Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

March 28, 2024, 02:29:39 PM

Login with username, password and session length

Recent Posts

 

RANDALL RG100 Direct out CLIPPING

Started by soundroi, February 02, 2010, 07:40:38 PM

Previous topic - Next topic

soundroi

Hi!  :)

I'm new to this forum so hello to all members. I'm coming here for some help.

I own a RG100ES head, one RG100HT rackmount unit, one RG100 Classic head and one Century 200 Head.

My questions are:

1/ Can I use these heads without my cabs? Any problems if working on max volume with no load?

2/ (The important question): ALL these heads have a "direct out" jack which I want to use to feed a Mesa Boogie 2:90 power amp. The problem is this direct out (+4 dBm) is clipping my processors, it seems to be a really hot line out. It happens in all the heads.

-Master volume pot in the heads goes from silence (in zero position) to total clipping (in 2 position), instantly, I can see it in the processors input LEDs. The processor can handle up to +4 dBu.

-I've tried this +4 dbm direct out into a mixer (its line out can handle up to +30dBu) and it overloads the input too.

-Could this extreme clipping be related to the lack of power amp load in some way? I can't understand what's happening!

I want to use two RG100Heads as preamps, being able to use their FX loops independently, then direct outs to processors, then to stereo power amp.

Thank you very much.


mensur

1.Do it like that, you will fry those heads.THESE HEADS CAN'T OPERATE WITHOUT LOAD!!!YOU MUST HAVE CABS ON THEM!!!!SERIOUS
2.That direct out is very hot, cause it serves for larger PA's.If it clips your powered mixer, probably the direct out pot isn't working properly.
3.Only way you can operate them as preamps, is to unhook the PSU for poweramp, so the only thing working in the circuit is the preamp, and you hook it to mesa or whatever via effect send jack.

J M Fahey

Hi soundroi (should I call you RandallGuy? ;))
99% of SS amps can be used without load all day long, without problems, BUT Randalls use 100% current drive outputs and go CRAZY without load.
To top that, the "Line out" isn't so, but simply they tap some of the *speaker* out and pad it to line level or whatever.
You might pad it a little more until your processors can stand it, but anyway it's coming from a freaked out power amp, so it's useless.
*If* you hook your Randall to a proper speaker, then you can use the line out to drive your 2:90 or whatever, obviously connected to  their own cabinets.
Tell me where you play, so I go to another show, because yours will be LOUD. :tu:

soundroi

Hi again, and thanks for your fast reply. :)

QuoteIf it clips your powered mixer, probably the direct out pot isn't working properly.

It's not a powered mixer, it's a Soundcraft mixer with +30 dBu headroom line in, and as I said ALL heads clip ery seriously that line in. I doubt 4 heads having the direct out not working... The only one that has a specific direct out pot is the RG100HT. The others (RG100ES, RG100 Classic, and Century 200 have the direct out level controlled by each channel master pot.

All of them clip. One electronic engineer told me today that I need at least a 10 dB atttenuation to feed a conventional +4 dBu line in. Would it be OK?


QuoteOnly way you can operate them as preamps, is to unhook the PSU for poweramp, so the only thing working in the circuit is the preamp, and you hook it to mesa or whatever via effect send jack.

That's what this friend of mine recommended, but I wanted to have a Parametric EQ and a compressor in the loop, and then use the direct out. Do you mean the direct out is located in the power amp section? So would it be the same to use the FX send out? I've read that some guitarists (e.g. Darrell, Lynch) used to overload the instrument input AND the FX return to obtain more gain and sustain.

Thank you very much.

Roi.

soundroi

I've just seen in the RG100ES manual (page 4, "back panel") here:

http://www.schematicheaven.com/newamps/randall_rg100es-rg80es.pdf

that the "direct out" is a "preamp output", not an attenuated speaker output, isn't it?

So if I unhook the power amp section, this direct output would be still active. (And I would still have to attenuate this signal 10 db or so to feed the "line in" in my FX unit).

Roi.

J M Fahey

Hi soundroi.
Whatever the User Manual says , the schematic shows clearly that the "signal output" is the speaker output attenuated by two resistors: an unspecified one but around 22K, and a 2k2 to ground; that signal goes to the "Signal Out" jack, just look a little above the speaker outs.
It won't work if you unhook the power amp.
Above the power amp itself you'll see the RG100HT, which must have been an upscale model, sporting 3 outputs: a jack one, an RCA one, and a low impedance balanced one.
All three come from the speaker side and all said before applies here.
Now that I lok at that scematic: the solution to your problem is
1) your real Pre-signal out is the effects Send jack.
2) You *must* use a shorted plug into the Effects Return to kill all signal that might reach the power amp.
3) "Tame" your Randall by soldering a 15K resistor from the left pin of R45 to the right one of R46.
Left and right as seen on the schematic, on the actual board they might point anywhere.

soundroi

Hi!

Well, I've contated an electronic engineer who finally will do the job.

One more question:

Quote) "Tame" your Randall by soldering a 15K resistor from the left pin of R45 to the right one of R46.
Left and right as seen on the schematic, on the actual board they might point anywhere.

Why? What's this about? And what do you mean by "tame"?

Thanx again.


J M Fahey

Your Randall is a wild beast, which needs to be tamed.
You have already experienced this; both Mensur and I , 10000 kM away from each other, are saying the same, there must be something behind that. ;)
Quote1.Do it like that, you will fry those heads.THESE HEADS CAN'T OPERATE WITHOUT LOAD!!!YOU MUST HAVE CABS ON THEM!!!!SERIOUS
QuoteBUT Randalls use 100% current drive outputs and go CRAZY without load.
The Mod I told you lowers that uncontrollable 100% current feedback to a tamer 30% to 40% *and* lowers the power amp gain to about half.
Why would you want the power amp slamming against the rails needlessly if it is not driving a load?
I suggest you mount a switch somewhere on the chassis, so you can apply this mod at will; if you connect a cabinet to the speaker out, turn it off.
If you leave it on, nothing bad will happen, it will just have a less buzzy sound.
If you are *not* using your head into a cabinet, go from the effects out to whatever effects you want and from them straight to the Boogie, you do not need to return to the Randall.

soundroi

Thank you very much again for your help! :)

soundroi

Hey! Another couple of questions for the experts, help needed!

1/ Well, my RG100 Classic haas really high gain, no need to use a Booster. But with ALL other amps I'm using a booster before the amp (and a Parametric EQ) to have infinite gain and that chainsaw metal tone. Is there any difference in them in this point, I mean, input gain?

2/ My RG100HT (blue rack unit) has an extreme hum noise problem, which I've seen is a common problem in this model if using high-gain settings. Is there any way to solve this? At his moment, and usin gain at 10 as I do, it is really hard to play it.

Thanks..

phatt

Hi soundroi,
Q1 is hard to answer without the thing in front of me.

Q2, well as it's a rack it implies that you are plugging into another Amp.
IF the 2 units are *grounded chassis* then there will be an earth loop created.
This is a common mistake when linking equipment together.
With high gain preamps not helping the situation.

You have to lift the *Signal common* from the *mains Safety ground*
to fix it. IF you have no idea what is being said then Get pro advice before messing with Chassis earth wiring.
Doing it the wrong way can have fatal conciquences. :o

The safest/cheapest way to *test/fix* if you have this issue is *cut* the common wire on one end of the audiocable that joins the 2 units. If the hum is greatly reduced then you most certainly have a ground loop happening.
you will then have to deside which way to go.
just something to consider.
Phil.

mensur

Quote from: soundroi on February 05, 2010, 07:56:48 AM
Hey! Another couple of questions for the experts, help needed!

1/ Well, my RG100 Classic haas really high gain, no need to use a Booster. But with ALL other amps I'm using a booster before the amp (and a Parametric EQ) to have infinite gain and that chainsaw metal tone. Is there any difference in them in this point, I mean, input gain?

2/ My RG100HT (blue rack unit) has an extreme hum noise problem, which I've seen is a common problem in this model if using high-gain settings. Is there any way to solve this? At his moment, and usin gain at 10 as I do, it is really hard to play it.

Thanks..
Q1 is hard to answer without the thing in front of me, too
Q2 isn't ground loop problem, cause RG100HT is RG100ES in rack unit(so it has it's own amplifier), the problem are main filter caps that are old and need replacement,that amp is very old, so the caps must be changed.Hum is present cause you have a large ripple current in the PSU, cause filter caps have done theirs.Problem is not in the preamp, cause it is 100% JFET design(2N5484 are low noise/microphonic amplifiers).

mandu

If the schematic is similar to what Soundroi quoted, you can need to use the effects out as the preamp out to your other amp or mixer etc. You will also need to plug a dummy phono jack into the effects return to prevent signal going to your randall poweramp section.
Thus you may not need any internal mods on the amp.

regards,
mandu