sizzle n fizzle

rgalpin · Post by **rgalpin** » Thu Apr 07, 2005 4:36 pm

I'm getting a sizzly - fizz in my sound. Hear it in the clip below. It's a JCM 800 2204 running into an H&K RedBox Pro with a duumy load - the RedBox sends the tapped signal to a 15 band EQ - and then to a SS power amp.

It doesn't really happen until about half way through the clip when I turn the guitar volume to 10 - the first part of the clip the guitar is on about 6.

You think the RedBox is doing this? I feel like it is the weakest link in my chain because I have never heard of anyone else using one for this application. I started tearing it apart to see if I could figure out a way to bleed the ultra highs (10k and up) to ground - and then I thought I would check with you all to see if anybody has any other ideas.

The RedBox has a Cabinet Sim Switch - this switch eliminates the fizz if you turn it on - but I keep it in the OFF position because it's too much - it sounds like a blanket over the cabinet.

And the EQ getting the signal from the RedBox has 6.3 and up buried.

the clip:
http://www.funnymoneyband.com/sw/2204_nfb_50k.mp3

ideas?

rjgtr · Post by **rjgtr** » Thu Apr 07, 2005 5:57 pm

Are you running into a normal guitar cabinet or a PA style cab. If you're using a PA cab, then you need to use the Cabinet simulator circuitry or you will get that fizzy sound. How is your graphic set? If you are boosting the highs this will contribute this kind of sound as well.

Otherwise you could simulate a cab simulator with your graphic by making a sharp curve above 5k-7k on the graphic.

What you are hearing is the natural sound of the amp when not put through a guitar cab.

Flames1950 · Post by **Flames1950** » Thu Apr 07, 2005 6:03 pm

I've got a Red Box, I used it in the last band I played in to eliminate one more mic bleeding through.
I've found it's OK when mixed through the PA with natural ambient guitar cab sound coming off stage at the same time. Recordings I have with it straight off the board and no ambient mic'd sound come across thin and fizzy to me though, much like you describe. I'd guess it's your culprit, barring too much preamp gain.

Billy Batz · Post by **Billy Batz** » Thu Apr 07, 2005 6:15 pm

This seems to be comming up lately. You dont need to use a cab sim with that slave setup if your using a guitar cab. The sim is meant to simulate the cab by rolling off highs and lows. Using the sim then a cab wouldnt sound very nice. You may be using a SS poweramp but the signal its amplifying is the saturated tube amp sound and thats exactly what it is. Its just like the amps output without a load or anything. just lower. The only time to use a cab sim is when going direct into a board or recording device. I dont have the same taste as you Im sure but you should still try a simpler setup first with just the amp, load, SS poweramp and guitar cab. Then compare it by adding those other things in. Its certainly feasible to use the Line out to the cab sim then the poweramp and a PA type speaker but if you have a guitar cab that doesnt make any sense.

rgalpin · Post by **rgalpin** » Thu Apr 07, 2005 7:31 pm

RJGTR - the cab is 4 x 12 Greenbacks 25w. Sorry I missed mentioning that - agreed that would make a big difference.

Flames1950 wrote:I'd guess it's your culprit, barring too much preamp gain.

Yeah, the preamp gain is too much - because when I turn up the guitar to 10 not only does the fizz get exaggerated but you can hear a lot of the integrity of the sound go out the window. It's a low output pick up - SD Pearly Gates - and I have "undone" all my previous preamp mods - and still there is so much preamp gain in this amp - it's unreal that some people say they need to mod a 2204 to get more gain! It's got tons. I tried replacing the 470K paralleled with 470pF treble peaking circuit that goes from the input jack to the preamp pot with a 68K as I have seen suggested in a number of places and that seems like way too much gain and sloppy bottom end right out of the gate.

Does anyone know what the calculated total resistance of the 470K resistor paralleled with a 470pF cap is?

So, if I back off the preamp a bit, where can I regain some of the drive I need to keep things in "over the top" mode without all the sloppy? In that clip, the Master Vol was 8.

At Dan's suggestion, I changed my negative feedback resistor value to 50K by parrallelling the existing 100K with another. And I think I like what it did - I don't know if I'm imagining this or not but it seems to have made the sound a little rounder and just slightly sproingier in the mids which I like - I never know if I'm really hearing these things or not...

rambling - thanks for the input.

Flames1950 · Post by **Flames1950** » Thu Apr 07, 2005 8:46 pm

Does anyone know what the calculated total resistance of the 470K resistor paralleled with a 470pF cap is?

It's not really a matter of total resistance unless you want to go through and figure it frequency by frequency. The 470pF is allowing high frequencies to pass around the resistor completely, resulting in more drive at higher frequencies. I think it works better simply to remove that 470pF cap so that all frequencies pass through the resistor equally. It's the same concept as the bright cap across the first two terminals of the volume pot. That cap can also be removed to make the sound darker at low volumes. (In the case of a pot-mounted bright cap, its effect gets less and less as the pot is turned up and its resistance goes down. It gradually becomes just as easy for the high frequencies to go through the pot as the volume reaches max and the resistance approaches zero.)

rgalpin · Post by **rgalpin** » Thu Apr 07, 2005 9:43 pm

Ok - so, if we want to remove the cap in order to even out the frequencies getting through but we don't want to alter the total amount of signal getting through - holy mackeral it just hit me - this signal is going directly into a potentiometer anyway - so it really doesn't matter how much resistance you leave in the line because you get the opportunity to adjust it at the preamp pot - the area we are talking about is in series with the preamp pot so the values will be added. That said, as long as you leave yourself with a workable range on your preamp knob you're ok.

Am I thinking straight on that?

Billy Batz · Post by **Billy Batz** » Thu Apr 07, 2005 9:55 pm

The preamp knob does alter a series resistance like the fixed 470k BUT it also has the ground on the other side. A pot wired up just with one side and the wiper in line with the signal path would alter ONLY the series resistance but when you adjust a volume/gain/preamp pot the major factor is the resistance between the wiper of that pot and the ground lug which controls how much of the signal is sent to ground or how much volume. The tone in that regard is at the mercy of the volume setting which obviously makes a much larger difference in this case. Se really the 470k is what you want to focus on. If you remove the bright cap on the 470k you can change the value of the 470k to your liking larger or smaller.

rgalpin · Post by **rgalpin** » Fri Apr 08, 2005 10:52 am

Ok - to see if I understand completely...

Are these drawings accurate as far as how the signal flows through the preamp pot?

Billy Batz · Post by **Billy Batz** » Fri Apr 08, 2005 11:01 am

Volume pots arent linear but yeah its correct. The signal on the wiper lug has a resistance between that and the ground which pretty much is your volume control. Thats the more important factor here. You can dial in the right amount of series resistance but that may or may not be the correct volume. The 470k is always the same at any volume.