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Author Topic: preamp for LM3886?  (Read 35686 times)

sugrhigh

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preamp for LM3886?
« on: January 12, 2008, 05:10:04 PM »
I'm using BrianGT's chipamp for my power amp stage...

What did you use?
What would you recommend?

I'm a fan of Marshall and Line 6 sound but that's not the definite sound I'm looking for.
If possible, I'd like a 3 band (bass, mid, treble) EQ but I can live without it.

joecool85

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Re: preamp for LM3886?
« Reply #1 on: January 12, 2008, 05:53:43 PM »
I'm using BrianGT's chipamp for my power amp stage...

What did you use?
What would you recommend?

I'm a fan of Marshall and Line 6 sound but that's not the definite sound I'm looking for.
If possible, I'd like a 3 band (bass, mid, treble) EQ but I can live without it.

I've yet to build an actual preamp, but I did use a Marshal DRP-1 preamp in front of my LM3886.  I've also hooked up my 1/2w little gem (LM386) amp up to it as a preamp, worked really well actually.  I'm thinking the next amp I build will be LM386 based preamp in the front end and LM1875 power amp.
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sugrhigh

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Re: preamp for LM3886?
« Reply #2 on: January 12, 2008, 11:35:12 PM »
I'm searching (without much success) for a DRP-1 kit but I can;t find one. I know you got yours off of ebay but I don't see any there or even at online music stores.

Where can I get/make one?
What else would you suggest?

joecool85

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Re: preamp for LM3886?
« Reply #3 on: January 13, 2008, 08:23:42 AM »
I'm searching (without much success) for a DRP-1 kit but I can;t find one. I know you got yours off of ebay but I don't see any there or even at online music stores.

Where can I get/make one?
What else would you suggest?

The DRP-1 has been discontinued for quite a while now, and they are pretty rare.  You can use any sort of mic preamp as well, I haven't done this myself but it should work great and would be a cheap way out.

This Berginger would be perfect:  http://www.musiciansfriend.com/product/Behringer-TUBE-ULTRAGAIN-MIC100-Preamp?sku=182482
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teemuk

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Re: preamp for LM3886?
« Reply #4 on: January 13, 2008, 11:18:09 AM »
The DRP-1 has been discontinued for quite a while now, and they are pretty rare.

http://www.matsumin.net/diy/jisaku1/DRP-1/index.html

sugrhigh

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Re: preamp for LM3886?
« Reply #5 on: January 13, 2008, 12:47:28 PM »
I'm searching (without much success) for a DRP-1 kit but I can;t find one. I know you got yours off of ebay but I don't see any there or even at online music stores.

Where can I get/make one?
What else would you suggest?

The DRP-1 has been discontinued for quite a while now, and they are pretty rare.  You can use any sort of mic preamp as well, I haven't done this myself but it should work great and would be a cheap way out.

This Berginger would be perfect:  http://www.musiciansfriend.com/product/Behringer-TUBE-ULTRAGAIN-MIC100-Preamp?sku=182482


I want these to be made purely DIY because I plan on doing a charity project based on the amps I build...
I may end up having to use a pre-made preamp but I would really like to avoid that.



The DRP-1 has been discontinued for quite a while now, and they are pretty rare.

http://www.matsumin.net/diy/jisaku1/DRP-1/index.html

I checked out the site and it looks overly complicated for my first build because there would be a lot of trial and error since the site is in japanese....



Anyway, what would you guys think about either the Thor, or English Channel from runoffgroove?
I would be buying the ready to build kits from olcircuits and converting them from stompbox to preamp....
Would there be problems?

joecool85

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Re: preamp for LM3886?
« Reply #6 on: January 14, 2008, 06:36:00 AM »
The DRP-1 has been discontinued for quite a while now, and they are pretty rare.

http://www.matsumin.net/diy/jisaku1/DRP-1/index.html

Thanks for the link!  I saved that pdf, could be useful later on.
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sugrhigh

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Re: preamp for LM3886?
« Reply #7 on: January 14, 2008, 07:15:53 AM »
It sounds great too, but would that circuit work?
Just have get the input levels right for the power amp correct?

syndromet

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Re: preamp for LM3886?
« Reply #8 on: January 15, 2008, 06:23:22 AM »
Preamp questions are kind of hard to answer without a little more info. We need to know what kind of sound you are looking for. A lot of stompboxes have more than enough gain to serve as a preamp, so you should look into some of those. I'm using a SansAmp clone with my LM1875, and it sounds superb. Can't beat that for versatility and sound quality, but they are kind of hard to build There are a lot of great preamps/stompboxes with a three band eq that are not overly complicated, and I suggest you look into the JFET circuits at runoffgroove.com.
Here are a few suggestions for distortion-preamps:
http://www.runoffgroove.com/englishchannel.html for a VOX AC30 like circuit.
http://www.runoffgroove.com/thor.html For a high gain Marshal like overdrive
http://www.runoffgroove.com/eighteen.html For a classic rock Marshal like overdrive
http://www.runoffgroove.com/umble.html For a dumble-like sound
http://www.runoffgroove.com/professor.html for a fender like-sound
http://gaussmarkov.net/wordpress/circuits/dr-boogey/ For a Mesa Boogie high gain distortion

I've buit all of theese myself, and they all sound great. I have also used a few as preamp, running on 9V, and they work perfectly.

All of theese are JFET based, and could be run of higher voltages (18v is ideal) for a little more head room.
You could also try the Krank Distortion Maximus. I havent tried it yet, but from what I've heard it sounds great for high gain distortion. It's based on a highgain bjf transistor and a LM386, and should be able to run of higher voltages too.

I would recomend you using one of these for the dirty channel, and a single inverted Lm072 as the clean channel. I'm using that myself, and it gives a perfect, sterrile sound, much like the infamous cleansound of the Roland Jazz Corus. It could also be cool to add a blend pot between the two channels, for a wide array of sounds.

Just my 2 cents of advice.


« Last Edit: January 15, 2008, 06:24:50 AM by syndromet »

darwindeathcat

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Re: preamp for LM3886?
« Reply #9 on: February 19, 2008, 05:08:29 PM »
Hey, how does one connect multiple preamps to the input of a poweramp? It would be VERY cool to build several of these runoffgroove jfet circuits into a combo amp. that way you could have multiple channels, all with a "clone" sound of the different amps those pedals are made to simulate.
  Would one simply connect the outputs of all the differnt preamps in parallel to the input of the poweramp stage? Or would one have to make sure that only one preamp is connected to the power amp at a time (ie. with a rotaryswitch ).I'm sure each preamp would have to have it's own input jack and control pots.
  I'm planning on making a lm3875 "gainclone" as a poweramp, and really would love to build several of these fairly simple ROG circuits as pramps for it... that would make a killer combo!
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sugrhigh

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Re: preamp for LM3886?
« Reply #10 on: February 19, 2008, 06:00:55 PM »
Hey, how does one connect multiple preamps to the input of a poweramp? It would be VERY cool to build several of these runoffgroove jfet circuits into a combo amp. that way you could have multiple channels, all with a "clone" sound of the different amps those pedals are made to simulate.
  Would one simply connect the outputs of all the differnt preamps in parallel to the input of the poweramp stage? Or would one have to make sure that only one preamp is connected to the power amp at a time (ie. with a rotaryswitch ).I'm sure each preamp would have to have it's own input jack and control pots.
  I'm planning on making a lm3875 "gainclone" as a poweramp, and really would love to build several of these fairly simple ROG circuits as pramps for it... that would make a killer combo!

i think using multiple preamps would ruin the tone, unless thats the sound your looking for

just my opinion

darwindeathcat

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Re: preamp for LM3886?
« Reply #11 on: February 19, 2008, 06:53:41 PM »
Hi Sugarhi, I meant to have selectable channels... Not to have several preamps running through eachother... In that case you are definately right... But many commercial amps have multiple channels, each with their own sound. I'm not one hundred percent sure, but I believe that each "channel" on a combo amp is actually a differnt preamp, and that they all feed into one power amp. My main question from a diy perspective, is whether or not you can have all the outputs of the preamps connected to the input of the poweramp stage at one time (ie have all the preamps in parallel, and getting powered, whether or not all of them have an input signal). In this formation, each preamp would have it's own input jack as well as controls, and in theory you could plug into two or more channels at a time (either with an external a/b box, or have different instruments/mics plugged into the differnt channels). This would definately be the simplest way to go.
   The other way I would think to do this is to have a single input, and use a double gang rotary switch to route the signal and power to the preamp circuit that you wish to be using at any one time. The outputs of each preamp would still be all connected to the single input of the poweramp, but the difference is that no power would be sent to the channels that are not used.
   I guess that you could also use the stereo-jack method to cut the ground if you wanted to still have a jack per preamp, but not have power flowing to the unused preamp channels.
   I wonder also, I guess if you can have two preamps feeding signal to the power amp simultaneously? I don't see any real reason why you can't... Would you need to stick a mixer stage in between?

   Anyway, I still think it would be really cool to build a DIY gainclone amp with multiple "voices"...
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sugrhigh

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Re: preamp for LM3886?
« Reply #12 on: February 19, 2008, 11:11:54 PM »
oh i see where youre going now

and i believe that is how combo amps do it

as far as input to the preamp, i would to something like:

----------------->power amp
|     |     |
|     |     |
|     |     |
p    p     p
r     r     r
e    e     e
a    a     a
m   m    m
p    p     p

1    2     3


and use a button of some kind to switch between them

joecool85

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Re: preamp for LM3886?
« Reply #13 on: February 20, 2008, 07:15:29 AM »
Just use open jacks and it'll connect automatically whichever one you are plugged into.  Just don't plug in 3 guitars, it could sound kinda nasty lol.
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teemuk

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Re: preamp for LM3886?
« Reply #14 on: February 20, 2008, 07:50:20 AM »
If I would use the circuits in that kind of parallel arrangement I would likely put some kind of a rotary switch to that setup and I would also try to switch at both output and input sides of the pre circuit just to eliminate noise (few hi-gain circuit in parallel may contribute a lot of hiss). If you do not "drop out" the "unused" circuits with some switching arrangement you need to consider the total impedance of all preamp final stages that are connected in parallel: Most of them have a resistor that ties the output to ground reference, when you parallel few of these the total resistance may end up being substantially low, there’s a good chance that some of the circuits cannot handle it and at at least it will effect the coupling/cut off frequency. The thing may need mixing resistors or buffers. I’m quite certain that you can’t just parallel the circuits and get away with it without any modifications.

Another issue is how wise this paralleling even is in practice. I mean, do you really need all those preamps or could you just work out an arrangement where you remove all the “unnecessary” parts and devise a couple of ways to make the circuits share the parts that are common to all. For example, quite a many of ROG circuits (and their variants) have almost identical attenuating volume and gain control arrangements, the final low-pass filter stage is similar in most circuits, most of them use FET gain stages where only differences are practically the values of gain and coupling capacitance/cut off frequency. These can easily be made switchable and controllable, which allows voicing one basic circuit with many alternative ways. Many ROG circuits also substitute a proper tonestack circuit with some simplified arrangement.

 

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