Best super clean boost or preamp that could be made stereo

[vanessa]

Well my mind for building pedals the past couple years has been mono, mono, mono...

Now I want to build a boost pedal (box) that is stereo. I just got my first iPod (yes I'm really the last to get anything), and I love it but the output, although great for headphones is not so great plugged into my AUX input in my stereo. I have to turn the iPod way up and the same for the stereo. There's also an issue of normalizing that I might want to tag on a limiter (but that's a whole other can of worms).
I would like to build a little ZVex type boost thingy (I think that's what his iPod thingy is?). Not tube or anything like that, just a booster to get the house rock'n so I can let my hair down and shake a leg (or two) on a Saturday night.

So I thought about the AMZ Mosfet boost as it's really clean but I would think I would want to build something that has a chip so that everything is matched. I would think all I would have to do would be is to have two boosts and a dual gang volume control? Like I said... Mono, mono, mono



-Van

[JasonG]

A friend of mine built a booster for his mp3 player more for sound quality reasons.I was surprised by how much better his player sounded. He got the schematic off of an audiophile website. That may be the way to go. Good luck!

[George Giblet]

Since it's hifi you don't want the coloration or frequency response shaping of a guitar booster.  All you need is a non inverting preamp constructed from a dual opamp, an NE5532 would be perfect; keep the bass roll-off to low frequency, say < 5Hz.  I'd start with a gain of about 5.  You want the ipod output to be set to a medium level, such that no clipping occurs on the ipod, then you set the gain.  It's up to you how you want to power the device eg single 9V or a dual +/-15V.

[PerroGrande]

I like the 5532 preamp idea that was posted.  The 5532 (or an OPA2134) is an excellent quality op amp for audio applications.  The dual-package configuration would reduce the component count of the circuit.  Of course, a purist would mention that there is the possibility of crosstalk between the two amps since they share a single package/wafer... I think the specs for this are on the datasheet, if you're concerned.

The other consideration is the power supply.  You can certainly run one of these on a single supply, but you have notably less headroom than with a split supply (or a larger voltage single supply).  If you have a way to measure the amplitude of the incoming signal (such as a scope or a meter that will hold an AC Voltage peak reading) you'll get an idea of how much gain (and correspondingly how much headroom) you need.  Not all op amps can run rail-to-rail, so you need to take these levels into account when selecting a supply voltage.

To control the volume, a dual ganged potentiometer (aka stereo) is exactly what you need.  These are available all over the place -- even Radio Shack sells one. 

On the other hand, you *can* build a stereo booster using two discrete mono boosters (one for left, one for right!).  Stereo circuits were built this way for years (and still are!).  If you like the sound of the AMZ Booster, you could build two of them, use the ganged pot for volume control, and add a balance control to the circuit (to make sure both channels are the same level).

[spudulike]

For an iPOD you dont want a guitar booster - impedance is all wrong etc.

Google for a CMOY amp (originator's site is Hedwize).
Pocket size using (eg) a 5532 and a TLE rail splitter for compensated virtual ground.
I have a couple of pcb's left lying around, the artwork is pd and theres a few different layouts depending on the sockets and pot you use. MartyMart built one and said he was impressed. I love mine 

[Dragonfly]

www.headwize.com has lots of projects designed for audio amplification and preamplification for ipods and such.

you might try there.

[Pushtone]

+1 for Headwize.com and the CMOY headphone amp.
Look in the Library for projects.

What diystompboxes.com is to effect pedals, headwize.com is to headphone amps.


There is also headroom.com if you prefer to buy instead of build.

[PerroGrande]

Headwize is a good site.  However, Vanessa is NOT looking to build a headphone amplifier...  The headphone output from the iPod is not providing sufficient input to the Aux In on the stereo.   A headphone amp is probably overkill for this and would probably end up overdriving the input on the stereo.  The 5532 circuit mentioned earlier is perfect for this application, as is the AMZ booster, a JFET Booster, or even a BJT booster...  A few dB of boost should be enough to solve the issue at hand.

A guitar circuit will work as a boost/pre-amp for an iPod as long as the circuit used does not have intentional frequency-based gain curves.  For an iPod pre-amp, a flat amp response is the order of the day.  The above circuits will perform this quite well as long as the correct values of coupling capacitors are chosen and no "tone controls" are added to the circuit.  Impedance is going to be largely a non-issue.  The iPod will probably be able to drive a much lower impedance than a guitar, so even a BJT-style booster should work.  Going with a high impedance input (like a JFet or an Op Amp) is not going to be a problem, either. 

[Dragonfly]

Headwize is a good site.  However, Vanessa is NOT looking to build a headphone amplifier... 

Thus the reason that I mentioned that there are "preamp" projects there as well. Also, you can easily adapt many of the circuits.

[darron]

you could possibly use two mono amps with a dual gang pot. or use a 2x LED/LDR combo instead. i've not done this but it's an idea

[netnut]

I have the same problem with my Zune and car aux input. A CMoy (OPA2132) that runs of the cig. lighter fixed me right up and it sounds wonderful. It is stashed behind the dash right next to the radio and runs off of the remote turn-on for my sub amp.

I made a board using DIY Layout creator that is about 1x1.25". No input pot. Just a 12" 1/4 extension cable cable cut in 1/2 and soldered directly to the board. I mad a small notch in the trim around the radio to snake the cables through. One goes to the Zune, the other to the radio. Done.

Edit: http://tangentsoft.net/audio/cmoy-tutorial/

[Fp-www.Tonepad.com]

stereo microamp should work well.

http://www.tonepad.com/project.asp?id=28

fp

[vanessa]

Lots of very cool options! Thank you all.



I'm not sure which one to go with. On that tonepad version would I use a dual gang pot for that?

[QSQCaito]

Since it's hifi you don't want the coloration or frequency response shaping of a guitar booster.

What's the hifi part on MP3?? Your signal is all compressed, reduced.. lost in some way. Hear the drums. hihats, crash.. all sound like psh, plain psh's.. Or when people applause, it is just horrible..
Anyway, we agree that we don't want the shaping of a guitar booster.

[George Giblet]

> it is just horrible

There is no generic "mp3" as far as quality goes.  There is a big difference between 128kbps or less produced on a poor encoder and 192kbps or more produced on say the LAME encoder (with proper filter settings).  My mp3's sound good as the CD.   I've heard some really bad ones and I don't know what the hell people do to them to make them sound *so* bad!

[QSQCaito]

> it is just horrible

There is no generic "mp3" as far as quality goes.  There is a big difference between 128kbps or less produced on a poor encoder and 192kbps or more produced on say the LAME encoder (with proper filter settings).  My mp3's sound good as the CD.   I've heard some really bad ones and I don't know what the hell people do to them to make them sound *so* bad!

As good as the CD, ok. But I swear no MP3 would sound as good as a GOOD cd, played through a heavily modified marantz cd player, krel amp, and 2 sonus faber speakers. You can even hear differneces between two cds different companies... and you'll notice even more differnece after you heat up the amp(it is SS, but you hear difference after half an hour of playing.

[MartyMart]

Lots of very cool options! Thank you all.



I'm not sure which one to go with. On that tonepad version would I use a dual gang pot for that?

I have a 1st generation 10 gig ipod - befor all the "FUSS" !! and it's VERY loud, I think they had complaints about
the output level. ( still works BTW - battery lasts only 1 hour though :-( )
The newer generations have all been just too quiet, mine's a 30gig "photo" model, I build the Cmoy headphone
amp and it's absolutely FAB !!
Similar version could be done for driving a stereo, in fact the Cmoy gives enough output for mine to kick the crap
out of a set of Altec powered speakers too !! ( they are expecting a headphone type input )
MM.

[Fp-www.Tonepad.com]

you could use a dual gang 1Meg -Rev Log (small bear?) or independent left/right volume controls.

Another option would be to pre-set the gain with resistors or maybe trimpots.