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
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
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.
Yes, that will work fine. Both amp boards and rectifier boards are 2.9 x 1.2"
The kits are always in stock.
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
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
No, it's not needed. As to proper grounding, check this link: http://www.diyaudio.com/forums/audi...-kit-building-instructions-4.html#post1518369
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.
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.
So, Gain=1+Rf/R3 is for power (or voltage), and 20log converts it to equivalent dB? Is that correct?
The formulae are for voltage gain and what you said is correct for voltage. Power is V squared divided by R, making the power dB formula 10 log instead of 20 log.
Thanks Bill.
Another question (for anyone):
Perusing the various diagrams and pictures of amp wiring in this thread, some show (and some don't show) a 10R resistor on the ground wire from the star ground point to the chassis. Should I build up the amp without that resistor, then only add it in if I have a ground loop problem, or is there some other reason I might want it? And how many watts should that resistor be rated for?
Another question (for anyone):
Perusing the various diagrams and pictures of amp wiring in this thread, some show (and some don't show) a 10R resistor on the ground wire from the star ground point to the chassis. Should I build up the amp without that resistor, then only add it in if I have a ground loop problem, or is there some other reason I might want it? And how many watts should that resistor be rated for?
Check schematic in post#7 and this explanation: http://www.diyaudio.com/forums/audi...ne-kit-building-instructions.html#post1508953
Peter, I'm getting ready to assemble the classic kit I purchased from you. Can I mount the feedback resistor directly to the chip as you do in the premium kit?
On another note, I have some Radioshack 60/40 rosin core solder. Is there a sound quality difference between the Radioshack solder and other brands such as Kester?
Thanks, Scott
On another note, I have some Radioshack 60/40 rosin core solder. Is there a sound quality difference between the Radioshack solder and other brands such as Kester?
Thanks, Scott
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I'm now in the process of building up my GC. I saw earlier in this thread that the optional LED pads on the rectifier board could use a recommended Panasonic LED part, which is rated for 20mA power consumption.
I plan to use this amp in conjunction with a subwoofer that has a 12 volt trigger input, which happens to draw "less than 20 mA" according to the manufacturer. It occurred to me that I could tap into the LED circuit on the rectifier board with a small trim pot or voltage divider to run a 12 volt trigger output from the GC, so that the subwoofer will turn on and off when I turn the GC amp on and off. Any reason that it wouldn't work, or that it might be bad for the GC to do this?
I plan to use this amp in conjunction with a subwoofer that has a 12 volt trigger input, which happens to draw "less than 20 mA" according to the manufacturer. It occurred to me that I could tap into the LED circuit on the rectifier board with a small trim pot or voltage divider to run a 12 volt trigger output from the GC, so that the subwoofer will turn on and off when I turn the GC amp on and off. Any reason that it wouldn't work, or that it might be bad for the GC to do this?
Peter,
Thanks for your input. I'm measuring 28.3 volts at the LED pad (with no resistor), so I know I've got to drop about 16 volts for roughly 20 mA current draw. Could I just install an 800 or 820 ohm resistor in the place designated for the LED resistor, then run the trigger wire right off the LED pads? The subwoofer appears to have a fairly wide range of tolerance for the trigger voltage, 12 +/- about 2v.