Sunn Model T Preamp Question

[Vlad7329]

Hello forum.

I am planning to make a Sunn Model T preamp to use it as a preamp into sound interface.

As I understand , there are two main uses to this type of devices: as a OD/distortion pedal, and as a preamp.

My situation is that I don't have an amp and my living conditions don't allow for loud playing.

So my idea is to build a Sunn Model T FET adaptation and plug it into my Scarlett 2i4.

I found two circuit diagrams as of now: the first one is from Benoit from Coda Effects:


As Benoit wrote in the comments to a respective post of his, this pedal requires an output buffer for optimal output impedance (this makes it usable as a preamp per se).

Adding output buffer (A Klon one for instance) is a no problem. But his circuit is high gain by nature, and I want it to be usable for clean sound.

So after some later investigation I found another adaptation (Sunn T form GuitarPCB https://guitarpcb.com/product/sunn-model-t-pcb/)



My question is as follows:

Does this circuit provide needed output impedance to use is as a preamp, or should I also add an output buffer?
My guess is that it does not differ drastically form what Coda Effects provided. So should also require a buffer.

Could you post some links on theory which covers knowledge that I need to understand this topic?
Maybe some key words?

[Vivek]

The Scarlet interface has following input impedances

Microphone 3k ohms
Line input 60k ohms
Instrument input 1.5M

The instrument input won't load the Sunn Model T

[GibsonGM]

The instrument input at 1.5Megohms, is so high that no, the preamp won't load it.

I assume you're using this with a DAW? If so, you may want to try using a cabinet simulator with some impulse responses with this, it will sound 100,000 times better!   I recommend "Le Cab" by Poulin, free.     https://plugins4free.com/plugin/958/         There are others.

There are many, many IR's available for free...I really like "God's Cab", you can find the package online.

[Vlad7329]

The instrument input at 1.5Megohms, is so high that no, the preamp won't load it.

I assume you're using this with a DAW? If so, you may want to try using a cabinet simulator with some impulse responses with this, it will sound 100,000 times better!   I recommend "Le Cab" by Poulin, free.     https://plugins4free.com/plugin/958/         There are others.

There are many, many IR's available for free...I really like "God's Cab", you can find the package online.

Hi GibsonGM,
What if a buffer is added before the output?
I am already using IRs with a cab simulator, but as far as I understood, having a preamp is an integral part to guitar sound. So basically using only IR is like using a cab without a preamp and/or power amp.

I'll try Le Can though, thanks for recommendation .

[GibsonGM]

You can find a LOT of free software amp sims to use with a cab sim, too, just for your info.... "Ignite Emissary" is one for heavy sounds, and "Blue cat free amp sim" more for rock and clean stuff...

That would give you software 'amp in a box' with no preamp stuff needed.  But I use a DIY tube preamp a lot of the time instead of an amp sim..and at times I do hit it with a treble boost or mosfet boost....or an eq, and so on.   Versatility can be very useful!

I was implying that you would use this preamp you are building with a cab sim inside your DAW     I'm sure you know, it will sound like harsh junk if you don't.  (or at least using the proper EQs to simulate a cab).   

Placing the preamp before your interface is basically like having an amp running into the computer.  Pedals are preamps in their own right. 

If you add an output buffer to the preamp, you will obtain a better impedance match....you will take the medium-level output impedance of the preamp and drop that to a very low impedance...which the interface will like.   However, you may not hear much difference.  I've built nearly the same and hear no ill effects from not having an output buffer.       

You could try this by running the preamp into a Boss pedal that is turned off, then into the interface, since Boss pedals are buffered when they are not active (but must have power).  Or, simply include it in the preamp output if you so desire      It's only a few parts...but don't expect any magic from it!      The interface Z is high enough to 'absorb' a bit of a mismatch, I guess I'm saying.

[andy-h-h]

I've built the Coda effects Sunn preamp.   For me it only sounds good with the boost on full - that's the only way I could get near the doom type sounds these are now famous for.   Run it without the boost and you have a fairly ordinary tone stack with a bit of drive.   I would not recommend it as a preamp before your interface. 

Personally I don't think there's anything wrong with going straight into a DAW via a decent interface and then using amp sims with IR.  Might just be me, but I found the amp sounds quite passable, but hated nearly every distortion or fuzz sound on the DAW.

[GibsonGM]

Yeah, that's been my experience too, Andy. I will use specific 'amps' in the DAW to get what I'm after...maybe Cypress TT-15 for a more 70s rock thing, and a mix of IRs (SM-57 and maybe a U-87) to get the 'room size' and tone I'm after.     Some (many) of the amp sims respond well to a boost at the interface input, minding that you don't clip the interface (!).   

Everything is more controllable than mic'ing your cabs 'for real', and no hardware = no setup hassle.  No re-tracking because the distortion wasn't high/low enough and so on. 

That said, sometimes using your own rig to record IS more fun or just what you want to do (mojo...), whether you're going direct or actually using mics.  We do make pedals to use them    I think one quickly learns what the AMP and spkrs are actually doing in real life (like you noting that the Sunn preamp doesn't really cut it 'standalone'), and then you learn how to get that with software.   Like anything else it takes time, tweaking, and study.
Everyone should build a preamp and jam it out, just to do it, IMO!   

 

[mdcmdcmdc]

Similar wheelhouse to the Sunn preamp, this Orange OR120 based design looks like it could be fun:



Also, a +1 for god's cab - it's a tremendously nice sounding IR pack.

[amptramp]

^^^

Love the SRPP stage in the Orange OR120 above just before the emitter follower output.  There has been a lot of theoretical discussion of it but this is the first piece of equipment I have seen that actually uses it.

[Vlad7329]

Thank you all very much for your input!

After some more research I have found that EAE Model feT has positive reviews on using it as a preamp - into audio interface.

A quote from the pedal's technical manual:

"The Model fet may serve as an overdrive pedal into an existing amp, as a preamplifier
going direct into a power amp (alternately into the effects return of an amp bypassing
the preamp), or even into a DAW running a cab simulation. In any of these applications
it is equal suited to clean or overdriven tones"

PedalPCB have their own take on it: https://www.pedalpcb.com/product/pcb107/

So I decided to give it a shot.

But this pedal/preamp schematic utilizes 2N5457 FETs, and they are quite tricky to find in my location.

Does anybody have experience replacing 2N5457 in this type of application? I already googled alternatives, but would like some first-hand experience.
What d'yall think?