MOSFET amp emulator and MOSFET Mu Amp

[POTL]

Hello
Last time I built a lot of amps in a box using JFET transistors
And remembered that when I was building the Box Of Rox, the Catalinbread RAH / WIIO sound was more saturated (albeit a bit noisier)
Tomorrow I want to collect a trial layout using MOSFET, you can share your experience in creating such schemes
In particular, is it interesting to create an analog of Mu Amp or how to replace the second tube in the circuit (V2A + V2B) correctly?
Since with MOSFET behave differently than JFET I'm not quite sure how to act properly.

[POTL]

If in nature there are schemes besides Zvex / AMZ / Catalinbread I would be glad if you share

[GibsonGM]

I think you should start reading about tube preamps, POTL!  There are many sources online... this guy has some great info and is a member here:
http://www.valvewizard.co.uk/gainstage.html

The idea with these preamps, as you show above, is that each one is a small amplifier.  A gain stage.  By cascading them, you can shape the tone of your signal, as well as add overdrive/distortion.   The amount of signal you feed into a stage determines if it will clip or not...and there are ways to shape how the clipping sounds (bias).    By reading about how designers do this, you will learn that you'd like your input signal to be boosted, clean and with as little noise, as possible.  Then you may begin to cut bass (to prevent blocking distortion and 'flabbiness'), and can selectively boost treble to gain more harmonics as your next stage clips.   You may shape more after that...bias the next stage more warmly, cut the extra treble to prevent shrillness (now that you've got what you want from boosting it!).

There is some thought that goes into designing these.   I thought you'd be interested since you said "creating these things"...if you want to know more, Merlin's site and others will show you how they design tube preamps.   Now, Mosfets and JFETs are not the same as tubes, but the PRINCIPLES are quite similar (nearly the same).    There are differences in the resistances you use for bias, etc., but you can steal...I mean, copy...from other designs to set you your basic gain stages.   Mosfets, Jfets don't clip like tubes do, but they DO have a nice overdriven sound IMO, which has been used countless times.

Then you need a buffer, to drive a tone stack...and you must choose which tone stack you want...there is a LOT that you can do with some fundamental information, starting with how a gain stage is created!   

Look at several preamp stages like BSIAB, and so on.  You will see that they have several gain stages, and often a buffer, tone stack, then maybe a boost on the output to bring the level back up.    This "topology" is very common...copy the pros and change components to your taste....

[POTL]

Thank you, I will definitely read
In fact, I already understood many aspects and even gradually develop my own schemes on JFETs, but I wanted to improve the sound of MOSFETs in the past, they gave the best result.
Regarding the lamps, I will certainly read the information on your link, thank you!
But I do not exactly plan on creating lamps (only if in the distant future)
1) Lamps are very expensive
2) I am concerned about a high voltage of 450 volts, or rather I even fear it

[POTL]

BSIAB is far behind
I collected about 10 different boutique pedals (Wampler, Catalinbread, JHS and others)
Then I saw the Ramble FX Marvel Drive assembling it, I realized that the sound of this effect is much more natural and closer to the sound of amplifiers than the devices assembled on the basis of BSIAB
Understanding the principle of Marvel I assembled almost all the classic amplifiers and several modern ones (thanks to the layout boards the amplifier assembly takes 15-20 minutes and for one free day you can collect everything your heart desires).
Today I was assembling the Marshall JCM 800 based on the original scheme and Marvel scheme, the sound was good, but I remembered about MOSFETs
In principle, I found something on the Internet, I will attach the schemes, all of a sudden come in handy.

[POTL]

Mosfet Mu Amp

2 variations of MOSFET booster (4&5 circuit)

[POTL]

.

[amptramp]

The top example circuit from two posts ago is NOT an µ-amp.  It is an amplifier with a current source load, meaning almost infinite impedance.  A useful circuit but definitely not a µ-amp.  For a proper µ-amp, check out this issue of Tube Cad:

http://www.tubecad.com/may2000/

The first article goes into the SRPP (shunt regulated push-pull, another name for µ-amp) and shows how to design it with tubes.  The design can only be approximate because the cathode resistor of the upper tube stage should be the reciprocal of the transconductance.  At 100 volts on the plate, a 12AX7 has a transconductance of 1250 µmhos, the reciprocal of that is 800 ohms.  With this resistance, the current in the upper stage will vary in the opposite direction to the current in the lower stage by an equal amount.  Since these two tubes are in series, the excess current has to go somewhere and this somewhere is the load.  A µ-amp will not operate properly without a matched load.  With a higher load, you get clipping which may make the basis for an interesting fuzz but you are talking about a linear amplifier here.  A lower load may reduce gain but will preserve linearity.

This was not all that popular as a tube stage since you had to have a tube cathode about 100 volts above ground and there is a possible problem with heater-to-cathode voltage.  Cascode RF stages did that but they did not have to contend with the hum that is introduced when a heater is at lower voltage than the cathode because their plate load was tuned to RF frequencies.  With MOSFET's there is no heater to contend with but you do have the variability of transconductance which means the upper cathode resistor may have to be selected for the specific MOSFET.  But there is no real problem with going away from equal upper and lower device swing, so this may not be the problem it appears to be.

[POTL]

The top example circuit from two posts ago is NOT an µ-amp.  It is an amplifier with a current source load, meaning almost infinite impedance.  A useful circuit but definitely not a µ-amp. 

Interesting
Since I do not have a technical background and do not speak English to the extent that I would like to not take everything correctly
What about the circuit that I compared with Mu Amp and infinite impedance, what happens if I assemble this circuit and plug it into the amplifier input, will I spoil it?
I apologize for the stupid question, the phrase about imidans somewhat embarrassed me =)

[GibsonGM]

Amptramp will come back with more for you, Potul, he knows more about these configurations than I do 

What I am saying is that if you study the basic tube amplifier circuits, they provide the same kind of information you would need to understand how mosfets and jfet gain stages are built.    No need to make a tube amplifier, but it is a place to start from. 

There are also places on the internet that tell more about the circuits you want...the Fetzer Valve information on www.runoffgroove.com  is good, and also read about the Tillman preamp circuit.    Then search for mu amp information...   

[POTL]

Thanks 

[POTL]

Amptramp will come back with more for you, Potul, he knows more about these configurations than I do 

What I am saying is that if you study the basic tube amplifier circuits, they provide the same kind of information you would need to understand how mosfets and jfet gain stages are built.    No need to make a tube amplifier, but it is a place to start from. 

There are also places on the internet that tell more about the circuits you want...the Fetzer Valve information on www.runoffgroove.com  is good, and also read about the Tillman preamp circuit.    Then search for mu amp information...   

I looked at this scheme
They use the J201 JFET
These schemes I understand and know how to build / modify
I want to understand how to properly replace JFET J201 (or similar) with MOSFET 2N7000 / BS170
JFET is the territory of Wampler is a good sound but generally flat
MOSFET is the territory of the ZVEX a bit noisier but the sound is more pleasant

I want to learn how to build something in the style of Zvex
Other circuits on JFET J201 / 2N5457 its I have been building successfully and modifying for a long time
MOSFET works a little differently, in particular they require the connection of virtual ground to the gate
In this I still have a lot of use
In any case, thanks for the answer!

[printer2]

Google is you friend. design linear mosfet, to start you off,

http://www.electronics-tutorials.ws/amplifier/mosfet-amplifier.html

[GibsonGM]

Yes, you will find very much on Google, and Youtube!! 

I will not say much about it, but I like to use the AMZ Mosfet Boost as a gain stage for things I build   You might want to look at that.  It is clean, and you can add things to make it do what you want (such as clipping diodes).  Do not forget the protective Zener diode when working with Mosfets.

You like ZVEX SHO?  Again, this is a gain stage.     Build them, and understand that the source potentiometer is setting the gain.

Look for "Mosfet amplifier tutorial" and "JFET amplifier tutorial" on Youtube...

They are very fun to work with, and sound almost like 'little tube preamps'    

[POTL]

Yes, you will find very much on Google, and Youtube!! 

I will not say much about it, but I like to use the AMZ Mosfet Boost as a gain stage for things I build   You might want to look at that.  It is clean, and you can add things to make it do what you want (such as clipping diodes).  Do not forget the protective Zener diode when working with Mosfets.

You like ZVEX SHO?  Again, this is a gain stage.     Build them, and understand that the source potentiometer is setting the gain.

Look for "Mosfet amplifier tutorial" and "JFET amplifier tutorial" on Youtube...

They are very fun to work with, and sound almost like 'little tube preamps'   

Zvex SHO and AMZ Mosfet Booster

I built them some time ago, for several times
I also used the first cascade in Catalinbread Rah
Sounds like Zvex seemed louder, AMZ and Catalinbread quieter, but less overloaded and the sound more balanced   

[POTL]

Google is you friend. design linear mosfet, to start you off,

http://www.electronics-tutorials.ws/amplifier/mosfet-amplifier.html

Thanks


Here is this picture, on the gates of the 2 resistors acting as a voltage divider, 1 of the three ways (most likely there are more of them) of getting food on the gates.
I am concerned about this half-food, if I could refuse it, then it would be possible to create more precise schemes.
Probably this is the key problem because of which I created this topic =)

[diy-tubes]

Please check Marshall JCM800 schematics (LND150)
http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/jcm800mvfSch.pdf
And this article can be good addition to the topic, imo:
http://amtelectronics.com/new/articles/Source_follower_HV_mosfet_as_cathode_follower.pdf
Sorry if it was posted previously.

[POTL]

Please check Marshall JCM800 schematics (LND150)
http://milas.spb.ru/~kmg/files/projects/jcm800mv/fet/lnd150/jcm800mvfSch.pdf
And this article can be good addition to the topic, imo:
http://amtelectronics.com/new/articles/Source_follower_HV_mosfet_as_cathode_follower.pdf
Sorry if it was posted previously.

Already read, but thanks anyway!

[POTL]

In general, I collected a few layouts today
As a basis, took the scheme Marvel Drive

For transistor bias i used resistors rated 1 megohm
Based on Zvex schematics

I also connected the trimmer resistors to the drains

In general, the sound was more interesting and saturated
But there are following problems
1) Working with the gain pot, the transistors open either closer to the maximum, or closer to a minimum
2) In the third cascade (mu amp on Mosfet) the bottom transistor is very hot
Resistors 1,3,4 is 1 megohm, The resistor 2 eliminated from the circuit the source of the transistor connected directly to ground, Capacitor 3 is 100n

3) A huge volume of loudness (I do not know whether it's plus or minus) on my 100 watt Randall amplifier I set the volume knobs and master by 1 division from 10

[POTL]

Any ideas how you can fix these problems?
1) Transistor heating
2) Incorrect work of transistors when using the potentiometer Gain