Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Preamps and Effects => Topic started by: sergscar on May 10, 2009, 12:42:24 PM

Title: Using Ruby circuit as a preamp (line out ?)
Post by: sergscar on May 10, 2009, 12:42:24 PM
Hi guys !
I'm playing a little with my Ruby amp, wishing to add some features to this little marvel.

One of the options I see is to use it as a preamp, pluggin' it to a old 15Watts' "Dean" amp I have found in a "twilight" zone of my house (a sort of "Lost & Found" room...  ;D )

The question is:
May I plug the instrument in the Ruby and create a line-out connection, which should go to the input of the Dean Amp ?

I've found (inside SSGuitar forum) a link to a line-out schema, which I post here below:

(http://img352.imageshack.us/img352/5324/lineout.jpg)

Additional questions:
- Should I use this from the Spk out of my Ruby ?
- Shall I disconnect the spk from the Ruby, or it can remain connected ?
- Can this connection damage the Dean ?

Thanks in advance for your help !

Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: joecool85 on May 10, 2009, 06:10:58 PM
I ran my little gem (similar circuit to the ruby, based on the lm386 still) directly into my Dean Markley K-20X with no problems.  I also ran it directly into my LM3886 poweramp, it worked wonderfully for me.  I'm sure others will have opinions on the matter.  I'm currently working on a simple preamp with clean and gain channels based on the lm386.  It's not a good chip for hi-fi (as a preamp anyway), but works great with guitar.
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: sergscar on May 10, 2009, 09:33:24 PM
Hi JoeCool, thks for your comments.

It's good to know that this may work. My only concern was not to damage the amp.
Maybe the output of LM386 is weak enought for non damaging the amp, and according to your feedback "...I ran my little gem (similar circuit to the ruby, based on the lm386 still) directly into my Dean Markley K-20X with no problems..." seems it won't.

Pls, keep us posted once your preamp project is finished !
In the meantime, i'll give a try to this configuration and post the results in the forum.
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: J M Fahey on May 11, 2009, 12:29:35 PM
Hi Sergscar.
You *can* drive a preamp or power amp input with Ruby´s speaker output and get away with it, only because it´s 9V powered and can´t put out a signal voltage higher that of any other 9V pedal , although at a *much* higher current level.
To play it safe, pad the output with two 10K resistors, one in series with the signal and the other to ground.
This both limits voltage (from almost 3V RMS) to half of it, but more importantly limits current to pedal-world levels.
An even better solution is to replace the 2nd resistor with a 10K pot to get any output level needed; it becomes a Master level.
Bye.
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: sergscar on May 11, 2009, 12:59:56 PM
Hi JM Fahey !
Nice and clear explaination.
So, I'd do this ONLY if running the Ruby on 9V (just as a reminder: LM386 can be powered at a max. of 12V !).
I'll do my homework and post some feedback.
Thanks !
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: J M Fahey on May 11, 2009, 02:14:55 PM
Hi Sergscar. In fact it´s the other way round: you *can* avoid using it (sort of) with a supply of *up* to 9V (I would be worried even then) but you definitely need to attenuate with higher supply voltages. Bye.
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: sergscar on May 11, 2009, 03:42:50 PM
JM Fahey, hello
You are right. I've just realized that expressed myself bad.
I was willing to say "... void to use it as a preamp if powered with over 9v...".
Anyway, this mistake generated a new light => I can even use it if powering with 12V, however, reducing the output current (maybe I've to use higher resistors).
Sorry and thks again !  :tu:
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: joecool85 on May 11, 2009, 07:39:18 PM
Just remember, runoffgroove.com has two pedals based off the lm386 - the big daddy and the grace overdrive.  They use a 100k pot as a master volume, similar to what JMF posted.
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: sergscar on May 24, 2009, 03:36:31 PM
Hi guys,
I've already done the preamp circuitry, as well as tested it with the Dean GTX12.

From the input jack of the Dean (inside the amp), I've soldered 2 wires, which I've added the 2 resistors (10k), as suggested by JM Fahey (see picture below)

(http://img188.imageshack.us/img188/5697/rubypreamp1.jpg)

In the preamp (Ruby-LM386), I've left the gain "open" (20db Gain), keeping the original 10K linear pot as volume control (see picture below)

(http://img43.imageshack.us/img43/179/rubypreamp2.jpg)

I don't know if by doing it this way it should react different than the "better solution" proposed by JM Fahey (replacing the "R2" - 10k resistor - with a 10k linear pot, for acting as a master volume). Comments on this issue ?

The result:
- Much clearer sound from guitar, if compared with original setup
- Louder volume, without necessity to get a higher gain (distortion) from the op amp

Question:
the new setup permits me to run the amp by its original input jack, as wel as through the preamp.
Should I notice any response's difference, in case I decide to use amp's original input jack, considering there's a "bridge" connection (R2 10k, as showed in the picture) between the + and - wires ?

Thks a lot your comments.
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: joecool85 on May 25, 2009, 04:41:24 PM
So are you able to get a good clear clean sounds even while playing chords with your guitar's volume up all the way?
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: sergscar on May 25, 2009, 09:48:24 PM
Hi Joe,
I wouldn't say "100% clean", but much more clear than before.
- In fact the Dean GTX12 doesn't produce any sound if gain pot set to "0", therefore, there will be some distortion, naturally.
- The treble and the mid seems much more "enhanced" and brighter than originally, but not losing the bass.

So far, I had a very good impression (I just tried it for abt 10 minutes), and after running the guitar directly on the amp (bypassing the pre amp) my son and I had the feeling that the sound was "fuggy", that's why I asked a particular question (quoted here below):

Question:
the new setup permits me to run the amp by its original input jack, as wel as through the preamp.
Should I notice any response's difference, in case I decide to use amp's original input jack, considering there's a "bridge" connection (R2 10k, as showed in the picture) between the + and - wires ?


Well, those are my first impressions, and I'm afraid won't be able to test it further until the next weekend.

If you wish, please ask specific questions abt the performance, and I'll post the results asap.
I'll also try to record some samples, posting it here, for your easy comparision.
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: joecool85 on May 26, 2009, 05:06:28 PM
Excellent, keep us posted!
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: sergscar on May 31, 2009, 06:19:22 PM
Hi guys, as promised, here you have the demos:

DEAN GTX12, without preamp => http://www.scarimbolo.com.ar/31MAY091_DEAN.mp3 (http://www.scarimbolo.com.ar/31MAY091_DEAN.mp3)
Preamp => DEAN GTX12 => http://www.scarimbolo.com.ar/31MAY091_DEAN_PRE.mp3 (http://www.scarimbolo.com.ar/31MAY091_DEAN_PRE.mp3)

You will notice the difference I've talked about... but, please, forgive my poor performance in the guitar

Doubts/questions, feel free to let me know.
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: joecool85 on May 31, 2009, 08:19:18 PM
Hi guys, as promised, here you have the demos:

DEAN GTX12, without preamp => http://www.scarimbolo.com.ar/31MAY091_DEAN.mp3 (http://www.scarimbolo.com.ar/31MAY091_DEAN.mp3)
Preamp => DEAN GTX12 => http://www.scarimbolo.com.ar/31MAY091_DEAN_PRE.mp3 (http://www.scarimbolo.com.ar/31MAY091_DEAN_PRE.mp3)

You will notice the difference I've talked about... but, please, forgive my poor performance in the guitar

Doubts/questions, feel free to let me know.

Wow, that sounds great!  I'm going to have to build another lm386 just as a test bed preamp and see what it does hooked to my lm1875 amp...
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: J M Fahey on May 31, 2009, 09:29:15 PM
Hi Sergio.
Incredible difference !!!
The "flat" Dean sounds dull and lifeless; the "SergScared"one is alive .
Congratulations.
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: sergscar on June 14, 2009, 09:55:05 PM
Hi guys,
I've finished the casing for the preamp.

Here I post some pictures of it:

(http://img199.imageshack.us/img199/5621/innerview1.jpg)
(http://img200.imageshack.us/img200/6070/fronttop1.jpg)

Another good thing is that I can use the pre-amp as "stand-alone" headphone amp which, by the way, sound very nice !
Just lack replacing the jacks, since I've used stereo ones, and sound is just audible in one of the channels...

Hope ou like.
Title: Re: Using Ruby circuit as a preamp (line out ?)
Post by: Brymus on August 17, 2009, 06:59:03 PM
I think it looks AWESOME Serg!
AND this thread helped me alot too,good info.