Hello,
This is my first post. I live way up in Oregon so and there not much in the way of repair shops or the like in this area. I am interested in learning how to do simple repairs and improvements on my own amps and equipment. I own a small squier 15 amp and would like to know if this amp worthless or are there ways to improve the sound? I have some 12" 8 OHM speakers, but I am wondering if it even has enough power to drive one of them. I would also like to know if I may be able to change any of the resistors or capacitors to open
it up so it sounds larger?
I would appreciate any help anyone could provide. Thank You in advance!!!!
Just changing the speaker will do more to alter the sound than anything else you do to an amp.
The ONLY thing an amp circuit knows is the impedance of the speakers you connect to it. It has no idea how many speakers there are, or their size or their ratings. so you can take the tiniest practice amp and connect it to a 4x12 cab. The difference in sound will be amazing. You just have to make sure you do not wind up with too low an impedance of speakers.
Try that before you start worrying about resistors and capacitors.
Hello,
Thanks I will try that. I was going to build a cabinet because I have a few 12"speakers I rescued
from organs.
I also have a 8" speaker I took from a surround sound unit, the bass part . Would that function as as amplifier speaker. The paper cone seems quiet thick.
The 8" audio subwoofer will be very unefficient and muffled, go for the organ 12" ones instead.
Or just arrange to borrow a friend's guitar speaker cab just to listen to.
15 watts is actually quite a bit of power. Many guitarists these days are turning to 15-18 watt amps for a whole bunch of reasons, not least is that with the right speakers they are more than sufficient for most small gigging (and in large gigs you mike them with the PA to give them some "legs").
What you are about to discover is that all drivers (speakers) and cabinets are not created equal.
Forget entirely about speakers that are for subwoofers, cars, or Hi-Fi. Musical instrument speakers are a different animal.
Ex-organ speakers are a reasonable prospect for guitar. They won't have a lot of power handling capability (but 15 or more watts is a very good bet), fairly wide bandwidth, and reasonable sensitivity (efficiency of conversion of electricity into sound).
The main drawback with amps such as this one is that the box is simply too bloody small to do the job properly, the speaker is choked so the cab can be small and more portable - which kinda defeats the reason for lugging it to the gig in the first place.
12 inch Speaker Cabinet build out with Lil Night Train
http://www.youtube.com/watch?v=y9DQhCAB0yE (http://www.youtube.com/watch?v=y9DQhCAB0yE)
(...and you've already got some speakers to try :dbtu: )
Hello,
I would like to thank everyone who responded to this post. I took all of your advice and used one of the organ speakers. I already had one mounted in a cabinet, so I removed all of the inner workings from the small Squier amp and installed it into the larger cabinet. I cannot believe the difference.
I still have a minor problem with scratchy pots but I am sure some electrical cleaner will help. I am
going to make the same change to a small RMS 200 practice amp I have.
Thank You one and all for the help pointing me in the right direction, and preventing me from doing
more harm than good.
:dbtu:
QuoteI cannot believe the difference.
That's the point ;)
Glad you went straight to it. :)
Quote from: SpareRibsI cannot believe the difference.
Yup. (heh heh heh). :dbtu:
Hello,
OK, I moved all of the inner workings into a larger cabinet. I cleaned all the pots and it is at the very
least a 100% improvement. It is really louder and a much more open sound as a result of I guess less of
the sound being confined to the small speaker cabinet and, the larger speaker.
Now I would like to know if there is a way to (for the want of a better term) thicken up the sound?
Are there any caps or resistors that could be changed to give it more of a tube sound. I think it would be
called sag. I know I cannot make a silk purse out of a sows ear, but it is all I have to work with at this time.
As always any help would be greatly appreciated!!!
Quote from: SpareRibsa 100% improvement
You do realise that is only
twice as good, don't you? :lmao:
As you are discovering, some rather nasty things happen when you shoehorn a speaker into a cab that is too small, but you only have to walk into any music shop to see the dominance of physics-free marketing types in commercial amp manufacturing - tiny little boxes that have no chance at all. Back in the days when valve Hi-Fi's were the only option there was a saying about speaker enclosures that "there ain't no substitute for cubic feet", and despite everything since it's still true.
I used to work for a company that made tiny hand-held radios (that honestly sounded pretty damn shocking) and my "party trick" was to hook one of these up to whatever big guitar speaker box happened to be available, and astonish everybody with the transformation. Bass! And how loud only 200mW could be into a proper speaker. The radio circuit was fine, just crippled by a 2-inch speaker in a tiny plastic box.
Quote from: SpareRibsAre there any caps or resistors that could be changed to give it more of a tube sound.
The Holy Grail! You want it
all,
now, right? Well don't we all.
I'll let you into a little secret - exactly
why valve amps sound like they do for guitar is a topic of endless ongoing debate, even among highly experienced experts. A key element is the output transformer and its magnetics, and since solid-state amps don't have one that presents a bit of a stumbling block.
Something simple you could try playing around with are the two diodes D1 and D2. These are the same type with the same forward voltage cut-in, and thus give symmetrical clipping of the signal. If you change one of these, say by putting a second diode (e.g. 1N914 o.n.o.) in series with one of them you will get asymmetrical clipping which will produce more second harmonic distortion, and this
might give you the "thickening" you seek. YMMV.
Otherwise you are just going to have to build yourself a valve amp (http://www.ozvalveamps.org/ava100/ava101lamington.htm). ;)
Hello,
Yes I am aware of the ongoing debate about tubes vs solid state. Any one can start a 10 or 12 page argument just mentioning either one on any forum. I also am aware there will be no holy grail fix to make either sound like the other. Maybe that is not the proper way to describe what I wanted to achieve now.
I think what you just suggested is exactly what I was trying to ask for, and that will just make the sound slightly darker if that makes any sense. Sound is hard to talk about as I am sure you know. One of least descriptive and the and most talked about things are speakers and guitar pickups. All of the way the sounds are described tell you very little. To me crunch, bottom end, scooped mid range, soaring highs, is a bit much. I usually know less after I am done reading the description.
I am going to look at the schematic and make preparations to do the mod you suggested. Thank You very much, and please know I am not a bleary eyed kid trying to turn this little practice amp into a
Marshall Double stack.
Quote from: SpareRibsI usually know less after I am done reading the description.
I know
exactly how you feel - "well that subtracted from the sum of human knowledge" or "there's ten minutes of my life I won't get back" or "WTF am I reading???", etc.
Valves vs. transistors is a whole other thing, calmed down a whole lot these days thank goodness; I just meant that concerning valve amps alone there is no unanimity on why they sound like they do.
One little point about the diodes; putting a couple of silicon diodes in series will be a pretty drastic change, and if you can find a
germanium diode to add in series with one of the existing silicon diodes you may get better results, or failing that a
Schottky diode. It's a bit of a shot in the dark, but it should be a pretty simple thing to try.
Let's know how it goes.
Hello,
I have a few of the Schottky diodes from disassembling various things in the past. Could you recommend a value? That would get the project back on track, as everything will be closed until Monday at the earliest. Thank you in advance.
You have? Great!
Different types of diodes, silicon, germanium, and Schottky, have different forward voltage drops, silicon 0.5-0.7V, while germanium and Schottky are closer to 0.1V. Otherwise it's whatever will physically fit, exact type number immaterial.
Your DMM will show you the forward drop in millivolts on the diode test range.
Go for it! :dbtu:
Hello,
OK, I have been doing research. I went back and pulled the amp apart. The diodes in the amp are as follows (D1-.617 - D2-.642.) I am thinking they are both the same value as the readings are so close.
The diodes I have go from (.742 to .485) that is the range between 10 of them. After taking the amp apart I eliminated the larger ones as the ones in the amp seem to be 1/2watt, or at least I think. I am going to use one of the ones closest in size to the originals.
What I would like to know now, is it your suggestion to remove one of the existing diodes and replace it with a different one ? If so I am wondering if the .742 would exceed a limit. The .742 and a .735 are the same as the ones in the amp as they are glass. The others are black material with silver markings. So would it be best to go up or down to start ?
I have an idea that having two different value diodes will cause somewhat of a ripple in the flow
of the current and slightly distort the sound coming from the speaker. Hopefully in a good way.
One more idea I would like get your opinion on, how about using two wires and alligator clips run to the outside of the amp to clip in different diodes without taking everything apart every time?
Anyway Thank You in advance for any information, you may provide, and for all you have given
me to date. I can't thank you enough. :)
Try it this way, pull the amp chassis out of the cabinet, then run a couple clip leads back to the speaker from the existing speaker wires. Now you can poke inside the amp all you want while it is running.
If you wonder what type each diode might be, look in the schematic. CR3,4,5,6 say 1N4003 by them, and that is the type they are. They don't have a value, they have a type number. CR1 and CR2 are used as clipping diodes and are type 1N4148, says right next to them. CR7, CR8 in the power supply are 12v zener diodes, type 1N4742.
PLEASE don't mess with any of the diodes other than CR1 and CR2. CR7,8 set the voltage for your ICs to run on, don;t change them. CR3-6 are simply rectifiers in the power supply. They need to be what they are.
CR1,2 act to clip the signal when it exceeds their junction voltage. Junction voltage is what your meter is measuring. How large they look is not the issue. 1N4148 is a small glass diode. There is no "limit." You could remove them entirely, the amp would try to be louder, but wouldn;t clip until the signal outgrew the IC they serve. I have no idea which diodes you were measuring, but the 1N4148 should have a junction drop of roughly half to three quarters of a volt. Germanium diodes have a junction drop about half of the silicon ones, 4148s are silicon. If you installed germanium diodes, the amp would clip even harder. CLip at lower levels. You can add an extra 1N4148 in series with each existing one, that will double the clip voltage, so the signal can get twice as large before clipping. SOme amp makers use LEDs for this. Depending upon color, LEDs have something in the 1v ro 3v range of junction drop. Remember, and LED is mostly used for its light, but it is nonetheless a diode.
If you stuck different pairs of diodes into CR1,2 places, you might get different amounts of clipping. If you mix types, say a 1N4148 facing one way, but an LED facing the other, then the clipping would be uneven. You might like that or you might not, up to your ear.
Diode forward voltage drops, (cut-in voltage or Vgamma) depends on a number of factors, the material; the type, signal or power; the current; and the temperature, among others, but we normally generalise that a silicon diode has a forward drop of 0.7V (or 0.65V depending on who you are reading). Schottky diodes are similar to germanium in that they have a forward drop around 0.1V.
I did a small model of this diode clipper in LTSpice, then took a spectrum of the output for a signal level of 0.1V, i.e. below the clipping level, for 1 volt, then 1 volt with a Schottky diode added in series with one of the original diodes.
(http://i1341.photobucket.com/albums/o743/Roly49/Solid%20State%20Guitar%20Amps/Clipsym0v1_zps6137edce.gif) (http://s1341.photobucket.com/user/Roly49/media/Solid%20State%20Guitar%20Amps/Clipsym0v1_zps6137edce.gif.html)
At 100mV and the diodes below conduction the output consists of just the 1kHz input frequency. There is a tiny content at 3kHz but it's 120dB down which would be totally inaudible.
(http://i1341.photobucket.com/albums/o743/Roly49/Solid%20State%20Guitar%20Amps/Clipsym1v0_zps6bb370aa.gif) (http://s1341.photobucket.com/user/Roly49/media/Solid%20State%20Guitar%20Amps/Clipsym1v0_zps6bb370aa.gif.html)
Lifting the signal level to 1 volt causes both diodes to conduct on peaks, and the result is new content of odd harmonics, 3, 5, 7 ... kHz. Now the 3kHz component is only about -12dB on the fundamental and should be clearly audible.
(http://i1341.photobucket.com/albums/o743/Roly49/Solid%20State%20Guitar%20Amps/Clipasym1v0_zps6761795f.gif) (http://s1341.photobucket.com/user/Roly49/media/Solid%20State%20Guitar%20Amps/Clipasym1v0_zps6761795f.gif.html)
Finally I added a Schottky diode in series with one of the existing diodes producing a composite diode with a cut-in voltage of around 0.8V against the other with 0.7V, giving asymmetric clipping. The comb of odd harmonics hasn't changed much, but even this slight imbalance now produces a strong comb of even harmonics, 2, 4, 6 ...kHz as well. While they are not quite as large as the odd harmonics they are still fairly large and their contribution will again be audible.
Quote from: Enzo on November 30, 2013, 04:39:08 AM
Try it this way, pull the amp chassis out of the cabinet, then run a couple clip leads back to the speaker from the existing speaker wires. Now you can poke inside the amp all you want while it is running. If you wonder what type each diode might be, look in the schematic. CR3,4,5,6 say 1N4003 by them, and that is the type they are. They don't have a value, they have a type number. CR1 and CR2 are used as clipping diodes and are type 1N4148, says right next to them. CR7, CR8 in the power supply are 12v zener diodes, type 1N4742.
PLEASE don't mess with any of the diodes other than CR1 and CR2. CR7,8 set the voltage for your ICs to run on, don;t change them. CR3-6 are simply rectifiers in the power supply. They need to be what they are.
CR1,2 act to clip the signal when it exceeds their junction voltage. Junction voltage is what your meter is measuring. How large they look is not the issue. 1N4148 is a small glass diode. There is no "limit." You could remove them entirely, the amp would try to be louder, but wouldn;t clip until the signal outgrew the IC they serve. I have no idea which diodes you were measuring, but the 1N4148 should have a junction drop of roughly half to three quarters of a volt. Germanium diodes have a junction drop about half of the silicon ones, 4148s are silicon. If you installed germanium diodes, the amp would clip even harder. CLip at lower levels. You can add an extra 1N4148 in series with each existing one, that will double the clip voltage, so the signal can get twice as large before clipping. SOme amp makers use LEDs for this. Depending upon color, LEDs have something in the 1v ro 3v range of junction drop. Remember, and LED is mostly used for its light, but it is nonetheless a diode.
If you stuck different pairs of diodes into CR1,2 places, you might get different amounts of clipping. If you mix types, say a 1N4148 facing one way, but an LED facing the other, then the clipping would be uneven. You might like that or you might not, up to your ear.
Hello Enzo,
All of your points are well taken. I will try a few things in the next few days. All within the parameters you have laid out. I guess the amp is older than the schematics posted online as I bought it I guess about 1985, the diode numbers are not on the board. The legend on the schematic calls diodes 1-4 (DS442). That may well be a substitute for 1N4148 but it does not make reference to it. I think I will try one in series to start. The graphs in Rolys post look promising and its an easy mod to start with. I will have to experiment with what I have for the time being.
Radio Shack here only sells flashlight batteries, cell phones, and coax cables. Everything else is special order. They will not be open until Monday anyway. The speaker change encouraged me to try and refine the amp, now that I know it has a little more potential than just encouraging people to junk it and buy a bigger one.
Thank you for your input and all of the valuable information you provide for not only me but
everyone in general. Without your guidance the landfills would be overflowing with good equipment that
would probably only need a 10 cent fix.
Hello Roly,
I am going to add the Schotty diode in series with D2. That should be a good starting point. Since I
now know that is the area that will have the most effect on the sound the speaker conveys that is where I will focus my attention. Enzo also had some interesting ideas about changes in the same area. So armed with all of the information I can now experiment without the fear of of billowing clouds of smoke. With a
soldering iron, DMM, and an assortment of hand tools, I feel there is nothing I cannot tear up.
Thank you again. I will probably be posting some results later today. Good or bad !!!!!!
This will probably be me later today :grr :grr :grr
Hello Roly,
I put a schottky diode in series with D2 as I thought that was more towards the end of the circuit. It is
exactly the sound I was hoping for. I can only try to explain it by saying, it took away the solid state brittle
sound and made it sound fuller and more resonate if that makes any sense. I cannot believe the difference
the 12" speaker and one diode made. Now I am going to do something very strange, I am going to call it complete and not make any further changes to it.
Thank you for all your input and assistance. I only knew what I wanted I had no idea how to make it happen. This is one of the better forums on the internet for beginners in electronic modding. Thanks again.
:dbtu:
Hello,
Thank you Enzo for your input and advice concerning my amplifier modification. It worked out great.
:dbtu:
Hello,
Thank you J M Fahey for your input and advice concerning my amplifier modification. It worked out great.
:dbtu:
It won't make any difference which diode you add the new diode to, either will have the same effect.
Quote from: SpareRibsIt is exactly the sound I was hoping for.
Amazing the difference a bit of 2nd harmonic distortion can make, eh?
That's what we like to hear - enjoy. :dbtu:
Hello,
Yes, The second harmonic has the effect of the technique musicians sometimes use recording several takes of the same song and blending them to come up with a harmony using more than one of them. I am
in awe how simple it was.
Now on to the next project. I have another small amp RMS-200, I was trying to find a schematic to no avail ! TO MY SURPRISE right in the middle of the board was the same little circuit, two IN4148 diodes and a 2.7K resistor. That is very encouraging because I just happen to have four more 12" speakers and a few of the Schottky diodes. It seems to get better and better. Now it seems some my hoarded up junk is not so useless after all.
So I am on my way to adventure, in the words of the Terminator (ALL BE BACH) !!!!!!!!
8|
Hello Roly,
Last night I added a diode to the RMS-200. I put it into the cabinet with the 12" speaker, same results.
Instant full rich sound. It is unbelievable.
I have a Crate GX40-C, it contains two amps and I think I see the same type circuit in both, coming off of the IC's. It is comprised of two diodes a resistor and a capacitor. I am wondering if I can achieve the same effect with that one ? Anyway I will have to remove it from the cabinet to see if it has the same configuration. The schematic from Loud Technologies is not very good. The lettering is not plain when it is magnified. I'll have to search around and see if I can come up with a better one.
Any suggestions would be greatly appreciated.Thank you in advance.
:)
Be careful, amps normally have a few diodes that can do significantly other things you don't want to mess with.
The dead giveaway of a clipper in the signal path is two diodes connected together in opposite directions (and generally not too far away in the circuit from the main volume control).
Just remember, all amps are different and YMMV; some amps respond well to this sort of mod, others not so much.
Hello,
I think you are right about this. I have a lame schematic for the GX40-C. I cannot read any of the values, and it doesn't seem to have the preamp on it so I guess I will hold off on that until I can find a better schematic. Anyway two out of three ain't bad.
Hello,
Well all of the small amps are done. I think I will check with the amp tech in town and see if he has acquired any hopeless case amps. There is a Guitar Center in town so there should be a boat load of Squier 15's around. They come with the starter packs, I can imagine its not long before the bigger amp bug bites, most especially since they sound so junky new.
I think that could be an untapped resource. The only problem would be acquiring larger speakers but I can struggle along. There is also a electrical recycling center close. That may provide some likely prospects for experimentation. Anyway on to the next hopeless looking project.
I would like to thank each and everyone of you for all of your assistance, I couldn't have done any of these things without all of your input.
:dbtu: