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[maurawkela]

In the newcomer section, i have posted my amp. I have finish building it and it sounds fine. With apologies to Mr Fahey, i have build the MXR Dist+, while it sounds good, i want a little more control.I have look at the various runoffgroove.com circuits, while i like them, there are less controls on them (is this a good thing).  Can anyone point out a preamp with the following specification to drive a TDA2030A Amp.

1. With volume, bass, mid and treble control.
2. Utilizing 12v power supply (i used a split 12 v for the amp)
3. No problem if based on either transistors or opamps.
4. Not very complicated. My circuit building skill is still at intermediate stage.

Thanks

[J M Fahey]

Congratulations, good work. 
I suggest you build the preamp from:
http://sound.westhost.com/project27.htm
Good, "Fendery" sound, with slight distortion if needed.
For anything heavier, build an external pedal.
Itīs originally powered with +/-15V, but will work very well with +/-12V.
You can buy his PCB (inexpensive, and can be mailed) or design and build your own ... or build it on perfboard.
Good luck.

[maurawkela]

Thanks for the quick reply. :-)

I have looked at that circuit earlier, will it be possible to cut the clipping diodes and restrict the volume controls to just one, instead of the volume and the master. To do that modification, what changes will be needed. Or do you suggest leaving things as they are.

[J M Fahey]

You *can* take them out if you wish, but you will save, what, 4 parts?
I would do that if it were, say, a Bass amp, but for guitar itīs always useful to have *some* crunch available,without being tied to an external pedal.

[Alexius II]

Hi,

just yesterday a friend brought me a beaten up amp - Epiphone EP10 which sounds horrible. It has half of the pots/jacks broken or damaged. He just told me: make it sound good... so I decided to replace the whole preamp, while keeping the same power chip - TDA2030. Since I'll be doing basically the same thing as you, I can post some photos of my progress if you want 

The "preamp" I've chosen is the Thor circuit from runoffgroove, as my friend mostly plays overdriven rock stuff... and there will be a classic marshall tone stack after.

Amp's current state is this: (I just pulled the guts out )
http://www.box.com/s/p7apqth18clq7doxqnpg

[joecool85]

Hi,

just yesterday a friend brought me a beaten up amp - Epiphone EP10 which sounds horrible. It has half of the pots/jacks broken or damaged. He just told me: make it sound good... so I decided to replace the whole preamp, while keeping the same power chip - TDA2030. Since I'll be doing basically the same thing as you, I can post some photos of my progress if you want 

The "preamp" I've chosen is the Thor circuit from runoffgroove, as my friend mostly plays overdriven rock stuff... and there will be a classic marshall tone stack after.

Amp's current state is this: (I just pulled the guts out )
http://www.box.com/s/p7apqth18clq7doxqnpg

Wow, it's been beaten with the ugly stick.  I'm curious how the transformation comes along.  Feel free to either post in this thread or start a new one.

[maurawkela]

@Alexius II Thanks for the info.

My TDA2030A has been lying around with just the main amp and speaker. Its good bragging value (NOI) in my circle. I've been concentrating on my work which is world apart from electronics (I'm a doctoral candidate for Sociology). So, i hardly have time these days. Your inputs will be really helpful. I've check out the circuit you are attempting and i find that i have most of the components. So, it will be really interesting. :-)

[Alexius II]

I too have lots of other stuff on my mind (getting my degree in civil engineering soon) so this project will be limited to Saturday afternoons, when I'm home 

I actually did use Thor as preamp before... here is a photo: http://www.box.com/s/vay73gx0e3v3lul14nla
It has a marshall tonestack + presence control (same filter as a mesa dual rectifier). The rotary switch changes treble caps. The two outputs are preamp out (buffered) and speaker out (there is a small LM386 amp inside). It sounds good with a good power amp and pretty poor with the internal 386 (this chip just eats all the treble out of the tone)

As far as the power amp goes, I will re-do it using the Valvestate 8010 schematic. The original was wired for "single power supply" which I find strange, since the transformer can do 18-0-18 (dc).

There is only one thing I'm not sure about. The amp (EP10) has two inputs. I would like to use both; the first as the "low hain" and second as "high gain". Each would have it's "own first jfet stage" (a fetzer valve) using a MPF102 or 2N5458 for low gain and 2N5457 for high gain. Voltage gain of the first input would be between 1 and 2, and for the second between 5 and 6. Do you see any problem with wiring both jfet stages' outputs together? Let me draw my idea: http://www.box.com/s/gcytboz847x5vqksdtly
You can see the original circuit here.

I can wire the input jacks in a way that plugging into one - shorts the input of the other to ground... and vice versa. Would this be ok, or have I missed something? Is it necessary to disconnect the output of unused jfet (using some sort of a switch)?

[J M Fahey]

You can wire those outputs in parallel, as drawn.

[Alexius II]

Great, thanks    This makes it far simpler.
...but, could switching (disconnecting) the unused stage have any benefits?

[J M Fahey]

Now that you are into it, why donīt you build 2 different input stages and join them with 470K resistors, like the Plexi inputs?
Then you will have 2 different sounds, as in the original one.

[Alexius II]

Not a bad idea 
I could keep one original stage (fetzer valve) and add a different stage. Would there be any problems useing a stereo 1M pot for both volume controls?

Today I encountered another problem. It seems I somehow understood the transformer wiring wrong the first time today I remeasured the transformer and under no load it seems to be at 26-0-26 VAC 

The only thing written on it is 40w, so I suspect it is around 24-0-24V (AC) under load.. which is quite a lot for tda2030. No wonder it was operating in single supply operation (around 35V DC, under no load). I guess I'll have to keep the power stage as it was.. since any voltage regulation will waste lots of power here

Until next weekend, I will order most the parts.. and take some time to "read" the power amp schematic from the pcb.