Line level to instrument amp input??

 

Unregistered guest
HI YA!
Picked up a Peavey 210 watt Bass guitar Amp to power my soon to get 15x4 infinit baffel speakers. good;now i need to attenuate Sony str945 sub line out to instrument in. Sony line out 2v @1K to Peavey 20mv @ 330k ohms in. Both unbalanced. Bin searching web under every concevable combination of search words and best I can come up with is a +4dbm pro-level to instrument L pad scematic. too much. Anybody?
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 5833
Registered: May-04


I'd say trying 2V out to a 20mV in is a poor selection of equipment on your part. Obviously the Sony doesn't output 2V at all times but the potential for overload is too likely. If you want to try the combination, I would turn the level of the Sony's subwoofer output down as far as possible and listen for distortion on peaks. If you set the level at -12db, you might get away with the combination. If overload distortion occurs, I would then call Peavey for further assistance. I would guess their advice would be to run their equipment with the recommended instrument level products. Why did you choose this amp for this application?




 

Moebius
Unregistered guest
If when you say the Sony output is 2 volts @ 1k you mean it's 2V at 1k ohms then this should be easy to do: basically all you need is a resistor in series with the Sony output to "pad it down" to a level that won't overload the Peavey input. (You'll already be dropping down the signal level some because the Peavey's input impedance is so much higher than the Sony's output impedance.) I don't know how to calculate the ideal value of the resistor you need, so (unless you get a more knowledgeable post) I'd suggest trying a resistor of somewhere between 10 kilohms and 100 kilohms, or else (for about the same price as a pack of resistors, a couple of bucks) a variable potentiometer rated at 100kilohms or thereabouts, which will allow you to vary the resistance (by turning the shaft) till you hear an optimum match (which is: lowest "white" noise (circuit hiss) that still gives no overload distortion). In either case, you will just be wiring this between the tip of the output plug (the + side) from the Sony, and the matching contact on the input jack of the Peavey. Easiest way to do this is probably just as an "in-line adapter": buy a female-phone to male-phone extender cable (straight, not curled, just because it's simpler) , cut that, strip the wires at both sides of the cut, insert the resistor or variable pot. between the two hot ground-wire ends (the two outer wires, the shield).
You can make all those connections with the small size (grey, 18-22 gauge) wire-nuts.t
 

bear paws
Unregistered guest
Jan;A simple attenuator is commen practice to drive differant impedances or voltage imputs. most common is speaker level to mic input. Why? because it was cheap and it works.This thing has [8]2N3772 pwr finals on a sink the size VW. The pwr trans is a 10lb. E-core,W/Full wave bridge rect. with caps the size of soup cans. Also it puts out 210w continious @1%THD. 240w @5%THD.Distortion @ 210w @1KHZ less than 0.2%. Peak out put 400w @ rated load 2ohms all day. Music power output 290w RMS @1%THD.Freq.Responce 3DB down @20 cycles to 15kc.[hertz for u youngens]8 chan.EQ + - 14DB. Variable slope and roll off control.This thing has the head room to wup BUTT on any 3.5inch throw voice coil speaker x 4 ALL DAY. Ergo infinit baffle 4X15inch. being a Pro unit there is no consumer hype bull ticky here.just a BASS amp.
Now; MOEBIUS. TNX! There-in lies the problem, the calculation.It would be good to match line out impedance from Sony to L-pad and also match L-pad to Peavy.its doable but the cal. for impedance match and votage drop is beyond me.As far as input jacks its no matter.cause peavy in is TRS. and sony out is RCA,all to change soon.
AS i said early i do have scematic for a 4dbm pro line level out but don't know how to covert the #.The line resistor is 50K then a 5K shunt from tip to sleeve. Obviously foil resistors never carbon for low volt audio circuts. So the short of the long is i need a 40 db PAD since consumer line out is -10dbu vs .pro line at +4dbu.Ah gee,u got to love this stuff.
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 5841
Registered: May-04


Well, your second posts sounds smarter than the average bear about these things. I didn't realize you were willing to solder in a pot to make the voltage drop. I would still recommend trying the system first with the receiver's sub out at -12dB. Since this is probably adjusted while the signal is in the digital mode, the output from this lowered level should be much cleaner than anything you will achieve with an analog pot. Since you don't know the calculation for the value, and it's been too long for me to remember the numbers also, I would say use a cheap 150kOhm pot to get the level adjusted to where you feel comfortable and then measure what resistance is in the pot and buy a good quality resistor to hardwire in place. If you can get the level lowered with the sub out settings, you should have less effect on the dynamics of the output with a lower value resistor in line.

While your amplifier sounds impressive, I still have to ask what you have against a Class D plate amp that wouldn't require all the padding down and would have no impedance mismatches. There are some fairly good Class D designs for sub use. Or, why not a used consumer amp such as an older McIntosh, Citation or Crown, etc.?




 

bear paws
Unregistered guest
Jan; Well the line out is of course anolog as is input. Soooo. I'm willing to and able to do much more than that. there is a lot more here than that. I'm a very big believer in impedence matching be it a balanced or unbalanced circut.I just may yet change over to a balanced out on the Sony. There is a balanced XLR input [2] one high one low sig.db on this amp.also along with the TRS high/low inputs.plus I still have to set up for auto on. Thats simple enough. Why do telephones work so well [other than Soutern Bell]? they have aways used isolated ground and balanced circuts, but I digress. A single pot {most are carbon based and creat noise even standing still at these kind of sensitivities{Peavey is 20mV @ 1kc [sorry,hertz]and then impedences change with freq. and gain and will not match no how.thats why you need either a L-pad, transformer match coupling,hot plate or a balanced taper pad for XLR connections.The L-pad is the simpelist and clean for a unbalanced TRS and will match both output and input Z. However the problem,though not unsolvable, remains I can't find a formula. Moebius is correct about low Z into high Z working ok but ok is not good enough!! Now the why. There isn't a consumer plate amp out there with those kind of numbers. The other amps, unless its a bass amp [Read as 15hz to 10khz], [this thing will go down to 10 hz @150w before it turns on the fan] , without a lot of wasted cicutry for mid and high range and,this has 8 chan rotory EQs for bass freqs only, plus they lack of power head room to drive 4X15inch looooong throw speakers at SPL's 80-90+ dba for low LFE for hours without fizz-wapping the power finals.I have nothing against any plate or consumer amps other than they really don't tell u everything [just lots of useless hype]even the snob appeal ones.I have several as we speak.You can't beat commercial/pro/industrial stuff.They just don't come in a fancy wrapper and has only the essentials,no fancy yellow green red LEDs with useless ununderstandable features. You want a stove to cook on or a show piece that can't boil more than a cup of water. Also i've never been the plug and play do it thier way type."can't get no satisfaction" Oh yea, the price was $10 at flea sale. It had a bad thermal breaker [$3]on the heat sink.I know $10 is risky but hey you can't win if you don't play. Actually I had been looking for a pro/comm.anyways. there are a ton of them out there with some very serious real numbers given up by defunct bands and studios. Been thinking about a pro mixer/EQ.These guys play alot harder and watch noise levels and distortion closer than the average audio bearphyle. TNX for ur intrest.
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 5843
Registered: May-04


A few more questions. First, I agree you can't beat the price you paid for this amp; but I have seldom seen any instrument amplifier that isn't running in a strict Class B operation. This isn't all that important when you bandwidth limit the amp's input but you'll have a pretty high level of notch distortion with this amp compared to a consumer product. No? Some people would argue this is more relative to a bass amp dealing with the long wavelengths. Also that power alone is not what is preeminently important compared to specs such as rise time and square wave performance where most instrument amplifiers lag behind consumer gear.



Second, how do you plan to convert the ouptut of the Sony to balanced out? And, what is there to gain by simply converting the Sony at the outputs when it has run single ended throughout its signal path up to the outputs? Are you running balanced outs from the source(s)?


Finally what is your IB set up?


 

bear paws
Unregistered guest
Jan. The horse is dead.
This is a Class A analog linear amp.Thus the massive power supply. remember the 10lb E-core
and soup can filter caps. This draws up to 700 watts @ 117volts to power those 8 Power transistors on a heat sink the size of a VW.and a 25cfm blower.Efficiantcy is not the strong suit here but fidelity is. I thought notch distortion only applied to class D when you have lag time between on & off of the pwr transistors? So Rise time does'nt apply. I've been wrong before,I think. Also why this has a seperate slope control for low end freq. roll-off. I can roll-off [sacrifice] deep end with out sacrificing overall tone or gain. Now distortion. The distortion level control is the element used to vary the amount of distortion present in the output signal by utilizing non-linear feedback.It has one. The harmonics control determines the over tones present in the distortion control and can be turned up to OVERDRIVE.It has that too. The 8 band active EQ/Crossover can boost or cut 12DB for a total of 24DB each freq. band. And it has a preamp gain control and a power amp volume cotrol to monkey with to boot. And if I don't like the sound when I'm done I'll write off the 13 bucks as EDUCATION and try some other unortodox uncoventional bizzar and "never heard of it"" can't be done" idea. .They pick up trash here on THURSDAYS.

Sony? don't Know yet. haven't look at the scematic yet.depends on the type of output but should be able to isolate ground from chassis and that has no bearing on inputs. Isolated/ balanced outs into other powerd units keeps ground loop problems away,even though the Peavy has a 2 postion ground switch.

IB will be 4 IB15 from AE of Custom Sound Solutions Mounted in cieling [Not recommened] or in 60x80 skylite side walls 2x2 opposed in a push pull config.{180 out of phase]with 2400cuft of insulated free air space. "the horse is dead"!

Back to my original post: I still need a Formula or specs for a 40db L-pad attenuator re: origanal post. ANYBODY??? TNX!!


 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 5849
Registered: May-04


Sorry to hear about your pony. Good luck.
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