A Black Box to Solve Everything

Tubes vs. solid state?? There's a thread out right now about this exact question (there always is), but I didn't want to take it off subject. So my question is; is there a device that could go between the preamp and amp that has variable harmonic distortion capabilities? I know there are tube buffers, but they are not really addressing the point because they use line level signals and don't have the distortion of a good 300B tube being pushed beyond its limits. My thinking is that of a black box with switches and knobs to adjust harmonic distortion to mimic different tube types. It would also have to have a bypass switch so we could readily and quickly A/B the thing. Any ideas?


Nifty idea, but I think those who enjoy tubes already know the sound they like best and have bought appropriate tube gear. Not at all certain as to what’s involved technically to mimic the harmonics of a myriad tube types, but it could be a lot of R&D and manufacturing loot for a device that would most likely see limited sales, relegated to a very small percentage of the world’s consumers. But, if you charge enough and people are willing to pay for it...

High risk, though. Maybe.

Can’t win a prize if you don’t buy a ticket!

Then again, can't lose your ticket money if you do and lose.

Can you tell I had waffles this morning?!

Yeah, I guess it would go the way of the QOL Completion Device. It would be cool though for people with solid state amps.

Sounds like something Bob Carver could create in a week!

My Carver Tuner, and Carver Cube Amp both had unique patented features that did what he said they did. He’s unique himself.

I think he said, pick any amp, he could create that amp's sound. Pick another, he could match it's sound

Yes, he called it the transfer function. So we need him to make a variable transfer function box.

@koestner It doesn’t solve your inquiry completely, but Modwright released his Analog Bridge about nine months ago. I was one of the beta testers for the unit. It is meant to be placed anywhere you desire, especially between preamp and amp if applicable, or just between a source and preamp. It’s not cheap, but it is very high quality and offers a good amount of flexibility in the three tube types it supports. 


In pro audio there are any number of devices and even more software products that emulate tube distortion.  Some actually use tubes, but most use DSP to achieve their sound.  They are widely used as an effect.

A company call Line 6 has a very well received line of guitar amps that DSP model a variety of tube based guitar amps.  They might not exactly nail a specific amp, but they get pretty close and can sound quite good in their own right.

The quest for the holy grail in guitar amps (SS amps that mimic tube amps) has been going on at least since the 70's when companies such as Gibson, Peavy and Yamaha offered such products. You can now buy a tube Fender Deluxe Reverb or its lighter, more affordable, SS counterpart. There are also numerous guitar effects pedals that aim to do the same. Kemper seems to be very popular with pro guitarists, currently. 

Tubes for guitar and tubes for hi fi have very different objectives. Audible distortion for a guitar amp is a desirable feature, not so for a hi fi amp. Two different worlds for the same technology.

Adding anything in the path of tube gear for hi fi runs the risk of masking the transparency that many hi fi tube lovers crave. It’s not uncommon to hear of SS hi fi amps that emulate the tonal balance of a tube amp (aka "tubey"), but they don’t necessarily have the same level of transparency that a good tube amp has.

Does your black box idea pertain to guitar, hi fi, or both?


I am not aware of any commercial products intended for HiFi but I know of a guitar effects pedal, Mercury IV (harmonic boost), by Spaceman Effects that has a dial for generating even order harmonics. I imagine two could be used in dual-mono, which would meet the OPs requirements. They are on reverb for around $300. Something like the Switchcraft SC600 Dual Adapter Box would enable you to convert to 1/4" TS/TRS to RCA and back.  I own this pedal and love it for guitar.  The pedal can color or be transparent depending on the settings and gear on either end of it.

It isn't as simple as adding higher tube distortion. The Carver concept of transfer function actually works though, to  signmake a solid state amp sound like a matching tube amp, which is exactlly matching the electrical output of two amps. But I suspect the reverse won't work, matching a tube amp to a solid state one. Carver did the comparison matching one of his amps to I believe a Conrad Johnson. The listening panel agreed(after 2 tries I think). And I personally spoke to Gordon Holt and he confirmed that Carver suceeded. 

About a year ago I watched a video (on YouTube iirc) in which Nelson Pass spoke about an amp he was working on, one that was intentionally designed to add harmonic distortion to the input signal. He also explained the rationale for doing so. I could be mistaken, but I think it may have been in an interview with Steve Guttenberg, recorded in Nelson's listening room.

Nelson Pass's DIY Nutube preamp kit allows for adjustment of distortion. Here is a description from the design document:

"The attraction of the Nutube in an audio circuit is the Triode character, allowing adjustment of the distortion by operating the device in a specific voltage/current load line. For a given amount of current through the tube there is a point at which the square law effects of Cathode current and Plate voltage cancel, nulling out 2nd harmonic distortion and leaving 3rd harmonic. This is the lowest output distortion setting.

If you increase the Plate voltage, the circuit takes on a positive phase 2nd harmonic distortion character, and if you lower the Plate voltage it has negative phase 2nd harmonic. These distortions increase as you adjust the Plate voltage farther from the null point"

THAT'S the one @clio09! So it's a pre-amp, not an amp. I'd love to hear Nelson and Ralph Karsten discussing the related subject together. Roger Modjeski too, but that's not going to happen.

Who wants their hifi rig to push a 300B to distortion? Hmmm...Pass is into "tube like" sound as illustrated by his XA-25. I have one and it sounds great but not particularly like tubes to my ears...I switch between that amp and a Dennis Had SEP.  SS guitar distortion pedals into a tube guitar amp can sound amazing. I have various ones including my old 1980 ProCo Rat that is my fave...a supposed magic Motorola LM308 transistor is the key to that tone.

I guess you could try a unity gain tube buffer which is normally used for impedance matching between components, I remember reading somewhere there was even a SS device which emulated the 2nd (and others?) harmonic of a tube and the distortion (magnitude of harmonic) was applied in variable steps. I can't recall where I have seen it, I will have a search.

Such digital signal processors already exist.   I've seen them and used them.   They can mimic tubes, all sorts of distortion, and create a unique sound in many ways:

The secret of the perfect sound

I'm not trying to be a wet blanket here, but why would I add another component in the chain? I happen to own multiple tubes, so play what you have, and be happy! JMO.

For you DIYers, Ethan Winer provides directions on how to build his Mojo Maestro box, which he states is: "...a simple box that can add distortion ranging from very subtle—to add a little grit to a sterile sounding instrument track or to help “glue” a full mix together—through severe clipping to add “mojo” or “dirt” to any musical source that will benefit. The Mojo setting also switches in a capacitor to gently roll off the highest frequencies to counter the added buzziness. With gentler settings, the overall effect is similar to running music through a tube amplifier or an analog tape recorder but without the added tape hiss and flutter.": https://audioxpress.com/article/you-can-diy-build-the-mojo-maestro

Many of us have used tube preamps with SS amps to bring some desirable tube qualities to our systems, and others use SS preamps and tube amps. In 1973 as a college kid I ran a PAS3x with an H-K Citation 12.  Later a Motif FET pre with av MV55 amp.  All worthy experiences.  There is no single silver bullet, for this or any other system voicing conundrum.

@bdp24 Yes a preamp and a reasonably easy kit to build. Nelson is brilliant with solid state devices and while Ralph and Roger are/were known for their brilliance with tubes, Ralph has now demonstrated he can manufacture a solid state amp with similar distortion characteristics as tubes. Somewhat of a little known fact, Roger's first amp to be manufactured was the one he designed for the Beveridge 2SW speaker. It was a solid state amp designed specifically for the woofer section. This required him to develop the RM-3 active crossover to act as a frequency dividing network as the 2SW required biamping. The RM-3 also used sold state devices.

Getting back to the B1, Nelson's choice of the Korg Nutube is interesting and I'm sure was selected to support his circuit requirement to allow for the adjustable harmonics. However, it's probably the worst tube I have ever dealt with. Many examples of this tube are extremely microphonic. I went through 3 of them building that kit and none of them were quiet enough. So I never could really test out the adjustable distortion feature.


Tubes for guitar and tubes for hi fi have very different objectives. Audible distortion for a guitar amp is a desirable feature, not so for a hi fi amp.

FYI, distortion ("overdrive") is not the sole goal or attribute of guitar amps/pedals that attempt to mimic tubes!  "Clean" tube tones are as prized as "dirty" tube tones as is the ability of some of them to mimic a variety of amps that are associated with different types of tubes. Some examples include but are not limited to: 6L6/6V6 for Fender, EL34 for Marshall, EL84 for Vox, etc. This seems quite in line with what the OP states:

My thinking is that of a black box with switches and knobs to adjust harmonic distortion to mimic different tube types. 









I have a BSG QOL Signal Completion processor in my system and I use it most of the time. It is not adjustable and I would not describe it as adding any sort of tube distortion. It affects the phase information in the signal and adds depth and focuses the imaging. I suppose one could describe these effects as tube virtues but I've never heard any piece of tube gear that has such a dramatic impact on the signal. I also have a Yaqin tube buffer which produces a very subtle difference - nothing close to what the QOL provides.

BTW, I've experimented with several signal processors and the QOL is the only one I use. It adds a very nice effect.

Isn’t this whole conversation a bit ironic? Trying to create a high tech solid state device to mimic the natural, 3 dimensional sound of a simple tube based circuit?  I always thought that the primary reasons why good quality tube amps can sound so good is the relative simplicity of their design w/far less components on the signal path & the high voltages they can swing? Not sure if an additional “ black box” would help this ?

Indeed, @jonwolfpell. I wince when I see someone describe an amp as adding "tube warmth" to the sound. That’s not what good tube amps do; what they do is not create the "cold, hard, dry" sound of bad solid state. I always loved the term J. Gordon Holt used to characterize the sound of the best tube amps: liquidly transparent.

I vividly recall the first time I heard "grain" in the sound of electronics. I was already aware of the term and concept from photography, and to then hear tiny little "clumps of sound" in the sonic "picture" a hi-fi was creating (one with solid state pre and power amps), in contrast to the grain-free liquidity of the sound the ARC system (pure tube, not hybrid) I was comparing it with was creating, was clearly audible.

The appeal of tubes to me has always been not what they add, but what they don’t.

@nonoise ....I don't want one of Those.

I'd have slapped it through the desk AND the floor beneath it X times by now....😏


I also have a BSG QOL, and I wasn't implying that it could do this task I am seeking, but rather this device I am inquiring about will probably end up as popular as the QOL. That is to say almost extinct. 

Listening to tube amps, I don’t hear the effects as desirable like some people do. It does seem though that a solid state amp can be made to sound much more like a tube amp than the other way around. So, I’m told you can run the output of a low powered SET tube amp through a voltage divider and into the input of a solid state amp, and then run the solid state amp out to the speakers. What you get is the sound of the tube amp sans its interaction effects with the speaker, which it is now buffered from by the solid state amp. So you’re hearing your tube amp playing into a very stable and high impedance load, which is what it would prefer. The real, messy impedance load of the speaker is much better handled by the solid state amp.

If you're looking to find what distortion signature you like here is an exercise I went through myself. In a DAW, I used Reaper, instantiate a tone generator plugin, saturator and an EQ with an analyzer. All on the same channel.  I used Fab Filter Saturn 2 and Pro Q.  All of these have a trial period long enough to do these tests. Start experimenting with tones to see what the harmonics look like. Make some presets with varying degrees of Second, Third etc...harmonics added.  Then play your music through your presets.  You'll probably develop a preference.  Then select equipment that tests similar to your preference.  

Generally speaking, if the signature is plainly audible on familiar music it's most likely a poor design or broken. Differences should be very subtle in well designed/built gear.