[Ramblingman]

Thanks for the replies guys! Ive now got heaps of reading to do, will let you know how i go for sure, i think im going to get hooked on modding things after this....

 

[joneeboi]

Good to know we could help, Ramblingman. Good luck on your mod.

Thanks, no_eye_dear and ruZZ.il, for adding your insights. I'm still a little confused about how the charging plates block the DC, but I think I can figure it out from what's been said, two or three of my textbooks, and the mountain of information stored in my professors' heads.

Wait, I think I got it.

i(t) = C*dv/dt, so if dv/dt=0, i(t)=0. Boy, that wasn't so hard. If an AC signal through a capacitor stays constant long enough, it becomes fully charged and nothing passes through it. Man, I just did a lab on this, too. Way to apply your knowledge, joneeboi. Huzzah!

It's good to hear you got your 4Gs completed, no_eye_dear. Which type of 4Gs were they? And what kind of dock did you convert? I need a docking station at home for my diyMods too, and I was thinking that'd be an easy way to swap caps in and out of it. Must go shopping today...

 

[ruZZ.il]

basically, yes. But nothing ever passes though it! (maybe tunneling electrons, but statistically close to none). It's 'almost' as if something passes though it. Think of it like a water pipe, in the middle of the water pipe is this stretched rubber sheet, like a balloon, the blocks the water flow. Obviously, the water wont pass through it, but if the water just oscillates, the balloon will stretch to accommodate or if the water tries to go in one direction, it'll go until balloon stretches and the elastic force is equal to the force pushing the water. The energy stored in the stretched balloon is kind of like the energy stored in the electric field created between the charges. So the i(t) in that equation is the 'current'(pseudo) in the circuit, but not actually the current 'through' the capacitor. I've seen this graphical representation somewhere.. maybe I'll find it later.
edit: more about it here.

 

[wgr73]

ruZZ, thats a very good illustration! Thanks for that!! Hey guys, I was also wondering what you mean when you say "DC" offset? I've seen it used around the forum, but I'm almost positive people are using it in the wrong way. Explain this please...

 

[joneeboi]

Thanks for that, Russ. You've shone the light on my eyes.

wgr73:

One context in which we speak of DC offset is in the troubleshooting stage of amplifiers. To see how much DC is produced and is being sent to the headphones, we measure the voltage between input ground and the left and right outputs. If things are working within reason, you can get between 0mV and 20mV. Anything beyond that isn't healthy for the headphones and indicates a big problem. For instance, I got measurements of ~2.4mVDC and ~7.1mVDC on the L and R channels (can't remember which) using the OPA2134PA opamp in my PIMETA's OPALR socket, but when I plop in the AD8620, I get 0.01mVDC or 0.00mVDC. We usually don't say mVDC, but I just wanted to be clear; mV will suffice since we're already talking about DC offset. I'm not sure how else we speak of DC offset, but that's one example that's oft mentioned around these here parts.

 

[wgr73]

Thats what I needed to know. So in other threads people are not using the term DC offset correctly. I was confused reading them, because I wasn't sure if I was remembering correctly...but you've confirmed that for me, thanks!

 

[wgr73]

What could cause DC offset: 1. In our case (DIYmod) 2. In general?

 

[ruZZ.il]

we're not filtering the dc offset in our case, we're filtring out the DC that the signal is created around. Generally, a signal oscillates the ground, but you'd need a + and a - power supply for that. What these DACs do is get, say, 5Vdc and 2.5Vdc, and the signal oscillates around the 2.5Vdc so let say you're creating a 1v sin wave at 50Hz, it would be 2.5+1*sin(50*2*pi*t). we just want the sin part, so the cap filters out the 2.5Vdc...

In general, DC offset could be cause by noisy feedback, bias currents, umm.. I don't know too many causes actually.. I'm sure Ti and Warren know all about it

 

[joneeboi]

In general, DACs produce a bit of DC, so it's not just a diyMod thing, but DACs in every application. Opus, Alien, they both use DC blocking caps at the output.

In amplifiers, DC usually comes from the source, and its magnitude is amplified by whatever's in the amp. Unless you use a DC servo, opamps, or coupling caps, you're going to get DC at the output. For instance, the Mini^3 doesn't have any caps in the signal path, so putting in any DC will amplifiy it by whatever gain in which it's configured. Some amps have DC blocking caps at the input right before the opamp, like the CMoy. Other amps have them right in the output signal path, like the Millett Hybrid (I think these are for DC blocking; for what other reason are they there?). Still others use a DC servo, like the M^3 (I think). The short answer is comes back to the first answer: DC comes from the source signal. It's up to both the source's and amp's designers/builders where and how they want to block them, whether at the source's output, amp's input, or amp's output, and whether they want to block it using a DC servo, implementing opamps (I'm not sure how it works, but I get this from hearsay), and our favourite method, using DC blocking caps.

The reason some stray from coupling caps is because they add non-linearities and colouration to the sound. They are the simplest solution to DC blocking, but that comes at a price. Using opamps for DC zeroing, say, in a balanced setup would require 6 opamps and other bits, taking up more space and costing you the price of 6 opamps and then some. I don't know how the DC servo bit works either, so you have to look that up if you really care. You'll eventually run into it in this DIY gig, somehow I've managed to avoid them. Google for the win.

Hope that helps.

Someone please correct me where I'm off.

edit: Right, they also come when you don't build your amp properly, but that I'm unsure of as well. Consult your local DIY guru today!

 

[wgr73]

Thanks guys, that makes sense!

 

[no_eye_dear]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif It's good to hear you got your 4Gs completed, no_eye_dear. Which type of 4Gs were they? And what kind of dock did you convert? I need a docking station at home for my diyMods too, and I was thinking that'd be an easy way to swap caps in and out of it. Must go shopping today...

Hi Joneeboi, a grey and a photo 40GB, I opted for the direct route to (1) keep thing simple inside the pod and (2) be able to interchange caps on the outside..... or even no caps

.... been doing some experimenting.
Transformers are another good option.....
I just got one of those Sync Chargers and put some small film caps in there for now but I have a collection of caps that I can change out in my amp (lots of room) so I may just leave it straight through.
I did attach a small steel plate the base of the sync charger though...... the interconnects kept pulling it over

Ultimately the dock will be in the top of the amp anyway.....

 

[darkfury18]

Quote:

Originally Posted by ruZZ.il /img/forum/go_quote.gif about as thick as a single strand in that wire I used! what REALLY helped me finally was to thread the wire through a little tube that held it in the right angle, like I mentioned above, but the single strand whose base was soldered to the other strands was slightly bent so as when the wire is pushed through the tube it would be perfectly aligned on top of the dock pin. Access is also a big problem, since my solder irons head was about as wide as the gap, so I had to come from above with the tip. in retrospect, it would have been heaps easier to do the normal mod. That being said, now that I've done it, it would be easier to do again, so I guess with some familiarity of the space you have to work with, its easier and do-able. Take a look at those pins before you decide to do it though, cause it's not the easiest thing I've done... but it works! and it worked well for a while, till I opened my ipod once too many times and somewhere along the line messed the clickwheel ribbon up. I've got a new one waiting for me at a friends house that I need to go pick it up. I'll be able to post impressions once I get more of a solid one, and burn the BGs in. I wont be able to comment on the differences between the 2 different mods till I hear the reg. one, but I doubt the difference is audible. Theoretically, the rest of the bypasses audio circuit is open and shouldt have any effect, but with a cap there I'm not sure if theres NO effect since there's still some charge swing on the other plate due to the voltage swing on the first, which may have some effect.. I dunno.. I do it for the mod, not so much the sound my ears aren't golden, so, ja know.. let us know how it goes!

Took 5 hrs to do the mod and make the LOD this evening

.

I basically did the same thing that you did except I used pin 17 and 24 since they were a little more accessible than pin 14. Used 26 awg Jupiter cryo wires internally and for the LOD. I also added a USB port on the LOD.

Initial impression... sounds a little boring (not sure how else to describe it) compared to the HP out?

 

[ruZZ.il]

BGs? give them time.

I got my clickwheel in. BUUUT. after closer inspection, I realized that I'd evidently heated up the tiny plug that the clickwheel ribbon slid into. This was a result of a tiny splatter of solder that got onto the pins, and I had to absorb it into some braiding to get it off. ugh. the plastic that holds the pins in place kind of melted down, which is what was preventing proper pin contact. I tried to peel it off a bit, or lift it, but it had stuck to the pins.. so, thats screwed. On the brighter side, it gives me incentive to try bypass the plug, new proj.

. I'll have some 36awg wire in teflon here soon that I'll solder to the plugs pins and 7 out of 8 wires go to the chip on the clickwheel, one goes to a little resistor. Should be a challenge, and satisfying if I pull it off. Alternatively, I'll be reviving an old mini with a flash card and a new battery soon

congrats on the mod! update us with burn-in impressions. BGs are a b*tch and a half to come around.

 

[joneeboi]

Seems my package hasn't reached you yet, eh, Russ? Give us an in-depth analysis of the airwiring of your click wheel. You always seem to choose the insane way of doing things, don't you? I'll add the warning.

And congratulations, darkfury18! Kudos on picking up on the pin 24 bit. I forgot that FireWire support was dropped in the nano. In that case, there are quite a few more unused pins that I hadn't considered, perfect for my iPod digital out DAC/amp.

And thanks for the extra info, no_eye_dear. Maybe I'll pick up one of those docks for my 3G which doesn't have USB charging. =T

 

[darkfury18]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif Seems my package hasn't reached you yet, eh, Russ? Give us an in-depth analysis of the airwiring of your click wheel. You always seem to choose the insane way of doing things, don't you? I'll add the warning. And congratulations, darkfury18! Kudos on picking up on the pin 24 bit. I forgot that FireWire support was dropped in the nano. In that case, there are quite a few more unused pins that I hadn't considered, perfect for my iPod digital out DAC/amp. And thanks for the extra info, no_eye_dear. Maybe I'll pick up one of those docks for my 3G which doesn't have USB charging. =T

Yup, 47uf Black Gates. I guess I just need to let everything burn in. The BGs, my mini3, and my headphones also

.

It's pin 7 or 24, depending on which pinout diagram you're looking at; it's one that's unused in all ipods. You gave me too much credit

but now i know there are more pins that I can use.

EDIT: I've been reading about the 1G nano and it seems that it sounds very very neutral from the line out, I guess that's what I'm hearing....