Differential Amplifier for iPod

[lgreen]

Well, having an Apple iPod, I wanted to hook it to the stereo, in particular my Gainclone and BOSOZ. I tried a number of connectors and none sounded that great. So in the DIY tradition I made me an iPod Accessory Box using chip line drivers (DRV134s, so this is why I think the thread belongs in chipamps).

This box has 8 batteries which provide plus and minus 6.4 volts DC or so, has RCA and miniplug inputs, and differential outputs due to including a pair of DRV134 differential receivers powered by the internal battery supply. Take a look on my Web Page or at the attached pictures (links). (This part of the web page should be active in a day or so.)

On the front panel is the iPod miniplug input, on the rear is a miniplug for providing DC to my Gainclone input stage. There is also a DIN 9 connector which provides all inputs and outputs, as well as DC on its 9 pins. Additionally, there are RCA inputs on the rear, so that the iPod or something else can provide single ended signals for differential conversion to the XLR connectors via the most standard connector.

This was intended to connect my iPod to my BOSOZ and GainClone. It works great. If I could have connected a USB or Firewire input on the back I would have, but I had no room nor did I know if analog was carried on those by the iPod.

Image of iPod Box from Front showing miniplug input from ipod and amber illuminated power switch

Image of iPod box from rear showing some inputs (RCA) and outputs (XLR, mini, DIN).

Image of iPod Box from Rear- Close Up showing RCA inputs, XLR outputs, DIN multi input/output, and mini DC output. As you can see I made a mistake in capitalization. Sorry.

Internal View - Top of board. Visible is the pair of DRV134 chips and the wires connecting to the rear panel. I'm not going to win any awards here for neat wiring.

Internal view- bottom of board. Shown is a 9 pin DIN connector so the front controls can be removable from the case when the front panel is disconnected. That way the rear panel slides out of the case with the board attached.

I started a few recent threads on the topic of iPods and Connectors. See threads #1 and #2.

Attached is an image of the box through the long end.


Well, as I said in my BOSOZ thread (above), I'm exhausted with this DIY stuff. You won't see anything new from me for quite some time. But let me know what you think and whether you like these or not, questions will be answered of course. Thanks for looking.

[wuffwaff]

Hi,

nice idea! Does the ipod sound better now? How does it sound?

William

P.S. can´t look at the pictures on your website

[carlmart]

Originally posted by lgreen
But let me know what you think and whether you like these or not, questions will be answered of course. Thanks for looking.

Very good looking job! Congratulations!

Just my non-critical 50 cents. Why don't you ditch that input connector and use a proper 1/4" jack?

One of the weak points in the iPod is the 3/8" connectors it uses. Mini-plugs are a potential source for bad connections, particularly if you plug/unplug it often.

Perhaps you should prevent that by eliminating the chance of that to happen at least on the amp end.

Advice: if you plug/unplug your iPod often, at the input or output, get a short cable adaptor (3/8" to 1/4" jacks). This is a professional advice.

Where did you get your lettering done? It looks very good.


Carlos

[carlosfm]

Igreen,
Nice idea, nice case.
Just a thought/suggestion:
Most portable devices have low output, and it is interesting to have an external box that amplifies at a gain of around 2x.
The gain is the point, I don't think there's an absolute need to go balanced.

[jtsjf]

it is cool- nice lettering on the box. I like that a lot, actually.

I wonder why you need a gain stage? I plug my ipod directly into my gainclone (BrianGT pcb's) and dang- it can get too loud for me, and it sounds very good.
I posted a picture of my system (with ipod) here:
Yet another new Gainclone (YANG?)
Jason

[lgreen]

Thanks, glad you like this.

wuffwaff
- this sounds damn good! Much better than just straight to the inverting, buffered GainClone. But its only been a few days so I'm not ready to go nuts yet.
- website is now operational.

Clamart
- agreed on the crappyness of the 1/8 miniplug connectors. In fact, I have modified a Kimber PBJ interconnect to have a 1/8 miniplug on the iPod end (kind of forced to do this unless you want to hack into the docking station) and RCAs on the other end-- stock on that end. Thus I don't connect to the Accessory Box with miniplug, unless I really want to, which I don't. Click here to see the Kimber cable/ connectors that I'm using with the iPod, or check out the web site (which is working now).
- I didn't go with 1/4" phono plug because I couldn't think of what other equip would use this, but with high quality WBT RCA plugs anything can hook to this little box. So that is why I use RCA rather than 1/4" phono. Also I ran out of room on the back panel!
-lettering was from Front Panel Express See here for a bunch of my comments about them. Note that this box was steel and they can only work with aluminum, so they fabricated a back panel of the same size as the original steel panel, and worked with the aluminum version.

Carlosfm-
I agree, voltage is usually minimal with these portable devices, but they do have to power headphones so I don't know what the problem actually is. With this circuit, I get a 2x gain as you noted, and boy, it helps a lot.

[carlosfm]

Originally posted by lgreen
Carlosfm-
I agree, voltage is usually minimal with these portable devices, but they do have to power headphones so I don't know what the problem actually is. With this circuit, I get a 2x gain as you noted, and boy, it helps a lot.

It's not a problem.
Most portable devices have around 500~750mv output, much lower than the CD standard of 2V.
As they are battery powered with just one or two AA batteries, PSU voltage is low and signal can't be amplified to "normal" line levels.

[lgreen]

I wonder why you need a gain stage? I plug my ipod directly into my gainclone (BrianGT pcb's) and dang- it can get too loud for me, and it sounds very good.

Its not that I need a gain stage, the problem I had is that both my Gainclone and my preamp are constructed with balanced (differential) inputs and of course the iPod is single ended. So I wanted to have full functionality and compatibility. In addition, my Gainclone has a provision to accept external battery power and I wanted to make a device that would supply that power. Thus, this Accessory Box serves both functions. I'm not going for loudness alone, and it really sounded awful before but sounds really nice now, and a gain of 2x isn't that much.

[jleaman]

if you use energizer Batteries The sound is wayyyybetter..

Said the bouncing bunny across the table !!

[jtsjf]

I'm starting to see here. So much nomenclature to learn....I've only thought of single-ended in terms of tube amps. I also noticed after reading your post again that you are running the amp in quite a different topology than the one I made.
Thanks for sharing,
Jason