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Messages - lefizz

#31
If anyone is interested i did a pcb layout
#32
Component overlay :-

#33
IF anyone is interested here is a pcb layout for the above 2 stage preamp.

Change R4 to cahnge initial gain its current set at 4 the second stage gain is variable between 2.6 and 11.

Put tone controls between Tone pad and Input2. It is currently untested but seems liek it might be useful to people building Lm3886 based chipamp, though gain have to be changed acording to your application
#34
Intereting to hear about your book, you have a garanteed sale here. I have been looking in many book shop in London and its all either pure valve stuff or just plain pot and cap swapping, or cable wiring stuff. Very limited all of it.

Thanks a lot for your advice again, so if the circuit will work i feel happier stuffing the board and actually starting to experiment. Tone control wise i will be trying a couple of circuits, from that useful site you linked to a while ago, one setup will be for an acoutic setup the other for an electric. Once i have values that work i will still up my pcb transfers if anyone is interested.

Do you think it is worth using film caps is these sorts of setups or would ceramic do to test?
#35
Two stage preamp with tone controls,variable input sensitivity and very low power draw.

http://www.redcircuits.com/Page69.htm
#36
Teemuk i read you are producing a book on guitar amp design is this in print yet, I think it would be very useful to me.
#37
OK that seems fair enough. What about those input impediance resistors and caps. Should i decrease the  value of r15 and increase the value of the input cap (c8) surely this would reduce noise in the second stage and since it isnt dealign with the guitar pickup this shouldnt matter?

Also i have fixed the gain in the first stage at 10, the more i think about this it seems too high. wouldnt something like 3 be better.
#38
Hi,

Here is where i have got to thus far. Pad labled Tone goes out to the tone controls and then come back into the second stage at the point labelled Input 2. The thing I am confused about is what i do on the input of the second stage, at the moment it is a near enough a replication of the first stage but i imagine i should change the input impedance (r15) and the input cap (c8).

As always any comments greatfully recieved.

Phil
#39
Hi Teemuk,

Yet again you provide a reallu useful post. I guess i should explain the basics of the amp i wish to build.
The amp will be used by a friend who is a professional busker on the London Tube, the real issue for such muscians is the fact that while busking is now legal and controlled the 'stages' have no power points therefore the amps have to run off batteries.

The only available one for electric guitars is the Crate Limo /Taxi series which while fine for messing about are far to fragile for day to day work.
All the buskers i know have at least 2 since they break down so often.

The amp i wish to make will be based on a tripath class-D or Class-T as they like to call it TA2021B, they make about 13 watts per channel into 4 Ohms clean.
I will be using a ready made kit from www.41hz.com, Amp 32 which is intended for hifi use.
I built several of these for hifi use an found them bo be excellent amps period let alone for the money, the bonus being the 80+% effiencey which should make the battery in the unit last a decent time. I do not know the input sensitivity of these kits however i believe that hifi typically works at around 2v, I may be wrong. This would mean that i would need a second stage with a gain of 10 judging by what you tell me.

To explain what i want in the amp, it will have two guitar preamp channels. Each with tone control, one with a Baxneldale setup for acoustic guitar, the other with a fender\mashal style dip in the middle range for Electric. I have these tone stack example you posted in my other thread.The elecric channel will have a bypassable fx unit (The English Channel) on the front.

Both these channel them go into a summing amps which will also have an input for a ipod/cd player before finalling going into the Tripath based power amp module.

From your post the it would seem to me the best option would be to have a fixed 10 x gain stage initially by removing the pot with a 1M input impedance. This should help drive the following tone controls after which we would have the opamp setup we have previously been talkign about with a pot and variable gain between 2.6 an 11 which should take use up to near 2v depending on the attenuation in the tone controls.

Temuuk, once again thanks for your help, you have been utterly invaluable in explaining these sorts of cicuits and the thing to consider.
You really have moved this project on leaps and bounds.

Phil
#40
I do  know the guy has very expensive guitars and his main acoustic and electric both have active electronics in them. Does this mean i should leave the 220k value alone or should i still go with something more like a 1M?

Thanks a lot by the way a am learning a lot and very quickly.

Do you think this circuit on its own would be enough to drive a passive set of tone controls and then on into the class d power amp or should a put a buffer after the tone controls?

phil
#41
Teemuk,

Thanks so much exactly the sort of comments i was looking for, I am commpletely new to this sort of thing.

1 Your bang on i forgot to change the gain marking after i had changed the layout.

2 What sort of input impediance should i use? 470k i really am guessing any input greatfully recieved

3 thanks i with try 10k

4 fair enough

5 what sort of value would you suggest?

I have etched some board already so i will post the pcb layout when i get to work tomorrow.

Thansk for your input
#42
Yeah they arent used, ethier 'no connect pins or bias ajustment pins which arent used in this application
#43
I have had a go at redesigning the circuit using the TI single supply handbook.
It avoids most of the pitfalls of the original though i am not expert.
If anyone in the know can comment that would be good.

I will try it with both a TL071 and a OPA134.
The OPA134 should sound better since it is a very high spec opamp btu you never know!
#44
Amplifier Discussion / Re: Battery Powered Class-D Amp
September 12, 2007, 07:39:01 AM
OK i have had a go at modifying the 'Guitar Handbook' preamp with reference to the TI single supply handbook to try and improve it.

I was thinking that this followed by a passive baxendale tone stack would be a pretty decent setup.

Could anyone have a look and check that it all seem in order?

I would use a TL071 or better for my version.

#45
Amplifier Discussion / Re: Battery Powered Class-D Amp
September 11, 2007, 09:24:38 AM
Has anyone tried the Little Rebel design, just cos it has a basiclly eveythign i need on the preamp i.e. a tl072 based preamp, full tone controls and a runs off a single supply.
I imagine for an aucostic guitar i would need to change gain controls and for my application remove the LM386 power section but i seem like a pretty good starting point.
Any thoughts

http://rebel.massberg.org/source/layout.pdf

http://rebel.massberg.org/source/schematic.pdf

Phil