Is it possible to get "tube sound" with just a tube preamp and chipamp output?

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Is it possible to get "tube sound" with just a tube preamp and chipamp output?

After looking at the tube-buffered inverted gainclone, and the high input impeadance of the LM3875 and LM3886, it led me to wonder: How hard would it be to make a basic tube preamp to retain the "tube" sound, while using a cheap and powerful chip-amp like the LM3886 or LM4780? I found the following preamp design with line-out; I'm wondering if it would work well as is. If it could be simplified to use a single tube, that would be ideal, but I'm not picky. (This is my first attempt at anything with tubes, and I don't even play guitars. However, my friends do.)

Linky to preamp:
http://www.kbapps.com/audio/tubeamps/preamp.html

I'd likely be using standard 4-ohm or 8-ohm guitar speaker drivers; I don't know much about speaker building, but one of my guitar-playing buddies is pretty darn good at woodworking. Would I want to use a ported enclosure, dipole, open bafle, or a simple "horn" style enclosure for the driver? I'd likely be using one like this:
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-473
With a standard LM3875 chip-amp running at 30W, it should be freakishly loud; it's got a 100DB sensitivity!

Hmm....I wonder how well 16 of them in a 4x4 line array would work?
 
Not sure what you mean by tube sound. But if you mean the sounds produced by turning it up past 10, then in short no. Overdrive harmonic characteristics produced by "tubes" are mainly in the output section class B with transformer. I think John Murphy has a good explanation about this on his RTA site.
 
To be quite honest, I'm not sure either. All I know is that tube amps do, in fact, sound somewhat different from solid-state amps.
A lot of the desirable noise does come from raising the preamp level so high as to make the output stage clip. If I read the schematic correctly, the second stage of the tube preamp does this by itself. That said, why not just use an output transformer and buffer the gainclone's input? It would'nt be making any changes to the sound; merely making it much, much louder.
 
Tube amps like any other include preamp and power amp. The overdrive distortion in each is a separate phenomenon. If you make a tube preamp, you will get the tube nuances of a tube preamp circuit. What you will NOT get are the dynamics of a tube power amp, and certainly no power tube distortion.

But your tube preamp will not sound like your solid state preamp.

keep in mind that you might listen to recordings of a tube amp played through your solid state stereo system. it still sounds like a tube amp.

Your hybrid design has merit, but it won't sound like a full tube amp.

Consider that even within all tube amps, when you encounter clean and overdrive channels, it is the preamps that are generating the different sounds. of course a tube power amp adds that certain something to the whole sound, but running into a SS power amp doesn't begate the tubiness of the preamp.

Most tube amp players don't get into power tube distortion anyway. it only occurs when you crank the amp to its max power levels.
 
If the distortion you are looking for is indeed created by the output transformer been overdriven, it might be possible to emulate the effect by using a simple interstage transformer. Something relatively cheap, or even a small mains transformer might work. The quality is not as critical because you don't need top or bottom reproduction. If using mains transformers you would need to go parafeed.
Consider a step down arrangement and drive the primary hard to get the maximum distortion. This should be a cheap and interesting experiement which others might well be interested in the results achieved. You could use a range of transformers to see what effect you get.

Shoog
 
You might also consider that a LOT of 'tube guitar amplifiers' actually are solid state EXCEPT for a single valve/tube - the Fender one in another thread uses a double-triode strapped as two diodes for clipping on the overdrive channel - and that's the only valve/tube in the unit.

Other 'tube' amplifiers have been produced with the valve not even connected, just a resistor feeding the heater to make it glow - a lot of it's just a marketing scam, aimed at gullible guitar players!.

However, adding a valve to your preamp will allow you to get the 'tube/valve' sound, it's up to YOU if you consider it worthwhile (some do, some don't). At least building it yourself you're not getting robbed by the massive cost increases!.
 
That's odd... copy and paste the url, it should open then.
Still, if you can't find it, go to the 2nd or 3rd page of the Solid State forum, "Single mosfet amp" :)
Oh, if you want real tube distortion (16%) i can give you the values for the ECC86 (one of the reasons why i wanted to make a tube-power follower hybrid was a guitar amp)
 
Simpleton said:
That's odd... copy and paste the url, it should open then.
Still, if you can't find it, go to the 2nd or 3rd page of the Solid State forum, "Single mosfet amp" :)
Oh, if you want real tube distortion (16%) i can give you the values for the ECC86 (one of the reasons why i wanted to make a tube-power follower hybrid was a guitar amp)
That would be great. I'm not opposed to using a high-voltage tube, though; I'd like to try the trick with the carbon-composition resistors. On the other hand, I've got a 25VCT transformer handy, along with some 12000uf caps (36000uf should be enough, I'd think) and assorted other random components. I love the simplicity; I'd also think that it might be possible to overdrive the transistor with the tube to make the clipped distortion so desireable in an amp.

Out of curiousity, would it be possible to, using a (much) smaller transistor in the circuit you had shown, reduce the power use so that it could be used with a chipamp? I hate to be so narrow-minded, but I want to build something LOUD, without the high cost of a powerful class-A amp. (Those power transistors are danged pricey.)
 
Spasticteapot said:

That would be great. I'm not opposed to using a high-voltage tube, though; I'd like to try the trick with the carbon-composition resistors. On the other hand, I've got a 25VCT transformer handy, along with some 12000uf caps (36000uf should be enough, I'd think) and assorted other random components. I love the simplicity; I'd also think that it might be possible to overdrive the transistor with the tube to make the clipped distortion so desireable in an amp.



You seem to have it the wrong way round?, it's the TUBE/VALVE that needs to be overdriven, if you overdrive the transistor you get transistor distorion.

Out of curiousity, would it be possible to, using a (much) smaller transistor in the circuit you had shown, reduce the power use so that it could be used with a chipamp? I hate to be so narrow-minded, but I want to build something LOUD, without the high cost of a powerful class-A amp. (Those power transistors are danged pricey.)

If you're wanting LOUD, you don't want class A, nor do you when you're looking for distortion anyway.

To recap, you're looking to build a LOUD guitar amplifier, and you're wanting to incorporate a valve stage to give the overdriven valve sound. A suitable size chipamp would do for the power amplifier, and use opamps for the preamp, with a valve stage added in the preamp (either switchable, or a seperate input) to give valve overdrive.

Perhaps a simpler option would be to copy the preamp stage of an old valve guitar amp?, a single double-triode should probably be enough, and feed that into a chipamp.
 
Nigel Goodwin said:


You seem to have it the wrong way round?, it's the TUBE/VALVE that needs to be overdriven, if you overdrive the transistor you get transistor distorion.



If you're wanting LOUD, you don't want class A, nor do you when you're looking for distortion anyway.

To recap, you're looking to build a LOUD guitar amplifier, and you're wanting to incorporate a valve stage to give the overdriven valve sound. A suitable size chipamp would do for the power amplifier, and use opamps for the preamp, with a valve stage added in the preamp (either switchable, or a seperate input) to give valve overdrive.

Perhaps a simpler option would be to copy the preamp stage of an old valve guitar amp?, a single double-triode should probably be enough, and feed that into a chipamp.

Which is what I intended to do in the first place! (Can you reccomend one in particular?)
Thanks for clarifying the overdriving thing, though; that had been confusing me for a while. (Sue me, I'm new to this).

That said, I think I'm going to try my hand at the amp design below, as I already have most of the parts. It's dead simple, and with a suitably efficient speaker, it might make a nice bass amp with a simple tone control section. Not loud, but I'd learn something about using tubes, and it would be cheap, too. (I might actually have one of those very tubes handy thanks to a lot I picked up from a garage sale!)

Also, could anyone link me to one of the Fender amps that uses a SS output stage?

Much thanks from a newbie,
Joe.
 
Let me see my notes... ah, here they are!

For a low voltage valve line stage, with an ECC86 (you can try an ECC88 for more distortion), you have:

Grid signal excursion : 1Vpp
Idle voltage: 8V
Idle current: 0,9mA
Vout(rms): 3,18V
Rcathode: 5,6KOhm
Ranode: aprox 4,4KOhm
B+: 12V
Distortion (2nd harmonic): 16,6%

This, together with a chipamp that runs o at 12V should get you running ;)

If you use a similar 2nd stage, fed from the 1st; the higher grid excursion will make even more distortion. Also consider that a guitar has nromally 1,5Vpp output when played strong, so the first stage distortion figures are only for a lower input ;)
I advise to use an opamp buffer stage following the tube stage(s), before the power amp.
 
Is it possible to get "tube sound" with just a tube preamp and chipamp output?

An interesting study, with blind tests indicate that you really can't tell a the difference between tube and SS:
http://milbert.com/articles/TvsT/tvtiega.html

And if you really want to get transformers in the circuit take a look at the results found here:
http://www.ssguitar.com/index.php?topic=75.msg785#msg785

In any case, you can build a small tube amp, with xformers and build it in a box with a mic that you play into a big SS amp.

Or you can add in a speaker simulator to the tube amp, and run a direct out to your power amp.

Many preamps - have got it "right" and do have a "tube" sound that everybody wants.

Here's a popular theory on tube sound.
http://www.paia.com/tubesnd.htm
They always show sine waves, but a guitar is a complex waveform. The fundamental may clip, the the high frequency has reached clipping. The effect is bass compression and HF continuing to gain DBs. Tube amps don't amplify highs very well were a SS amp does. So a trick to make a SS amp sound better at clipping is to retard the highs.

Or better yet - round up a few amps and effects. Stick them behind a curtain and have some friends adjust the sounds and you try to pick what you actually hear as sounding best.

If you going to DIY - skip the tube and check out the many SS distortion schmatic. You'll have more fun, you might find or create your perfect sound that nobody else has.
 
An interesting study, with blind tests indicate that you really can't tell a the difference between tube and SS:

For clean sound, it is really10x hard to tell difference. But when playing with distortion, tubes and SS are very obvious.

As mentioned by others, tube crunch involved a lot in combination of the power tubes, output trans and cone breakup. Simply overdriving preamp section (like marshall valvestate) just doesnt cut it (to my ears).

However, if rock and roll is not your cuppa tea, hybrid can be more than statisfactory. Fender bassman is a good preamp to copy, IMHO.
 
I agree with the previous post, simply overdriving a preamp tube just isn't going to cut it. There are at least three sources of main distortion in a guitar amp and you are only addressing the simplest one. Simply raking up the 2nd order harmonics is likely to produce a horrible sound.

My suggestion of introducing an interstage transformer is simple and will offer at least two types of the distortion you are looking for. It also gets around the fact that the output of your tube stage is likely to be much to high to drive a chip amp with the result of horrible chip amp distortion. Clipping a chip amp is not a good thing so you need to keep the input well bellow clipping the chip amp. The other alternative would be to use the valve as a cathode follower - but this reduces distortion rather than increasing it.

Using a 10VA mains transformer in a parafeed setup, with a 240V to 6V step down ratio is likely to saturate fairly easily, cost next to nothing and give a useable input to the chip amp for a sensible tube preamp output.

Shoog
 
Think of it like this.
You can play back a recording of a good "sounding" guitar on your home stereo and it will - "sound good". Your home stereo is a clean amp. You're hearing the signal in, but louder. Warm in = Warm out, crunch in = crunch out, clean in= clean out. No sense having the amp and speakers color the sound - they should just reproduce it.

Treat your guitar and signal processing as if it's the recording.
Get yourself a good power amp, like a hypex, and concentrate your efforts on the signal processing.

Also check out the software route which is popping up in every studio you can imagine.
IK "Guitar Rig"
NI "Amplitute 2"
Or the tons of freeware and shareware plugins, for example:
http://www.voxengo.com/downloads/?highlight=boogex#boogex

All IMHO, 2 cents worth, ...
 
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