Please review my guitar amp plan (high level)

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38eighteen

Member
2007-11-08 9:18 am
  • #1
    Hi,

    I have decent (maybe) theoretical understanding of electronics from high school etc. I have never put it to practical use other then building a couple of simple kits. I have reasonable wood working skills and access to most tools.

    My 13 year old son has been playing guitar for over a year now and has demonstrated that he is keen to continue. I would like to upgrade his amp for him. He is currently using the Squire SP-10 that came with his guitar.

    I have done a bit of reading (including the "Solid State Guitar amps worthwhile??" thread and a lot of stuff referenced from it) and it seems that amps are a very personal choice. He does not yet have enough experience to make a very informed choice :) He will also almost certainly want to upgrade his guitar soon as well so I don't want to spend a lot on an amp.

    Here is my plan...

    - Build a head and 2x12 box. 2 pieces for easier carrying. 2x12 because I have some old 12" drivers that should be OK for starters.

    - Build 2 x LM1875 power amps using the schematic from the data sheet.

    - Build a TL082 based pre-amp using the schematic from the data sheet.

    - Build 1 or 2 effects from runoffgroove.com to put in front of the pre-amp with appropriate switch capability - 1, both or neither in the path.

    My rationale is that this is modular and can be incrementally improved as he "grows". It is also not a huge investment so I can abandon it if the whole thing is a flop. I'd love to build him something tube based but with his lack of experience (to know what he wants) and my lack of knowledge/experience it is just not an option. Maybe next time...

    I'll need some help from "you" though...

    1. Does this sound like a reasonable plan?

    2. Is the the schematic on the TL082 data sheet even a pre-amp?? :)

    3. I know that most of the circuits on runoffgroove.com are intended for use in stomp boxes. Can you suggest some that might be good general "basic" effects that could be easily modified to wire into the cabinet? I am concerned about matching sensitivity between the various devices, but as they seem to be designed to chain together I'm not sure if I need to be - does it depend on the ones I choose? Should I just build a simple, "clean" amp and keep the stomp boxes external?? (I think he would want at least 1 distortion built-in...)

    I've got a few more questions, but they are not worth asking yet...

    Thanks,

    Brian
     
    3

    38eighteen

    Member
    2007-11-08 9:18 am
  • #3
    OK, but is that going to give a clean channel to run other effects through? Or, do I just need to make sure that any other effects I build (or he gets elsewhere) have enough gain to drive the power amp? Will this restrict him sharing/swapping stuff with his friends, or do most/all effects have enough gain?

    Thanks,

    Brian
     
    B

    blindsjc

    Member
    2006-11-28 9:35 pm
  • #5
    Hi friend,
    Using the tonemender project from runoffgroove.com
    as your preamp could be much better than the TL082
    datasheet project. I'm using it this way with very good
    results, worth to try.

    If you want a volume control that can make it zero volume
    just use a 120K resistor (25x aprox.) in the place of level
    pot and use a 100K pot in the output. My tests give full
    output from a LM3886 amp using this configuration but
    I think you can set it with even more gain. Just an idea
    for a really flexible and simple preamp.

    Hope this info help in some way, sorry about my poor
    english. Thanks a lot and good luck.

    Blindsjc
     
    3

    38eighteen

    Member
    2007-11-08 9:18 am
  • #6
    I had seen that one and thought about it. But, I am probably going to use the ROG Thor as the pre. I have ordered all the bits to make it as an effects box. If my son likes the sound he can get with Thor through the clean channel of his current amp I will take it out of the effects box and use it as the pre amp. If not, I'll make another circuit for the box and keep trying...

    I've also changed the rest of the "design" as well :) I've been reading a fair bit more and am thinking that I will probably use a single LM3886 rather than 2 LM1875s for the power. I was thinking 1 amp per speaker, but I have realised that the current drivers I have will be no good for anything other than proof-of-concept for the look of the box. I am going to need to buy a real driver so it will probably just be a 1 x 12. Now that it is only 1 x 12 a combo will be manageable for him to lug around...

    I still need to experiment with the sound of the Thor once I get it built as well - he is keen to have a nice clean channel so I might need to build the vanilla TL082, or maybe the Tonemender, as well.

    Thanks,

    Brian
     
    B

    blindsjc

    Member
    2006-11-28 9:35 pm
  • #8
    38eighteen

    Ok friend,
    Just take care to not use a hi-fi style preamp
    or amp for guitar, at beginning it sounds good,
    clean and musical, but along a band you will feel
    that something is really wrong. For your LM3886
    amp I suggest the project below:

    http://sound.westhost.com/project19.htm
    But, add a feedback resistor, works fine.

    Andronico

    About the GT2 pre... Can it handle another distortion
    before it? at the clean configuration? I'm in process
    os construction (pcb finished) but don't know too much
    about the circuit. If it can, is a really good pre option too.
     
    T

    teemuk

    Member
    2004-11-02 8:51 am
    Suomi, Finland
  • #12
    Brett

    Brett

    Member
    2002-01-07 6:02 pm
  • #13
    My experience tells me otherwise. If you think a couple of R O/P Z is going to make it sound like a tube amp, get any SS amp and add a resistor in series and tell me if it sounds remotely like a tube powerstage. It won't, or they would have been doing it for 20+ years.
     
    T

    teemuk

    Member
    2004-11-02 8:51 am
    Suomi, Finland
  • #14
    In fact, guitar amp manufacturers have been employing the mixed mode feedback at least since the 70's or early 80's. That's more than 20+ years.

    However, I never said that this technique would make a solid-state amp sound like a tube amp. Yet, the effect that increasing the output impedance has on the frequency response is very audible.

    This effect is also one of the ingredients in “tube sound”, along with OT saturation, softer (sometimes asymmetrical) clipping and occasional bias drifts during overdrive. I believe that none of these variables alone can be pinpointed as an exact cause for “tube sound”, though: For example, not all tubes clip “softly”, some tube amplifiers (such as Hiwatts) hardly introduce OT saturation, push-pull amps do not clip “that” asymmetrically etc.

    As far as I see it, the “tube sound” is just a concept that lies in the head of the listener. Each and every one of us has a certain mental image about it and these images can differ a lot from each other, don’t you think. If adding few resistors can audibly alter the tone in to a (subjectively) better direction then why say that it “isn't much of an issue in tone”?
     
    P

    praga37

    Member
    2008-05-13 12:00 pm
  • #16
    That's my opinion...

    If ever you want to consider a valve amp instead of solid-state, give your son the best little amp one could get for the money, namely the Orange Tiny Terror; a 17 w class A single channel of pure British tone (and frighteningly loud for such a small box, let me tell ya...).

    OR, build one up by yourself from scratch using various kits available on the web. (hours of fun... years of pride!!!)

    But, don't get fooled by the guys who tell you that modelling amps (sansamp for instance) will give you the sound and especially the tone of a hot-rodded classic Marshall or Fender tube amp. With the recent resurgence of small boutique style valve amps by Orange and Epiphone (check the Valve Jr), it all proves the point that solid-state technology could never attain the tone generated by valve amps.

    Being virtually the most ignorant man alive in regards to how a valve amp works (or a solid state amp for that matter...), I choose the easy way out and bought this little amp made by this guy from Ontario (http://search.ebay.ca/_W0QQsassZontariomaximus). It duplicates the aforementioned Orange TT but with (seemingly) some improvements. Needless to say, this little thing has tons of tone and it satisfies my tonal needs much better than my Marshall JCM-800 did. I also bought a pair of new Made In England Celestion Greenbacks and I am currently in the process of building a 2x12 cab; the head will follow.
     
    Nordic

    Nordic

    Member
    2005-09-01 7:17 pm
    users.tpg.com.au
  • #17
    Here is an idea.. liberate the squire amp part from the box and turn it into a head.. It is likely miles ahead of what you are planning now, and I have yet to hear one of these baby amps that does not sound pretty nice when connected to a decent speaker... their downfall is the horrible little drivers they ship with...

    I am in the process of building a "small" amp head now too... valve preamp and discrete power amp.... untill such time as I can afford an output transformer and output tubes... The valve pre cost me about $50 exluding pots..s for controls
     
    B

    blindsjc

    Member
    2006-11-28 9:35 pm
  • #18
    Hello Dear Friends,
    I'm really in tubes amps today,
    started with the Matchless HotBox stompbox,
    little amps and now I'm winding my own OPT
    transformers and will have my SloClone made
    soon. Now I see, a real jump in production
    since last november.

    This forum improved my know how like a bomb,
    thanks a lot for any of your lessons my friends.

    Blindsjc
     
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