Trying to get a better drive sound from the 25R. Looking at the schematic of the 15R and the 25r the difference in the two circuits seems to only be the switching and two diodes. What would be the purpose of D1 and D2 in the 25R drive circuit?
As a general rule, these little beginner amps are already optimized for what they are.
I don't think there's much to be made to "improve" the sound, at least speaking of amps made by the "Big Ones", say Marshall, Fender, Peavey, Laney, Crate, remember they *know* how to make a good amp.
They are very good for what they are, and there is *NO* mod that will turn them into Mesas, Soldanos, Diezels, Engls or top line Peaveys.
That said, the area where cost-cutting causes most damage, is on the speaker (and attending cabinet).
If you can wire an external speaker jack that cuts the internal speaker when you plug a cable there, and you hook it to the 4 ohms jack of a Marshall 4x12" or equivalent box, you will be *blown* by it, no kidding.
Power, sound, chuggy lows, good non buzzy highs, the works.
I assume you are playing LOUD.
Try to do it at least once, get somebody to let you plug your modded amp there (I mean the new jack).
You'll be amazed.
Being poor and not able to afford anything that glows in the dark I have to work with what I have. NO I don't play loud I hardly ever turn it above 3. I play at home for my own pleasure not giging too old at 56 for that. I would like to replace the nickle and dime opamps with some OPA2228's. Just wondering what the hell Fendr put the stupid diodes in there for. If they are not needed for the JFET switching circuit it would sound better without them. I don't want to start changing things without a plan. Would also like to get a Ramrod speaker in there.
Just re-read the post above your reply,,, JM Fahey is no mug 0:)
Heck replacing opamps in such an amplifier is just thowing money out the window.
Phil.
Why are the diodes stupid? And if you don't like D1,D2, I see no reason you wouldn;t hate D3,D4 and their LED buddies as well.
Those are clipping diodes, when the signal reaches a certain amplitude, they start clipping it - it adds distortion. They also serve to limit signal excursion into the later stages.
I would agree that replacing the op amps won't accomplish much. Nothing at all wrong with TL072s. Keep in mind that this amp is not a hifi amp, no guitar amp is a hifi amp. The amp is not designed to faithfully reproduce the input signal, in fact it is not designed to RE-produce anything. The amplifier is a primary producer of sound, it is part of your instrument. Guitar amps are of limited bandwidth. A guitar speaker will be rolling off the highs over 3kHz to 5kHz, and the amp circuits generally are not much interested in anything over 5kHz. SO "improving" the circuit to have video bandwidths and lighting fast slew rates won't do anything for you.
Hi Freddie.
Fully agree about your Ramrod idea.
If you can build a somewhat larger box for it, even better; you said you won't be carrying it around much.
When I said "Loud" I did not mean "upgrading" to a 50 or 100W amp, but to let loose the one you have now.
I'm sure you are very annoyed at the buzzy thin sound you have now, and most "solutions" consist in heavily cutting the top end, which will kill the buzz, but also sparkle, definition, the works, and not adding needed bass.
Your Ramrod or equivalent "serious" guitar speaker will give you a much better tone, and using the amp "loud" as , say, above 6 or 7, will clip the annoying peaks *without* cutting definition.
To lower power somewhat, you can buy an 8 ohm speaker which will lower your power to about 15W.
Anyway, good tone requires certain minimum levels, the best 1W amp in the world may *record* excellent but your ears will think otherwise.
As far as OpAmps, diodes, etc., the maximum has already been squeezed from them.
I was asked why d1 d2 were stupid. Well they are whats known as hard clipping diodes. The problem with the distortion is it is too hard. Getting rid of the hard clipping stage would leave only soft clipping like a tube screamer pedal sounds so much nicer.
Looking at the schematic from Fender.com for this amp, it already uses a form of soft clipping. If you look at the clipping stage (looks to be the first half of the second tl072 in the signal path, kinda hard to tell with the blur filter fender seems to have for this pdf), that is the method of clipping used in the Timmy pedal, with a pair of leds substituted for the second pair of diodes. The resister before the junction between the diodes and leds increases the soft knee characteristic turn on of the leds. All the pair of diodes are doing is to raise the clipping threshold by .6vdc, giving you a clip point of approximately 4.4vdc p/p. Having scoped more than a couple of these circuits, the waveshape is a soft turn on. I will leave it to those who are busier arguing about it than playing as to if this style of clipping is more "valve/tube" like, or not. Be that as it may, the only thing that would be accomplished by removing D1&2 is to lower the clipping threshold, pushing things to the square wave distortion point that much earlier. And make your output signal 33% quieter.
The caveat in all this is how much gain previous preamp stages have given the signal, and how close the signal peaks come to the power rails. Again, thanks to the Fender blur filter, this is rather hard to calculate.
The main point to take from this, is that the amp is doing the job it is designed for. It's problems come from inadequate cabinet size for the speaker. The speaker itself is not the worst I have ever seen, but it is crippled by the cabinet. I have seen some folks kind of tame the ice pick from these by using a Jensen Mod 10 to replace the stock speaker. Your mileage may vary, and like clipping diodes, most of what you hear on the internet about speakers needs to be taken with a very large grain of salt.
And by the way? Those "hard" clipping diodes? The tubescreamer uses three of them in pretty much the same configuration to produce it's sound. Only difference is the crappy op-amp used in the TS. If your fender was using the same JRC4558 that the TS used, I could see changing them out. The magic in the 4558? They cost Maxon and Ibanez $0.012 each. The Fender uses TL072's which are just fine. And depending on your soldering skills, none of the op-amps are socketed, and these traces lift up awful easily.
The folks above gave you some very good advise, and they do know what they are doing and have been doing it for many decades. That is what is neat about this place, no BS and folks that have been there.
Quote from: J M FaheyIf you can wire an external speaker jack that cuts the internal speaker when you plug a cable there, and you hook it to the 4 ohms jack of a Marshall 4x12" or equivalent box, you will be *blown* by it, no kidding.
Totally Agree. Speaker upgrades generally give you the biggest bang for your buck, and the smaller (and cheaper) the amp, normally the bigger the improvement. Cone area can do wonderful things for a small "economical" amp.
Thing is, "nickle and dime opamps" such as the TL07x-series are these days
so good (compared to crud like 741's or even 4885's), and so cheap for what they are, it's just stupid.
For a while I had a love affair with the LM833 Dual (now apparently discontinued) and used them in several retro-fits and referbs, and also in the preamp upgrade for my stage Twin-50 keyboard amp. In 50 years in electronics they are the closest thing I've ever seen to a "perfect" amplifier, dead silent with oodles of gain to boggling frequencies.
Originally the preamp gain came from "low noise" BC109C's, but still had quite a significant and audible noise floor.
The pre I built to replace it was nominally the same except it used LM833's (at a buck-and-a-half a pair) for the gain.
The first shock was the bandwidth - it initially oscillated like crazy at 455kHz (!) and I had to specifically limit the bandwidth to 33kHz, down from 5MHz, to ensure stability.
The second shock is that it is now
so quiet you can't tell if it's turned on without looking at the pilot light. {It can be a little unnerving on stage actually because now there is no audible clue that you have left the gain really cranked and are just about to give everyone an unintended blow-wave.}
Quote from: FreddieI was asked why d1 d2 were stupid. Well they are whats known as hard clipping diodes. The problem with the distortion is it is too hard. Getting rid of the hard clipping stage would leave only soft clipping like a tube screamer pedal sounds so much nicer.
How "hard" a diode clips depends mainly on the conditions it is operating under.
An anti-parallel silicon diode clipper has a nominal cut-in or knee at 0.65V ... or 0.5, or 0.7 depending on how you measure it, who you have been talking to, the web sites you have been visiting, wind direction, humidity, the Dow-Jones, and the state of your ulcer.
Because it's actually a temperature-dependent
curve.
(below, top-right "Forward" quadrant)
(https://dlnmh9ip6v2uc.cloudfront.net/assets/4/4/a/5/b/5175b518ce395f2d49000000.png)
And a real diode;
(https://dlnmh9ip6v2uc.cloudfront.net/assets/0/2/2/c/c/51781965ce395f8350000000.png)
Forward voltage depends on the current.(both images thanks to: https://learn.sparkfun.com/tutorials/diodes/real-diode-characteristics (https://learn.sparkfun.com/tutorials/diodes/real-diode-characteristics))
If you drive this diode pair (via a resistor) with a signal of say 10Vpk it will hard limit at around 0.65V, but if you drive it with a signal of around 0.65Vpk it will only slightly depress the extremes, very soft clipping. Now if you increase the dive to say 1V pk you will get heavier compression of peaks (but still "soft") and some compression of louder parts. Increase the drive again to say 2Vpk and the peaks will be hard limited and all the rest progressively soft compressed according to its amplitude. Back up to 10V drive and you've got rock-hard shred.
What gets interesting with diode clippers is that if they are
asymmetric, one voltage is greater than the other (the classic being mixing a silicon and germanium diodes or different coloured LED's) then the spectrum of the output suddenly contains a whole lot more second harmonic to go with the third which is already there.
These days it is so easy to make the electronics good cheaply that cost-cutting hits other part of the design such as speaker choice, cab size, material and thickness (and you can't fix wot ain't broke).
QuoteI was asked why d1 d2 were stupid. Well they are whats known as hard clipping diodes
Why is everyone overlooking the simple fact that these diodes are practically
connected to the inverting input, which practically sits in 0V under normal operating conditions. These diodes do next to nothing when the amp operates normally but I suppose Fender has found out they offer somekind of transient/surge protection either for the switching FET or the opamp itself since they widely seem to be using this scheme in their amps.
But ordinary signal clippers they aren't. More akin to those diode clamps that hook up to supply voltages; operation only when things would go south otherwise.
The most funny part is that I've seen people copy these Fender circuits right down to these protection diodes but sans the FET switching, which effectively means wasting two diodes for nothing.
I'm wondering if the design, using the GP diode clamps, is for ESD suppression. :-\
That will teach me not to check the circuit before commenting. :-[
You are quite right, with the FET Q2 on they will have no practical effect.
So what
are they for? My
guess is that without these diodes when the FET is off it would see the full output swing of the previous op-amp, and that this might be enough to bring it into conduction on peaks. Maybe.
Quote from: gbonoI'm wondering if the design, using the GP diode clamps, is for ESD suppression. :-\
Doubt that; not connected directly to the outside world, TL072's are pretty robust, and in the middle of the amp but nowhere else.
In fact this already has a pretty fancy clipping network around U2-B (D3, 4, 25, 26 and R22). My comments above should be related to these diodes, not D1 and D2. Sorry. :'(
Can I look properly abashed? I will blame it on my laziness on not searching for a readable copy of the schematic. I had noticed the protection diodes, but not having things legible, I assumed (there is THAT word again) that we were not talking about these, as they are not clippers. My response was from seeing the circuit, but not values, around U2b, the "timmy" clipping arrangement. I think that when the OP talked about clippers, we all automatically zoomed into the clipping stage of the pre amp. I did. Sorry. Grumble grumble. No cookies (biscuits) and milk tonite... No Arnott's for me.
Yes, suitably abashed :-[ , and I don't even have the excuse of a fuzzy circuit - I just assumed; incorrectly. xP {'tho I think the "Arnott's" reference will be lost on most - they are an Aussie biscuit maker.}
Perhaps this one is more readable;
http://elektrotanya.com/fender_frontman-25b_sch.pdf/download.html (http://elektrotanya.com/fender_frontman-25b_sch.pdf/download.html)
Can anybody please provide Frontman 25
R
schematic?
The one linked above is for Frontman 25
B
:duh
Thanks.
By the way, Frontman 15R (or not R) would be interesting, since it has been also mentioned .
These were posted on MEF by Enzo a while back... Thanks Enzo! :dbtu:
Thanks, Dr G. Much easier to read.
Roly, I was introduced to Arnott's when I spent a couple of weeks in the Siding Spring - Coonabarabran region doing astronomy a few years back. Since, I've found that Costco/World Market in the states actually imports them. I would rather they imported the very tasty Brothers in Arms Shiraz I was also introduced to that trip, but at least the vegemite display is very small. :cheesy:
Quote from: bobhillSiding Spring - Coonabarabran
Quoted on some control systems when they were building it - didn't get the job. :-\
(http://resources1.news.com.au/images/2011/11/30/1226210/561405-trish-adams.jpg)
Many uses. You can even eat it.
Hey bobhill i know its the wrong place but is there any way i can a scmatic on that toby amp :dbtu:
Hi there, I'm totally new in here, and would like to share my experience with this "cheesy little amp". I shot mine (FM 25R) for just 40 Euro on Ebay. First of all I was not very satisfied with the sound, hence I began looking for mods. 1st thing I did was changing the std. Op Amps to OPA 1234, which reduced the ground noise significantly, but did not improve the sound in any way. Hence I swallowed the bitter pill, bought an Eminence Legend 1058, put it in and what should I say? That did the trick! Since then chords are popping like pearls out of the amp, it is loud enough to stand drums, bass and 2 sax in our little Jazz combo. Bass fundament has improved as well. I cannot say anything about the drive channel, because I'm playing 99,9 % clean.
I have got another Fame 60 Watts combo with tube pre-amp, but that pales in comparison to my Frontman. Maybe I'm going to exchange the Factory mounted speaker and put a Legend in as well. Let's see...
Greetings to all, keep jamming.
FlyinTune, great first post and very helpful. It seems the number 1 thing on most of these cheap amps is speaker. After that it's always a good idea to check over wiring and make sure things are properly grounded and jacks not worn out.
Quote from: Tobyguitaramps on February 14, 2014, 01:22:59 PM
Hey bobhill i know its the wrong place but is there any way i can a scmatic on that toby amp :dbtu:
pm sent
Greetings all, first post here. Glad I found this thread. I'm officially a fan of the Frontman 25R. The clean tone that comes out of this thing is pretty amazing. Best clean tone I've come across. Now the weak point of this amp is the noise floor, which is higher than I would like, and also that this thing is built presumably using the cheapest components available, which implies that durability will not be something to count on.
So I've been pondering the idea of having a point to point version made of this amp using all top shelf components (clean circuit only, no hi gain section, aux in or headphones out). I would then put this circuit in a new chassis and cab.
Anyone care to comment on how crazy this idea might be?
I'm not a tech BTW, so I don't know all the details involved in amp circuit design.
Thanks for any input!
It could be done, but would be a long arduous process. I say go for it, it'd be a great learning process.
Quote from: joecool85 on May 19, 2014, 08:24:28 PM
It could be done, but would be a long arduous process. I say go for it, it'd be a great learning process.
Thanks for your reply. Would you say it would be an arduous process for an experienced tech, or only for a inexperienced beginner like myself?
It would be arduous for an inexperienced person. An experienced tech wouldn;t do it, really. I don't mean this unkindly, but it strikes me as like taking your lawn mower apart and having all the parts precision machined to NASA tolerances.
What is cheap about the amp is the labor to make it. The controls on the panel are cheap, sure, but even "good" ones don;t cost much. The speaker is super cheap. But equating the cost of parts with durability is not fair, I think. The transformer may be marginal, but unless you abuse it, it ought to go forever. Same with the cheap speaker.
I buy "good" resistors for my shop, and they cost a penny. Fender pays a lot less even than that for a resistor, but resistors don;t burn out on their own, they burn when transistors elsewhere fail.
If it is noisy, then one of your op amps is noisy, I'll bet my lunch money. A new one of the same type will probably cure it. or you could buy some "low noise" op amps for a few cents more. Hifi guys like to find esoteric Burr Brown op amps for their stereos, but I think that is a waste of money and effort.
I think a point to point version of this would be a pain in the butt to make, How will you be mounting and wiring those ICs? You can buy nice fancy $5-10 controls, and what you will have is controls on the panel with a more industrial "feel" to them when you turn them. Electronically they will be the same.
And after all that, any amp sounds like the sum total of all its parts. You build an all new one, and a new one made of different parts, there is a good likelihood it will not sound the same as the original.
It would be a good project to learn about amp construction though.
Quote from: Enzo on May 19, 2014, 09:45:52 PM
It would be arduous for an inexperienced person. An experienced tech wouldn;t do it, really. I don't mean this unkindly, but it strikes me as like taking your lawn mower apart and having all the parts precision machined to NASA tolerances.
What is cheap about the amp is the labor to make it. The controls on the panel are cheap, sure, but even "good" ones don;t cost much. The speaker is super cheap. But equating the cost of parts with durability is not fair, I think. The transformer may be marginal, but unless you abuse it, it ought to go forever. Same with the cheap speaker.
I buy "good" resistors for my shop, and they cost a penny. Fender pays a lot less even than that for a resistor, but resistors don;t burn out on their own, they burn when transistors elsewhere fail.
If it is noisy, then one of your op amps is noisy, I'll bet my lunch money. A new one of the same type will probably cure it. or you could buy some "low noise" op amps for a few cents more. Hifi guys like to find esoteric Burr Brown op amps for their stereos, but I think that is a waste of money and effort.
I think a point to point version of this would be a pain in the butt to make, How will you be mounting and wiring those ICs? You can buy nice fancy $5-10 controls, and what you will have is controls on the panel with a more industrial "feel" to them when you turn them. Electronically they will be the same.
And after all that, any amp sounds like the sum total of all its parts. You build an all new one, and a new one made of different parts, there is a good likelihood it will not sound the same as the original.
It would be a good project to learn about amp construction though.
Thanks for your reply.
I realize this idea defies common sense and conventional wisdom to a certain extend.
If the existing circuit is not inherently doomed to early failure then I would be happy to only upgrade any components that would help reduce the noise level. As you say and also was mentioned on an earlier post, I believe there is an op amp that can be upgraded to improve the noise spec (?) I should look into that.
Hi TC5 welcome.
The question of "quality" components is a bit misleading ... well very misleading actually, and in practice not really an issue.
Resistor, capacitor, whatever, as long a component meets or exceeds its ratings/specs and isn't faulty, then the "quality" of that component is rather a moot point.
Take the much hyped "paper-in-oil" caps. Paper dielectric caps went out with buggy whips and button up boots and I wouldn't take a box full if they were sent free and post-paid - they are just rubbish. Then there are the forgeries, e.g. "classic" caps that are repackaged common components to look like something rare and special.
It may seem reasonable that an amp built with say 1% components will work better, sound better, than one built with 10% components - but it won't. In fact with the very best test instruments you are unlikely to tell which is which. A major point of a good circuit design is to make it immune to such variations and more (which is one reason I'm suspicious of any circuit covered in trimpots, like a certain "Blackface" FET preamp). This is what Monti-Carlo, MiniMin, and MaxiMax analyses are for.
Suppose we have an amp that has no audible noise with your ear against the speaker and every control cranked. Now you can certainly fit lower noise opamps in the preamp, but to what end? If you can't hear any residual noise with your ear against the speaker (and there will always be some noise in any circuit, even if you can't hear it), what advantage is there in reducing it to an even less audible level?
Microphone and vinyl pickup preamps are special cases because the signal level is so low, but for guitar level signals a hundred times higher the LM833 is as near a perfect amplifier as you could wish for, so why pay four times as much for an op-amp with 1/4 the noise if the noise from an LM833 is already down in the order of nanovolts?
I know it's hard to believe, but there are actually people out there who make preposterous claims and use techno-baffle-waffle to part the innocent from their hard-earned. Just about everything you have read on the net about "tone" components is bunkum - at best "true but not exhaustive", and at worst utter bulldust.
As long as the components are "good enough", meet their ratings, then it rapidly comes back to a question of circuit design, how those components are being applied.
As it happens I've just had a drawn out long-distance wrassel with a troublesome Frontman. I still have a lot of respect for names like Fender and Marshall, but just as builders can have a runaway winner, they can also produce the occasional dog.
Factoid - Fender repair agents here in Australia refused to even look at this particular one when they found out a) it was a Frontman, and b) out of warrantee. The saga we had nailing the fault in the output stage could well explain why - it was an utter dog to service. For every transistor carrying the signal forward there were another three (+/-) for protection, so there is roughly a 3/4 chance that any fault will be in the protection and not the actual amplifier, and so it turned out in this case.
In itself output stage protection is a "good thing", but whatever protection scheme(s) you decide to use you have to add new components, and simply doing so adds potential failures. The whole idea of OP stage protection is to make the amp more reliable, but there is a point quickly reached where adding more protection components actually starts to make the amp less reliable again.
Building an amp is an arduous process. The main difference is that an experienced builder or tech expects to have to deal with a seemingly unending stream of details to attend to; it can come as a bit of a surprise to a first time builder.
Solid state preamps can contain all sorts of tone bending wrinkles, but generally speaking solid state power amps are pretty neutral when it comes to "tone", the speaker and the cabinet it is in has a much larger influence (which is why taking even a tiny amp and connecting it to a respectable speaker such as a 4x 12 quad box can make it sound much better; not loud, but rich). Leaving aside pre-crippled amps like the Roland Cube series, most amps already do a lot better than the speaker they are connected to/supplied with.
I certainly encourage you to have a go at building an amp or two because you'll learn a lot, but mainly because it's a great feeling of achievement to play through an amp you have built yourself.
It also places you in the driver's seat if you are not satisfied with the sound, and when (not if) it needs any service. You already have all the circuits, and know where every component is because you put it there, and if you want to try something such as a different tonestack it is not a matter of making a big-bucks bet at your local music shop on the basis of ten minutes evaluation using an unknown guitar in a noisy shop.
Aside from agreeing with Enzo's precision lawnmower, the Frontman is the last circuit I would suggest as a first build project. There are a raft of simple but effective designs out there for valve (toob), discreet transistor, or chip amps up to about 50-60 watts, and any of these would be a better proposition for a newbie.
Thanks very much Roly for the thorough rundown. Quite informative.
What got my attention with this amp is that compared to many other amps (mostly all tube) I put next to it, this little guy gives me the best clean tone. Boggles the mind how the cheapest amp sounds best (to me anyway)!...
I can see now that the design of this circuit is what makes it a disposable amp. Quite unfortunate.
So I gather that this passage below from your earlier post would not apply to the Frontman, and there is no op amp in it that can be upgraded to lower it's noise floor?
Quote from: Roly on February 09, 2014, 03:25:34 AM
Originally the preamp gain came from "low noise" BC109C's, but still had quite a significant and audible noise floor.
The pre I built to replace it was nominally the same except it used LM833's (at a buck-and-a-half a pair) for the gain.
The second shock is that it is now so quiet you can't tell if it's turned on without looking at the pilot light. {It can be a little unnerving on stage actually because now there is no audible clue that you have left the gain really cranked and are just about to give everyone an unintended blow-wave.}
Not exactly.
They gave you a couple options, you pick which one applies .
1) What he (and Enzo) said that if you don´t hear any noise (or it´s inaudible when actually playing, not at 3 AM in a silent bedroom) it´s not worth replacing it with an "exotic" .
2) And if you have "unbearable" noise, then maybe you have a bad Op Amp, in which case replace with *same type* (you are not improving but repairing).
3) and if you hear some background hiss, it might be useful to use, say, a $3 low noise Op Amp instead of the original (excellent, by the way) $0.50 one.
Although don´t be surprised to find little improvement.
But beyond that, don´t waste money.
The only big improvement in beginner type amps comes from fitting a much better speaker.
Which won´t improve noise by the way, but audible power, punch, body, clarity.
EDIT: in case you wonder, the Op Amp which *might* improve noise floor is U1 TL072 type (a 50 cents part) , which I guess they are suggesting replace by LM833 (a, say, U$3 part).
No need to buy the one Nasa uses to listen to signals from Saturn (not kidding) which has half the noise of the LM833 for, say, 500U$.
NOTE: we are all guessing you are referring to a subtle "hisssssss" you hear in the background **with guitar volume ant tone controls on 0**
Any other noise (buzzing, hum, etc.) which you can hear while playing usually comes through the guitar pickup picking ambient noise and interference, a different problem unrelated to Op Amp changes.
Quote from: J M Fahey on May 20, 2014, 09:15:50 AM
Not exactly.
They gave you a couple options, you pick which one applies .
1) What he (and Enzo) said that if you don´t hear any noise (or it´s inaudible when actually playing, not at 3 AM in a silent bedroom) it´s not worth replacing it with an "exotic" .
2) And if you have "unbearable" noise, then maybe you have a bad Op Amp, in which case replace with *same type* (you are not improving but repairing).
3) and if you hear some background hiss, it might be useful to use, say, a $3 low noise Op Amp instead of the original (excellent, by the way) $0.50 one.
Although don´t be surprised to find little improvement.
But beyond that, don´t waste money.
The only big improvement in beginner type amps comes from fitting a much better speaker.
Which won´t improve noise by the way, but audible power, punch, body, clarity.
EDIT: in case you wonder, the Op Amp which *might* improve noise floor is U1 TL072 type (a 50 cents part) , which I guess they are suggesting replace by LM833 (a, say, U$3 part).
No need to buy the one Nasa uses to listen to signals from Saturn (not kidding) which has half the noise of the LM833 for, say, 500U$.
NOTE: we are all guessing you are referring to a subtle "hisssssss" you hear in the background **with guitar volume ant tone controls on 0**
Any other noise (buzzing, hum, etc.) which you can hear while playing usually comes through the guitar pickup picking ambient noise and interference, a different problem unrelated to Op Amp changes.
Thanks. Yes the noise I'm referring to is amp background hiss, present when no guitar is plugged in.
Quote from: TC5 on May 19, 2014, 07:55:28 PM
Now the weak point of this amp is the noise floor, which is higher than I would like
I had a Champion 110 which is the predecessor of the 25R and I agree that it's a noisy beast. I did a bunch of work to try to figure out where the noise comes from and narrowed it down to the circuits before the tone control. I finally gave up and sold off the beast.
On the other hand, I had really good results with a Fender Reverb Amp (predecessor of the 15R). The judicious use of aluminum foil around the reverb unit, grounding wire from PCB to chassis etc resulted in near silent operation. Since I'm totally non-scientific, I can't say which exact change tipped the noise switch. Please look at my "NAD" thread for details.
Quote from: TC5 on May 19, 2014, 07:55:28 PM
So I've been pondering the idea of having a point to point version made of this amp using all top shelf components (clean circuit only, no hi gain section, aux in or headphones out). I would then put this circuit in a new chassis and cab.
It can be done, but it will be (a) tedious and (b) you will probably end up with a higher noise floor.
The plus point I can see with a fresh ground-up DIY approach is that you can encase the whole thing in a shielded enclosure which "may" help with the noise.
Quote from: Roly on May 20, 2014, 05:51:57 AM
Aside from agreeing with Enzo's precision lawnmower, the Frontman is the last circuit I would suggest as a first build project.
^^^ agree x10000
The Fender SS pre-amp circuits are really VERY complex compared to some others that I've seen.
I would humbly suggest the Vox Pathfinder 10 circuit as a good starting point for a DIY build. It has a very simple PRE->GAIN->TONE approach with just 3 op-amps. The same design approach (including clipping diodes) are used in the Pathfinder 15R, SS Cambridge Reverb, AC15VR (with transistors) etc.
Quote from: bluesky6narrowed it down to the circuits before the tone control
The residual noise of amplifiers, be they VHF or audio, are normally dominated by the noise figure of the first (or first couple of) stages. If there is anywhere sensible to fit a "NASA" op-amp it's in the input stage(s), and maybe in the following stage(s).
Often you can demonstrate this (somewhat) by isolating the main amp from the preamp with a shorted plug into the Main Amp input. This isolates the main amp from the preamp, and will normally result in a noise floor so low it's difficult to measure much less hear.
Quote from: TC5having a point to point version made
I hope you are rich, or ready for disappointment. I wouldn't even bother giving you a quote because I know what I'm doing and my time alone would dominate the cost; corollary, any quote that is "reasonable" and not several times the price of a new Frontman could only come from somebody who doesn't really know what they are doing and you are going to get burned when they discover they are out of their depth - seen it before.
And if you are going to have an amp built by somebody who doesn't know what they are doing - you may as well cut out the middle-man and build it yourself, right? ;) The main reason I built all my own gear was because I couldn't afford commercial gear, and it became a habit.
Mass production reduces the individual price of an amplifier very considerably, but a hand-built one-off, even a direct clone, becomes a lot more expensive when you factor in the cost of a skilled tech to build it.
Commissioning a build also bypasses several of the advantages of actually doing it yourself, learning, being empowered over your gear rather than a victim of it, or hostage to a builder who may lose interest, service techs who have to deal with a unique beast (which no tech particularly likes because the assurance of a factory build is off the table).
bluesky has some more good suggestions for first builds.
Quote from: Roly on May 20, 2014, 02:11:41 PM
I hope you are rich, or ready for disappointment. I wouldn't even bother giving you a quote because I know what I'm doing and my time alone would dominate the cost; corollary, any quote that is "reasonable" and not several times the price of a new Frontman could only come from somebody who doesn't really know what they are doing and you are going to get burned when they discover they are out of their depth - seen it before.
And if you are going to have an amp built by somebody who doesn't know what they are doing - you may as well cut out the middle-man and build it yourself, right? ;) The main reason I built all my own gear was because I couldn't afford commercial gear, and it became a habit.
Mass production reduces the individual price of an amplifier very considerably, but a hand-built one-off, even a direct clone, becomes a lot more expensive when you factor in the cost of a skilled tech to build it.
Commissioning a build also bypasses several of the advantages of actually doing it yourself, learning, being empowered over your gear rather than a victim of it, or hostage to a builder who may lose interest, service techs who have to deal with a unique beast (which no tech particularly likes because the assurance of a factory build is off the table).
bluesky has some more good suggestions for first builds.
Yes of course DIY would be the better way to go, but the learning curve would be too steep for me to tackle at this time. Probably best to stick with common sense and forget about this little amp as a long term investment. In any case whoever designed the circuit achieved a seriously good result IMO. The low end that comes out of this thing is especially good.
Quote from: bluesky6 on May 20, 2014, 10:07:16 AM
Quote from: Roly on May 20, 2014, 05:51:57 AM
Aside from agreeing with Enzo's precision lawnmower, the Frontman is the last circuit I would suggest as a first build project.
^^^ agree x10000
The Fender SS pre-amp circuits are really VERY complex compared to some others that I've seen.
I would humbly suggest the Vox Pathfinder 10 circuit as a good starting point for a DIY build. It has a very simple PRE->GAIN->TONE approach with just 3 op-amps. The same design approach (including clipping diodes) are used in the Pathfinder 15R, SS Cambridge Reverb, AC15VR (with transistors) etc.
I had a Vox pathfinder 15R. It was a good amp that also offers a lot for the money, but the tone of it compared to the Frontman was a bit too nasal and boxy for my taste. This is where the Frontman works for me. It's not nasal, boxy or midrangey like many other amps I compared it with. The voice is super clear or maybe somewhat scooped, which is where my preference is.
Truth is, typical 15W beginner amps are very good, but drive a *terrible* speaker in a very poor cabinet.
A distinguished Member of this Forum posted a very sobering video, himself playing live with his *very* successful 90's Australian band.
Watch it and guess what amps he used.
There´s a wall of Marshalls visible, which if you look closely are turned OFF 8| :loco :duh
The actual sound comes from a tiny SS (of course ;) ) 15W Squier amp , backstage sitting on a road case, close miked by a Shure SM57 jammed against the grill cloth.
http://youtu.be/3QEjiJ56Zac
Our friend answers to the nickname "onebaldbloke" , I guess you will find who he is in the video ;)
KIller band by the way. :dbtu: :dbtu:
Quote from: Freddie on February 11, 2010, 06:37:11 PM
Trying to get a better drive sound from the 25R. Looking at the schematic of the 15R and the 25r the difference in the two circuits seems to only be the switching and two diodes. What would be the purpose of D1 and D2 in the 25R drive circuit?
Hello,
I would like to say, I have two solid state amps (Squier 15, and a really cheap RMS 200 amp) by using the advice given to me from these same guys, the difference is remarkable.
The most effective modifications were using a 12" speaker, offsetting the clipping diodes, removing the back from the amplifier cabinet, no other changes. Offsetting the clipping diodes was the only thing that required soldering. It required two diodes I had pulled from things I had already disassembled.
The only reason you still have questions is because you haven't done it yet.
Hello, this amplifier have.. High overtone... sound very acute (treeble) in higher volume, if I replace speaker I will fiz this?
Sorry, I dont speak english, but this forum is the BEST! :dbtu:
If you plug this amp into a larger speaker in a larger cabinet it will sound much better.
What's your original language/where are you from?
Quote from: J M Fahey on March 14, 2015, 01:49:40 AM
If you plug this amp into a larger speaker in a larger cabinet it will sound much better.
What's your original language/where are you from?
I from Brazil :)
So.. I will replace the speaker or plug in other box with 12" speaker :)
Since Alex318798 is located in Brazil.. this tidbit may be worth considering (re: speaker replacement, etc)
I just replaced an 8" (8ohm) speaker in a small Fender "Champ" SS amp.
After doing a bit of searching, I ended buying one of these and absolutely love it:
http://www.jblselenium.com.br/marcas/upload/92bfa5f243b04dbb0f536749ec68ef94.pdf
It's made in Brazil under/by the Selenium JBL brand. Apparently, JBL bought Selenium and now many of the Selenium branded speakers are being made available as buyout/clearance type items. I got mine from Parts Express for $25USD. Although, it's nominally listed as a "PA" type driver, it works well for a small guitar combo amp -- surprisingly well in fact. If you read the reviews posted by users here: http://www.parts-express.com/selenium-8pw3-slf-8-driver-8-ohm--264-330 you'll see that nearly everyone that uses it as a guitar (or even bass, in some cases) reports very favorable results with it. Build or buy a cabinet for it (the Q factors are pretty high, so it pairs best with a rather large box..) and viola! great tone, power-handling in a compact size.
The 8PW3 has:
good freq. response for guitar (70-8000Hz)
good power handling (125W RMS)
"8ohm impedance" (measured mine at 6.9 ohm)
reasonable sensitivity/SPL (92db)
..oh, and a nice balanced tone too.
If you don't like the 8" driver, maybe check out a 10" or 12" as well.
Hope this helps,
-PhE
THANKS!
you think this is better than the original speaker? And de cabinet can be opened or should be closed?
THANKS!
Hi,
Alex318798, welcome. I'm in Victoria, Australia.
Lots of good advice in this thread. :dbtu:
Generally; the smaller the amp is, the more important the speaker and cab is. Take any of the micro-amps, 1-10 watts, or pod/MP3 player &c&c, plug it in to a genuine guitar cab and the improvement is often astonishing, not loud maybe, but richer and fuller.
TC5 asked me a specific question back in May that I missed.
Quote from: TC5 on May 20, 2014, 08:21:30 AM
this little guy gives me the best clean tone. Boggles the mind how the cheapest amp sounds best (to me anyway)!...
...
So I gather that this passage below from your earlier post would not apply to the Frontman, and there is no op amp in it that can be upgraded to lower it's noise floor?
Quote from: Roly on February 09, 2014, 03:25:34 AM
Originally the preamp gain came from "low noise" BC109C's, but still had quite a significant and audible noise floor.
The pre I built to replace it was nominally the same except it used LM833's (at a buck-and-a-half a pair) for the gain.
The second shock is that it is now so quiet you can't tell if it's turned on without looking at the pilot light. {It can be a little unnerving on stage actually because now there is no audible clue that you have left the gain really cranked and are just about to give everyone an unintended blow-wave.}
Simplicity vs. Complexity.
Some of the most highly coveted amps here are vintage classics that have very basic circuits, simple and effective.
Fender 5F2
(http://i.imgur.com/Ssc2L9d.jpg)
Very buildable early amp clone.
Contrast these with any of the modern generation of "cyber-amp" with a built-in Fx box (pioneered by the very same company! F****r).
...I digress...
The cct I have shows TL072's in the pre's. These are good, but following the maxim that "the first stage sets the noise floor", so a lower noise dual such as an LM833 could be just dropped in ad-lib to possible advantage - YMMV.
After that it becomes a bit of a research project - what, exactly, is this residual noise, and it's source (in
this amp, not a fault but a design limit (so we are now into
re-designing the amp))?
Quote from: Alex318798And de cabinet can be opened or should be closed?
It could be either. Open back tends to be brighter, closed back fuller, but a bit duller.
Quote from: Alex318798this amplifier have.. High overtone... sound very acute (treeble) in higher volume
As you seem to have too much treble, too many tops, I would go with the sealed style with a large internal volume, a 12-inch in 50 Litres minimum, and this would tend to bring the top and bottom back into balance more, a little less treble, a bit fuller bottom end to compete.
It's late Sunday evening, but I am glad I bothered to lurk back here..
Alex, Roly's advice is very good (as always I have noticed). So let that be a good reference or guide with regard to the speaker situation. I built a cabinet very similar to what Roly described (12" speaker in 50 ltr+ cabinet) and am very happy with it. The bass/bottom end is almost overkill, but I can tame it via EQ and 'tone' adjustments. Fender SS amp with big sealed speakers can produce a big 'boxy' and 'boomy' sound -- so be ready to twiddle with the tone settings a bit until you get a sound you like.
Also, just wanted to mention or offer, that in general Fender SS amps take pedals and [external] preamps pretty well. My experience has been, that when I reach a point where I feel something is lacking soundwise, I put another gadget into the signal chain (compressor, EQ, noise gate, etc) and can usually get what I want by refining the 'baseline tone' without having to change amps.
I should note that my 'metal days' are long since behind me (ah yes, power chords on the bridge pickup with a tube amp dimed out... :duh) but, now prefer a cleaner jazz/blues type tone with only a hint of breakup when I push things. 8)
One of the best sounding combos I ever had (pun intended) was my 1990s era Princeton 112+ Reverb (the 65W combo with 12" speaker) boosted by my B. K. Butler REAL TUBE (single 12AX7 tube preamp). Oh man, that was tone to die for....
I don't have any specific ideas about which 12-inch driver to put in the box, but I would suggest going for between 50-70L capacity (you can always pad it away, but you can't add it if you don't have it to begin with); and driver efficiency in dB/W being very important, particularly if you want to actually gig a small (15W amp) in small venues, bars, pubs, clubs...