adjusticator distorted / noisy newbie opamp question

[sonic66]

Hi,

built an adjusticator to place in an  FX's loop, but am having some problems with it.

Using aTL071C , it works well but is noisier than i would have hoped for, too much hiss,  the amp itself is quite quiet,

so i tried  a NE5534 it also noisy, and it seems to distort at any level, ( either befor the amp or in the loop )


I've checked the voltages, powered using a battery.  The v+ is 9.45, and the v- is connected to ground.... is that the problem?

should i use a voltage divider setup and put 9v on V+ and  4.5 on V- , disconnect the v- from ground
 
some help would be appreciated.




(  metal fim for the 0.1 input cap, and  electrolytic for the  all the 10mf  caps )


http://www.geofex.com/circuits/Adjusticator.gif

[BrianJ]

TL071 and NE5534 are not pin for pin compatable!  (You knew that right?)  Further more, 5534 cannot be used in unity gain circuits, they are unstable at gains less than 3.  They also require a small "external compensation" cap across pins 5 and 8.  That said, I have never seen a circuit for the adjusticator,  i might have know idea what I'm talking about.

TL07 opamps are noisy.  They were the first opamp of their kind and haven't changed much over the years.  There are plenty of other choises, but you won't heae about many of them in music related forums.  I love the Lf411cn for single opamp circuits, it's a little more expensive.  Also check out the Burr brown OPA134 / 2134 /4134.  They are pin for pin to the TL07 stuff.   Awesome sounding but more expensive.

LF356 is good too.

[BrianJ]

Sorry.   I only adressed half of your post. V+ should be +9v and V- should be ground.  The circuit has the bias set up properly.  I think the 5534 is just not suited to the circuit.   

[sonic66]

Hi, BrianJ

Thanks for replying

I have the datasheets here in front of me, pins 2, 3 and 6  are the same , and pin 7 and 4 are the the same the other pins arn't connected in the circuit anyway.

Fixed the Fx lop fro grounding problems, haven't tested the circuit again for noise , still i don't know whay  NE5534 shouldn't work in place of TL071?

will do some googling to try find out


Thanks for assuring me about the bias, will keep a look out for the ic's you mentioned.

[d95err]

I think it is a headroom issue. 9V is probably not enough, since the FX loop is probably +4dBm or even higher. Try using two batteries in series to run it at 18V (no other modification to the circuit needed).

[sonic66]

Just tried 18v with the TL071 and it works well to a point.  Turning the gain up  beyond that point the sound fizzes out and cuts off.

Still the NE5534 and also a 741 i had lying around  sound distorted.

I don't mind using the Tl071 , with the gain of the adjusticator  low for setting a good level to the pedals that follow it , the noise isn't that bad, ( seems to have improved)

but i need to find a way to reduce the volume befor it hits the opopamp.


Should the 100k resistor  to the opamp input be changed  to 500k or 1m ( i know that this will also reduce the minimum gain)?

The amp i'm using is a Marshall lead 12 , i've added switching jacks between the output of the  volume pot and the input of the  next stage

see http://www.drtube.com/schematics/marshall/3005.gif