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Author Topic: Frontman 25R mods  (Read 28771 times)

TC5

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Re: Frontman 25R mods
« Reply #30 on: May 20, 2014, 09:57:03 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.

bluesky6

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Re: Frontman 25R mods
« Reply #31 on: May 20, 2014, 09:58:54 AM »
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.

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.

bluesky6

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Re: Frontman 25R mods
« Reply #32 on: May 20, 2014, 10:07:16 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.

Roly

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Re: Frontman 25R mods
« Reply #33 on: May 20, 2014, 02:11:41 PM »
Quote from: bluesky6
narrowed 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: TC5
having 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.

If you say theory and practice don't agree you haven't applied enough theory.

TC5

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Re: Frontman 25R mods
« Reply #34 on: May 21, 2014, 02:57:49 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.

TC5

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Re: Frontman 25R mods
« Reply #35 on: May 21, 2014, 03:05:14 PM »
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.
« Last Edit: May 21, 2014, 04:54:10 PM by TC5 »

J M Fahey

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Re: Frontman 25R mods
« Reply #36 on: May 23, 2014, 09:24:00 AM »
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:

SpareRibs

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Re: Frontman 25R mods
« Reply #37 on: May 23, 2014, 05:38:39 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.

Alex318798

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Re: Frontman 25R mods
« Reply #38 on: March 13, 2015, 05:57:46 PM »
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:

J M Fahey

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Re: Frontman 25R mods
« Reply #39 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?

Alex318798

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Re: Frontman 25R mods
« Reply #40 on: March 14, 2015, 01:57:33 PM »
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 :)

PhredE

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Re: Frontman 25R mods
« Reply #41 on: March 15, 2015, 12:57:35 PM »
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

Alex318798

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Re: Frontman 25R mods
« Reply #42 on: March 15, 2015, 11:09:44 PM »
THANKS!


you think this is better than the original speaker? And de cabinet can be opened or should be closed?

THANKS!

Roly

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Re: Frontman 25R mods
« Reply #43 on: March 15, 2015, 11:18:39 PM »
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.

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?

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

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: Alex318798
And 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: Alex318798
this 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.
If you say theory and practice don't agree you haven't applied enough theory.

PhredE

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Re: Frontman 25R mods
« Reply #44 on: March 16, 2015, 12:03:37 AM »
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....

 

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