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Old 28th July 2014, 06:01 AM   #1
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Default upgrading a cheap guitar amp

First off I'm brand new to this and have VERY little experience but I want to learn so this post is for a learning project not to try and build the world's best amp out of cheap parts. I have some quality guitar amps already so rather than suggest go buy a better amp, I'm hoping to get some help.

I have read a lot of blogs, forums and watched a ton of youtube vids but can't seem to get what I need, so I'm here looking for basic knowledge.

Here's what I have... a $35 10w guitar amp. I want more out of it and wanted to learn on it rather than my nice amps. It's labeled as "esteban g-10" ... yup, the crap you get when you buy one of his guitars (don't worry, I didn't buy his guitar, just the amp for a project).

I wanted to upgrade the 5" speaker to a 6" one. Problem #1 then arises.... I don't know if I should get a 4ohm or 8ohm speaker?

I can not find the skematik for this amp since it's a cheap amp probably made by multiple factories overseas (each week made by a new factory that could do it cheaper I presume) so do I go safe and get 8ohm and possible lose volume?

If anyone knows how to find the skematik I'd love the help. Tips on what ohm speaker to get? I found a 6" Jensen (15w) in both the 4 and 8 ohm version online and am tempted to try one out.

I'd love to know more on how to get more power and am willing to learn how to do the work but honestly, I am NEW to this and although I can solder, I don't know 1/2 the things forums talk about... where do I start?!?!? If I posted a pic of the board maybe that would help people tell me what to replace? I'm not trying to get a 50's tweed tube amp sound out of this, just improve the sound but really the point is to learn about this kind of stuff. Remember when you first started? That's me ;)

Sorry for the long post. Thanks in advance for the help!!!
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Old 28th July 2014, 08:04 AM   #2
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What is the power amplifier?, it's probably an IC - so read the number off it.

Also measure the voltage rail it runs off - these two items will allow us to tell you what impedance speaker you need.

Essentially if it's designed for an 8 ohm speaker and you fit a 4 ohm, it will try and output 20W instead of 10W, and kill itself.
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Old 28th July 2014, 08:15 AM   #3
JMFahey is offline JMFahey  Argentina
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Agree and add.

After we know what the actual power/impedance is (supply the data asked by Nigel) , yes, the 6" Jensen Mod in the proper impedance will be a huge improvement compared to the generic original speaker.

Killer little speaker.

And in the future, maybe you build a better amp and will be able to use this speaker there.
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Old 28th July 2014, 11:59 AM   #4
teemuk is offline teemuk  Finland
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It is very easy to measure the impedance. Multimeter will read DC resistance of the voice coil, which is usually only a bit less than the nominal rated impedance.

I don't know if change from 5" to 6" is much of an upgrade. At least I wouldn't do it. Bigger speaker will improve things but I'd step up to at least 8-incher or probably 10" - 12", which however likely requires a cabinet change too. It will be much louder and "fuller" sound with a bigger speaker but then it comes down to whether a 30W cheapie amp is really the right platform to waste considerable amount of money to modifications.

Quote:
I'd love to know more on how to get more power ...
Power does not equal loudness. If you want loud then look for speakers with high sensitivity rating, if you want headroom and clean response at loud volume levels then look for amps with high output power (>50W). Generally trying to rebuild amps to higher power is not worth the effort because - to make a long story short - it tends to require an entire rebuild of the unit. Often its just simpler and less expensive to buy an amp with the right power rating from the start.
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Old 28th July 2014, 07:30 PM   #5
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Quote:
Originally Posted by teemuk View Post
Power does not equal loudness. If you want loud then look for speakers with high sensitivity rating, if you want headroom and clean response at loud volume levels then look for amps with high output power (>50W). Generally trying to rebuild amps to higher power is not worth the effort because - to make a long story short - it tends to require an entire rebuild of the unit. Often its just simpler and less expensive to buy an amp with the right power rating from the start.
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Old 28th July 2014, 09:31 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

TBH its vey cheap amp, various versons but similar electronics,
rated at 12W mains input, i.e. real power output is less, but
I guess it will do about 10W with loads of distortion involved.

You won't learn much about good amps playing with a cheap amp.

Being small it must be sealed back for any semblance of bottom end.
IMO 2" of acoustic foam inserted in the back will do it some good usually.

Changing the speaker to a different driver can do a lot of things.
Make it more suitable for acoustic rather than electric for instance.

However both of the two basic styles are double port vented :

Click the image to open in full size.

Click the image to open in full size.

And here things get very awkward in terms of changing the driver.
You can't just fit any other driver you like, it much match the box.

You need to know things like Vas, Fs and Qes of the driver, internal
box volume, work out the tuning of the dual ports and possibly change
the tuning to suit a chosen new driver suitable for the box volume.

Can be done - but you need to know your stuff. Having said all
that, a driver that is way better (and more expensive) than the
original should be a lot better, but it has to suit the cabinet.

rgds, sreten.

Personally I converted the headphone out of my very cheap
8" bass practice amplifier to a speaker out, and used to use
it with one of the 15" PA speakers we use for live, stored
where we used to practice together, it worked very well.
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Last edited by sreten; 28th July 2014 at 09:54 PM.
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Old Yesterday, 03:42 AM   #7
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So being new I'm not exactly sure what an IC number is, I'm providing the info I see listed. Input is 120v 60Hz and the output shows 11VX2 0.5

The speaker tested to be 8 ohms so I'll stick with that (and get the Jensen 6" 15 w) so I don't blow it up.

Teemuk, I'd love to go to 8" but can't fit one in the box that I have and this project is really about learning on this one, but thanks for the input. I'd like to up the watts if that's possible. I know that may be pricey. The project isn't about the money though. I just don't know electronics and I feel like as a musician I should know more about what I use.

Sreten, the second pic you posted is the amp I have. Any idea how I can get the skematik? I see there are lots of variables to boosting power, and sadly those terms you used I'm not familiar with... that's where I get lost. I read forums, watch vids and try to learn these things but since they have no "meaning" to me it's hard to conceptualize and apply them.

Why don't they teach this kind of stuff in school anymore?!? My Dad and grandpa can build anything and my generation got left behind on a pliable skills. Feeling frustrated. Not giving up though....
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Old Yesterday, 03:43 AM   #8
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Quick follow up... can I rebuild the amp from scratch? Is that a better (cheaper, easier) option that might teach me more about what is going on with in the amp???
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Old Yesterday, 04:16 AM   #9
Enzo is online now Enzo  United States
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Rebuild from scratch? Of course you can, after all the amp is just a box with stuff in it. remove the stuff and you can build whatever you want in the box.

The basic problem here is you have the equivalent of a lawn tractor, and you are thinking you can turn it into a sports car.

IC number. If you look inside the thing, along the edge of the circuit board somewhere, you will fins a little part screwed to the metal or to a metal piece. It will have 5 legs in a staggered pattern. It probably says something like TDA2030 on it, though other numbers are possible. heck it might fool me and have a fancier part, but I doubt it. These amps are cheapies. IC means Integrated Circuit.

Quote:
I'd like to up the watts if that's possible. I know that may be pricey. The project isn't about the money though. I just don't know electronics and I feel like as a musician I should know more about what I use.

I assume you mean make it louder. Power is not loudness. If you could double the power of the thing it would only be three decibels louder. That is not much, about enough to notice and not much more. A new speaker that was 3 decibels more efficient would accomplish the same exact thing but without changing the circuits.

I applaud that you want to learn about your stuff. First lesson is realistic expectations. Changing the speaker is THE single most effective way to change the sound of an amp. Realistically, if you had some circuit knowledge, you could tweak th tonal response of the amp easy enough. But increasing power is not easy. The amp starts with a power supply - the part that makes all the operating voltages. The amp itself just controls that power instant to instant to move the speaker to the music. The only way to increase the power is to enlarge the power supply.

Think about your car. If you want more horsepower, you need a larger engine. Changing the transmission won;t increase the power.

To increase the power supply would mean from the start a new power transformer. Once you increase the voltage and current capability of the power supply, THEN you could look into what you;d have to do to control it with your amp circuit. And all of that amounts to what you said - gutting it and building something new in it.


Why don;t they teach electronics in schools anymore? Because in most places there are darn few jobs in electronics.
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Old Yesterday, 04:29 AM   #10
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Hey Enzo, thanks for the reply. I know I've got a lawn mower (crank start, rusted and probably a leak in the fuel line) to work with. I don't expect to turn this into boutique amp by any means. If I can improve the sound (tone) and learn something along the way I'll consider it a success. Bonus if I can then apply this knowledge to other amps, my mics, pickups etc

I don't need more power/volume per se...I've got big amps for volume. I'd love to improve the tone at louder volumes though. That's where I'd like to learn what to tweet and modify. That's why I thought I needed the skematik.

Sorry if my post hasn't been too clear. Obviously a noob here and not sure of the terms. I'm a musician, not an electrician
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