Need design help for new guitar amp project, payed help $$$

[Planobilly]

Hi Guys and Girls,

I need some assistance for the design of a new 100 watt guitar amp. The idea is to combine the functions and sound of two amps into one. The clean channel needs to replicate the sound of a Fender 1960's era Baseman and the drive channel needs to replicate the sound of a modern EVH 5150. There is some possibility for the need of the integration of a vintage Lexicon Alex effects unit. I have schematics of the Bassman and EVH 5150.

This is a bit complex to describe here. If you know someone who would like to take on this project please PM me with your phone number or I can give you mine. Please respond here if you intend to PM me.

I think this will be a fun project and getting payed to do it only makes it better!!

Thanks,

Billy

[Christe4nM]

Being an electric guitarist myself I can understand where you’re coming from. Yet though conceptually simple, in practice your idea is quite difficult to create for a number of reasons.

The first is that for you as a guitarist it’s all about the sound that you get. Hence you got this idea in the first place, am I right? Now any tube/valve amplifier builder will tell you that the sound you get comes from more than just the circuit on paper. The actual layout plays a big role too. We electronics engineers try to get rid of all undesired parasitic effects in our circuits, however it seems that guitar amplifier designers actually kind of ‘use’ these. They design more or less by ear first, and by electronic engineering standards second. I am confident that I’ll be able to put the circuits together, into a layout, and put the whole thing together for you, as could many of us here. Still I there no way I’m getting into a project like this, because I know beforehand it WILL sound different from the amplifiers which sound you want to replicate. Only an exact copy can do that for you.

That touches the second issue. Any electronics engineer will ultimately be able to transfer those circuit diagrams into a working amplifier. However, there is a big chance you will be disappointed by how it sounds to your ears, how you ‘feel’ the guitar’s response to the amplifier etc. These are quantities that aren’t measurable, and for many of us a step into audiophile/audiophool territory. (Even though I think in this particular case it might be more of a grey area between engineering and musicianship.)

The third problem is costs. By the time you get the amplifier you want, the material costs will most likely have exceeded the costs of buying both amps separately including an amp switcher pedal, wiring and the minivan to transport them to your gigs.
The reason is that everything will be a one-off: there’s no comparison with commercial amplifier manufacturers on price point since they buy parts by the many. Also you are going to get a first prototype and revisions of that prototypes before the result comes anywhere near what you want. All that costs quite a bit in parts. That’s material costs, let alone the labor costs… This is commercial design work and should be met with a commercial hourly rate imo. And count on many hours too, more than you think it will be right now. Probably more than twice.

I’m not saying it can’t be done. I do say: be very aware of what is involved in getting there, and be prepared that it won’t sound the same as “just those two amps with an amp switcher pedal”

That said, I do hope you find someone who is experienced in guitar tube amplifier design and able to get you there. As a guitarist, getting a great sound out of your setup is very rewarding in itself.

[Planobilly]

Hi Christe,

Thanks for your response. I am under no illusion of the potential difficulty involved in this concept. My best guess is the end results will be a compromise of some sort at best.

I have been ask to produce this amp for another guitarist. This artist is on tour worldwide and stages amp in several places in the world, in the USA, Europe, and Asia. He has requested that if this can be done, the requirement would be to provide at least six amps, perhaps more.

A little about me. I play guitar, repair amps, and build amps. I build reproductions of vintage amps from the 1950s and 1960s. These are one off  new projects and I generally repair mostly vintage amps. I have no background in electronics or mathematics. I am 70 years old and only have been doing this for less than two years. I am retired and started all this for fun. Like many things I have done in my life, I just jumped in the deep end of the pool and learned to swim. As you can imagine, this has not been an easy process!!..lol At this point, I can repair any tube/value amp I guess. Building reproduction amps has been fun and successful. My approach to electronics is more from a standpoint of physics than artist, but I clearly understand that in the final analysis sound and touch response is the only thing that really matters to the player.  Well...there is the comical insane "mojo voodoo" ideas that seem to pervade the music world...lol There is also the comical resistance by some EE type to use things like carbon comp resistors. Well, hell, I understand they are less reliable and very noisy but if thev produce the sound one is looking for then use them. It is our job as designers to give the end user what they want to hear.

Now, some of the realities. I can reproduce any schematic, BUT, the final results will not be an exact copy of the original and it will not sound exactly like the original. There are many reasons this is true. The main reason is that the components that were used in 1960  can not be acquired today. Close but not exact. Everything in electronics is a compromise....we are constrained by the laws of physics.

So...to the current issue. I need someone with EE skills and have no expectation that the schematic will necessarily  results in what is needed. I just don't have the skills to do everything that is needed by myself. I also am not sure that this can even be done as "one" amp. I am not even sure if one model of speaker can produce the two widely differing sounds we need to produce.

Too the extent that it is possible for a project of this nature to be successful, I believe that what is needed is a good EE to keep me from going down too many dead end  streets and be able to answer some "what if" technical" questions. I will do the experimental hands on work.

Final word...there is always a budget for everything in life. I don't know what the hourly rate for a EE of the type I need  or any idea really of how much time will be required. We are not dealing with some kid in his bedroom and also not dealing with a multi million dollar client...as best as I know at the moment. At any rate "it is what it is" and the cost will either be acceptable to the client or not.

Thanks for reading through this long winded post...lol

Cheers,

Billy

BTW..I assume by the flag on your post you are from the Netherlands/Holland/ Pays-Bas/ the low country...not 100% sure. I never know just what to call "Holland"...lol

[Planobilly]

Hi Blueskull,
The owner is sending me one of his EHV amps and I own several Bassman amps. The EVH will arrive in a few days. I have the schematics to both amps. I assume some of these parameters can be calculated or software modeled based on the schematics.

I have some limited skills in making the measurements you are asking about and a limited amount of test equipment. I have no skills with DSP.

Thanks,

Billy

[nctnico]

Some randon thoughts:
A DSP and a class-D output stage would be an interesting solution to pursue. The DSP can be used to mimic any kind of distortion envelope where the class-D stage (maybe open loop) would provide efficient amplification. The first step would be to fully characterise the guitar amplifiers. Still the case and the speaker also play a major role in how music sounds. That will be harder to capture because it will involve resonances of the case and non-linear behavior of the speaker. Last but not least that will somehow need to be translated into the new speaker case and speaker. This won't be a simple project and it will be hard to quantify if it sounds good or not.

[Planobilly]

Hi nctnico,

Thanks for the feedback. I am sure that a pure solid state amp could get close to the required sound. Having said that, I have personally never played a SS amp that truly sounded like a tube/valve amp. I have no personal bias for SS or tube/valve as I own and play both.

The actual answer to what the user wants is actually dead simple. He is happy with the EVH amp and happy with the sound of a Fender Bassman amp. The only question is how to get both amps in one "box" and on one circuit board and a foot switch to switch between the two.

Both of these amps have four 6l6GT output tubes operating AB push pull. I would assume building a Bassman preamp section on a redesigned board of the EVH could be switched to the EVH 6l6GT output tubes. I have not looked at the inverter design in the EVH yet, so it may need an additional inverter section also. We would be stuck with some speaker compromise most likely. The case of the Bassman and the EVH are both open back and about the same dimensions and may not present much of an issue.

LOL...I need to get off the internet and do some work as I have two new amps I just finished on my bench in the final testing stage before delivery. Work always gets in the way of interesting conversations here on EEVblog...lol

Cheers,

Billy

Cheers,

Billy

[edavid]

Some randon thoughts:
A DSP and a class-D output stage would be an interesting solution to pursue. The DSP can be used to mimic any kind of distortion envelope where the class-D stage (maybe open loop) would provide efficient amplification. The first step would be to fully characterise the guitar amplifiers. Still the case and the speaker also play a major role in how music sounds. That will be harder to capture because it will involve resonances of the case and non-linear behavior of the speaker. Last but not least that will somehow need to be translated into the new speaker case and speaker. This won't be a simple project and it will be hard to quantify if it sounds good or not.

This technology was developed years ago, and is widely available off the shelf.  You buy a "modeling preamp" and connect it to a flat PA system.  I doubt the OP is interested in this solution, since it would leave him with nothing to do 

[Christe4nM]

Warning: long post 

BTW..I assume by the flag on your post you are from the Netherlands/Holland/ Pays-Bas/ the low country...not 100% sure. I never know just what to call "Holland"...lol

Holland is what most people call it, after two main provinces
The Netherlands is the official name
Les Pays-Bas is how the French decided to call our country

Personally I prefer The Netherlands

---

I already said I play electric guitar myself, so I couldn't help but keep thinking about how I'd approach this. (Still won't be able to take on the project for several reasons, sorry)
One question you need to know the answer to is the reason that the guitarist in question doesn't want to use both amplifier as they come. Does that have to do with too much hassle moving two sets of amplifiers, or whichever. This is to figure out the core question behind the suggested solution of creating both into a single amplifier.

Still, some possible solutions in no particular order:

1)   
A modelling amplifier with flat response monitors and line out to PA. The way to go in that case is the Axe FX II from Fractal Audio. It receives high praises and several recording artists have switched to using this processor unit for their live tours. It is supposed to sound so close to the original amplifiers it cannot be distinguished albeit in a recording studio maybe. It’s dynamic response to the way you play is also said to be very close to a real tube amplifier. Over at The Gear Page for example there are many posts about it. (One warning about that forum: there are quite a few examples of snobs and audiophools over there, so read between the lines to figure out who knows his/her stuff and who just has too much money, but YMMV)
I also can understand that there are many players out there that want the 'real deal' tube amplifier behind them on stage and simply don't want a modelling processor, however good it might be.

2)
One amplifier head each of the Bassman and the EVH 5150. Maybe put them together in a single flightcase. Use something like a Radial Switchbone amplifier selector to switch between the two. Depending on the guitarists requirements you can use one speaker cabinet, or more than one if different speaker types (V30’s, greenbacks etc) are required.
You can always go out of your way and create a complete ‘rig’ where everything sits in one big flightcase on wheels, effects all through a midi controlled looper, amplifier channel switching too; and the guitarist only has a midi controller switchboard in front of his feet.

One close example I could find would look like this:


(You'd still need to turn a Bassman combo into a head + speaker cabinet)

3)
Basically the same, but now you try to get the circuits of both amplifiers into a 19” rack sized chassis for easier building.

4)
Design the desired amplifier into a single chassis.

A few things to figure out before getting started:

Power supply
tube amp power supplies aren’t the most well engineered actually. But somehow those inefficient, not really completely DC power supplies play a role in what guitarists like about a certain amplifier. (The VOX AC30 comes with a tube diode, which for modern electronics engineers is plain weird, but for guitarist seems to be great for the overall sound produced.)
In other words: figure out the similarities and differences between the two power supplies. From an engineering point of view, you’d want to combine everything into one power supply circuit and one single transformer, if possible. It might result in that you need a custom made transformer in that case.

Preamplifier circuits
I’d suggest you keep those as close to the original as possible, including physical layout. Inevitably you need a few signal relays to switch signal paths between either preamp circuit. I’d suggest to find pictures of the inside of main brand channel switchers like Mesa Boogie’s or Bogner’s top of the line models to see which relays they use.

Power amplifiers:
Now you might already know, but the power amplifier including the output transformer does quite a bit on shaping the ‘color’ of the sound. Worst case you’ll need to recreate both amps completely from power supply to preamp and power amp including using the same transformers as the original or aftermarket replacements. So one thing to test is what it sounds like if you use the Bassman’s preamplifier’s output into the EVH’s power amplifier stage. If that sounds OK, you only need to replicate the EVH’s power amplifier stage. (If not, than you might really be better of trying to get two separate amplifiers in a single space and only switch where the guitar/speaker signal goes to/comes from.)

Effects loop
Placed between pre- and power amplifier; you probably need a buffer stage before the effects loop output and a likely a buffer at the return. Being part of the signal path their circuits and layout will somewhat shape the sound. You need to decide whether you want the effects loop to be a parallel circuit or a serial circuit, or either but switchable. Maybe copy this from the EVH circuit?
IMHO it is best to keep the effects separate from the amplifier. You can always put the effects processor into the same physical case of course.

Speaker choice
This is completely up to the guitarist’s taste. With a bit of luck only one type of speaker suits his/her needs for both clean and overdriven sounds. In any case I'd suggest separate cabinet. (I do know of some guys who use two sets of speakers in a single 4x12 cabinet. Not sure if he uses all together or in two pairs with two separate inputs to the cabinet)


I hope this helps you / your-designer-to-be to get started somewhere.

Since you have experience building replicas you might get a lot further by yourself than you think: say you are able to create a system design where the main parts of the circuits are just 'existing modules' that need the right interconnections. In that case you might be able to create the replica circuits yourself and only need a third party for the right interconnects and channel switching design. Just thinking out loud here.

Anyway, this is where I sign off. Best of luck!

- Christean

[Planobilly]

Hi Christean,

Thank you ever so much for the intelligent, to the point, and useful post. The ideas are dead on point. Perhaps I will not need as much help as I thought. We will see on that issue.

Again, thanks for your kind input.

Cheers,

Billy

[tautech]

Perhaps I will not need as much help as I thought. We will see on that issue.

And if you do I suggest Tim is your man.
https://www.eevblog.com/forum/profile/?u=92330

[Planobilly]

Thanks Tautech,

I will ping Tim at some point in the near future.

Cheers,

Billy