Is it possible to get "tube sound" with just a tube preamp and chipamp output? - diyAudio
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Old 6th May 2006, 02:28 AM   #1
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Default 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/showd...number=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?
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Old 6th May 2006, 05:42 AM   #2
infinia is offline infinia  United States
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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.
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Old 6th May 2006, 06:09 AM   #3
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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.
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Old 6th May 2006, 08:46 AM   #4
Enzo is offline Enzo  United States
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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.
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Old 6th May 2006, 12:56 PM   #5
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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.

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Old 6th May 2006, 01:04 PM   #6
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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!.
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Old 6th May 2006, 01:22 PM   #7
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Check this thread of mine.
The tube is a line amp feeding the power follower. You can see some really nice triode distortion :P (iirc, some 5%)

http://www.diyaudio.com/forums/showthread.php?threadid=78576
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Old 6th May 2006, 01:46 PM   #8
Bazukaz is offline Bazukaz  Lithuania
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Hi,
Here is an interesting article how to get lots of second hamonic distortion.All you need is a carbon composition(not film) resistor and high voltage across it :

http://www.geofex.com/Article_Folder...carboncomp.htm
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Old 7th May 2006, 01:27 PM   #9
Tyimo is online now Tyimo  Hungary
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Hi Simpleton!

Quote:
Check this thread of mine.
I can't find that thread! I am very interested for a good tube line amp for feeding my power follower!

Tyimo
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Old 7th May 2006, 01:32 PM   #10
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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)
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