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Old 11th October 2012, 12:42 PM   #411
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Do you mean the article?

It's here:

Arpeggio Loudspeaker
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Old 11th October 2012, 04:01 PM   #412
waam68 is offline waam68  United Kingdom
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Default Speaker impedance question

Hi
I ordered the kit from the store and am looking fwd to building what will hopefully turn out to be my first real go at a solid state amp. Both sets of my speakers are vintage and 12 to 15 ohm impedance. I did manage to build a 3.5w diytube Getsetgo amp a couple of years back that drives them just fine so I'm hoping the 5w ampcamp will be more than enough. Should I look to change any components to drive these speakers? and/or would it be better to consider upping power supply voltage? (I did read the original JLH article and while a lot of it went over my head it suggested a higher power supply voltage for that amp into a 15r load). Although I like to solder my knowledge is more basic than I would like.
Mike
Ps great that you guys have put together a high quality beginner level project.
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Old 11th October 2012, 04:55 PM   #413
Variac is offline Variac  United States
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At the top of pages there's a blue menu bar and one choice is "Articles" You'll find the article there about the Arpeggios.
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Old 11th October 2012, 07:19 PM   #414
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Looks like the complete kits are all gone. All sold out or change of kit packaging?
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Old 11th October 2012, 08:23 PM   #415
nr12 is offline nr12  Germany
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Mine just arrived today! Thanks guys!
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Old 11th October 2012, 10:05 PM   #416
N Brock is offline N Brock  United States
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I took some measurements today.

My math tells me the output resistance of the ACA is around 2.4 ohms.

I'd like some confirmation, either from Mr. Pass or someone else who has taken measurements that this is a reasonable number.

This is how I calc'ed 2.4 ohms:
Connected a frequency generator to the input, 1kHz and 1V (should be arbitrary.)
Connected a scope to the output.
Measured the output voltage with no load, 6.4V
Measured the output voltage with a 10 ohm load, 5.2V
Measured the output voltage with a 5 ohm load, 4.3V

I then used the equation on the previous page to find that the measurement with the 10 ohm resistor gives an output impedance of 2.31 ohms, while the 5 ohm measurement gives an output impedance of 2.44 ohms. They were 5% resistors, the calculations are within this tolerance. I measured the resistors with a multimeter, but I generally don't trust readings down that low.

Best,
Nelson
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Old 11th October 2012, 11:07 PM   #417
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Because the gain is non-linear as I showed in reply 274, the output impedance will be non-linear. Try different signal levels, you should get different numbers.

Last edited by Loudthud; 11th October 2012 at 11:16 PM.
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Old 11th October 2012, 11:23 PM   #418
N Brock is offline N Brock  United States
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Quote:
Originally Posted by Loudthud View Post
Because the gain is non-linear as I showed in reply 274, the output impedance will be non-linear. Try different signal levels, you should get different numbers.
Ah ha, I missed that post, thanks for pointing it out. It seems then that matching the output impedance to a speaker like the arpeggio is a bit more complicated than I previously believed. I'll have to put some more thought into this one.
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Old 12th October 2012, 06:10 AM   #419
Variac is offline Variac  United States
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Quote:
Originally Posted by vdi_nenna View Post
Looks like the complete kits are all gone. All sold out or change of kit packaging?
The complete kit just puts three different items in your cart:
the parts kit
the pair of heatsinks and
2 PSU's

Just the PSU's (power supplies) are out of stock. If you click on the kit you get the parts kit and the heatsinks in your cart, and no PSU's, but you aren't charged for the PSU's...

I'd suggest getting what you can and then ordering the PSU's later when they're back in stock. They'll be back in stock soon, but the parts kits are running low but itwill be 2 months before we make up more ...
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Old 12th October 2012, 06:56 AM   #420
Jason is offline Jason  Australia
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Quote:
Originally Posted by vdi_nenna View Post
Looks like the complete kits are all gone. All sold out or change of kit packaging?
That was my mistake - somewhere last night in between moving all the categories around I forgot to re-add the bundle. It's fixed now But as Mark says, we're out of PSUs for the time being. We'll have more PSUs next week.
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