Thanks Fahey for the great explanations. I learn much from them.
I've tried to simulate Little Rebel's tone stack as Roly suggested. (It's my first time with these softwares btw.) Yes, it has weird freq response.

I'll go for valvestate 10 then. Btw (maybe a silly idea) if I want to run the preamp from single power supply, say 12V, how to do it? Just as simple as connecting some bias resistors to op-amps?

Quote from: Roly on August 10, 2012, 09:41:31 AM

Really, the question you have to answer first is "what do you want?", more bass, more treble, more control range?  Then we can have a look at which components to change in value that might give you what you want.

I think my friend meant more control range. He also said lack of bass. Can you suggest value changes? Actually what I want is to learn more about this unique tone stack.

Quote from: J M Fahey on August 10, 2012, 10:48:11 AM

It's basically a ripoff of the Marshall "Guv'nor" family pedals,
with a bass boost added (since it will typically drive very small speakers) , straight driving a flat LM386 amp.
A FMV tone stack will probably sound buzzy (that's why the other one was developed).

I have compared the two, and indeed they are identical from input to clipping diodes. But I'm still confused about the bass control. I haven't seen anything similar to it. Can you give me some more explanation about it? So I can learn more about these things. <3)

Quote from: J M Fahey on August 10, 2012, 10:48:11 AM

A FMV tone stack will probably sound buzzy (that's why the other one was developed).

Buzzy means too much treble? Will the active filter help?

Quote from: J M Fahey on August 10, 2012, 10:48:11 AM

If you want to homebuild an amp, go for, say, a Valvestate 10.
KILLER little amp

Yes, it's already in my list. I'm not sure about the supply voltage. Is it +/- 18V?

Thank you so much for the answers. :dbtu: :dbtu:

My friend said Little Rebel's tone control is too subtle. Can anyone explain what topology it is and suggest modifications? I just can't figure it out with my limited knowledge. xP

Having read Temuuk's book (great job Temuuk!), I am trying to change the tone control to active FMV. I also use the remaining op-amp as active low pass filter to cut high freqs. This IS my first attempt in modifying / designing an amp. Please point out any mistakes as I tend to copy & paste schematic fragments and glue them altogether. :duh
Any comments and suggestions are welcome.

Thanks for the replies. I guess I just don't have enough resources to build fet preamps. Don't have DVM and required skills.  xP
The most comfortable way for me would be op-amps then...

You're welcome. Glad that helps.
Headphone volume pot is a very cool idea. Worth to try. :dbtu:
Post pics or vids or youtube link or whatever in this thread when your amp is completed. I can't wait to see how it looks and hear how it sounds.

I'm using the schematic at the FAQ section of runoffgroove.com. Sorry I can't give you direct link, I'm replying from my cellphone. It's very simple, really. Connect a 10 ohms resistor from jack's ground to speaker out negative.
But instead of 10 ohms, I use 220 ohms/2w because it's still too loud for me. Works for me, but I don't know if it's technically correct.
Use plastic socket. It needs to be floating. Grounding it will make VERY loud hum.
You can wire it so when you insert headphone jack, it will break the connection with the speaker.
Don't expect too high. This is the simplest way. The sound will be a bit dull. A cab sim will do better.

Hopefully this helps.

I am wondering with C29 (47u). Usually the orientation is the other way around ie. the (-) side connects to power section. Any thoughts?

Is there any unnecessary parts?

Is Red Circuit really that unreliable? Actually I'm planning to make some of their circuits. Guess I'll have to reconsider.

Sorry for late reply. Been rather busy.

Quote from: Loudthud on March 02, 2012, 11:44:53 AM
... The way you have it connected inbetween selections when you are moving the switch, the output will go to max voltage. Leave the resistors connected and simply short them out with the switch.

Good point. I was thinking part/cost reduction but didn't think about safety.

Quote from: phatt on March 02, 2012, 06:15:07 AM
... The 470uF on the output only needs to be small,, maybe 10uF but you may need to put a bigger Cap on the input side to get rid of hum. 
I'm assuming a normal Transformer plug pak is in use?
IF it is a *switchmode type Plugpak* then you will be better served by throwing it in the bin as some are horrendously noisy and are not designed for use with sensitive audio circuitry.
Phil.

I had opened the adaptor and found a transformator, some diodes, resistors, and capacitor. I guess it's not the switchmode one. I'll try the cap thing.

I'll try all of your suggestions and post voltage measurements later. Thanks for the quick replies. :tu:

I came across with this guitar amp schematic: http://www.redcircuits.com/Page52.htm. I am interested in making a preamp based on it.
Obviously I don't know if I'm doing it wrong, so any correction would be VERY APPRECIATED.
Can I power it with a 9V battery?

I was building this preamp: http://www.redcircuits.com/Page120.htm. Nice result indeed with battery pack. I even got good result with 9V battery (instead of 18V which is recommended). <3)

The problem started when I used a cheap wallwart adaptor. I got annoying hum which also distorts my lower notes. So I decided to make some kind of voltage regulator using LM317.
BUT I couldn't get rid of the hum. Thinking that I got a defective part, I replaced the LM317. Still same result. xP

Here are the measurements with analog voltmeter (intended output was 9V):
With 18V input, the output was around 15-16V.
With 12V input, the output was around 10V.

I guess there is no regulation at all. :duh

Could anyone point me any mistake I made? My plan is to make an internal voltage regulator in the preamp. I made it switchable between 9V and 12V. The schematic was taken from the LM317 datasheet.

Thanks phatt, J M Fahey, and joecool85 for mentioning my build.  <3)

It's quite an easy project, as it's my 3rd build after Little Gem and Ruby. Make a switchable jfet input buffer before the preamp for better clean sound, like the first schematic shown here: http://www.muzique.com/lab/buffers.htm.

If you want loudness, use low wattage speaker. If you want better sound, use a real guitar speaker cabinet like  Fahey suggested in my thread. :dbtu:

You won't regret building it. Nice and cheap. I love it. <3) <3)

Looks nice. :dbtu: :dbtu:

Be careful with the pad size, though. Reducing it a little won't hurt.

Sorry for the late reply. I've been busy lately.
I've watched the video and wow... that was driven by a 1/2 watt amp(??!!!) OK, I get the message. :dbtu:
I guess size does matter.
I've read many good words about Jensen speakers. :dbtu: But there is budget problem here.
My build is only about 25 EUR total, so an 18 EUR speaker will be considered next time for a bigger and better project. Thanks for the suggestion.

Thanks for the quick reply.

I thought I can "simulate" a 4x12" cabinet on a 6" speaker using Condor. My amp has a nice bass end (at least to suit my taste). But it also has *harsh* treble frequencies which you can't hear on the video (thanks to the poor quality of the mic, lol ).

I am dreaming of a small 6" practice amp with a frequency response similar to 4x12". Is it actually achievable?

Why don't you try to build Little Rebel? It has sustain and even feedback if you are close enough. Makes you feel like on a big stage. :dbtu: And that sound is coming from a cheap 6" speaker. <3)

A thread about my build: http://www.ssguitar.com/index.php?topic=2483.0
A "demo" video (sorry about my poor playing): http://www.youtube.com/watch?v=3BO4j-4KXXs

A very rewarding practice amp build. <3) <3) :dbtu: :dbtu: