Sounds amazing! The schemo OTOH looks like a mace...

Quote from: J M Fahey on December 29, 2010, 04:10:16 PM
Hi tchrist.
I'm not "clashing" with our friend teemu's opinion (far from it), because I simply didn't even *look* at the "small" Fet amp, just went straight to the "big" one, where I saw no curve bending, bias shifting, etc. at all, at least in the scope images posted by the author.
All I saw there is a little top rounding, *very* easy to get by far simpler means.
And the "tube artifacts" are generated in a far better way by the excellent Transtube circuit.
Maybe driving a real world speaker things change.
Differences of  *opinion*?
Sometimes yes, and that's good, or the World would be quite boring.
If you can get that transformer wound for such a low price, and build the amplifier, go for it, and post results here.
Happy Xmas and New Year to everybody, y felices fiestas para ti.

I didn't mean "clash" in a bad way. Differences of opinion are mandatory in order to evolve. For what i know, the designer of the small PA wounded his own TF (if you look at the page for the small amps, you'll see there are few windings). I respect everyone's opinion and i take in consideration that english is not our first language (at least to both of us and Teemu, don't know if Phil's 1st language is english)

I just asked the guy who designed for some info. It looks like this 2011 I'll need money, so I better start selling my body, ha ha.

Que planes para año nuevo?

Thanx everybody.

Well, the Fet PA looks interesting and the clips got me thinkin' about 'em. What i wanna do is a series of modules, pretty much like those old modular stereo systems you used to put one over the other.

I cannot afford expensive preamps, rack effects or tube amps. But near to chinatown we have a place called "Paruro". Blocks and blocks invaded by stores and galleries dedicated to sell and/or make electronic components. In example, the power transformer, winded by hand, can cost me ~US$20.

Quote from: J M Fahey on December 29, 2010, 05:31:52 AM
Hi tchrist.
Those are interesting ideas, very experimental and quite far from a finished product.
Not bad as a concept, but the waveforms he shows are SS type , not tube type, so the main object of getting so complex and expensive (just ask for a quotation on his output transformers) is not achieved.
No te rompas la cabeza contra una pared.
Just build a tried and true chip amp, from 5 to 150W; *or* a real tube one; again from 5W to 100W, and experiment with the preamp, stomp boxes, etc.
Good luck.

Quote from: phatt on December 29, 2010, 07:52:50 AM
Hello tchrist,
Not sure where your heading but I agree with JM Fahey's last post. 8|
That stuff is Way to complex for little benifit as a tube power stage will still be better.

I did have a listen to the clip, Turning the knobs did little to effect any real change in sound.
Also a servere lack of bass but that's a matter of taste.

A note on tube preamps ,, it's a dog chase tail thing as the real benifit of Valves is in the power stage not in the preamp stages.
So if you want to throw money at something then build a Valve power stage and leave all the tricky complex preamp stuff for SS. Cheaper and Easier to fault find for the hobby types.
These days anything with an AX7 inside a preamp will sell.
IME, Complex valve preamps are no better than what can be done with transistor/chip circuits.
Sure if money is no object then go nuts but the cost is significantly higher with Valves.
Phil.

I know it is too complex (but I'm in denial)  and with half the effort/components I could build a small chip amp. The knobs where almost useless; and I know most of the "valve" sound comes from the powertubes. But I hear it telling me "build me, c'mon..."

I saw lots of youtube videos with DIY JCM800 preamps (only) and they sounded good. And I was expecting some kind of PA to get me closer to tube sound. There are some guys who built those JCM800 2203-style preamps and used chipamps. They sounded good, but there was something missing.

Quote from: teemuk on December 29, 2010, 07:34:19 AM
I don't know... to me at least the MicroPA output looks pretty much like one coming from a generic tube amp: somewhat rounding up on the clipping onset and it even features the same type of crossover/blocking distortion mechanism due to shifting bias point. But, I think those scoped waveforms are either from running to a resistive load or the amplifier's response stays fairly linear regardless of load impedance. So the mechanism where amp's gain interacts with a reactive load is not showing up in there. Otherwise, it pretty much nails the "PP tube power amp thing".

Now, your opinion kinda clashes with Fahey's and Phil's. And somehow, feeds my obssession. Could you tell me more about it? I see the values of the micro PA and they're pretty Marshall to me (470ohm, 10k, 4k7 tail resistor, 220k bias splitter, etc), but the structure is slightly different. And while the 5w Fet PA uses the same structure as a Marshall, it has different values. Do you have any sugestion or explanation for that?

Thank you to all three, and please, excuse my lame english and my OCD. And happy new year to all of you.

Hello everybody.

It's been a while since my last visit. I've been investigating about some tube preamps, since i've been wanting to have a multiple preamp with lots of modes and shinny lights.

But I'm also lookin for a poweramp to use my preamp. I've been considering lots of poweramps: Chips (TDA/LM), transistors (ála Randall), 5w Single Ended (AX84), 20w SE, 20w Push-pull, etc.

Today I was checkin' my bookmarks and found this site i visit a couple of months ago: http://milas.spb.ru/~kmg/index_en.html

He's an active member of freestompboxes, and has some pretty interesting stuff. Guy knows his biz. And they were two projects: a Fet Micro poweramp for recording (and or practice); and some Fet poweramps. And a Celestion V30 Simulator. Three projects, like I said.

I just wanna know if anyone at this forum is familiar with those projects, if someone has build 'em and have any opinion.

The Micro PA looks pretty interesting. Is a kind o' transistorized version of a Marshall PA, includes OT, V30 Speaker Sim and Speaker Saturation Simulator.


Here are the links:

Micro PA
http://milas.spb.ru/~kmg/microfetpa_en.html

Fet PA
http://milas.spb.ru/~kmg/fetpa_en.html

http://www.freestompboxes.org/viewtopic.php?f=2&t=9487
http://www.freestompboxes.org/viewtopic.php?f=13&t=8582

Quote from: Krank on March 03, 2010, 01:06:19 PM
I knew that but I've tried really hard and can't find that schematic anywhere, could you please help me?

Teemuk posted a link. Go there and register.

It's the same as the old MG15, but with two speakers.

Quote from: Zappacat on October 28, 2009, 01:37:16 AM

Quote from: THChrist on October 11, 2009, 01:20:48 PM
Hello everybody!

I wanted to bla bla bla

I was really excited about seeing this schematic until I got to the "page not found error" on photobucket.  Why not post it here?

Well, i made a few changes (at DIYstompboxes) and i forgot to edit it over here. Sorry.

Here's the final version of the MPD:

http://i20.photobucket.com/albums/b228/Anti-Idiot/MPD-Simple.jpg

As you can see, stage 3 comes before stage 2. in order to use the stage 3, u need to turn on the stage 2.

Hello everybody!

I wanted to share this with you. It's a simplifyed version of the pramp I'm desingning. It consists of multiple bypassable stages, switchable mods and it was designed using 3 Marshall Amps: 1959SLP (1 stage + pre-eq gain), JCM800 2203 (2 stages + pre-eq gain) and JCM900SL-X (3 stages + pre-eq gain). Each stage consists of a Noiseless biased SRPP using FETs

There are switchable mods: Bright cap, Boost (only for modes 2 and 3), Thick (for the 3 modes) and modable Tonestack (33k-470p/56k-220p/46k-690p).

I recommend you to use @15-18v

Here's the schematic:

http://i20.photobucket.com/albums/b228/Anti-Idiot/MPD-SingleVersion.jpg

EDIT: I forgot, please excuse me for not numbering each component, i'll do it ASAP. If you need to point something out, the reference is: 1st stage, 3rd stage, 2nd stage and pre-EQ stage. Also, the LED is a multicolored LED (R/G).

This is a single version. the other version should have 3 gains and 3 tonestacks with volume per channel (15 pots), output buffer, master volume, internal switching using relays (for bypassing stages and switching the gain/tonestacks), external channel switching (using this switching) and poweramp w/presence & resonance (this one). BTWm there's a mistake in the PA section, change the value of the 100u cap to 1u.


Please ask.

here's the v2.0

http://img97.imageshack.us/img97/9199/jcm900slx.png

yeah, i saw the JMP-1, and it was too much of a mess. i wanted something more in the vein of those Caswell #39 amps (with motorized pots, but it uses some CPU thingy). I guess i'd go with the analog and simple solution (buy those 18 pots). my brain hurts...

Hi everyone. I'm about to built a 3-channel SS amp. Since i want different EQ & gain controls for each channel, i wanted to know if there's a way of doing it without using  18 pots (vol, bass, mid, treble, gain & presence; x3). I thought about using LDRs, but that led me to use (again) 18 pots.

Another thing with the regular pots is, since i'd use relays to switch from one pot to another, the signal will be cut for a while (producing a big pop).

For what i want, i need some kind of digital potentiometers and some "memory device" (to save at least 3 presets). I don't need to save a gazillion of presets, only 3.

Pretty much like those new Marshall MG Series 4, they have a "simple" panel (and my amp is inspired by the beast of a billion pots, the JVM).



Please excuse my lame english

Quote from: J M Fahey on June 26, 2009, 01:17:01 AM
Hi THChrist. Good for you. You can upgrade your amp anyday you like. Start with something good and simple, enjoy it, and in the future add what you want. The problem with speakers is that most available (besides expensive specialized guitar speakers) are built as Hi Fi woofers, or even worse, Car Audio. Low efficiency, muddy sound, the works. ¿What do you have available in Peru? You should look for "extended range" speakers, nor woofers or worse, subwoofers, no rubber or foam borders but plain paper ones, etc. Maybe the Selenium 12PW3 is available there, it´s acceptable as a guitar speaker.

Well, since i don't have too much options here, i was thinkin' about using some recicled speakers (from broken 15w amplifiers). What scares me is the wattage of each speaker. I need to find a "Cabinets for Dummies".

Thanks for your patience Fahey.

well, i'll take your advice and follow the KISS principle (you wanted the best... no, wait, Keep It Simple Stupid).

I guess 100w isn't necessary now (since the trend is to use mic'ed cabs or DI)

I'll use 1 TDA. Now, about the speaker, what do i need?

Something like this (pardon the lame drawing)

If I use this configuration

http://www.guitarraonline.com.ar/electronica/circuito1.gif

can i use an output transformer and make a NFB loop in a circuit like this?

http://www.runoffgroove.com/tc-tone.png