the same thing but this time I dropped the *AnyWatt Valve PowerAmp* and used the old faithful DDC circuit instead.

Not quite the sustain of the Valve rig but actually a little more versatile.
The first part is clean (just the FPV Pedal into Laney) then DDC and the $8 hifi Graphic EQ added.
Phil.