Combining Preamp And Power Amp

[longngocvu]

Hello,

I'm planning on building a sustainer for my fat strat and i'm having a problem with the circuit.

I found 2 circuits: one is the Fetzer/Ruby and the other is from this site: http://strib.fr/?p=46 (scroll down a bit and you'll see the preamp and the power amp)

But it's impossible to find these components in my country:

-the transistor in the pre-amp of the Fetzer/Ruby.

-the TBA820M in the power amp of the other circuit.

So do you think if i could combine the Bob Blick pre-amp and the Ruby power
amp together?

If yes, do i need to add or change something in the circuit?

Or can anyone recommend a whole new circuit?

I know there's a huge topic about DIY sustainer but i don't think there was anyone having the same problem as mine so it would be really great if you could help me!

Thank you,

Edited August 1, 2013 by longngocvu

[curtisa]

But it's impossible to find these components in my country:

-the transistor in the pre-amp of the Fetzer/Ruby.

Many N-channel JFETs will work in that position. The Fetzer/Ruby schematic gives three possibilities - MPF102, J201, 2N5457. Others that will likely work (ignoring pinout differences) are BF244, BF245, 2N5457, 2N5458, 2N3819...

-the TBA820M in the power amp of the other circuit.

If it's hard to find the TBA820 don't bother with it. Given the same operating parameters there's nothing it offers that the LM386 can't do.

So do you think if i could combine the Bob Blick pre-amp and the Ruby power amp together?

If yes, do i need to add or change something in the circuit?

Yes, it will work at the expense of added circuit complexity. Use a FET input opamp (TL071 or TL081) for best results. Experiment with different values of Rg (between 22K and a couple of hundred K).

Be prepared to do a lot of experimentation with a DIY sustainer. While many managed to get the circuit to work the basic design is quite temperamental, and there are just as many people who weren't as successful. Don't set your sights too high and you won't be disappointed

[longngocvu]

Thank you so much Curtisa!

Unfortunately, i can't find any of those subtitudes either ((

I'll go with the combining option. So you think i should replace the lm741 by TL071 or TL081 and change the value of Rg?

Sorry for asking again, i'm beginner.

Did you build a DIY sustainer yourself? If yes, could you share some experience?

Thank you,

Long.

[Prostheta]

Is it not easy to import these components to Vietnam? It might be worth considering eBay.

[longngocvu]

@Prostheta:

How do you know that i'm Vietnamese? You can tell by my name?

Is it not easy to import these components to Vietnam? It might be worth considering eBay.

Yes, i can always buy some on Ebay, but the cost is ...well, not too high in general but it is, in fact, pretty high for me and for some DIY projects like this, not mention the troubles i'll get myself into at the custom (they have really strict policies and the duty is freakin' high).

You see, that's why i have to think of other ways:(

regards,

Long.

[Prostheta]

It's in your public profile info ;-)

Ah, yes I guessed that there would be something prohibitively expensive such as dutys or tax. It explains why you're hunting for the best equivalents with whatever you have available.

741s are current-hungry. I would certainly use a TL0x1 in their place. I don't think you need to alter the negative feedback gain resistor Rg just because you are using a different op-amp. In the circuit he has replaced Rg with something like a 1MOhm trimmer potentiometer. That might be a good idea for you too.

Welcome to the board, Long!

[longngocvu]

Thank you Prostheta!

It's in your public profile info ;-)

Silly me

[curtisa]

'll go with the combining option. So you think i should replace the lm741 by TL071 or TL081 and change the value of Rg?

Sorry for asking again, i'm beginner.

Rg sets the gain of the opamp, and to a degree is not dependant on the type of opamp you use.. The bigger the resistor the more gain. I only mention experimenting with this resistor because you may need to dial in a certain amount of amplification to get the sustainer to operate correctly. Too little gain and the sustainer won't move the strings. Too much and you'll end up with something that is a noisy, oscillating mess. Prostheta's suggestion of a trimmer in its place is a good idea.

Did you build a DIY sustainer yourself? If yes, could you share some experience?

I did, and while I did manage to get it to work it wasn't without its problems. It was never capable of "clean" sustain, which is something I was really keen to have it do. When the sustainer was operating with a clean guitar tone there was always a lot of distortion superimposed on top of the guitar signal. Reducing the drive to the sustainer removed a lot of this unwanted overdrive, but killed off the responsiveness of the sustainer. If I was playing the guitar through an amp on a distortion channel it wasn't so bad as I could mask the noisy sustainer in the amp distortion, but if I wanted to use it for more "ethereal" clean sounds it would sound like mud.

The driver needed to be set quite close to the strings too, and if I were bending strings on the highest frets it would often bottom out on the strings. Uneven string response was often experienced by many users - the sustainer would work beautifully upwards of the 12th fret on the 3rd string, but there'd be nothing on the 6th string below the 5th fret. The driver and circuit is quite low-tech (the driver is nothing more than a couple of hundred turns of enamelled copper wire on a hunk of steel, and the basic circuit is lifted straight from the datasheet of a 30 year-old chip), and probably contributes largely to the varying experiences that everyone has with it.

In the end I let the DIY sustainer go and bought an Ebow. For the occasoinal use I got out of the sustainer it ended up being more useful to me to use a sustaining system that I could apply to different instruments. Knowing what I know now about building and modifying guitars, If I were to go down the sustainer path again I'd probably buy a commercial system like the Fernandes or Sustainiac.

If you think you can work around its quirks and idiosyncrasies, and don't mind a bit of experimentation, I still think it is a worthwhile project to undertake. You learn a lot about electronics and modding guitars along the way, and when it does eventually work to your satisfaction it opens up a lot of interesting possibilities in your playing style.

741s are current-hungry. I would certainly use a TL0x1 in their place. I don't think you need to alter the negative feedback gain resistor Rg just because you are using a different op-amp. In the circuit he has replaced Rg with something like a 1MOhm trimmer potentiometer. That might be a good idea for you too.

My suggestion for the TL0x1 opamp was more about the higher input impedance being more suitable for loading guitar pickups but yes, current demands of the LM741 should also be considered in a battery-powered system such as the sustainer, and the TL0x1 will out-perform the ancient 741 on that, and many other points too.