1. Line out from your amp
2. Build a preamp
3. Buy a preamp
I know it seems basic, but it is important to remember. Just a power amp is not a guitar amp. Not even close. You need a preamp not only for tone, but also to boost the signal so you can get full potential out of the power amp.
Would something like this be useable. Or is a 9v powered unit
not enough output to be useable.
Is there a good DIY preamp? GGG and Tonepad show some projects as a preamp
but they are really just a booster. That couldnt be used right?
i wouldn't say that any project couldn't be used per se. if it works always depends on the input sensitivity of your power amp and, to a degree, on the supply voltage of your circuit;
many of the projects at www.runoffgroove.com can be converted to being good preamps
especially if you run them on 18v or 30v.
there are some useful links in the schematics section of the forum as well,for example
under " various schematic websites"
If I use a flipster as A preamp on a LM3886 Poweramp, What is the best voltage to run it at, I would need a seperate transformer wouldnt I?
Would It have to be a toroid or will a normal transformer do?
You can use power off the other transistor, but its not really recommended, and its easier with a separate one. A regular CT transformer should be fine.
Sweet I think that will be the go then, Can you add a mid pot to the flipster.
And does anyone know what the mid contour switch on the fender FM65R changes, It sounds way better with it on, I always use it
you can add something like this ( sorry about the bad drawing )
make both caps something like10n or 15n. you could also use your favourite marshall/fender-style tonestack.
another thing: i guess the flipster is able to drive a poweramp easily with 9v; playing with different voltages
can be fun though because you can use it to fine-tune the way the preamp responds to picking and the volume pot of the guitar. there have been some complaints on other fora because some people felt that the ROG designs were not loud enough; i suppose that's partly because the speaker sim filter in the end is a little lossy.
Thanks a few questions though.
-Where would you put that mid control in the circuit
-What is the highest voltage the flipster can take
-Will this Run Off Groove design be loud enough for the purposes that I want to use it for
"Would something like this be useable. Or is a 9v powered unit
not enough output to be useable."
I recon a 9V preamp is more than enough, depending on the gain of the power amp.
Let's take a power amp with gain of 22 (a lot of gain-clones use this). Power rails of +-25VDC.
Maximum output voltage of the amplifier will be less than the rails, lets take 24 as an example. With a gain of 22 we get 24V/22 gain = 1.09 V input signal for max voltage.
Now your preamp has 9V, If you use op-amps you'll get 4.5 volt rails. Your output only needs do be 1V thus you have headroom of 3.5 volts depending on the op-amp.
This is all really simplified I know but it gives the idea
"Would It have to be a toroid or will a normal transformer do?"
There is no difference exept that the toroid is usually smaller than a normal El transformer.
Toroids also have a bigger inrush current. In a preamp you won't be using a 300VA transformer so it's not a problem.
For a preamp the transformers are small enough to give you with both options open.
I wouldn't go with a toroid for a preamp simply because they are more expensive and also don't normally have ratings under 90VA or so, and you don't need anything that big for a preamp.
a 9v circuit is plenty big enough depending on it's design.... my DR Boogie and JCM800 emulators are more than enough to push my solid state DuKane 60 watt amp that I use from time to time, with no other preamp circuits at all... Matter of fact, I have to turn 'em down because they get to be almost too much of an input for the amp...
At the moment I'm using a Thunderchief as an outboard preamp with a TW Mosvalve power amp. Drives it with no problem all by its lonesome. Put a booster or OD in front, and it becomes a monster. I've done the same with the ROG 18, even the Fetzer, and will soon have the English Channel up and running for the same purpose. I wonder about those who have problems with ROG circuits not being loud enough. I'm guessing the problem is with the way they try to use them (as stand-alone amps maybe?), or problems with their gear.
I'm thinking I'd like to use an external preamp setup on the 3886 I want to build, but how would I go about this? Do I simply run my guitar thru the offboard preamp like i would a pedal, into the 3886 poweramp with another patch cable?
Also, how would I go about adding a line-out to my amp? I'd like to use it as a preamp until I can get the money and time to build a preamp.
Yup, thats exactly how you would use it. As for the line out, it depends, what do you have for an amp?
I've only got a little 15w Behringer. . . would the modeling thing be an issue for creating a line-out? I hope not, as I enjoy a couple of the sounds I can get out of this thing. . . It's a shame the little speaker doesn't do it justice.
Follow the directions here:
So all i have to do is add a speaker-out to the amp, then add this jack onto it? Seems way too simple! 8)
Yup, I did that to my Dean Markley K-20X and love it.
I'm not wrong in thinking that just about any type of booster and overdrive circuit or what have you can be used as a preamp, am I? I saw mention of a Thunderchief being used - does this mean I could use similar ROG circuits (such as the Eighteen or Mockman) as a preamp?
In theory, yes you could. None of us have done it yet (this board is quite new), and so if you want to try it, let us know. The only thing is, it may not drive the poweramp to full potential, but you can adjust the gain from 22 on the poweramp boards. <- That is in reference to the LM3886 boards a lot of us got from chipamp.com
Since school is out I now have some time to finally finish my LM3886 amp.
I have an enclosure from an old amp the no longer worked and it is absolutely perfect for this, not to big but everything fits comfortably and all the original buttons are still good so i can use all the orignal controls on the front panel.
As for using the flipster as a preamp im not so sure anymore, my main concern being that from what I can gather it always has overdrive which varies depending on the input volume. If this is the case then this isnt really what im after. I want somthing to emulate a clean ampeg sound, is there anything beside the flipster like this (solid state).
I have also decideed to put in an inbuilt distortion channel as there is space in the enclsure to do and the faceplate has the spare controls for this also, what im looking for is a mesa boogie recto simulator (or somthing similar, not sure ive named the amp right either but I think the message gets through).
Another is thing ive thought about for the preamp is to use a tube preamp and make it a valve/soluid state amp. Has anyone else done this and if so has it been worth it? I had very mixed reponses about whether or not a solid state power amp does a valve preamp justice and keep the "warmer" tone the most valve amps have
I don't personally know anyone that has done the tube front end, but I do know it has been done. Lots of companies sell them like that.
Hey guys, I'm new here and love the site.
I just ordered the stereo LM3886 PCB's (one Power supply, 2 amps) from chipamp.com and plan on driving it with my newly acquired Boss GT-8 Multi effects modler.
The LM3886 PA's will drive 2 homebrew 1X12" cabs with Jensen speakers.
Has anyone else used a GT-8 (or other MFX modler) with these gain clone PA's?
So, could something like a "Noisy Cricket" be used as a pre-amp? And the "OUT" from the Cricket go to the INPUT of the power amp? Basically take the output of the Cricket and put it into the input of a 3886 or TDA2040 amp?
And which amp would provide the master volume?
If I'm correct, the noisy cricket uses a LM386 right? If so, then yes, it should be possible. You would want a pot between the LM386 and LM3886 to control volume and a pot before the LM386 to control the gain.
I'm actually working on developing a LM386 based preamp circuit. You'll want to check the board periodically over the summer because I should be starting a prototype within the month or so. I'm hoping to have a "final" version before September.
The Cricket has a pot for gain control. But the volume isn't between the 386 and the output. So I'd need to add one between the two? Or could you just add a 'MASTER' volume for the output of the power amp? Or is it better for the power amp just to run it at a steady setting and use the pre-amp to regulate the volume?
The master volume for the power amp is normally a pot BEFORE the power amp, hence why I recommened it. If you've never built a larger amp, it is understandable why you wouldn't know that.
Correct. Never built the larger amps. Trying to teach this old dog a new trick.........
No problem. It was only a couple years ago I was a complete novice myself. If you have any more questions, please feel free to ask. It's always good to get new people building amps and stuff. It's a great hobby.
I have a few different setups myself , however , here is the real deal a power amp requires 1 to 2.6 volts to operate correctly. most of the new stompbox multi effect monsters(Roland , Digitech) can put out up to 2 volts , plenty to drive any good power amp.
From the NatSemi
Low Voltage Audio Power Amplifier
The LM386 is a power amplifier designed for use in low voltage
consumer applications. The gain is internally set to 20 to
keep external part count low, but the addition of an external
resistor and capacitor between pins 1 and 8 will increase the
gain to any value from 20 to 200.
The inputs are ground referenced while the output automatically
biases to one-half the supply voltage. The quiescent
power drain is only 24 milliwatts when operating from a 6 volt
supply, making the LM386 ideal for battery operation.
n Battery operation
n Minimum external parts
n Wide supply voltage range: 4V–12V or 5V–18V
n Low quiescent current drain: 4mA
n Voltage gains from 20 to 200
n Ground referenced input
n Self-centering output quiescent voltage
n Low distortion: 0.2% (AV = 20, VS = 6V, RL = 8W, PO =
125mW, f = 1kHz)
note: comes in two versions;
low LM386N, M-1 12Vsup/0.75Wout, and
high LM386M-4 18Vsup/1.5Wout.
Vsup = 12V
Voutpk = 6V
Av = +26dB (from datasheet)
dB = 20 * log10(Av)
10^(26/20) = 19.95262315 times
Gain = x20
6/20 = 0.3V or 300mVpk in for full output.
Could I get some guidance on how to select 'equivalent' transistors, for example where a J201 or MPF102 is specified but not available. Apart from just googling 'J201 equivalent', is there way to select based on specs in the data sheet? At present I am planning a preamp to go in front of my TDA2003 amp.
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The first thing you need to know about JFETs is that the specs can vary quite allot. So much so, that it is hard to design a circuit that will operate for any JFET that meets the specs you find on a data sheet. The usual fix for this is one or two trim pots.
On the vast majority of JFETs, you can reverse connections to the Drain and Source with no change in performance.
The first thing to look at is Gate breakdown Voltage. BV(GSS) is a term you might see, it means Breakdown Voltage, Gate to Source with Drain shorted to Source. For a J201, the number is 40V. For the MPF102 the number is 25V. Most circuits don't provide any input protection and a big negative input Voltage will damage the JFET. Sorry, that's the way it is.
The next thing to look at is called I(DSS). It means Drain Current with Gate and Source shorted (to ground). It's usually specified at some Drain Voltage like 5 or 10 Volts. For the J201 the spec is 0.2 to 1.0 mA. For the MPF102 the spec is 2.0 to 20 mA. You have to look at the circuit the part will operate in, but generally try to keep the minimum I(DSS) of the replacement at or above the minimum of the part to be replaced. Try to keep the max I(DSS) less than twice the max value of the part to be replaced.
The orientation of the pins may be different for the replacement part. You will have to check this. J201 and MPF102 have the Gate at one end of the package. Same place the Collector would be on a 2N3904. Most Euro parts have the Gate in the middle. Keep in mind that you can swap Drain and Source. This can be a real PITA if the layout uses inline leads instead of a triangular pattern.
There are lots of other specs like gain and leakage, don't lose any sleep over them, just get some parts to try and be done with it. Beware of fake parts from China, but they might actually work.
Thanks for that. I think this one may fall into the correct range.
I note that the datasheet says , it used for '... low level switching...chopper-stablilised amplifiers...' etc. DOes that have a bearing on my intended use?
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these are the ones I've tried without success but maybe I need to mess around a bit more
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The J109 would make on OK low level amplifier, but is a challenge to bias and has almost zero chance of working in any J201 or MPF102 circuit without substantial changes. Notice that there is no maximum given for Idss. The parts will melt or explode if you try to measure Idss with DC. This is typical on switching type JFETs. They depend more on R(on), channel resistance.
The J175-77 are P channel. I've used them where I needed a P channel, but they are weird.
Thanks for that. Think I'll just get some MPF102 and J201's as recommended.
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OK I built up a buffer with MPF102. Definitely brightens the sound compared to going directly into my Kemo 40w power amp but less so in front of the TDA2003 or the LM386. This is using a 6" speaker, and fairly short guitar cables. Now to try it via my 1x12 and longer cables.
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