building the "Solid State Tube Sound" preamp...

[darwindeathcat]

Hi all, I'm new to the list, and am about to embark on my first major "from scratch" amp project (i've built a few general purpose amp kits, and modified several existing amps). Instead of starting with the de rigour noisy cricket or little gem, I came across a schematic at this site: http://members.tripod.com/gillcar/id24.htm for what seems to be a very cool and easily built "tube clone" preamp circuit. Before I place my smallbear and electronics goldmine orders for parts, however, I wanted to ask the list if anyone knows or has built this circuit? Does it work? Does it sound good? Is it worth my time? Are there any known flaws in the design or any essential mods I need to know? Any help I could get would be greatly appreciated...

BTW I play blues harp, and plan to use this to get good tube style blues tone to feed into my vintage 20watt pa amp...

[darwindeathcat]

Well, I guess nobody cares, but I went ahead and ordered the components and am going to build this thing anyway... Maybe I'll write about my results...

[R.G.]

I can't tell you much about it other than the stuff that Gabe puts out as an explanation for why his solid state stuff sounds just like tubes is technical gibberish. It may or may not sound good. But whether it does or not is not because of the reasons promulgated for it.

[darwindeathcat]

Well, I just built this over the weekend. It sounds really really good! I am a blues harmonica player, and I built this because I wanted to a "tube sound" at an affordable price. I really think that this circuit does that. I'm ran a couple of my homemade customized dynamic and piezo mics through it last night, and then into the "line in" jack on my crappy old Solid State 20w PA amp and 2x10 cab. It sounds to me MUCH warmer (ie. tube-like) than either plugging the mics directly into the PA's mic preamp jacks, or using my legendary pignose to preamp the signal (and much less noise too!). I added a "simply wonderful tone control" and a 100k volume pot, and opted to have a drive pot as well as the the gain pot pictured in the circuit. I haven't experimented too much with it yet as I haven't boxed it up yet (I'm waiting for the paint to dry on the enclosure), but so far I am VERY pleased with this thing. By the way I used .47uf coupling caps which I heard somewhere help "voice" amps for harp by allowing more bass... Once I box it up, I'll add this to my line up in the following manner Mic->Dano Fish and Chips EQ->Modded Dano Fab Echo->SSTS Preamp->Solid State PA->2x10 cab

If anyone is interested in sound samples or pictures, just let me know and I'll post some...

My next project will be a LM3886 or LM3875 power amp that I will build into my cab, thereby eliminating the crappy PA amp all together!

[J M Fahey]

Dear Darwin. I checked and laughed a lot on Gabe´s site . 99% of his "technical" explanations, are , to talk softly , gibberish .  Anyway, the preamp you built is not bad at all, it´s just a very basic bipolar transistor preamp, input and output buffered by MosFets, total gain around 25 ((15k/500)x0.9x0.9)), flat response, which probably explains your finding it "warm" over the regular preamp from your P.A. Going from 1uF to .47uF doesn´t change the audible response, buy may help in reducing somewhat "pops" and "thumps"  They move upwards the lower frequency limit; the first one from 2Hz to 4 Hz; the second one from 3Hz to 6Hz (approximate values). It might even drive directly an LM3886, please try it and post your results. Keep experimenting, just don´t buy Gabe´s $399, 8 Ft. speaker cable to get a "better, Oxygen Free" warm sound or his "Passive Preamps", a.k.a. empty boxes with a pot. 
Bye.

[darwindeathcat]

J M,
   Thanks for leaving me a reply on this old thread... This was my first posting here, and in the months since then, I have learned A LOT more about this kind of stuff. That preamp was my first successful build, and I think I was more blown away that I had builtit and it actually worked! Since then I've built more things,a nd heard more circuits,a nd read a lot more. Back then I was still under the illusion that it was "tube sound" I was looking for. Now I know that waht I'm looking for is amplification with tone that sounds good with the Harmonica. Getting that tone has a lot to do with harmonicas and microphones, but also amplification for the frequencies of sound that harmonicas generate. These are very different from guitar frequencies. In fact, harmonica amplifaction shares more with bass guitar  and for regular human voice (not singing, just talking) amplification than it does with guitar amplification.
   I now think that I was just lucky that this particular circuit happend to also sound good for harmonica. It probably has to do with it originally being designed as a microphone preamp rather than any "magic" properties of the design (ie. all the tube emulation theory that gabe writes about at his site)... I'm now experimenting more with FET preamp/overdrive circuits and trying to figure out ways to tweak them for harmonica amplification. If you (or anyone else) has any ideas about this, let me know! I'd be glad to hear them!

[Jack1962]

Sounds cool Darwin, changing the coupling caps does voice an amp(any amp tube or SS) also the bypass caps will as well.

                                              Rock On