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Alembic f2b preamp with lnd150 depletion MOSFET

Started by Claulogic, March 14, 2022, 11:24:27 PM

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Claulogic

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Hi, I'm new to this community, I'm looking into famous preamp stages and I found a job done by KMG with the depletion mode LND150 mosfet, I'd like to be able to do it but honestly I don't know anything about electronics and working with those high voltages I have a greater respect then I am in these places to see if someone could help me to get the best results, I do not ask them to carry out the project but if they guide me, and where I live I can find someone who knows about electronics and works with those voltages that mount me all work.

The preamp stage I would like to make is the alembic f2b stage by adding a source follower at the end of the second stage to run it with long cables. for source follower stage use this work https://amtelectronics.com/new/articles/Source_follower_HV_mosfet_as_cathode_follower.pdf

On the other hand, I attach the schematic with the lnd150, the only thing missing is to get the values ​​of the resistors in the -Vbias circuit and the capacitor, thanks in advance.

http://file:///C:/Users/marti/OneDrive/Desktop/Claudio/AFET2B2.png

P.D: If there are problems with the link, send me your emails and I will provide you with the schematic.

phatt

I'm a bit lost ,,What For ???

Fig 1A in the link shows 2 triodes, 3 R's and 1 Cap.
that's a 4 part count circuit. = simple

Fig 1B shows 1 tridoe 1 LND150,, 5 R's 1 Cap and 7 Diodes. = Not so simple

total 13 part count verses 4.

All to emulate a triode,,, Likely easier to use a triode.
That way you know what you will get.
Phil.

Claulogic

Well, maybe I didn't express myself in the best way, my bad, I want to use the preamp as a pedal in the smallest possible format, to connect it to the power section of a katana boss 50/25w it would be more or less comp>dist&over>modulations>preampF2B> delay>reverb>rotaryspeakersim>powersectionkatanaboss more or less like that I should also experiment to get the best results, and honestly I don't want to use the tubes because of the time limit of hours uses and everything else, besides I want to learn about this for use it for future projects

phatt

That's Ok that helps a bit,, but you have a heck of a lot going on there and I could fill pages trying to explain the issues you are about to face and you still may not fully grap the issues.
But I'll try.

1/ what is the alembic magic box?
Well it's a fair bet it just a Tone control unit and because famous people used them it's now a legendary device and now likely overhyped.

Truth is you can use many tone shaping devices that will deliver the same result. (may even be better)
The Alembic is simply an extra tone control in the signal path and ANY extra tone control device will work because most guit amps cannot alter the tone shape Enough to deliver the sounds for the modern player.

I assume you are basically by passing the preamps of the Katana and just using the power amp and speaker?
If so then Know this;
The power stage is likely class D and as sure as the pope is catholic the speaker is a super efficient hi SPL driver and they most often sound very harsh. With a lot of distortion the sound becomes very brittle.

Clue to Amp Speaker combinations.
If the Amp is dark you use a bright speaker.
If the amp is very bright you use a dark speaker.

This whole game is about a thing I call system tone. You have to build each section so as to enhance the right
frequencies in the right place.
As example;
If you plugged the Alembic into the front end of the Katana you will never sound like Pink Floyd simply because the system tone of the Kat will have way to much bandwidth. They are as harsh as hell. 
Why do I know this? I've been asked by a sound teck recently to help him get a decent tone from his 100W Katana. As he has envied my setup which is my own design perfected over the last 30 Years of building land fill, but once in a while I have had success. <3)
BTW, this hobby takes a long to time to perfect but once you learn to understand Whole System Tone it becomes obvious that you are far better to subtract that to keep on adding.
As example;
Distortion is easy to get with modern equipment but the tone shaping is the key,, try plugging a dirt pedal into a hi fi amp with full bandwidth and the bass will fart and the extreme treble will rip your ears off.
Good guitar circuit design requires a deep understanding of the freq spectrum.

learn to understand the most basic observations;
Train your ears to recognize what freq you are hearing.

note that 95% of any note you can play on a guitar is below 1,000 CPS (1kHz) add a couple of octaves for the  harmonics = 4kHz. past that it becomes crap and just destroys any chance of note definition.

The speaker in your Kat is likely well over 100Db at 5khz. That is why they sound so in your face harsh.
But they are extremely loud.. Wow!! which of course impresses the novice who has tin ears but it sells amps to the masses and roland gets rich,, meanwhile the kids still don't know why they can't reproduce the magic that they hear from the big players.
---
Ok your signal chain;

FWIW, I have dirt pedals at the front end then> mod FX into a compressor> then Cab sim> into a tone control.
The Amp I use is an 80's SS basic Keyboard Amp (No freaky tone alterations designed by fools who thinks more dist is better)
The reason My compressor is AFTER the Distortion pedals is to keep the levels within a set SPL range.
The issue with nearly all dirt pedals is if you stomp on one the volume often jumps way too high. (or not high enough)
So if you have a Compressor After Dirt it keeps everything within a set SPL range. The other way does not work for me as I play live So I can't stop and re-adjust on the fly. :duh

Now back to your tone control;
My tone control is my own Design (as is most of my gear) This will deliver a big round Bass and a Treble that is crisp but not harsh. I've built many now for happy players.
You are welcome to the design.
Assuming the Alembic is just a stock Fender tone stack then it will suffer the same drawbacks as the Fender tone circuits.
My tone circuit was designed to overcome the limitations of the Fender tone controls. the big difference is ALL 3 knobs actually Work.
Mid cut actually cuts while bass stays big and round.
Fender tone circuits suffer from too much interaction between the 3 controls. (Marshall stack is even worse)
Cavet, there will be exceptions to this general observation but this is what I've found with most of the amps I've been around.

If you are new to building circuits then there are DIY ways to save time and money. I only build stuff that is single sided PCB and use the Laser print method to make circuit boards. My eyes are to old to start trying to make tiny PCBs with surface mounted bits you can't even read  xP
I hope some of the above helps you on your tone chasing endeavors,
Phil.

Some comments about the PhAbbtone here;
https://www.ssguitar.com/index.php?topic=1136.0
But build the V4 version posted here.
Adding piks of my pedal setup

g1

Quote from: phatt on March 17, 2022, 03:20:14 AM
Assuming the Alembic is just a stock Fender tone stack
Pretty much.  From the Alembic website:

"The F-2B was inspired by the Fender Dual Showman amplifier. In the late '60's, we routinely added preamp output jacks to Dual Showman amplifiers and substituted an external power amplifier for the built-in quad 6L6's, most usually a MacIntosh 75.

The F-2B came about to provide the same preamp functionality in a rack-mounting package, as the Dual Showman was considerably wider than the standard 19 inch rack
."

Claulogic

ok thank you very much for the information, and all the review, but it is not really the answer you expect but if I am interested in doing the phabb tone, it is good to have a tone shapping in a small format, really I have not bought the boss katana yet, simply I tried it and said for 25w it sounds decent, and well I had the idea of making a preamp to use it there although the preamp that I like the most is the hiwatt one. The reason why I exposed the Alembic or Fender Bassman one is because it is simple as far as it goes and I more or less wanted them to explain to me how to find the cutoff voltage and all the other parameters to be able to carry out other projects later. but the pahbb tone to start is excellent I will do it.

PD:but now that he's telling me about the katana, I think I'll back off and look for another amp that meets my expectations, thanks, it just saved me from a tantrum hahaha

Thanks phill

Tassieviking

My curious little eyes saw a Phatt Box with compression and OD in it.
What would a man have to do to get that circuit ?  Beg, borrow,  ??
Thanks for the FabbTone circuit Phatt, I might have to make it next.
Michael
There are no stupid questions.
There are only stupid mistakes.

phatt

Quote from: Claulogic on March 17, 2022, 08:50:41 PM
ok thank you very much for the information, and all the review, but it is not really the answer you expect but if I am interested in doing the phabb tone, it is good to have a tone shapping in a small format, really I have not bought the boss katana yet, simply I tried it and said for 25w it sounds decent, and well I had the idea of making a preamp to use it there although the preamp that I like the most is the hiwatt one. The reason why I exposed the Alembic or Fender Bassman one is because it is simple as far as it goes and I more or less wanted them to explain to me how to find the cutoff voltage and all the other parameters to be able to carry out other projects later. but the pahbb tone to start is excellent I will do it.

PD:but now that he's telling me about the katana, I think I'll back off and look for another amp that meets my expectations, thanks, it just saved me from a tantrum hahaha

Thanks phill

That's ok, sorry if I'm not understanding your request.
i.e. What do you mean when you ask for *Cutoff voltage*?
It's a basic fender tone stack which will work from about 250Volts quite well. Which itself means more real estate for the Hi voltage supply on your board. You also need a heater supply to run the Valves. not an easy build. 8|

So you posted the Alembic with FET mod and I see zero benefit because you need one triode so you save no space by adding a mosfet. and you have 1/2 an AX7 sitting there doing nothing.
If you want all SS then look for KMG's postings here as he has made complete Amps from FET's,, Very impressive stuff but not simple for someone with only basic Leky skills.

BTW If you like HiWatt then the PhAbbtone IS the HiWatt Tone stack I just refined/reworked it into a pedal format. Runs from 9 to 18Volts.

I have simulated as well as real world tested many of the tone stacks and I came to the conclusion that Dave Reeves HiWatt tone circuit gives the best results. Even Mark Huss will agree that the Tone section of HiWatt Amps is a big part of the sound.
Even the famed Dumble tone stack with it fancy Rock/Jazz switching still suffers from the interaction issues of the fender tone stacks.

The best I can make out is, For what you wish to do you don't need valves, You need knowledge which is far more useful than just assuming you need a messa stack to be a great guitar player.
You can blow big money chasing brand names If you catch my drift. winky.
Phil.

phatt

Quote from: Tassieviking on March 17, 2022, 11:19:52 PM
My curious little eyes saw a Phatt Box with compression and OD in it.
What would a man have to do to get that circuit ?  Beg, borrow,  ??
Thanks for the FabbTone circuit Phatt, I might have to make it next.
Michael
Yep that took a long time to come together.
That is a simple light triggered Comp with and extra drive circuit wedged between the comp and the Cab sim.
The compressor is from FSB site (Free Stomp boxes) A retired teck chap lives on that site called *Mictester* came up with a *Really Cheap Compressor*. A very clever chap. :dbtu:

It is unique in that Unlike a lot of comps this one actually adds grit the harder you drive it. much like the triode rattle you get from hard driven triodes.
I've owned a few Comps and the Boss ones are just way to clean and except for the CS3 the earlier CS2/1  units are noise prone, and they are prone to pumping. :trouble
I even tried to build a few but I gave up because the noise issues are a pain.  :grr
I went right off Comps for some years but then Mic came up with this one and It worked a treat.
Super clean comps are for studio but don't work for Rock guitar sound. IMHO. xP

Link is here;
https://www.freestompboxes.org/viewtopic.php?t=8581&sid=18c2603e67d802c43c8f08b2b3b38269

The Extra drive is just a simple diode clipper stage for an extra bit of grit.

The Cab sim idea was a highly tweaked Nobels SST1 (think rockman rip off) I only used the Cab sim part.
The output has a basic top cut filter (Edge) as well as a simple level shift on the output, for when you just need a slight volume lift which has no effect on distortion.
-----
Re the PhAbbtone.
The Schematic assumes you know how to wire up input switching and such as well as add a Led.
As mine is on all the time then No need for a stomp switch. a toggle is cheap. :P

As should be obvious I'm old and don't care much for fancy painted boxes and flashy knobs. Heck all that extra work and cost and it won't sound any better, so flat black is kool for me, wink.

My tone circuit has been tweaked to improve a few little issues because it's only running from low voltage.
If you wish to use the original HiWatt values there will be some problems so I'd suggest you stay close the schem values.

What may not be obvious is that these are Hiz tone circuits and you can plug a passive PU guitar straight in. You could use a buffer in front but as it works so well why bother.

Watch your layout as like ALL HiZ stuff they are prone to pickup noise.
Anything above R1 & R3 is sensitive.
so use of expensive ultra low noise opamps won't help much.
If you have a lot of pedals which introduce a lot of gain then I suggest you rethink your layout.

My pedal board is deathly quite because of good supply grounding and insightful use of gain settings on dirt pedals. 8|
The phAbbtone used into other hot rodded Amps can be a bit hissy but again then so are most hi gain amps.

re schematics for the PhAtt Box,, give me time I'll have to dig for the files. I have so many schematic files it's just getting on top of me now.
I think the original is here somewhere on these pages but that was long time back.
Most of my successful circuits are here on SSGuit

Phil.