Headroom Mods for “Little Will” Lite2b Circuit

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Zackfw
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Headroom Mods for “Little Will” Lite2b Circuit

Post by Zackfw »

Hey there everyone- sorry if this has been covered before, I’m having trouble navigating the search page.

I just ordered a Little Will board from guitaramplifierpcb.com to do a Valve Jr conversion and am looking for ways to increase the amount of headroom in it.

Any tips? Any related threads you could point me to? Again, apologies sorry if I’m doubling up topics here. Thank you!!
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by JMPGuitars »

Hi, welcome to the site!

I'd tell you the first step is to build the amp stock and make sure it works before you consider any mods. You might not think you need more headroom once it's built. If you do still feel that way, it will be helpful for you to check your voltages and see where they're at before starting any mods.

Thanks,
Josh
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Zackfw
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by Zackfw »

So I finally managed to get some time to put this thing together and it works!

It sounds awesome and I get the HYPE on these things but it is definitely a bit lower headroom then I’d prefer.

My voltages are all pretty spot on to the ones in the VJ Conversion instructions provided on the Guitar Amplifier PCB website. How might I go about adjusting this more to my liking?

Thank you for the help
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by Daviedawg »

Hi Zack. I haven't built a Lite ii. But looking at the different versions of the schematic the plate resistor for the preamp 12ax7 seems to vary from 100k up to 150k. Since that affects the plate voltage I think that the higher values will result in more headroom (or the reverse for more gain). What is the value for the equivalent resistor in your version?

Dd
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by Daviedawg »

Just another thought. If you have other lower gain preamp valves such as a 12AY7 to hand you could substitute that to see if you get near what you are looking for.

Dd
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Zackfw
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by Zackfw »

Thanks for the reply DD, I appreciate the help.

My build uses 100k so maybe I can start there.

Also I’ve read a bit about some 470k grid leak resistors being lowered to 220k to increase the headroom a bit. Are these the ones going into V2 (R11/R12) or are these the ones after V2 going to ground (R14/R17)? Is this a mod worth looking into? I’ve attached a schematic for reference on this here: http://rh-tech.org/public/z_stingray_pc ... c%20v5.pdf

As much as I like the character of this amp, I’m more interested in learning about electronics and understanding how adjusting different components changes the circuit.

If this turns the ‘Marshall’ into a ‘Vox’ or even a ‘F**der’ I guess I don’t mind! Mostly trying to understand what is happening inside that gives these amps their specific sound.
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by geoff 1965 »

Hello Zack,
R14&R17 are your grid leaks,you can try 330K or 220K for the headroom.first though safely make a note of your voltages like Josh said which will give you a reference point for comparing when swapping resistors etc.
do you know what plate dissipation your el84's have? running the tubes a little cooler gives a bit more headroom.
good luck tweaking and keep safe working on the amp,if your not sure on something just ask,the guys on the forum are very helpful.https://youtu.be/w9B0Rhr_Y-E
https://youtu.be/L3rRk3eSTnA
p.s. here's a couple of youtube video's showing how to check plate dissipation safely
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by rock_mumbles »

If you followed the Baby Will schematic etc. ... You have an increased headroom amp (circuit) because of the split load plate on the first plate resistor ...

Is the amp too dark?
Did you use the stock VJr power transformer?

If you used the VJr PT it doesn't really supply enough voltage or current for the circuit ... I have changed the preamp dropping resistor (R5) from 8.2k to around 4.7k with underrated power transformers ...
Increased preamp voltage will make the amp cleaner and brighter
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by crgfrench »

Adding a negative feedback loop will increase headroom.
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by zaphod_phil »

crgfrench wrote:
Fri 08/19/22 6:44 pm
Adding a negative feedback loop will increase headroom.
And kill some nice harmonic sparkle. So just increase the anode voltage, remembering to adjust the cathode bias resistor

But who in their right mind would want to increase this 18W amp's headroom?? 8O that's a desecration! :x
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by Bieworm »

zaphod_phil wrote:
Wed 09/07/22 1:04 pm
crgfrench wrote:
Fri 08/19/22 6:44 pm
Adding a negative feedback loop will increase headroom.
And kill some nice harmonic sparkle. So just increase the anode voltage, remembering to adjust the cathode bias resistor

But who in their right mind would want to increase this 18W amp's headroom?? 8O that's a desecration! :x
Lol!! It's mostly the other way around... that's why I looooove my Tremolo TMB amps.. they break up when the slightest volume kicks in...

Did I ever declare my love for the Tremolo TMB?😀😀😀
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by Bieworm »

Well.. I must say I played it clean the other night, with the gain on 3. It does have a very impressive clean tone too. This one does it all for me, and every time I build or play another amp this feeling gets confirmed. And I've uilt quite a few since...
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by zaphod_phil »

zaphod_phil wrote:
Wed 09/07/22 1:04 pm
crgfrench wrote:
Fri 08/19/22 6:44 pm
Adding a negative feedback loop will increase headroom.
And kill some nice harmonic sparkle. So just increase the anode voltage, remembering to adjust the cathode bias resistor

But who in their right mind would want to increase this 18W amp's headroom?? 8O that's a desecration and not how I designed it.
But if you're so set on a clean-sounding 18W,my best recommendation is Trinity's SIII, which has some really sweet clean tones :)
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Re: Headroom Mods for “Little Will” Lite2b Circuit

Post by crgfrench »

zaphod_phil wrote:
Wed 09/07/22 1:04 pm
And kill some nice harmonic sparkle. So just increase the anode voltage, remembering to adjust the cathode bias resistor
Including NFB as a switchable option increases the versatility of almost any amp. Rob Robinette has a good description in his amp mods page, https://robrobinette.com/Generic_Tube_A ... ack_Switch
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