If I understand correctly, my- goes to pin 2 & positive to 3 of 1/2 of the NE5532, positive 18v to pin 8, ground to pin 4. Then, I use a pair of matched resistors to create a voltage divider which would give me 9v to pin 5, pin 6 then combines with pin 7 for my output?
preamp, not passing signal.
- Thread starter Leek
- Start date
Help Support GroupDIY Audio Forum:
PRR said:
I've read it. Im missing something. Since im not using a +/- power supply, I must use a virtual ground by using a pair of resistors as a voltage divider to provide both the +/- at the output. Since the virtual ground is half way between 18v and ground, I'd feed the divider into the non-inverting input of the 2nd NE5532 (it's dual) and then feed the inverting input to pin 7 giving me both at output?
A picture is NOT a schematic!Leek said:
1) Your schematic defines what you want to do. Get your schematic right first.
2) Then you make breadboard or PCB bla bla to replicate what is on your schematic.
3) You have to formally check that your breadboard/PCB/bla bla is EXACTLY what your schematic shows.
Trying to work out what a circuit is doing from a pic is a lot of guesswork ... especially if the circuit has never worked properly
BRAVO!! That's the best & clearest bit of info (a nearly complete schematic) you've given us.
It could still be better .. eg I hate the background and what's the resistor between pins 1 & 3 of the XLR for?
BTW, its good to number your components .. eg R1, R2 etc. Saves a LOT of confusion
The worst fault is your "pins 5, 6 and 7 to reference ground". This may cause problems and probably increase the current consumption needlessly ... the output is usually undefined if the +ve & -ve inputs are connected together.
It should be like this.
I leave you to fill in pins 5, 6 and 7 as a worthwhile exercise .. but if you drew this, even without the pin numbers, people versed in the art will know exactly what you mean and intend.
By trying to describe it in words, you have managed to confuse even the most experienced gurus among us
Attachments
Thank you Ricardo. The resistor at the input of the XLR was a drawing error. I've changed the 2nd amp in the NE5532 to what you provided. Thank you guys so much for the help. I know I've been a hassle, but the knowledge is almost priceless. Now to work out my BC547/BC557 preamp stage and the unbalanced 1/4" output.
Get some light on your paper. Crop the image.
Yes, qm7jkyxtb will work.
One minor point: the 10K:10K divider adds 5K to the audio resistance of the un-numbered 100K which should match the other un-numbered 100K. Also it injects half the supply crap into the amplifier input. A cursory review of single-supply plans shows we usually put a cap on the Vref.
Now back up. This is a Microphone preamp? It is not just a balanced-unbalanced function. Mike signals are weak. We need to recover the signal with least harm.
The microphone is a 200 Ohm resistor giving both precious signal and annoying hiss. Now you have added 2*12K of resistors which hiss but do not produce precious signal. This is not the lowest-hiss mike input around. Even if the 12K were 1K each, such mike inputs have audibly excess hiss.
Yes, qm7jkyxtb will work.
One minor point: the 10K:10K divider adds 5K to the audio resistance of the un-numbered 100K which should match the other un-numbered 100K. Also it injects half the supply crap into the amplifier input. A cursory review of single-supply plans shows we usually put a cap on the Vref.
Now back up. This is a Microphone preamp? It is not just a balanced-unbalanced function. Mike signals are weak. We need to recover the signal with least harm.
The microphone is a 200 Ohm resistor giving both precious signal and annoying hiss. Now you have added 2*12K of resistors which hiss but do not produce precious signal. This is not the lowest-hiss mike input around. Even if the 12K were 1K each, such mike inputs have audibly excess hiss.
PRR said:
So, I need to match the two 100k resistours? Get a cap between the Vref (1000uf,25v electro) to ground. Also, replace the 12k resistors with matched lower ohm (gonna try 100 ohm 1% metal film) resistors to help get rid of hiss. I will replace this on my schematic and post the new updated one for review soon.
Gene Pink
Well-known member
Leek said:
Per your most recent schematic, an exercise:
1) Calculate the no-signal voltage at pin 3 of op amp 1A.
2) Calculate the no-signal voltage on the base and both collectors(?) of BC547
3) Op amp 1B, you almost got that, but where might be a better place to connect pin 5, other than ground, or in this case of a single-ended supply, the (-)rail?
You might consider using op amp 1B as a second stage, instead of a discrete transistor. In my opinion, op amp design has a shallower learning curve than using discrete transistors.
I believe I have a good feel for where you are in the whole EE learning curve, congrats on getting this far, you are getting close to a working pre amp, but there are still some basics (hint-capacitors) that you missed. How well it works, will take a bit longer. I encourage you to stick with it.
Gene
Gene Pink said:
Thank you Gene. I'm still working everything out. I could use the NE5532 as the second stage. I do also have another NE5532 and a few other amps. I'm not quite sure what caps I've missed. But, I will definitely spend more time figuring it out. Can you perhaps provide a little insight where to start with the missing caps?
Also, I have a few BC547, BC557, 2N2904 and I'm wanting to incorporate them for the low noise and sound. Possibly even add transformers after I get a working transformerless circuit. I plan to develop and learn as much as I can. I'm not looking to build a forsell or neve quality preamp, but to learn and use as much knowledge as I van to mod myexisting equipment or to build pieces I want.
Heikki said:
So, connect C3 to the resistor leads to put it in parallel, keep the + towards the supply voltage and - towards a 100k resistor to ground? Also, no experience with transistors. I have no idea how to come idea how to come up with a good output stage. R4 is in series with R3 (with cap in parallel). I made a mistake in drawing.
Here is what I've drew now.
https://postimg.org/image/jetwp1m45/
