Help me please!

[Leek]

I'm new to preamp design, but I'm good with a soldering iron. I have recently began building a preamp. I'm using a Balanced line transmitter/receiver to balance my I/O for XLR's. My preamp stage is a NE5532 op amp style circuit. I have 0.1uf Wima caps between each +/- power input on each op amp. I'm using all Wima (Film) 1% caps for the entire circuit. Resistors are all Vishay metal film 1%. My power supply is supplied using a Hammond 161G28 Transformer, .5% caps/resistors and 7812/7912 regulators. Decoupling is provided by Wima 0.1uf caps in entire circuit.

Input Stage TL071
Preamp stage NE5532
Output stage OPA2134
Power :  Hammond 14v-0-14v with 7812/7912's

Balanced line transmitter/receiver schematic (http://sound.westhost.com/project51.htm)
The only exception is I'm using the OPA2134 in the transmitter circuit for it's better quality.


NE5532 preamp schematic (http://www.next.gr/circuits/Pre-MIC-microphone-preamplifier-2-CH-by-IC-NE5532-or-LF353-l40881.html)
Identical using all Wima/Vishay 1% components.


PSU schematic (http://www.electroschematics.com/6247/12-volt-dual-power-supply/)
Identical using .5% components.

My question is, what kind of quality can I expect from this. My soldering is neat and etc. How would it compare to the cheap preamps in a digidesign 002 for example? I'll be using standard recording mics like a SM57, 421 or 414. I hace phantom supply for the C414 as well will add one to the circuit eventually.

 

[PRR]

Welcome.

Fancy-brand caps and 1% parts won't fix the hiss you will get.

The preamp you link to "works" but has self-hiss comparable to a 414 and 3X higher than a SM57. If you only do loud rock, it may be fine. Last time I had to use a preamp of this class, the background hiss was quite audible in a large and not soundproofed rehearsal space, though masked when the student rockers/jazzers were playing.

It is unbalanced input. So many situations "need" balanced inputs to reject AC hum/buzz that balanced is now universal.

Phantom Power really works best with true balanced inputs.

If you thought to use Rod's #51 fig 2 to take a balanced mike to an unbalanced preamp.... this is a LINE level design. Mike is 100X weaker than Line. Hiss level which is insignificant at Line level is obtrusive at Mike level.

Sight unheard, I bet the digidesign 002 inputs will have less hiss, and that it will matter on some recordings.

It doesn't take a lot to get good low hiss at Mike level. But you don't get what you need (huge devices) from commodity chips. There are several "$10 preamp" projects using special mike-amp chips which are really very fine (better than nearly all mike inputs 1928-1972, and comparable to many good studio preamps of recent years). You can also use two $0.39 transistors with several op-amps and get just-as-good 99% of the time.

I would think Rod has better mike preamps? Though some of his stuff is simply functional rather than super-kewl.

 

[john12ax7]

Are you building a microphone preamp? If so you definitely do not want a tl071 differential input stage, you want something less noisy.

I would suggest one of the all in one solutions to start with, results can be pretty good. Something like the an INA163 or one of the THAT corp chips.

 

[Leek]

How can I eliminate the noise? I'm wanting to make this a decent mic preamp. Would using the TL071 as balanced input not be acceptsable? Perhaps simple transformer balanced input? Where to start? I can pick up a Triad TY-250P to start a design around for the output. Possibly a OEP mic input transformer? But, where to start? This is all new to me.

 

[Leek]

can someone help me develop a simple balanced "mic" Input stage with a OEP Z21808C?  My preamp and output stage should be fine?

 

[Leek]

I have

Resistors
(6) 100k Vishay 10%
(4) 1k Vishay 10%
(2) 47k Vishay 10%
(2) 10k Vishay 10%
(4) 4k Vishay 1%
(2) 3.3k Vishay 1%
(6) 100 Vishay 1%
(4) 6.8k Vishay 1%
(8) 10k Vishay 1%

Capacitors
(2) 1000uf 25v 1%
(4) Wima .22uf 1%
(8) Wima 0.1uf 1%
(2) Polystyrene .22uf 10%
(2) Tantalum 33uf 10%
(2) 220pf 5%

Op Amps
(2) TI BB OPA2134
(2) TI TL071
(1) TI NE5532

Regulators
Various 7812/7912's

Transformers
(4) Behringer OT-1
(1) Hammond 161G28

Rectifiers
Vishay 1A 400v


How can I make a balanced mic preamp with XLR connectors using these?

Would (http://www.8085projects.info/image.asp?picture=Balanced%20input%20microphone%20amplifier%20using%20NE5532.jpg) be better? I'd have to use 2 TL071, Ne5532 and OPA2134's instead of numerous 5532's?

 

[gyraf]

Hi Leek,

It seems like you're trying to work "backwards" here: The TL071/5532 opamps are good for line level work and moderate gains - but for microphone input work you need to think it differently.

Take a look around these forums - there are a lot of very good discussions and descriptions of what is important in microphone front ends.

Some of the newer easy-to-use  integrated mic preamp chips will give you at least as good performance as you'd be able to squeeze out a good and expensive handful of discrete components.

Jakob E.

 

[Leek]

Would the OPA2134 make a decent build? 0.00015% THD, CMRR 87dB seems to be pretty quiet? For example a circuit like (http://www.tradeofic.com/Circuit/783-BALANCED_MICROPHONE_PREAMPLIFIER.html) but using the OPA2134 for better specs? The unbalanced output could then be balanced using a balanced line transmitter to XLR's.

 

[ruffrecords]

Would (http://www.8085projects.info/image.asp?picture=Balanced%20input%20microphone%20amplifier%20using%20NE5532.jpg) be better? I'd have to use 2 TL071, Ne5532 and OPA2134's instead of numerous 5532's?

That is a good basic design. You can use the OPA2134 instead of the NE5532s.

Cheers

Ian

 

[Leek]

Would (http://www.8085projects.info/image.asp?picture=Balanced%20input%20microphone%20amplifier%20using%20NE5532.jpg) be better? I'd have to use 2 TL071, Ne5532 and OPA2134's instead of numerous 5532's?

That is a good basic design. You can use the OPA2134 instead of the NE5532s.

Cheers

Ian

Just one question, then I'm off to try my luck. If I were to use a potentiometer for gain, where would I solder the pins of the potentiometer?  Pin 1 is ground, 2 to the circuit output, 3 to the input?

 

[ruffrecords]

Would (http://www.8085projects.info/image.asp?picture=Balanced%20input%20microphone%20amplifier%20using%20NE5532.jpg) be better? I'd have to use 2 TL071, Ne5532 and OPA2134's instead of numerous 5532's?

That is a good basic design. You can use the OPA2134 instead of the NE5532s.

Cheers

Ian

Just one question, then I'm off to try my luck. If I were to use a potentiometer for gain, where would I solder the pins of the potentiometer?  Pin 1 is ground, 2 to the circuit output, 3 to the input?

In the schematic referenced above you can change the gain by replacing R5 with a pot. I you use a 47K of 50K pot with a 1K series resistor you should be able to vary the gain from 40dB down to about 6dB.

This circuit is a standard instrumentation amplifier with a few minor tweaks to make it a mic pre. It is a pretty common configuration for a mic pre. Check out the $5 mic pre which uses the INA217 which is an instrumentation amplifier for audio applications:

http://www.audiomasterclass.com/the-famous-5-preamp-everything-you-need-to-know

Check out the INA217 datasheet here:

http://www.ti.com.cn/cn/lit/ds/symlink/ina217.pdf

Cheers

Ian

P.S. You can use the fourth op amp in the opa2134 to creat a balanced output.

 

[Leek]

I have a bunch of cheap b10k potentiometers. Would that be suitable for R5? And, i'm assuming  where r5 was would be soldered to pin 2 and then pin 3 would be soldered to the  5532 pin 3 like r5 was?

 

[abbey road d enfer]

Would the OPA2134 make a decent build? 0.00015% THD, CMRR 87dB seems to be pretty quiet? For example a circuit like (http://www.tradeofic.com/Circuit/783-BALANCED_MICROPHONE_PREAMPLIFIER.html) but using the OPA2134 for better specs? The unbalanced output could then be balanced using a balanced line transmitter to XLR's.

That's a "good basic design" for a high-level microphone, but the noise performance is not very satisfactory. The 1k resistors alone add 10dB to the source noise. OPA2134 instead of 5534 won't change that. Noise performance is absent from the description; a good reason for that is that it's not good.

 

[Leek]

Would the OPA2134 make a decent build? 0.00015% THD, CMRR 87dB seems to be pretty quiet? For example a circuit like (http://www.tradeofic.com/Circuit/783-BALANCED_MICROPHONE_PREAMPLIFIER.html) but using the OPA2134 for better specs? The unbalanced output could then be balanced using a balanced line transmitter to XLR's.

That's a "good basic design" for a high-level microphone, but the noise performance is not very satisfactory. The 1k resistors alone add 10dB to the source noise. OPA2134 instead of 5534 won't change that. Noise performance is absent from the description; a good reason for that is that it's not good.

Would changing the 1k's too 100k or higher help? I'm not looking to build a 1073. But a decent sounding preamp of better quality then cheap audio interfaces.

 

[abbey road d enfer]

Balanced line transmitter/receiver schematic (http://sound.westhost.com/project51.htm)
The only exception is I'm using the OPA2134 in the transmitter circuit for it's better quality.

It's probably the worst choice you could make in taht position; I'd rather use unbalanced/impedance balanced.

NE5532 preamp schematic (http://www.next.gr/circuits/Pre-MIC-microphone-preamplifier-2-CH-by-IC-NE5532-or-LF353-l40881.html)

That is a very basic mic pre, of poor performance because unbalanced and not proper impedance-wise.

PSU schematic (http://www.electroschematics.com/6247/12-volt-dual-power-supply/)

Why not, although you could use dual 15V for better headroom.

Identical using .5% components.

Pure waste of money. Anyway electrolytic caps come in +/-5% tolerance at best.

My question is, what kind of quality can I expect from this.

Nothing as good or even close to your 002. Building quality gear is not cherry-picking. You need to study the schematics of renames gear, for example the SSL4k and 9k.

 

[abbey road d enfer]

Would (http://www.8085projects.info/image.asp?picture=Balanced%20input%20microphone%20amplifier%20using%20NE5532.jpg) be better?

Yes, that one would be better because it's balanced, but again, the sum of the 510r resistors and the 1k gain resistor induces 10dB superfluous noise.

I'd have to use 2 TL071, Ne5532 and OPA2134's instead of numerous 5532's?

What's wrong with 5532?

 

[Leek]

Would (http://www.8085projects.info/image.asp?picture=Balanced%20input%20microphone%20amplifier%20using%20NE5532.jpg) be better?

Yes, that one would be better because it's balanced, but again, the sum of the 510r resistors and the 1k gain resistor induces 10dB superfluous noise.

I'd have to use 2 TL071, Ne5532 and OPA2134's instead of numerous 5532's?

What's wrong with 5532?

Could you point me in the correct direction for a balanced 5532 or OPA2134 mic preamp using what I have. I want to build something of equal or better sound then my 002.

 

[abbey road d enfer]

Would the OPA2134 make a decent build? 0.00015% THD, CMRR 87dB seems to be pretty quiet? For example a circuit like (http://www.tradeofic.com/Circuit/783-BALANCED_MICROPHONE_PREAMPLIFIER.html) but using the OPA2134 for better specs? The unbalanced output could then be balanced using a balanced line transmitter to XLR's.

That's a "good basic design" for a high-level microphone, but the noise performance is not very satisfactory. The 1k resistors alone add 10dB to the source noise. OPA2134 instead of 5534 won't change that. Noise performance is absent from the description; a good reason for that is that it's not good.

Would changing the 1k's too 100k or higher help?

No. The higher these res, the higher the noise. But other considerations prevent the use of 10r resistors.

I'm not looking to build a 1073. But a decent sounding preamp of better quality then cheap audio interfaces.

I understand that; you have to acknowledge the fact that these "cheap" preamps are cheap because they are mass-produced, and that their designers have pulled a number of hairs finding ways to make them cost-effective. It's very hard to beat the objective performance/price ratio of a Mackie/Audient/Yamaha/MOTU/... mic preamp.
Just check our specific project pages; very often our members build preamps not for absolute preformance, but rather for subjective reasons.

 

[abbey road d enfer]

Could you point me in the correct direction for a balanced 5532 or OPA2134 mic preamp using what I have. I want to build something of equal or better sound then my 002.

No. Unless you want to use about 100 of them in parallels, just to achieve the noise performance you would have with the adjunction of an input transformer (expensive) or a few bipolar transistors. And I can't guarantee anything about "sound"; maybe we could talk about frequency response, distortion, headroom or noise...

 

[Leek]

Understandable. Thanks for the information. If I built (http://www.tradeofic.com/Circuit/783-BALANCED_MICROPHONE_PREAMPLIFIER.html) using OPA2134's, how could I eliminate noise? When you say noise, are you referring hiss as in feedback like from a guitar amp? I've heard of the 5$ Mic pre, it sounds clean. How can I not achieve this with a OPA2134?