Tiny new tube amp info thread! (WIP)

Discussion in 'Amps & Cabs' started by Heket, Mar 29, 2013.

  1. Relic61

    Relic61 Well-Known Member

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    I really like Wades idea of taking the back off and then cutting a tight fitting piece that leaves the top or middle open to breath some sound out from the back yet keep some air inside around the bottom to maintain some kick & push. Sometimes I have also found a cab can fall to $#it when there is no back at all. Think of a bass drum with no front head compared to a ported front head. It all about what we do with the air movement we have to work with.

    Fender is fond of the partial open back on most of there combo amps and for many years has had great success leaving the bottom part enclosed with an open middle. This design really fills a room and has the effect of dispersing the sound all around the amp and not just out in front of it. Cant beat it for close quarters gigging or band practice where the only place to stand is a foot or two right in front of your amp.

    I personally have been battling that issue for the last couple of years being I had come to prefer the tightness of the old tube Marshalls heads and tiring of some of the aspects of typical Fender sound reproduction. That meant having to deal with finding the right cab so I can both hear myself where I'm standing and get that thumpy slap to the pant leg tight low end when playing. Mostly all the great sounding cabs that did that were completely enclosed. That meant their sound was directed way out in front of me and not necessarily where I had to stand! Which also meant I had the hardest time hearing my true tone and had to deal with a false representation of my tone where I was basically forced to stand. That was entirely due to the directness & projection of the various cabinets I tried, IE; Marshall 2x12 & 4x12 angled & straight, Fender 4x12 stereo angled and a Dr Z 2x12 large enclosure & other quick forgettables that didn't last a song or two before unplugging them. Quite annoying as well as that whole scenario promotes the desire to keep turning up up up (yeah that's it), until it sounds good right where I'm standing or until somebody starts making faces or asking to "turn down".:mad: Things were really loud (but still a lot of fun) for quite a while. I had to find an answer and ended up going to partially open back designs once again, simply because of the often restricted space I always seemed to be forced to play in. It just works so well.

    How did I solve my dilemma and preference for that vintage Marshall tube amp sound & amp characteristics? My two most used favorite amps now ended up being the unique, surprisingly loud, versatile and tasty little Fender SuperSonic 22 which has me totally impressed and does an amazing job for 2 6V6 power tubes and a sweet playing 76 Marshall master vol 2x12 combo amp which still beats that SuperSonic in the tight low end department. Both have an open back design that really gets things done from both where I'm standing and anywhere else in the room. Ah the years of torment I could have saved if I had found either of them sooner than I did.

    I never had these problems before as I had used Fender combos prior to tiring of their sonic limitations. Before that it was a 1x12 100 watt Music Man RD with again, a partial open back. Hmmm.. what made me think I could get a closed cabinet to work in the first place in such tight quarters? Was I looking to relive my younger Marshall stack glory days? Fact is using a stack definitely puts the sound where you can hear it quite well even when standing in tight quarters but that is just silliness at this point in life and a sure way to ruin what hearing I do have. Nuff said, back to the open backs for me.

    Forgive me for reflecting on my own personal experiences with cabinet issues and if they seem not to directly correlate to the small amp problem scenario we have here. My hope is that it just elaborates on the potential a speaker cabinet can offer as the dramatic differences can easily not even be thought of as a solution to an amp 'problem'. Maybe somebody can relate to that and possibly find their own answer reading about it here and not have to actually go through it all themselves. I'm sure there are closed back cabinets that do a decent job throwing sound around themselves but as a general rule if we want to hear ourselves standing up close to and on top of our amps and we are looking for some liveliness to our sonic output, we are needing to be looking at an open back cab design that gets the job done.

    Now Keep feeding your little amp rock n roll appetites and they are only sure to grow.

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  2. Sootio

    Sootio Well-Known Member

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    Barry has laid it all out there, folks. You have to be quite aways in front of a closed back speaker to actually hear it. A closed back bass cab throws a wave about 30 feet long. Partially open backs give you ambient sound plus a little throw. Best of both worlds.
     
  3. thinkgreen

    thinkgreen Active Member

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    That makes sense. I know from hifi speakers that the design has to be right. My thinking is that this little vox speaker is so tightly pack in that I wonder that the air inside is stopping the speaker from vibrating as it should and giving that muffled sound. To me the tone is good bit is sounds like its in a closed suitcase lol. I like Wades idea to give it a little opening.

    I had a look at my daughters bass amp and although its of a closed back design it dose have a large baffle running to the front, I suppose to allow the bass response to come forward without bouncing of the wall or what ever else it could bounce off.

    What it all comes to is the design of the cab also has an effect on our tones. And the more I look in to it, the more questions it throws up lol
     
  4. Tobacco Worm

    Tobacco Worm Well-Known Member

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    I wasn't going to go into a great bit of detail on cab design as it is far more complex than just making a box and sticking a speaker in it. There are working formulas that are used to design the correct cab-to speaker-to amp, that work well. I just don't have days to explain them.... Below is basically for combo amps and smaller enclosed cabs...

    A good rule of thumb is to have a rear baffle that covers approx. 35%~40% of the lower half of the cab. If it still lacks solid projection to the front and too much is going out the back, then adding about 1/2 of the width of the lower baffle placed at the top of the rear opening is about all that can be done to "close up" the amp and still let it breathe for tone. In short what you'd be doing is creating a broad horizontal port for the cab. This is about the ideal open back cab. This make the best arrangement for combo amps by the way.

    Odd stuff like Newton's Law of action with the equal and opposite reaction bit comes into play with speakers as they do move both ways, remember? Having a fully enclosed cab allows the air outside the cab to be pushed forward, out and away from the cab. The push to the rear is contained within the cab creating a secondary movement of air forced against the cone. You have air that is moved by the electronic impulse to the voice coil and cone, then a secondary from behind the cone. Thus the big booming tone of the closed back cabs. Porting the cab with an extended tube has proven to provide a good working relationship with the speaker and the solid backed cabs in that the tube is open near the rear and allows some of the air movement within the cab to escape via the port tube. The air moves to the rear but a portion of it escapes to ease the dullness know to be heard yet still allows a portion of the interior air to "push" the cone again.

    Placing foam, carpet, or other fabric items within a closed cab is actually absorbing and disrupting that back air flow. By having it in place gives the perceived notion of reducing the influence of the closed cab, however, the air is still trapped within the enclosed cab and is merely dispersed a small amount but it's still present and does not escape. The interior pressure from the cone's movement is still present. Padding is not porting.

    Bear in mind what we hear is air being moved by the speaker cone. The speakers actually push air in various patterns and our ears pick up this movement and transmit that to our brain where we "hear" it. It is a physical action and not an electronic one we actually hear from our amps. So we can plot and plan all we want with tubes, special caps, and amp designs, but the bottom line is that the speaker and cab have far more to do with your tone than what kind of amp you use for the most part. Yes,the amp does aid in shaping the signal to the speaker, but it is not the final product used for the moving of the air to you, the listener.

    Disclaimer deluxe!!! Do not attempt to port your cab unless you have studied and been trained to do so! As I said, there are formulas for this and if one simply bores a 2" hole somewhere in the back or front of their cab it may be far worse if one had left it alone. Don't port your cabs. But you sure can get some nice poplar or fir about 1/2" thick or better and cut and trim it to fit the recessed areas of the rear of the cab and use existing screws to hold it in place. You can take this baffle and test it in different locations on the back as well. A moderate size below and a slightly narrower one above. Or even bring the top down to the lower and have a top opening. This will only cost you the wood and not a whole new back if ya go cutting it up. Once you find what sounds right, paint it or cover it with tolex if you like to make it pretty. That way if you decide to sell or trade the amp or cab, you can put the original back on it. Not everyone likes modified gear as we all know.

    Well that's the old Worm's take on making a closed back or fully open back cab, into a good working tone aid in your amps. This may not be for everyone to play with, but the above information is sound and has been well practiced by myself and other schooled techs out there. Happy baffle making folks!!:fingersx:

    Wade
     
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  5. Relic61

    Relic61 Well-Known Member

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    Boy Wade you sure broke that down in depth brother. I don't see anyone having any questions after reading that excellent dissertation on audio tectonics but if they do I'm betting it will be a real good one. Anyway, you sure put a lot of effort into that answer.

    I cant wait until you got your vast experience & knowledge put together like you were talking about doing. I personally think you should talk to a publisher and see if there is a viable market and interest. If the above is an example of what could be found in that book I think you would have a winner on your hands. But then again I am one of those nerds that would buy those types of books. I guess I'm your kind of nerd Wade. Sign me up for a first edition printing.
     
  6. thinkgreen

    thinkgreen Active Member

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    wade that's the best answer I've read. And I've read a few over the last few nights, most of what you read is sort of do this or do that, and not give any reason as to why and tbh I'm not going to start cutting or play with anything just because someone on YouTube or Internet says it sounds better.

    You have written an explanation and the left the reader to make there own mind up. I agree if your wealth of knowledge was put of to paper it would inspire people for generations.

    Thank you yet again you have put some sense and perspective a subject that most of us don't think about
     
  7. Tobacco Worm

    Tobacco Worm Well-Known Member

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    Ah shucks guys, you're making me blush.... It's just that I have been trained in this sort of thing and would continually study when I was in the business. My customers didn't really care about how I made things work and sound better. They were interested in positive final results. If I went at things with no knowledge, training, or background then I would fail. If I failed then I'd loose a customer. So it was a matter of learning the right way and knowing how to do it right the first time. That way I kept my customers and got more when they'd tell their friends. There was a method within the madness you see!:naughty:

    I don't think I'm book worthy by any means, but I do like to help folks with what I can. Since I can't even hold a screwdriver for more than a few minutes I'm classed as a crippled tech. So those who can, do. Those who can't, teach!

    Barry made some good points and the photo of his new amp there shows how Fender makes good use of the split baffle design and allows for tube cooling with the recessed cut in the upper baffle. And with a tube amp this is a consideration that we must take into account as well. Remember those old tube radios and such that had that masonite back with all the holes and slots? Ventilation for the tubes and made openings for the air movement in the radio's small box. Things are often taken for granted when looked upon in everyday life, but if you stop and study them, you'll see much more there than meets the eye.

    So you guys and gals have fun and if there's something that I can contribute to I will. And in the same token, if I don't know, I'll sure as heck say so too!
     
  8. Relic61

    Relic61 Well-Known Member

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    Wade, I wish you would reconsider the book thing. You are easy to read and follow as well as comprehend. I'm saying you should take some of these thought out and articulate posts you've already spent the time on and put these into a small collection for a publisher/marketing agency to look at for a book. I'm telling ya, all you need is a catchy title and you're golden. Maybe "a Guitar Techs Guide to Success" "Everything You Wanted To Know About Rock N Roll Guitar Repair B.W.A.T.A!" or "Rock N Rollers Repair Handbook" even thusly..."the Guitar Repair Handbook" "Amp Repair Handbook". etc etc... I'm just throwing out ideas but I know that you read better than some of the books I have labored through seeking knowledge on my favorite subjects, guitars and amplifier.

    I know Biddlin is writing and being published and I'm sure he could point you in a fruitful direction. Just don't poo poo the idea as too silly. I think it is totally marketable and when properly titled & packaged it will actually make you some money and bring you the recognition you have more than earned for your years of work in this area.

    One more book tittle... "The Rock N Roll Repair Adventures of....
     
  9. Tobacco Worm

    Tobacco Worm Well-Known Member

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    Barry, it's funny in a way in that old Bill across the road is addicted to "Improper Internet Tech" and ruined the entire fretboard of a strat with a huge file!:wow: Then, I was still fully functional and did a full re-fret job to correct his mistake and took his file away from him. Later when a buddy gave him an old Gibson tube amp that had been fully butchered, we rebuilt it from the ground up into a fully functional amp like it was when new. Between the many hours I've put in with him teaching him as much as I can on guitar and amp repair, he's come up with the idea on making a blog featuring my teaching in chapter form. I told him I ain't nuthin' special and was content to show folks what I can from what I know. In all modesty I can say that I was good at what I did, but again I don't really have the ego to do the self-promotion thing.

    When in the PD I was an instructor in our academy and wrote a few training manuals and such, but that was the PD. There's so many books out there on guitar and amp repair that I can't see where I could really be of any real impact on what's already there. As we say here in Texas "I appreciate the flowers." (a complement) but really I can't see me doing such lofty things as that. Kinda makes me feel weird or something just thinking about it.:naughty:
     
  10. thinkgreen

    thinkgreen Active Member

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    You are very modest Wade. There are many things I'm good at, by I find it very difficult to put in to words and have a real hard time trying to instruct or explain something. You have a knack for it.
    Although we have never met and on reality most prob never will Unless I won the lotto lol but I can honestly say, you are one of them people that makes people's lives richer for knowing you
     
  11. Tobacco Worm

    Tobacco Worm Well-Known Member

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    Are you sure about that? I am a little crackers at times!:laugh2:
    [​IMG]

    But thank you just the same. :)
     
  12. Sootio

    Sootio Well-Known Member

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    FWIW, my brother has an Orange 1x12 cab that he wanted to make open back, so he emailed the folks at Orange, and they advised him to take the back off and cut a 4inch strip from the very center of it, then put the remaining pieces back on. He screwed the 4 in piece into the bottom of the cabinet in case he changed his mind. Looks like Relics Marshall photo, and sounds much better IMHO.
     

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