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Author Topic: Some noob questions.  (Read 8342 times)

QReuCk

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Some noob questions.
« on: June 21, 2012, 06:47:47 AM »
Hi all.
I'm new here and would like to ask some questions you may have answers to:
I've got an old 15W mono chanel SS combo. The brand name is Avenger and the model name is FA15. I've found no schematics or even serious review of this amp, nor any info on the brand.
Features are simplistic: A gain knob, a Volume knob, a master know, and a 3 band EQ. There is a 6' small speaker in it (closed back).
I also own a Peavey Envoy 110 Sheffield, which I consider a great sounding amp, but cannot obtain with it the beautifull crunch I am able to hear with the avenger. I've read numerous times that SS amps are supposedly unable to produce a good sounding clean, but I swear this little low end thing sounds just as good and dynamic as a Fender Blues Junior as far as light crunch is what you want to hear. There are a few problems though:
1° the gain know is unusable: Adds a lot of harshness. More harshness than distortion I think, so this amp is limittated to various slight overdrive tones. My feeling is that this works as designed (poorly, but as designed).
2° the volume know is good for settings from clean to average overdrive. Only trouble is that the range on the pot is not optimal: volume at 0: no sound, volume at 0,5: clean, volume at 1: clean with a tiny bit of crunch when striking the strings heavily, 1.5 to 2: nice slight crunch to light overdrive, 2 to 3 nice overdriven sound. Past 3 or a bit more, it becomes too fuzzy for my taste.
Mind you, I have humbuckers on both my axes, but even with reduced volume on the guitar pot, I kind of regret not being able to use the full range of the volume pot even when the gain one is on 0.
3. I'm affraid it lacks a bit power when playing with my drummer. No external speaker output, and no real preamp output to direct it to my peavey, which as no power amp input or effect loop return for that matter. So chaining both amps would use the Peavey preamp in the signal chain.

I realize my knowledge is limitted, but:
1° Do you think I can make some testing directing the headphone out of the Avenger to the instrument Input of the Peavey without damaging any of these amps? If so any recommandation on the settings of both amps?
2° In case this test is not possible, is there any way to anticipate what part of the Avenger produces this nice tone and dynamics? I would like to know if there is some probability the nice crunch and dynamic response may be lost if I find a way to direct the préamp of the avenger into a poweramp and speaker (probably guitar type ones).
3° do you think there would be some mod possibilities to have the gain knob dropping some highs when rising the gain and some other mods to change the range of the volume knob?

Not a question, but might be the goal after all:
If tests indicate that there is a possibility that this preamp + external power amp and speaker retains the very specialized tone I have, I could be tempted to use its preamp as an alternative to the one built in the Peavey. That would obvioulsy call for some work (a power amp input for the Peavey, a true preamp out for the Avenger, some A/B switch, etc...), but if the result has a chance of being good, why not?

Roly

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Re: Some noob questions.
« Reply #1 on: June 21, 2012, 08:11:45 AM »
This? (attached)

http://en.audiofanzine.com/guitar-amplifier/avenger/

Whatever you read, you listen to music with your ears, and if this little amp is giving you a sound the bigger one isn't, well that is the truth.

1. Yes, you should be able to connect the headphone output of the Avenger to the Low Gain input on the Peavey without causing damage to either amp.  The first time you will need to inch the controls up on each amp until you find a comfortable level.

2. Generally speaking a solid state amp in overload produces a wide range of harmonics and it is the speaker and its enclosure which act as a filter for this more general excitation; so often with a small amp such as this much of what you are hearing it the speaker and enclosure.  This means that you may not get what you expect out of the headphone socket.  The only way to be sure is to try it.

If you get what you want, fine, but if not you may consider using a mike in front of the Avenger's speaker and using the Peavey to amplify this, although you may need to be careful to avoid audio feedback.

Not a question - not an answer  ;) ; yes both amps can be fitted with sockets that allow preamp out and main amp in.  This would normally be done with a couple of switch sockets inserted somewhere around the final volume control/main amp input, thus creating an effective Fx loop, pre out/main in.

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

mexicanyella

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Re: Some noob questions.
« Reply #2 on: June 21, 2012, 09:19:08 AM »
I can relate. In my case, the tiny amp I love the sound of is a Peavey Audition 20, and lucky for me, it has a line out jack. Also lucky for me, the line out jack's signal level is low enough that it can drive an amp's instrument input pretty well. Anyway, here are some suggestions.

1: rather than reworking the amp to achieve a better range of attainable cleans or semi-cleans at the controls (or a less "immediately harsh" sound on the gain channel), consider reducing your signal level to the amp in some way other than just turning down the guitar volume...

...I tend to lean toward single-coil pickups with their lower output and thinner sound, which lends itself well toward varying your distortion level by playing intensity...but a lot of people love humbuckers and aren't comfortable on single-coils, so maybe that's more extreme than you want to try...?

You could lower your pickup height for starters and see if you could mellow the punch of those humbuckers a bit.

You could incorporate a pedal in your signal chain that gives you the option of turning down the pedal's signal output; sometimes that can work. I use a DOD Bi-Fet Preamp pedal as a clean boost in front of the little Peavey for solos or single-note parts. BUT I've also used it with the signal turned down slightly a few times over the years, where it functioned as a signal cut with an added tone knob on it. Maybe that would help you out. Another alternative might be an MXR Micro-Amp, and there are other pedals with output level controls on them.

You could incorporate a compressor in front of the amp, which has lots of possibilities. You could use it to cut the signal to the amp slightly as mentioned above, but you can also tame the peaks of your attack going into the amp so you have less spiky waveforms, which makes it sound cleaner, more pleasing and less harsh. Without sounding like cheesy overcompression.

You could shell out for some lower-output pickups, or if your existing ones have four-conductor leads you could rewire them so that each humbucker is two coils in parallel rather than in series...cuts output some, in the direction of a single-coil sound. Or you could add some switching capability via a mini-toggle or a push-pull volume or tone knob and have series/parallel capability on your pickups, so you could switch to a lower-output, cleaner sound and switch back again.

If you don't like the headphone signal as a line out, due to level compatibility, an alternative to modding the circuit is picking up a DI box with a speaker-level input. The amp's speaker output is fed through this on its way to the speaker, and the DI pulls out a line-level signal. Some have speaker emulation filters so that the DI signal can go straight to a mixer or recorder. Behringer makes a cheap one that a lot of people praise online. The Hughes & Kettner Redbox is a well-known one with emulation in it, but it's more expensive. I have a discontinued BBE unit called a DI-10 that has been pretty handy...both for the use I described above and in recording direct distorted tones from a distortion pedal, etc.

This thread might give you some ideas, and you could as "SSer" joecool85 to describe how he added a line out to his Dean Markley K-20X...or maybe he'll see this and chime in.


See if any of those options work in your situation. If that little Avenger amp has a tone you like, hang onto it!
« Last Edit: June 21, 2012, 09:42:16 AM by mexicanyella »

QReuCk

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Re: Some noob questions.
« Reply #3 on: June 21, 2012, 09:54:59 AM »
Thanks a lot for your answer Roly.
Yes, exactly this model. The audiofanzine review is pretty much the only reference to this amp I have been able to find, and as you could read, it's pretty much biased. My ears tell me that the "on-the-verge of crunching" sound is as good as it gets (plenty of warmth, dynamic response etc...) but that's pretty much all about this amp.
So I guess I will test the headphone-to-low-input trick before going any further in my reflexion.

Mexi: wow, these are some unexpected suggestions that make a lot of sense. I have 2 electric guitars: One is an old Yamaha RGX 110, which has just an humbucker and a volume control. This pickup-although a passive one- is already lowered to the max and even like this, still requires to use the -6db pad on the Peavey... With this guitar, the Avenger is super difficult to use and never clean. The other one is a Bennett AV6 ltd (some sort of nice LP copy). Don't want to mod this axe as it is great as is and it is a birthday present from my wife. Modding the Yam is a consideration, and to tell you the truth, I am considering using a splittable HB with a coil tap circuit. Buying another electric is not an option yet (next one will be a nylon electro-accoustic, and it won't be cheap if it has all the features I want).
Anyway, the compressor/clean boost thing might be a good bet. I still have to test some units, but I might use it even with the Peavey or with my current nylon guitar (which has just an aftermarket piezzo and no preamp built in) so that could be a good multipurpose buy.

Thanks again guys, this forum is really a fantastic ressource for us who are tired of the "you-should-by-a-15W-tube-combo-instead" type of answer.

mexicanyella

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Re: Some noob questions.
« Reply #4 on: June 21, 2012, 12:47:23 PM »
It may well be that none of my ideas get you what you want, and I understand the appeal of making a circuit change over amassing a pile of additional front-end gear. But I thought I'd mention those things because I've had success with some of them.

Coil-tappable humbuckers might be a solution; that will certainly give you a lower output when switched that way. Another option if you don't really need a humbucker sound, per se, is to swap in a humbucker-sized single coil. Gibson P-94s are supposed to be P-90 guts in a humbucker-sized housing, so they drop right in. But they're not cheap. Guitar Fetish has some humbucker-sized single coils like the Surf 90 (sort of DeArmond-ish, I think) and the Dream 90 (more P-90ish) and they are much less expensive. Might be an interesting thing to do to that one-pickup Yamaha, whether you mod the amp or not. Check out "Phil X," "The Drills" or "Powder" on Google or Youtube. He plays a sort of SG-shaped ESP guitar with a P-94 in it instead of a humbucker, but he's interesting to watch no matter what.

QReuCk

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Re: Some noob questions.
« Reply #5 on: June 22, 2012, 08:13:28 AM »
My limited english as striken here...
What I was (eroneously) refering too as a "coil tap circuit", is actually a redirection of the coil tap itself to a pot with one end shorted to ground. So this pot have the capability of partially shorting one of the coil, enabling a continuous variation from single to humbucker. Some internet research proved that it has been done in various forms. One can be found pages 13 and 14 of the chapter 5 doc in this page:
http://www.peavey.com/support/technotes/
Actually, if any beginner wants to learn one thing or two about concepts of sound treatment to emulate a "tube sound" the chapter about transtube is also a pretty good read - although highly biased to try and sell some Transtube stuff (which are good and versatile amps by the way, just not able to replicate one precise type of sound I would like to have in addition to what the envoy110 is giving to me).
Anyway, I've got some testings to do with my current stuff. Maybe I will be back to you after this week end.

QReuCk

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Re: Some noob questions.
« Reply #6 on: June 28, 2012, 04:52:54 AM »
OK, I tested chaining the Avenger into the Peavey through the headphone out of the Avenger. I don't know if the preamp of the Avenger has an overall gain of less than 1 or if there is actually an impedance mismatch (I've read that instrument inputs have a fairly high impedance (like 1K or so)while headphones are supposed to be anywhere between 16 and 64 ohms, but this headphone out of the Avenger is clearly very bad at driving the Peavey's instrument input. With maximum settings for the headphone and volume at 10 on the Peavey, the sound in the Peavey speaker is not any louder than the guitar direct in it with volume at 1.

As far as tone is concerned, it's difficult in these conditions to know for sure, but the sound is pretty similar to what can be heard with the Avenger alone: dirt and warmth come in really early and sort of keeps it's texture.

Now that I know for sure that it's the preamp (or is it? maybe the headphone out has its own mini power amp, but in this case they did a pretty good job at reproducing the exact same behaviour as the power amp and speaker in it) of the Avenger that introduces these dirt and warmth, I think I'll try to open it in order to see what it's made of. And if it's accessible, I might try to put a resistor in serie with the volume pot to have more usable range on it...

or put some stompbox with a good "level" setting in my to-buy list.
I think I would be interested in some sort of EQ with the following specs:
- a low pass with Fc tweakable from 2Khz to 6Khz or a bit more (would be nice if it's a high order one I guess, but it's not that critical as the tone pots of the guitar add their own low pass filter anyway)
- a high pass with Fc tweakable from 60kz to 500hz (for the double purpose of preventing the amp to amplify frequencies that should not be there in the first place and to remove muddiness if needed)
- optionally some usable mid cut (not a big fan of mid cuts, but can help to shape the tone, especially if there is a distortion stage after it)
- a gain stage that should be tweakable from -15db (maybe the passive filters  can do this alone) to at least +15db (-15 should help me using the Avenger in a usefull range of tone, +15 or more could be fun with the Peavey and definitely usable with my piezzoed Nylon). A gain stage that amplifies the whole signal is prefered to individual band-specific amplification that could be found in some graphic equalizer.

I realise that this looks a lot like a PhaBB Tone, but I don't think I have the skills and patience to build one. So if you know about a stompbox commercially available that can do similar functions, that would be great.

Roly

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Re: Some noob questions.
« Reply #7 on: June 28, 2012, 11:43:04 AM »
Firstly, in this case the impedance of the source and driven circuits is unimportant as long as the source impedance is much lower than the driven circuit.  In this case the headphone output should have a source impedance very much lower than the input impedance of the following amplifier, and thus be able to provide more than enough signal voltage to drive it, so your result of insufficient signal is most unexpected.

The voltage at the headphone output should be at last equal to the output of a guitar, and more likely 500mV to a volt, several times a guitar output, which should be enough to drive the Peavey crazy, even on its insensitive input.

Did you try it on the more sensitive input?

It doesn't really matter where the dirty tone is coming from as long as it is coming out of the headphone socket.  The problem now is to understand why the headphone socket is so poor at driving the Peavey input.

Does the lead you are using to plug into the headphone socket have a mono plug (no ring)?  If so it is possible the plug is shorting the signal via the ring contact in the socket.  If you pull the plug out about 1cm the tip of the plug should make contact with the ring contact in the socket and you may get a very strong signal.

You should try to measure the AC output voltage from the headphone socket when the amp is driven hard, and you should get at least a fraction of a volt and perhaps as much as a couple of volts.
If you say theory and practice don't agree you haven't applied enough theory.

Jack1962

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Re: Some noob questions.
« Reply #8 on: June 28, 2012, 02:27:46 PM »
Impedance of a guitar ranges from 4K ohms to 24K ohms , the lower impedace of the headphone will effect the quality of tone , however it should still work.

mexicanyella

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Re: Some noob questions.
« Reply #9 on: June 28, 2012, 11:46:02 PM »
QReuCk,

I have not tried what's suggested in either of these links, but maybe someone here can comment on them. I'm inclined to try this on an old *15-watt single-channel tube amp* I have (ducks).

QReuCk

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Re: Some noob questions.
« Reply #10 on: June 29, 2012, 05:56:32 AM »
Thanks a lot guys.
How could I be dumb enough to not have thought of the mono jack used?  :duh
Well, only stereo 1/4 cable I have currently is the amplifier side of my footswitch cable. Not ideal as it splits it into 2 distinct cables with mono jacks at each end, but that should do the trick for testing purpose.

Roly, where the "dirt" comes from is actually a usefull information for me as I feared that the poweramp/speaker part of the avenger could have played a big part in the overall tone of this amp, effectivelly putting a stop in any project to re-direct it's preamp to a better poweramp and speaker.

If mono cable proves to be what causes the very weak signal out of the headphone and a stereo one enables to correct this and "drive the peavey crazy", then it may have a potential to turn my system into something interesting (even it could still benefit some mods, but I'll see that later).

STDog

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Re: Some noob questions.
« Reply #11 on: June 29, 2012, 08:03:14 AM »
Well, only stereo 1/4 cable I have currently is the amplifier side of my footswitch cable. Not ideal as it splits it into 2 distinct cables with mono jacks at each end, but that should do the trick for testing purpose.

That's actually good, as the second amp has a mono input jack, so you just want one side from the headphone jack anyway.

mexicanyella

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Re: Some noob questions.
« Reply #12 on: June 29, 2012, 08:47:08 AM »
Whoops! Just realized I forgot to include the links I mentioned in my last post. Typing late at night...

http://www.rru.com/~meo/Guitar/Amps/Kalamazoo/Mods/ezlo.html

http://music-electronics-forum.com/t10582/

Roly

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Re: Some noob questions.
« Reply #13 on: June 29, 2012, 10:34:26 AM »
I think the impedances are a non-issue here; the headphone output is likely to be 220 ohms or less (perhaps very much less if it has a buffer and isn't just tapped off the main output) and the input of the Peavey is likely to be no less than a few tens of k ohms and perhaps as high as a meg.

The output level from the headphone socket should be several hundred millivolts, perhaps more, and should be several times the sensitivity of the "deaf" Peavey input; so it has got to be something silly like a mono plug in a stereo socket, or something has died somewhere.

But having done this sort of thing more times that I can poke a stick at, the little amp should drive the Peavey nuts.  I was expecting, if anything, a problem from having too much drive.

{The characteristics of an un-buffered guitar pickup is actually quite interesting;
http://www.ozvalveamps.org/pickups.htm
}

Yeah, well I've seen the Kalamazoo link before.  The main problem with picking up a signal from the speaker circuit, however you do it, is that the speaker also acts as a pretty effective microphone and I gave up using this method when doing band recordings.

A better scratch method is to pick up the guitar signal from the other input socket (which often already has suitable resistive isolation built in).  A better line output is to pick up the signal across the Master volume control.

{In the Kalamazoo article he remarks that connecting directly across a speaker is potentially harmful to the sending amp, but the real danger is actually to the receiving gear by presenting tens of volts to an input designed for perhaps one volt.  He's also concerned about impedance matching which is unimportant in this application - line inputs typically have an input impedance of 47k while line outs are only a few ohms. This is about voltage transfer, not power transfer.}

The Music Electronics Forum advice look pretty much in line with the sort of thing I do.  Generally the speaker acting as a microphone is less of a problem with high power amps.  This is because you are aiming for about 1 volt (at full output) across 600-odd ohms to the desk, and if the amp has an output of 30 or 40 volts at full output then you will be using a resistive attenuator (or step-down isolation transformer, or combination of both) with a ratio of 30 or 40 to 1, and any "microphone" pickup will be reduced by the same ratio.  With a small low powered amp you will use a much lower ratio and background pickup may become a problem.


I should clarify; when I said where the specific sound is coming from "doesn't matter" I was being pragmatic - it's coming out the headphone socket, so that's okay.  It would become a major concern where it was coming from if it was in the speaker but not in the headphone socket (which was a possible outcome).

Unless you happen to use cans a lot, why would you expect a mono amp to have a stereo headphone socket?  As it happens, as a soundie I do use cans a fair bit and have several pairs kicking around, so I'm well aware that they are normally stereo.  A mono plug in a stereo headphone socket would certainly explain a most unexpected result, but simply not fully inserting a mono plug will allow its tip to touch the socket ring connection and things should get loud (and prove that is what the trouble was).
If you say theory and practice don't agree you haven't applied enough theory.

STDog

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Re: Some noob questions.
« Reply #14 on: June 29, 2012, 11:00:24 AM »
Unless you happen to use cans a lot, why would you expect a mono amp to have a stereo headphone socket?  As it happens, as a soundie I do use cans a fair bit and have several pairs kicking around, so I'm well aware that they are normally stereo.

I would expect the headphone out to be a stereo jack because 99% of the headphones are stereo, and plugging stereo phones into a mono jack just give you one side working.

So, you send the same signal to L & R on the stereo jack and then you get sound to both sides.

Maybe a really old amp would have a mono phone jack (back when most home audio was still mono), but I don't recall seeing a mono jack for phones on equipment made since the mid 70s.