Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Preamps and Effects => Topic started by: joecool85 on April 25, 2006, 08:47:57 PM

Title: So you need a preamp - here are your options
Post by: joecool85 on April 25, 2006, 08:47:57 PM
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.
Title: Re: So you need a preamp - here are your options
Post by: Fixr1984 on June 18, 2006, 12:06:59 AM
Would something like this be useable. Or is a 9v powered unit
not enough output to be useable.
http://aronnelson.com/gallery/Mihkels-layouts/MarshaValveTube

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?
Title: Re: So you need a preamp - here are your options
Post by: el mo on June 18, 2006, 04:54:31 AM
hi,
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"
Title: Re: So you need a preamp - here are your options
Post by: DreamSeller on June 18, 2006, 05:19:50 AM
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?
 
-Dream
Title: Re: So you need a preamp - here are your options
Post by: joecool85 on June 18, 2006, 07:31:03 AM
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.
Title: Re: So you need a preamp - here are your options
Post by: DreamSeller on June 18, 2006, 09:02:18 AM
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

-Dream
Title: Re: So you need a preamp - here are your options
Post by: el mo on June 19, 2006, 07:20:28 PM
you can add something like this ( sorry about the bad drawing )
(http://i10.photobucket.com/albums/a129/eu_anarchy/out.jpg)
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.
Title: Re: So you need a preamp - here are your options
Post by: DreamSeller on June 21, 2006, 11:36:15 PM
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

Thanks

-Dream
Title: Re: So you need a preamp - here are your options
Post by: Wynand on June 27, 2006, 03:55:15 AM
"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
Title: Re: So you need a preamp - here are your options
Post by: Wynand on June 27, 2006, 03:59:09 AM
"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.
Title: Re: So you need a preamp - here are your options
Post by: joecool85 on June 27, 2006, 07:14:55 AM
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.
Title: Re: So you need a preamp - here are your options
Post by: Bob N on June 27, 2006, 09:06:13 PM
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...
Title: Re: So you need a preamp - here are your options
Post by: ildar on August 10, 2006, 06:54:15 PM
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.
Title: Re: So you need a preamp - here are your options
Post by: Dr.Beat on September 20, 2006, 04:55:52 PM
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.
Title: Re: So you need a preamp - here are your options
Post by: joecool85 on September 20, 2006, 06:13:23 PM
Yup, thats exactly how you would use it.  As for the line out, it depends, what do you have for an amp?
Title: Re: So you need a preamp - here are your options
Post by: Dr.Beat on September 20, 2006, 06:41:19 PM
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.
Title: Re: So you need a preamp - here are your options
Post by: joecool85 on September 21, 2006, 07:07:05 AM
Follow the directions here:

http://singlecoil.com/docs/out.pdf
Title: Re: So you need a preamp - here are your options
Post by: Dr.Beat on September 21, 2006, 08:42:42 PM
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)
Title: Re: So you need a preamp - here are your options
Post by: joecool85 on September 22, 2006, 07:45:26 AM
Yup, I did that to my Dean Markley K-20X and love it.
Title: Re: So you need a preamp - here are your options
Post by: Dr.Beat on September 24, 2006, 09:56:18 PM
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?
Title: Re: So you need a preamp - here are your options
Post by: joecool85 on September 25, 2006, 08:34:20 AM
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
Title: Re: So you need a preamp - here are your options
Post by: DreamSeller on December 03, 2006, 02:49:26 AM
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

Thanks

-Dream
Title: Re: So you need a preamp - here are your options
Post by: joecool85 on December 03, 2006, 07:55:13 AM
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.
Title: Re: So you need a preamp - here are your options
Post by: b1ggjoe on May 22, 2007, 08:03:02 AM
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?

Joe
Title: Re: So you need a preamp - here are your options
Post by: XinTX on June 15, 2007, 09:13:36 AM
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? 
Title: Re: So you need a preamp - here are your options
Post by: joecool85 on June 15, 2007, 09:26:39 AM
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.
Title: Re: So you need a preamp - here are your options
Post by: XinTX on June 15, 2007, 10:11:10 AM
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?   
Title: Re: So you need a preamp - here are your options
Post by: joecool85 on June 15, 2007, 10:20:13 AM
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.
Title: Re: So you need a preamp - here are your options
Post by: XinTX on June 15, 2007, 10:26:22 AM
Correct.  Never built the larger amps.  Trying to teach this old dog a new trick.........
Title: Re: So you need a preamp - here are your options
Post by: joecool85 on June 15, 2007, 01:15:47 PM
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.
Title: Re: So you need a preamp - here are your options
Post by: Jack1962 on April 08, 2008, 02:55:31 AM
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.

                                     Rock On
Title: Re: So you need a preamp - here are your options
Post by: Roly on May 03, 2014, 08:42:32 AM
From the NatSemi datasheet;

Quote
LM386
Low Voltage Audio Power Amplifier


General Description
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.

Features
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.