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Old 18th December 2001, 06:09 AM   #11
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More notes:
--There are five Zener diodes in the front end. Please observe that the anode (the end without the stripe) is marked "A." Yes, I suppose I could have done a "C" (or "K") for cathode on the other end, but I trust that you folks can live with it.
--Heatsinks for the front end differential are mounted thus:
Q1's heatsink mounts "normally," i.e. the fins project towards the input hookups, cupping the device itself.
Q2's heatsink is mounted "backwards," i.e. the fins point back away from the device towards the rail hookups.
--There are three electrolytics on the front end board. Note the plus signs.
--I'll work up a tidy parts list after I've had some sleep.
--Folks, look this stuff over. If anything isn't clear, ask. As I told Geoff, I'm so used to the layout that I tend to take things for granted. I tried to look at the boards with fresh eyes, but there's no guarantee that I've made it properly clear.
Oh, Geoff, thanks again for the conversions from pseudo-BRD to GIF.
Goodnight, folks...

Grey
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Old 18th December 2001, 08:23 AM   #12
Freddie is offline Freddie  Sweden
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Thumbs up Thanks...

Thanks for the PCB layout... I will start to build an Aleph 30 this weekend.

/Freddie
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Old 18th December 2001, 10:35 AM   #13
hifi is offline hifi  Sweden
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have you done any meassurments on those boards?....or i mean on the amp when it is finished...just want to compare numbers with the original aleph ;-)


/micke
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Old 18th December 2001, 03:36 PM   #14
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Freddie,
Check the art carefully to make sure that it will work for a 30--I haven't checked how suitable it is for other Aleph models. Note that I made no provision for R1 & R8. I matched my front end devices instead. If you want, there's no reason you couldn't tag them in underneath the board.
Micke,
If you mean specifications like distortion and such, no. One, I'm not set up for it. Two, they don't correlate to sound quality. Three, at the time I was just glad to see that everything worked properly (circuit boards okay, no wiring errors, water-cooling sufficient, etc.). It did meet power into 8 ohms, though.

Grey
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Old 18th December 2001, 06:28 PM   #15
Eric is offline Eric  United States
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Grey: Thanks for sharing your work! I have a more general question for you (or anyone else). What effect does increasing the input impedance have in terms of matching to other equipment and/or output level of the amp? I think I remember reading something to the effect of increasing the input impedance makes the amp more sensitive to lower level input signals (higher output with lower input)... Is this correct?

Thanks for the help!
Eric
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Old 18th December 2001, 06:57 PM   #16
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I don't think that's correct, but if you are willing to
forego balanced operation, you can have an
arbitrarily high input impedance on the positive
input. 1 Meg would not be out of the question
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Old 18th December 2001, 07:13 PM   #17
Freddie is offline Freddie  Sweden
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Grey,

I've checked the art. The front end of the Aleph 30 is the same as the 60... So the layout will work good.. A few resistors with different values that's all.
I'm going to start building the front end on friday

/Freddie
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Old 18th December 2001, 07:20 PM   #18
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Eric,
There are good reasons, both pro and con, for various levels of input impedance. I chose to use the higher Zin because I'm running a quad-amped system and it would allow me the option of using a simple cap into the Aleph as a first order crossover. Not that you can't use a cap at a lower Zin, but then the cap has to be bigger, and it's easier (and lots cheaper) to find small values of polystyrene/polypropylene/Teflon/etc. than it is to find larger ones.
Now, as far as gain (sensitivity) goes, the resistor that sets the Zin for a device forms a voltage divider with the plate/collector/drain or cathode/emitter/source (for a follower) of the previous stage. The higher the Zin of the second stage, the more voltage develops across that part of the divider. In tube circuits, it's not uncommon to see grid resistors of 1-2M, although 100-500k is more usual. Solid state impedances tend to be an order of magnitude lower. It takes a fair jump in Zin to make a difference, though, once you get above a certain point.
For what it's worth, I seem to recall measuring the gain of the 2.60 at one point and finding that it was spot-on for a 2, in spite of having the 60 input network.

Grey
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Old 18th December 2001, 07:30 PM   #19
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Freddie,
Cool.
Good luck.
You might have just saved me the trouble of doing another layout for the small amp...and anyone who saves me time (which I'm perpetually short of) is my best buddy for the day.
Note that a couple of the traces shifted over by miniscule amounts during the conversion process. (Not Geoff's fault--there are just too many links in the chain of programs between my doing the art and the final GIF.) Watch the clearance where some of the traces sneak between two pads. At the comparatively low voltages that we're talking about it shouldn't be a problem, but if your PCB process will allow you the luxury, you might want to touch up those clearances, just for cosmetic purposes if nothing else.
If we can discover a program that will do a good job of exporting an image, we won't have to fight this battle in the future; but Paul's got a separate thread going for that.

Grey
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Old 18th December 2001, 07:35 PM   #20
Eric is offline Eric  United States
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Nelson and Grey: Thank you for your quick replies! Nelson, thank you again for your willingness to share your work with us!
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