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Old 23rd March 2010, 07:31 AM   #1041
Wavne is offline Wavne  Canada
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I was wondering what type of capacitor to use for the snubber on the parallel 4780. Also what resistor type and rating for the resistors.

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Wayne
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Old 23rd March 2010, 10:39 PM   #1042
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Any polypropylene cap will work, I was using BC Components from DigiKey. As to resistors, 2W Panasonics are fine
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Old 24th March 2010, 12:02 AM   #1043
koogar is offline koogar  United Kingdom
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Hi Peter

just wondered if the classic and premium
LM3875 Amplifier Kits are in stock at the moment to order ? .

also do you happen to know the board dimensions for the rectifier board and the amp board so i can play around with a layout .

i will be running 6 or 8ohm so looking at 250-300 va 25v x2 sound ok ?

Thanks

Rupert
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Old 24th March 2010, 04:37 PM   #1044
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Click the image to open in full size.

why on those grounding there is an RCA panel mount installed far from the other RCAs? what's the function?
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Old 24th March 2010, 05:18 PM   #1045
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I think somebody wanted additonal ground connection.


Quote:
Originally Posted by koogar View Post
Hi Peter

just wondered if the classic and premium
LM3875 Amplifier Kits are in stock at the moment to order ? .

also do you happen to know the board dimensions for the rectifier board and the amp board so i can play around with a layout .

i will be running 6 or 8ohm so looking at 250-300 va 25v x2 sound ok ?
Yes, that will work fine. Both amp boards and rectifier boards are 2.9 x 1.2"

The kits are always in stock.
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Old 24th March 2010, 05:29 PM   #1046
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Quote:
Originally Posted by Peter Daniel View Post
I think somebody wanted additonal ground connection.




Yes, that will work fine. Both amp boards and rectifier boards are 2.9 x 1.2"

The kits are always in stock.
is that necessary if we want to make star grounding?
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Old 24th March 2010, 05:36 PM   #1047
koogar is offline koogar  United Kingdom
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Thanks for the quick reply Peter one other thing
in UK we have been harmonized with the EU so our voltage is stated at 230v but in reality the UK still use 240v taking this into account would a 25v x2 toroid be still ok or should i go with 22v x2 bearing in mind the extra 10v with increase the toroid output ?

Thanks

Rupert
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Old 24th March 2010, 05:47 PM   #1048
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No, it's not needed. As to proper grounding, check this link: Commercial Gainclone kit- building instructions
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Old 24th March 2010, 08:31 PM   #1049
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Hi Peter,

I have ordered one of your premium LM3875 kits, and I'm eagerly awaiting its arrival. I see from reading the "user's guide" on your web site that the stock parts are set up for 33dB gain. I know from experience in my system, that much gain is likely to be too high. I used to own a power amp with 32dB gain, and had relatively little usable range on my preamp volume knob. My present power amp has 26dB gain, and that seems to be about right for volume range.

If I understand correctly from the "user's guide", to lower the gain I would increase the value of R3, which would be the Riken 680R supplied with the kit. Before I order additional parts, I just wanted to check my math.

Using the formula from the "user's guide", Gain=1+Rf/R3, the stock part gives 1+(22.1K/680)=33.5dB. Using 820 ohms for R3 should give me 27.9dB, and using 910 ohms should give me 25.2dB. Am I correctly understanding what values go where?

And does the use or omission of R1 on the amp board have any impact on the circuit's gain?

Sorry if this has already been addressed elsewhere in this thread, but I could only manage to read through about 25 of the 100+ pages.
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Old 24th March 2010, 11:28 PM   #1050
Bill_P is offline Bill_P  United States
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Gain(dB)=20 log (1+Rf/R3)

If R3=1.2K, then gain=25.8dB

R1 has only a very minor effect on gain.
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