[j-curve]

Did you notice when CD players first came out that they played louder than your tuner, cassette deck etc.? I did, but I soon grew accustomed to the difference and forgot all about it until recently when I got my digital parametric equalizer, full of fancy A/D & D/A converters and stuff.

If you too have one of these:-

or maybe one of these:-

or any other piece of gear which starts its job with an analog to digital converter and offers a selection of input levels such as:-
Studio Level = 4 dBu = 1.23V RMS = 2 dBV
or
Line Level = 316mV RMS = -10 dBV

then suddenly, the fact that:-
CD Level = 2 Vp-p = 707mV RMS = -3 dBV
becomes an annoyance.

Why? Use "Studio" inputs and you lose >5dB of dynamic range, risking hearing the noise floor or the hiss of the dither signal. Use "Line" inputs and you're asking for overload problems and digital distortion.

Here's a simple solution - the REDUCER! This thing is designed to reduce an audio signal by 7dB when driving a 10k-ohm load, putting you back into the safety zone when using the "Line" inputs of your digital gear from a CD player.

Asleep yet? Here's what you need:-

2 x RCA plugs with nice big back shells
2 x RCA panel sockets
2 x 4.7k resistors
2 x 5.6k resistors
plus about 10cm of insulated hookup wire.

You need to check that that the RCA sockets can be screw fitted into the back of the RCA plugs! The end result will be the sexiest looking and most robust little electronic gizmo I've ever put together:-

From bottom to top: a completed REDUCER, an unscrewed REDUCER and all the leftover bits.

Here's what we're making:-

Tips for Constructors:- This is a simple circuit but the physical assembly is a challenge due to the limited space inside.
1. The soldering is a bit fiddly and everything needs to be cut neat and short, ie. the resistors and the tabs on the plugs and sockets.
2. You need about 35mm of hookup wire which you'll connect to the centre pin of the socket before fitting the socket into the back of the plug shell.
3. Join the 5.6k resistor to the earth tab of the plug first, then join the 4.7k resistor to the centre pin. Wrap the free end of the 4.7k resistor once around the free end of the 5.6k resistor before soldering the connection and cutting the excess away.
4. Join the hookup wire to the resistor junction.
5. Turn the plug a couple of turns anti-clockwise to "untwist" the hookup wire before screwing the plug together. That way the hookup wire won't get too twisted by the time it's all together.
6. If the finished reducer produces no output, then you may have broken the hookup wire. Another possibility is that the resistors are shorting out against the metal casing, in which case you'll have to open it up again and bend the resistors slightly towards the centre.
Good Luck.

The reducers REDUCING!

CD Player -> REDUCERS -> Cable -> Line Inputs

 

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[Orpheus]

i'm confused. why would you want to reduce the signal level? if you reduce it, your pro stuff will simply amplify it more. right?--or use another transformer to bring it back up to volume... which can be just as bad... (especially with those Behringer units you have.... believe me, anything in those things cannot be cheaper)

if you simply plug your lower level "CD input" into your pro stuff, all you have to do is turn the volume up a little more than with a true 4dbu pro line level, which is not big deal. besides, i don't think all CD players output the same level. my Tascam CD5000's signal is REALLY hot coming from even the RCA outs. some of my other stuff is quieter... the 4dbu thing is just a guideline... but equipment varies.

 

[lini]

I've recently built a similar voltage devider - just with different values to convert a line level into a microphone level output, because some modern notebooks only have a mic in but no line in. And I also built it into a little tin mint box right in the middle of a cable, to make it an adaptor cable istead of an adaptor plug in order to avoid unneccessary transitions - I chose the mint box as the plugs themselves were too small to fit in the resistors...

Greetings from Munich!

Manfred / lini

 

[lini]

Oh, yes, by the way: I've built another one of these - that time directly into the plugs of a pre-to-power-amp cable - years ago. This can come handy when you're suffering from pot imbalance in the lower areas of the volume pot, or when the output level and input sensitivity of pre- and power-amp are not well matched. In my case, I wanted to bring the volume range "from loud over really loud to horribly loud" down to "from silince to loud"...

Greetings from Munich!

Manfred / lini

 

[Rameish]

Hmm,

Seems you and Russ Andrews agree that the output from a CD Player (2 volts typically) will overload most pre-amp inputs.

 

[j-curve]

Orpheus,
I see what you are saying about external versus internal gain but the noise generated by the op-amps is negligible. I think it's more important to operate the A/D and D/A converters across their full dynamic range, which is what the REDUCER allows you to do.

Quote:

Orpheus: ...especially with those Behringer units you have.... believe me, anything in those things cannot be cheaper

Yes, cannot be cheaper and still satisfy the designer's specification(!) These days almost everything from your diodes to your underpants is made in China, no matter what brand you buy. Behringer hardly needs my support because they are churning out good designs and quality gear at unbelievable prices. The 24-bit Crystal DACs and ADCs in the DSP1124P are well regarded and the 4580 op-amps are an industry standard for studio gear. I did some online research into Behringer before purchasing and decided that I was prepared to pay the return shipping cost and exercise my consumer rights in case I got a dud.

 

[Orpheus]

hmmm.....

but i've never had a CD (or any other consumer product) have an output so hot that it clipped a preamp/amp. in fact.... my CD player, professional Tascam CD-RW5000, has outputs REALLY hot. i mean.... that thing is so loud that i have to turn down the preamp on my mixer all the way down. ...now, i know that this might make a case for your argument... however, with the preamp down, it still has maybe 10-20db more headroom above the loudest CD i have before clipping on the mixer... i just like to keep everything maxing out at the 0 point on the meters. i've also plugged the CD player straight to my MG Head before, and i've never had problems.

hmm... maybe i'm misunderstanding your argument... can you explain "Why? Use "Studio" inputs and you lose >5dB of dynamic range, risking hearing the noise floor or the hiss of the dither signal." i'm not sure how you would lost dynamic range using "studio" inputs. ...please explain, i'd like to learn more. i'm sure you know what you're talking about to come up with this contraption.

"This thing is designed to reduce an audio signal by 7dB when driving a 10k-ohm load, putting you back into the safety zone when using the "Line" inputs of your digital gear from a CD player." --i guess that's what i'm questioning. i don't think it's necessary to reduce that level. i mean, isn't that why pro stuff runs at 4db reference anyway?... cause a lower signal level results in more noise and distortion after being amplified? ...perhaps if you've experienced clipping before, i guess. but like i said, i've never had a signal too hot that it clipped anything in my studio.

...i think that if you "think it's more important to operate the A/D and D/A converters across their full dynamic range," then you should get the signal as hot as possible without clipping into the converter. ?--i think that makes sense. reducing the signal level would result in the converter being used in only a portion of its full range.

?--if i'm wrong, please correct me. ...i love to learn more about this stuff.

 

[j-curve]

Hi Orpheus,
The thing is, I'm not running a whole bunch of studio gear, just the digital parametric which doesn't have any gain controls but has a choice of Line- or Studio-level inputs. The difference between these is about 12dB, a voltage ratio of about 4, and standard (consumer) CD-level lies smack bang in the middle. If I choose Studio level inputs on the EQ then I don't drive the ADCs full-scale, so I lose some dynamic range. On some CDs, especially if they are conservatively recorded, I can hear background hiss. Sure, I've got headroom to burn but it's never going to get used in that configuration.

The alternative is to use the Line-level inputs. The clipping I referred to is nothing to do with any of the analog amp stages, but is a result of driving the Line-level inputs straight from a CD player and overdriving the ADC - ie. it's a hard, digital clipping. What you said about getting the signal "as hot as possible without clipping into the converter" is exactly right. A volume control would be overkill (and messy) so I built the reducers.

 

[Orpheus]

oh. okay... that's weird. i never experienced clipping in that kind of situation.

...hey, in you have two pictures here... one of the eq, and a feedback stopper.... do you use that feedback thingy? what possible application does it have in a home!?

 

[j-curve]

Quote:

Orpheus: you have two pictures here... one of the eq, and a feedback stopper.... do you use that feedback thingy?

The "Feedback Destroyer" is actually one-and-the-same as the digital parametric EQ(!) It's a DSP1124P (details here). I've never used it for destroying any feedback, but it has such a function which searches for feedback-like tones and tunes the parametric filters as notches to nuke them out.

 

[nately]

I want to use something like this to go between my pre- and power- amps for my speaker system, but have zero DIY skills. Anyone have any experience with the commercial audio or pro audio versions of these? $35-$40 doesn't seem outrageous, since I imagine (remember, 0 DIY skills) it's close to $10 in parts.

Found this, 6db and 12db versions:
Harrison Labs

These are shorter and might put less strain on my amp's jacks, but come from across the pond:
Rothwell

I don't have any clipping problems or anything, but my volume control is too sensitive in the 8-9 o' clock range which is where I usually am.