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How to boost audio

S

SFM-Ptgal

Connecting and unbalanced cd player to a balanced input gives me a lower level than the cart machines, for example.
How can I boost the level without having to turn the fader almost fully clockwise?

T.i.a.
 
Rob Stutson said:
SFM-Ptgal said:
Connecting and unbalanced cd player to a balanced input gives me a lower level than the cart machines, for example.
How can I boost the level without having to turn the fader almost fully clockwise?

T.i.a.
Click to expand...

You need an unbalanced to balanced amp (i.e. Henry matchbox). This will do the job quite inexpensively: http://www.artproaudio.com/products.asp?type=90&cat=13&id=77
Click to expand...

Thanks! They even have a representative in Portugal. 70€ is the price... not expensive. Expensive in my context. :-[
 
You can build an unbalanced to balanced amp out of a TLO72, a couple of caps and 10 K resistors. Good fidelity, about 20 db gain wide open. Requires bi-polar supply usually +/- 15 volts. AS I remember, need a 27 pf cap from the output to positive input to keep stray CB calls out of it, & 100 k variable to set gain.
 
Street price fpor the Rolls unit was like $50 a couiple years ago, the Henry Engineering box was just over 100. The Henry has an internal suply and is a bit ruggeder.
 
I always used to get the RDL Stick-Ons and velcro them to the back of the device (make a pig-tail out of RCA cables that came with the unit). One gotcha though: if you intend to run multiples of those, you need the PSU splitter they sell - just paralleling the PSU leads is an invitation to trouble.
http://www.rdlnet.com/product.php?page=54
-D
 
TomT said:
You can build an unbalanced to balanced amp out of a TLO72, a couple of caps and 10 K resistors. Good fidelity, about 20 db gain wide open. Requires bi-polar supply usually +/- 15 volts. AS I remember, need a 27 pf cap from the output to positive input to keep stray CB calls out of it, & 100 k variable to set gain.
Click to expand...

Can you direct me to that circuit, please?
 
Don't have a way to scan the schematic, but the circuit is simple enough to describe. This is a 10 k input unbalanced to balanced output low-z, usually runs around 20 db gain, and is a pretty flat (frequency response) out to around 15 kc. or so.

Parts list: 10 K-ohm resistors (1/4 watt fine) qty. 8
2/ 100 Ohm resistors; one 15 turn 100k pot.
47 uf electrolytics, (3); two .01 mylar or similar caps for power supply rails by-pass; two 27 pf. ceramic; TLO-72 IC.

The TLO 72 is set up as two separate amplifiers. The first stage is pin 3, non-inverting input (+), pin 2 inverting input(-), and pin 1, output. The second stage, pin 5 non-inverting input, pin 6 inverting input, and pin 7 output. The first stage provides the positive going portion of the balanced output, the second stage is fed from the first into the inverting input and provides the negative goi8ng portion of the balanced output. Gain is set with a feedback resistor on the first stage. The 27PF ceramics provide frequency compensation so the amp is not too broad. Requires a bi-polar power supply, +15 vdc to pin 8, -15 vdc to pin 4, use the two .01 mylar caps to bypass the supply rails to ground.

Circuit: Unbalanced input to pin 3 of the IC through a 10K resistor, 10 k from pin 3 to ground. Pin 2 connected to ground through a 10 k, then 47 uf cap. Pin 2 and Pin 1 connected together through the 100k variable resistor. The 27 pf ceramic parallels the 100 k variable between Pin 1 and pin 2.

The output of the first stage from pin 1 goes through a 100 ohm resistor, then a 47 uf cap. (this could be non-polarized, but polarized seems to work fine). This is the (+) output portion of the balanced out. The output side of the cap is connected to ground through a 10 k resistor.

Another 10 k resistor goes from Pin 1 of the first stage to the inverting input (pin 6) of the second stage. The non-inverting input (pin 5, is grounded through a 10 k resistor. The "feedback loop" on this second stage is a 10 k resistor paralleled with another 27 pf ceramic. The output of this second stage, pin 7, goes through a 100 ohm resistor and another 47 uf cap. The output side of this cap is also coupled to ground through another 10 k resistor. This will be the low (-) side of your balanced output.

I usually build these things on little perf board cards available from Radio Shack, which have traces etched for dual-in-line IC's. Then I mount them in a utility box with RCA phone jacks in, since a typical use is for boosting the output of consumer Cassette or CD players to "line level" to feed a console.

Power supply can be made with 7915/7815 regulators...here's a circuit I found with a quick Google search; you can probably find others that are more legible...

http://www.elecfree.com/circuit/power-supply/power-supply-regulator-15v-15v-1a-by-ic-7815-7915/
 
TomT said:
Don't have a way to scan the schematic, but the circuit is simple enough to describe. This is a 10 k input unbalanced to balanced output low-z, usually runs around 20 db gain, and is a pretty flat (frequency response) out to around 15 kc. or so.

Parts list: 10 K-ohm resistors (1/4 watt fine) qty. 8
2/ 100 Ohm resistors; one 15 turn 100k pot.
47 uf electrolytics, (3); two .01 mylar or similar caps for power supply rails by-pass; two 27 pf. ceramic; TLO-72 IC.

The TLO 72 is set up as two separate amplifiers. The first stage is pin 3, non-inverting input (+), pin 2 inverting input(-), and pin 1, output. The second stage, pin 5 non-inverting input, pin 6 inverting input, and pin 7 output. The first stage provides the positive going portion of the balanced output, the second stage is fed from the first into the inverting input and provides the negative goi8ng portion of the balanced output. Gain is set with a feedback resistor on the first stage. The 27PF ceramics provide frequency compensation so the amp is not too broad. Requires a bi-polar power supply, +15 vdc to pin 8, -15 vdc to pin 4, use the two .01 mylar caps to bypass the supply rails to ground.

Circuit: Unbalanced input to pin 3 of the IC through a 10K resistor, 10 k from pin 3 to ground. Pin 2 connected to ground through a 10 k, then 47 uf cap. Pin 2 and Pin 1 connected together through the 100k variable resistor. The 27 pf ceramic parallels the 100 k variable between Pin 1 and pin 2.

The output of the first stage from pin 1 goes through a 100 ohm resistor, then a 47 uf cap. (this could be non-polarized, but polarized seems to work fine). This is the (+) output portion of the balanced out. The output side of the cap is connected to ground through a 10 k resistor.

Another 10 k resistor goes from Pin 1 of the first stage to the inverting input (pin 6) of the second stage. The non-inverting input (pin 5, is grounded through a 10 k resistor. The "feedback loop" on this second stage is a 10 k resistor paralleled with another 27 pf ceramic. The output of this second stage, pin 7, goes through a 100 ohm resistor and another 47 uf cap. The output side of this cap is also coupled to ground through another 10 k resistor. This will be the low (-) side of your balanced output.

I usually build these things on little perf board cards available from Radio Shack, which have traces etched for dual-in-line IC's. Then I mount them in a utility box with RCA phone jacks in, since a typical use is for boosting the output of consumer Cassette or CD players to "line level" to feed a console.

Power supply can be made with 7915/7815 regulators...here's a circuit I found with a quick Google search; you can probably find others that are more legible...

http://www.elecfree.com/circuit/power-supply/power-supply-regulator-15v-15v-1a-by-ic-7815-7915/
Click to expand...

While this is certainly a good idea, by the time you buy the parts and invest your time to build this - you could have bought the ART or Rolls box and the costs would be about the same.
 
This would cost me about $25 plus my time, but I usually buy caps and the like in quantity when I am ordering other stuff & keep them in stock. Our friend in Portugal may not have access to some of our stateside sources such as Radio Shack( for the little $1.98 circuit board), but he may also find the finished imported products more than he would want to spend after adding in any local tariffs, etc...
 
TomT said:
This would cost me about $25 plus my time, but I usually buy caps and the like in quantity when I am ordering other stuff & keep them in stock. Our friend in Portugal may not have access to some of our stateside sources such as Radio Shack( for the little $1.98 circuit board), but he may also find the finished imported products more than he would want to spend after adding in any local tariffs, etc...
Click to expand...

The hardware isn't hard to find and it's cheap. All I need are skills to decode and apply TomT's hints into a breadboard ;D
 
Looks good for the price. How well the circuit performs? I have come across simple circuits using that chip which were rolled off above 10 kc.; while other circuits were nice and flat. Matter of design and component selection.

Also--wonder what goes in the two empty IC sockets???
 
Re: Here!

SFM-Ptgal said:
LA_Guy said:
http://cgi.ebay.com/NE5532-HI-FI-ST...12050QQcmdZViewItemQQ_trksidZp1742.m153.l1262


Problem solved.
Click to expand...

I might go for that. What do u guys think about it? is it a reliable circuit? ::)
Click to expand...

Yeah it's probably a very reliable circuit. The NE5532 and NE5534 are probably the most popular chips out there as audio amplifiers in broadcast gear. In fact, I'm almost certain that's what's in the Henry Matchbox, which is pretty much the standard that most of us use in US broadcasting.

The one thing you don't have with this circuit is a balanced output. But that may be OK if you're not in a heavy RF field. I'd definitely try it if I were in your shoes.

(Though you may take more personal pride in it if you do it Tom's way.)
 
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