Frontman 25R mods

[DrGonz78]

These were posted on MEF by Enzo a while back... Thanks Enzo!  :dbtu:

[bobhill]

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:

[Roly]

Siding Spring - Coonabarabran

Quoted on some control systems when they were building it - didn't get the job.   




Many uses.  You can even eat it.

[Tobyguitaramps]

Hey bobhill i know its the wrong place but is there any way i can a scmatic on that toby amp :dbtu:

[FlyinTune]

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.

[joecool85]

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.

[bobhill]

Hey bobhill i know its the wrong place but is there any way i can a scmatic on that toby amp :dbtu:

pm sent

[TC5]

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!

[joecool85]

It could be done, but would be a long arduous process. I say go for it, it'd be a great learning process.

[TC5]

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?

[Enzo]

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.

[TC5]

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.

[Roly]

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.

[TC5]

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?

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.}

[J M Fahey]

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.