Hey, search out 'blue tone" amplifiers... they are successfully doing what you want to do...

aha! I just KNEW it was too good to be true... I'm no math whiz, but something about the amount of power being thrown at it for the return did not add up... I was hopeful for a low parts count discreet power amp project that would sound halfway decent and still deliver some decent amplification (you know, bigger than ten watts!)... Anyone know of a proven circuit like this? Something fairly simple and not ridiculously expensive that a relative newb could fool around with? I still might build this thing to see how it really does sound...

I found a schematic for a ridiculously simple FET-based power amp on this site: http://www.oliveaudio.com/index.php?page=3
The schematic I'm looking at is the UCLA3 (I can't figure out how to attach a picture to this post). The site says it's capable of 17w with a single +60v DC supply! Does this seem right? If so, this could be a ridiculously cheap and EASY power amp project for ANYONE! Combine this sucker with any of the ROG preamps (the ROG "distortion" pedals are actually preamps) and you'd have a killer small amp that would sound really tubey!

Thoughts anyone?

Teemuk,  I noticed that you didn't comment about a speakers rated SPL level... I have read at various sources that an SPL of 95-100 is seriously desirous for amplifier speakers. I seem to remember that the SPL (sound pressure level) is a measurement of air pressure created by the speaker movementtaken at one watt at one cm from the cone??? is this right? anyway, what is the minimum SPL one should consider? for example, I have some speakers with an SPL of 86. Are these not powerful enough for use with a guitar amp?

Hi all... I have now uploaded a video of a head to head of this preamp, both set to a clean and to a dirty tone, with the built in preamp in my PA... There is nothing at all in my effects line. It's just harp (Bb Blues Harp), mic (simple lo-Z dynamic element), preamp (either the SSTS pre, or the PA pre), PA. Nothin' else! Take a look at this one, I really think people will hear what this thing is capable of...
 
http://www.youtube.com/watch?v=f6OcNZjEu0U

If you like it, let me know!

Cheers,

Isaac

Thanks for your comments (and compliments on a tidy build)! Yeah, after the fact I relized I should have just run it into my PA amp, and comped it with the PA's mic preamp... When I get a bit of free time, I'll definately make another vid of that... I used the schematic for the "original" version, not the schematic with all the tone circuitry. It's the schematic that comes with a PCB layout. Be sure to note that I opted to add the "drive" pot, which is an extra bit of schematic you can download lower down on that page... The box i used is a steel cashbox--the kind used at low budget "community events" that only has a small slot on the top, and a generic keyed latch. It's of fairly thin metal (maybe 1/8'' at most), so I probably wouldn't use it as stompbox, but it was great for this project (and it's really easy to change the battery). I got it used at the thrift store for $1.
   Yeah, I'm not to hung up on obtaining "true tube sound", but I definately am on the quest for a SS design that has very smooth ("tubelike", if you will) distortion characteristics, and that does not use clipping diodes (just don't particularly care for the way they sound)... So far, I'm really happy with this design, but I thought I'd get some opinions of people that have heard a lot more devices than I have... My next projects will all be based on various ROG fet-based pedal designs (the professor tweed, the odie, and the fetzter valve to be exact)... Thanks for you input! I really appreciate it! And stay tuned for the next vid!

I'm a relative noob myself, but we've had a great discussion about using those ROG pedal designs as preamps in the thread "Preamp for lm 3886" that here in this forum. Several of the ROG designs are available as kits from OLC. You can also get a kit from Tonepad.com for a similar JFET preamp to the one you referenced...
   The bottom line (as I have been able to figure it out) is that YES you can use those tube-emulating pedal designs as preamps. They should all run at 12v with out any design modifactions (since you use adjustible trimmer-resistors to set the bias for the transistors in all the ROG designs, and I believe that the bias voltages would be only thing you need to change to make them run on 12V instead of 9V)...
  I'll let the more experienced members here add to my comments if I have mispoke...

Hi All,

   I built this "Solid State Tube Sounding" preamp from a schematic found here: http://members.tripod.com/gillcar/id24.htm, and I reported it earlier in a thread over in the newbies forum.
   Well... I finally got around to recording how is sounds! I posted a video on you-tube of me playing through it with a couple of different effects. You can check it out via the following link: http://www.youtube.com/watch?v=zVD97PAx4qc
   I'd really like to hear your feed back as to how it sounds. Although *basically* know what a tube amp is supposed to sound like, I have never owned one, so I am not sure how close this preamp gets. I do think that it sounds really good, and definately sounds *better* to my ears than a standard solid state preamp... Now, the question of it sounding "tubey"? Well, I'll let you decide!

Jaxon, take a look at active thread "preamp for LM3886" over in the preamp forum. We are currently discussing just this issue!

Quote from: syndromet on February 27, 2008, 04:10:11 PM

Quote

Then, I guess I'd have at least a gain pot per channel, and perhaps a couple of switches (for grit and whatnot, depending on the circuit I would choose). This way, you can have each channel adjusted the way you like it, and when you switch into it, you don't have to fiddle with any pots. Perhaps a volume pot per channel is not necessary if I have a master volume control right before the power amp? I'd stick a tone stack after the preamp stage, so it would be a common setting.

This is a hard one. What makes the JFET emulators sound somewhat simular to the emulated circuit has a lot to do with frequenzy shaping and tone controlls. Leaving the tonestack after the circuits, and finding the values wich sounds good with all preamps could be a PITA. Even if you find a tonestack wich does the job great, you will probably loose some of the caracteristics of the preamp ith just one tonestack.

Quote

    I totally see your point here. I was thinking to avoid the "mess of offboard wiring" since this is where I usually screw up! But I did not look closely enough into the justification of why each circuit uses the tone controls it does have... I also agree that it would be best to have each channel totally set up the way you like it (gain, vol, AND tone), so that when you switch to it, you get just what you want with absolutely no need to tweak any settings!

great choice of preamps. Personally i would dropp the BM Ruby for an eighteen, simply because I think the Proffessor tweed an the BM Ruby sounds a lot like each other. I also think the eighteen is the best pedal designed by rog ever...

   I haven't built a proffessor tweed yet, so I'll take your word on it's similarity to the BM ruby (which I have built and really like). I took a listen to the Eighteen over at the ROG sound sample page and it does sound really good! It also seems like a pretty darn easy one to build (why I also like the odie and the prof tweed: great sound and simple builds). So I think that I'll have the fetzer valve up front (possibly switchible from unity to 20dB, like you say) then the switch to bufferless verisons of the Odie, the Eighteen, and the Tweed, and a clean channel (totally passive, except whatever effect of the fetzer input buffer).

[/quote]
I would personally go with the 3886 if I were to use one of the lm chips. I recomend you to look at the kits at www.41hz.com . I built an AMP5, and it sounds great with guitar. There is almost no need for a heatsink, and they recuire a lot less power per watt than the lm chipamps. This means that you will be able to build a lighter and more portable amp with a higher output.

[/quote]

    I was thinking of the lm3875 because of the wattage rating of the speakers I was planning to use are only 30w (and 8ohm)... I do not wish to over power them! I've looked at the "class T" kits over at 41hz, and I'm glad that you have given one a shot... It's good to hear that they make good amps for guitar... Another option that I might take is to use a tda7396. This is probable a chip that never gets used for instrument amps, but it does have some interesting possible advantages. It's a class AB, in BTL configuration, so it's capable of high output wattage even though it's a single supply chip (It's meant for car audio).  The datasheet indicates that I can get about 30w into 4ohm (my two 8ohm speakers in parallel) powering it at +15vdc. I have an old ATK computer power supply sitting around that I can use to get that voltage quite easily, nicely regulated and at any ampage I'd like. I can also plenty of other voltage levels out of it to power all the preamps! It would save me a crapload of time, and an even larger crapload of money, not having to build all the powersupplies and rectifiers I'd need if I were to use a traditional transformer.
  These chips are going for $2.29, and the circuit will only require something like 6caps and one resistor(I'll post a schematic if interested). Can't get too much simpler than that!
  Anyway, I think I might start to build this one over the weekend... At least I'll start puting the preamps together... Keep the advice coming though, it really helps!

I was just perusing Syndromet's transistor pinout encyclopedia that he just posted on anther thread, and I noticed that the Jfet's used in most of the ROG circuits (mpf102/j201) have the same pinout as all the MosFets he listed. I know the main differenced between the BJT type of transistors preclude them from being used when a FET type is called for, but what is the difference between Jfet and Mosfet in terms of functionality? Could one stick, say a BS170 mosfet in the place of a mpf102 in a circuit? What would be the result of such a swap (ie. smoke and flames, or just different sound, or nothing?).
  The reason is that I have a bunch of BS170's I got cheap in a bulk purchase, but I only have one mpf102 left in my parts box... I already finished the project that required the BS170's (the solid state tube sounding preamp. See the newbie forum for that thread), and want to start fooling with some of the ROG designs for my multichannel combo amp (see the "preamp for lm3886" thread in this forum)...
  Any sage advice would be greatly appreciated!

Quote from: syndromet on February 27, 2008, 06:58:20 AM
II would drop the buffers, and use the preamps straight, just for simplicity. I think most of the ROG designs buffer the signal anyway.

    Actually, following teemuk's advice I was thinking that I would extract the buffer portion of the ROG designs, and put a single buffer in front of the switch (input buffer in my schematic). I think that most of the ROG designs use a very similar buffer. Either way, I think a simple fetzer valve can be used to replace the stock buffer in any of their designs (I know this is definately true for the ruby). I think your right about diching the output buffer. Then, I guess I'd have at least a gain pot per channel, and perhaps a couple of switches (for grit and whatnot, depending on the circuit I would choose). This way, you can have each channel adjusted the way you like it, and when you switch into it, you don't have to fiddle with any pots. Perhaps a volume pot per channel is not necessary if I have a master volume control right before the power amp? I'd stick a tone stack after the preamp stage, so it would be a common setting.
   The easiest switching would definately be a double gang rotary (or a dpdt if you only have 2 channels), and wire it to switch like in my schematic. Each preamp circuit would always be getting power, but would not be connected to a signal at it's input or output unless switched to. A footswitch would be very useful, but I have no idea how they work, so I couldn't even think about designing one!
   Right now I'm think of building a 4 channel setup with the channels being 1)Proffessor Tweed 2)bassman ruby 3)Odie 4)Clean ...

Maybe a lm3875 for the power amp?

Okay, some more searching through ROG schematics has yielded this: http://www.runoffgroove.com/doubled.html
The "double d" two channel distortion. I'm mainly looking at this schematic for the switching applications, and not for the particular distortion schematics used.
Basically it goes like this:

                                         |---distortion/preamp1---|
I ->Input Buffer-->Switch 1A-/                                   \-Switch 1B-->Output buffer-> O
                                         |---distortion/preamp2---|

Here, Switch 1 seems to be a DPDT, and the buffers are active JFET one transistor types. Each distortion/preamp channel has it's own volume and gain controls. It seems possible to stick a common tone section before the output buffer (or after? or replaced it with the tone section?). Following this would be the poweramp volume control, then the poweramp itself... Seems pretty straightforward... Any suggestions?

First off, I am NOT an expert in this. But I have successfully measures AC secondaries on transformers that I scavanged out of old audio equipment, and that had no markings on them. I believe that as long as you are sure which end is the primary (ie. if it still has a mains power cable and plug attached), you are fairly safe testing the secondaries with a standard multimeter. The issue of very very very unsafe voltages comes into play if you don't know which end is which. If you accidentaly attach the secondaries to mains power, you may be dealing with thousands of volts coming out the otherside (the transformer transforms UP instead of down if you connect it backwards).
   I have measured secondaries of around 30 - 40 VAC with my small multimeter with no issues. Mind you, I attach the meter to the secondary wires with test clips, turn the meter on the right setting (for AC voltage reading), and then stand back and plug the transformer in... I read the meter at a distance, then UNPLUG the transformer before I disconnect the meter. I do this just to be safe, and it's always better to be safe than sorry!

Okay, this is a fantastic thread! I'm learning a lot here....

    I didn't consider that paralleling the preamps would lower the overall output impedance of the preamp stage... That is a very important point. I assume that this effect only matters if each of the circuits are getting power. However, as you say, there could still be a "hiss" problem introduced by all the latent unused circuitry of any preamp channels left connected but unpowered (as I suggested to do in my previous post).
   I've been examining the ROG circuits, and I noticed exactly what Teemuk was saying: that there are many redundant elements between the designs... In fact, I've got a prototype circuit I've built that uses a 4PDT switch to flip from a "noisy cricket" to a "bassman ruby". These circuits only differ in a few places, and I use the switch to reroute these parts from the components of one circuit to the other.The same MPF102 buffer transistor and LM386 are used for either mode... As of now, I've got the noisy cricket part working, but I have some dead short in the bassman ruby portion, so it doesn't work... In theory, the switching I devised should work though...
    So, here's my new set of questions for this idea:
1) If you used the rotary switch method, would you wire it to intercept the signal between the preamp stages and the poweramp stage?
2) I suppose if you only had two preamp stages, you could get away with only DPDT. I'm think specifically here of the fetzer valve for a "clean", and a proffessor tweed for a "dirty"... This may be the easiest first build for a multiple channel amp...
3)I think I would use a passive buffer at the input of the poweramp stage like the circuit posted over in the tda7293 thread. Would that be enough compensate for any changes to the output impedance of the preamp stages? I'm asking this because I still wonder if it's possible to have two signal sources being fed into the power amp at the same time with only a simple type of buffer. It may be that an active mixer stage would need to be built between the pre and power stages for this to work, and I don't know if i'm willing to attempt that...
4) Also, a nice option would be to also have a jack that connects directly to the poweramp  input for connecting external preamps. How would this factor into any impedance matching calculations (just add another value in parallel, right? should decrease the total output impedence of the preamp stage when the external is plugged in, and increase back to normal when unplugged).

Thanks for the responses so far... Like I said, this is a really great thread!