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Old 23rd March 2004, 05:01 AM   #21
digi01 is offline digi01  China
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It may be that my picture is too big,do not send.
Supplement PRE-line sch again,I use a pair of 15v batteries to supply power.
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Old 23rd March 2004, 08:20 AM   #22
Ropie is offline Ropie  United Kingdom
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[i]Does this DIY stuff ever end or do you just keep doing it?

Kofi [/B]
Unfortunately it's a nasty affliction to shake off.

As for the attenuator - don't worry, there are plenty of people who can help you and the results really are worth more than any fancy cables

If you have a look at this website - http://uk.farnell.com/jsp/home/homepage.jsp - (it's a UK one but there is a US version) you can type in the product codes for the bits I used to make mine:

Wafer / Dummy Wafer (146057 / 146059) - these are what you attach the resistors to, the difference between the two is that the dummy wafer has no moving parts (and is a bit cheaper as a result). You only need to change contact with one end of the resistor as you rotate the switch mechanism; the other ends are all connected to signal ground.

Switch mechanism (146046), Spacers (146044). Then once you've put it together you can solder your resistors in place.

Take a look at this diagram (copyright of Nick!)
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Old 23rd March 2004, 08:24 AM   #23
Ropie is offline Ropie  United Kingdom
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As for your cables, you could try bi-wiring if your speakers have four connection posts on the back. Then you could use your new monster cable for the woofers and try some different wire for the tweeters, until you get a nicely balanced sound.
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Old 23rd March 2004, 12:42 PM   #24
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Digi,

Thanks for the schematic. I'm going to investigate all the options for the preamp here, and your schematic looks a bit easier to handle.

I have to admit that I am attracted to the link to the preamp that matjans posted, so I may give that a whirl.

Where did you get your design? Did you design this yourself?

Ropie,

Thanks for all the fantastic information. I am now very interested in getting the parts for the attenuator. I think that Newark In One is the US version of Farnell, so I'll get the stuff from there. Of course, what would my gratitude be without any questions...

I think I'll go with the resistor values posted on Nuuk's site (great site, BTW), and I may go with Riken resistors since that's what's in my GC and I like the sound.

Can I make two mono attenuators here or do I need to go with one stereo attenuator? The reason I'm asking is (and its a stupid one) that I have already mangled the breadbox with two holes for two pots, so I really wanted two thingees to fill in the holes so it doesn't start to look like my previous Ghettoclone.

Also, I'm assuming that the dummy wafer goes at the far end of the attenuator away from the switch. Well, actually, maybe there's only one real wafer and the rest are dummies. Wait that's not right, I am the dummy. Yeah, that's right.

I'm sure I'll figure this out as I start to build, but I guess I'll need to know how many of each to order. I'll check out Nuuk's site in the meantime for more information...

This looks like a fun project, so thanks a lot for the guidance! Jeez, I guess I should mail you a beer or something. Hope you like warm Schlitz in a plastic bag! OK-- that may not pass customs. Wait... Mrs. A could knit you some ear muffs... or maybe a nice took with ear flaps! Long Johns maybe?

Kofi
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Old 23rd March 2004, 01:26 PM   #25
Ropie is offline Ropie  United Kingdom
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Hope you like warm Schlitz in a plastic bag!
How did you know?!

The stepped attenuator in the sketch I posted is stereo, ie: it is dual mono. If and when you buy the bits you will need two real wafers and two dummy wafers (and eight spacers). Mount each one on the switch mechanism in this order: spacer, wafer, spacer, dummy, spacer, wafer, spacer, dummy (as the famous song goes ).

The resistors are then soldered between the first wafer and the dummy, as shown, all the way round (This is a twelve-step design so there will be 12 resistors per channel + the series resistor which is soldered to the input of the attenuator, located on the real wafer). This makes one channel so then you do the same thing between the other wafer and dummy for the other channel - et voila, a stereo attenuator!

Basically, you are making two attenuators on one switch mechanism. If, as you say, you want two separate attenuators for the two holes you've already made, you will need two switch mechanisms with one of the wafers and dummies on each. There is no problem with this but those switch mechanisms are not cheap at approx $8 a shot

It is all a bit long winded explained like this but it is not really too difficult (believe me, if I can do it...) but when you get the bits to play with it will become clear what's involved. And you will end up with a soild little device that will last for years and sound wonderful. Feel free to email me for further advice if you get stuck.

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Old 24th March 2004, 12:48 AM   #26
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Been too busy today to reply and say thanks for all your help, so here it is:

Thanks for all your help!

I'll likely order the parts this week and I'll E-mail you with any additional questions (I'll try not to have any).

Kofi
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Old 7th April 2004, 05:37 PM   #27
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OK-- I got distracted and built new speakers (Lyras) instead of the attenuator because I was dissatisfied with my old pair. See my posting in Loudspeakers here.

Of course, now I am concerned that the midrange and bass speakers are not being driven enough at low levels and are getting some distortion. Even at higher levels, the midrange and tweeter seem to distort at certain frequencies. Maybe its the crossover, but I am inclined to think that my power supply is too small, so I'm thinking about upgrading it.

I currently have a +/- 18V trafo, but I'm thinking about getting a +/- 24V for an upgrade.

Can the Gainclone (LM 3886) handle this into 8 ohm speakers? Do you think this will solve the problem or at least diminish the distortion?

Kofi
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Old 8th April 2004, 12:17 AM   #28
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Anyone?
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Old 8th April 2004, 12:44 AM   #29
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Sure I'll chime in....















get back to working on world peace. We could really use it now.
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Old 8th April 2004, 02:26 AM   #30
paulb is offline paulb  Canada
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Quote:
Originally posted by Kofi Annan
I currently have a +/- 18V trafo, but I'm thinking about getting a +/- 24V for an upgrade.

Can the Gainclone (LM 3886) handle this into 8 ohm speakers? Do you think this will solve the problem or at least diminish the distortion?

Kofi
Look closely at the LM3886 datasheet - the power dissipation curves. Do you mean a 24-0-24 VAC transformer? That would give you about +/- 34V. Look for a curve that shows total power or device dissipation at +/-34V (68V total) at 8 ohms.
I think that is within spec for voltage, whether it can handle the resulting power dissipation depends on how big your heatsink is.
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