Rectifier board/parts are from Audiosector, AMP boards are not.
Transformer is 18 0 18 and I have 2 X 10,000 uf/50V with snubber parts on rectifier (single bridge/single transformer)
This is what I did, added a jumper between PG+ & PG- on rectifier and a jumper between output grounds on Amp pcb (speaker output ground(s) are also taken from these points) , both these jumpers are connected with a wire. The center tap from transformer is connected to the middle of this wire.
AC mains usually hover around 255 Volts, transformer secondary shows 20 0 20 and when I measure from center tap on transformer and V+ & V- on amp boards I get +/- 28 VDC
Without a volume pot and any input source I get 77 mV on one board and 125 mV on other.
Does this all sound OK ?
LM3875 kit input sensitivity
Hi I wonder if somebody could advise me. I already have one LM3875 kit from Peter but not built yet.
I really want to build a 4 channel amp for active home-made speakers. I was planning on using a MiniDSP 2x4 for the crossover and eq and volume control.
The original MiniDSP 2x4 has a maximum output of 0.9V rms. The MiniDSP 2x4 HD has a 2.0V rms output.
Ideally I would like the amps to be running at maximum power when the MiniDSP outputs a full signal.
Any ideas how close a match this would be with either MiniDSP or any recommendations for changing the gain on the chip amp to suit.
Ideally I would go for the 2.0v MiniDSP 2x4 HD.
Hi I wonder if somebody could advise me. I already have one LM3875 kit from Peter but not built yet.
I really want to build a 4 channel amp for active home-made speakers. I was planning on using a MiniDSP 2x4 for the crossover and eq and volume control.
The original MiniDSP 2x4 has a maximum output of 0.9V rms. The MiniDSP 2x4 HD has a 2.0V rms output.
Ideally I would like the amps to be running at maximum power when the MiniDSP outputs a full signal.
Any ideas how close a match this would be with either MiniDSP or any recommendations for changing the gain on the chip amp to suit.
Ideally I would go for the 2.0v MiniDSP 2x4 HD.
you choose an amplifier gain to give you the sensitivity you require.
If you know you have both 2Vac output and 0.9Vac output, then choose a sensitivity of 0.9Vac to just reach clipping of the power amplifier output, from that lower level source.
If you know you have both 2Vac output and 0.9Vac output, then choose a sensitivity of 0.9Vac to just reach clipping of the power amplifier output, from that lower level source.
Hi Peter,
Finished building My amp with your premium kit, wich I have been enjoying a lot since the beginning of 2017. Fantastic setup!
Thanks everyone also for the deeply valued replies and comments.
While listening with my headphone last week, I noticed a very low volume "popcorn", scratchy sound coming from left channel only. Been testing every combination and it's not the speakers. It is not volume dependant either. I only notice it when volume is very low, between tracks.
Checked rails voltages (31V and -31V), dc offset (5mV to 32mV).
R1 is a piece of wire
Everything seems to play normally. But I am just a bit worried that it hides something worse over time. What could it be????
Finished building My amp with your premium kit, wich I have been enjoying a lot since the beginning of 2017. Fantastic setup!
Thanks everyone also for the deeply valued replies and comments.
While listening with my headphone last week, I noticed a very low volume "popcorn", scratchy sound coming from left channel only. Been testing every combination and it's not the speakers. It is not volume dependant either. I only notice it when volume is very low, between tracks.
Checked rails voltages (31V and -31V), dc offset (5mV to 32mV).
R1 is a piece of wire
Everything seems to play normally. But I am just a bit worried that it hides something worse over time. What could it be????
Hi, you may try installing small capacitor as explained here: http://www.diyaudio.com/forums/audi...-kit-building-instructions-3.html#post1516522
Already done! Could it be damaged? I cannot test capacitance of such a small value capacitor, my meter does not go that low on its scale. I will try to remove it and see what it gives.
Any model/style/ you recommend?
what if it's not changing anything?
Any model/style/ you recommend?
what if it's not changing anything?
Just tried without the 290pf cap removed. Noise is still there, only with more RF noise. the cap was doing its job I guess 🙂
Looks like it's from a different source
Looks like it's from a different source
is you amp inside a metallic enclosure?
If so then you can add RF attenuation where the cables enter the enclosure.
I generally use 47pF from Signal Hot/Flow to Signal Cold/Return on the back of the RCA/XLR socket.
And 1nF on the speaker terminals from both Hot and Cold to Chassis.
And a mains IEC socket with an integrated canned filter. Select the lowest current rating to get the highest RF attenuation.
If so then you can add RF attenuation where the cables enter the enclosure.
I generally use 47pF from Signal Hot/Flow to Signal Cold/Return on the back of the RCA/XLR socket.
And 1nF on the speaker terminals from both Hot and Cold to Chassis.
And a mains IEC socket with an integrated canned filter. Select the lowest current rating to get the highest RF attenuation.
alright, will try this out as soone as I get the parts.
Am I crazy? no ground connection on load side? : AC115-250V 6A Unipolar Solder Lug Terminal Power Line EMI Filter CW3-6A-T | eBay
Am I crazy? no ground connection on load side? : AC115-250V 6A Unipolar Solder Lug Terminal Power Line EMI Filter CW3-6A-T | eBay
I see a connector for ground on LINE side (based on the picture on the ebay link). However, ON the schematic drawn on the part, I see a ground connection between the 2 caps in parallel near the LOAD side.
Just want to make sure that I have a proper earth ground connection If I use such a device on my AC wall connection.
Just want to make sure that I have a proper earth ground connection If I use such a device on my AC wall connection.
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mmm ok .
My headphone jack has 1x left, 1x right, and the ground. Both my output ground are connected togheter at the jack. How do implement the 1r resistor? I'm confused...
So far, I've just connected 1x 100r to both left and right channel hot signal.
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So you nearly short out each headphone speaker with a 1R resistor? Best case scenario is that you have 32ohm headphones. Worst case is 600ohm headphones. So 28V out of the amp gives you around a quarter of a volt to drive the headphones? This won't provide enough volume.
If I wanted to drive headphones with a chip amp I would change the gain of the amp to 10 for lm3886 or lm3875. Then I would add a permanent attenuation circuit on the input. If I were super cautious I might put a 100R resistor on the output of the amp and it would be a low wattage resistor because headphones inherently contribute to the total resistance seen by the amp resulting in very low power output.
Unless you have some way to mute the amp on power up and down I would not leave my headphones plugged in during turn on and off.
If I wanted to drive headphones with a chip amp I would change the gain of the amp to 10 for lm3886 or lm3875. Then I would add a permanent attenuation circuit on the input. If I were super cautious I might put a 100R resistor on the output of the amp and it would be a low wattage resistor because headphones inherently contribute to the total resistance seen by the amp resulting in very low power output.
Unless you have some way to mute the amp on power up and down I would not leave my headphones plugged in during turn on and off.
Maybe something like this schematic. This schematic ignores capacitors and power supply. Just giving an idea for attenuation and gain as well as current limiting the output.
If you have a pop on turn on then it could blow the headphones if they are plugged in when you turn it on. If you turn it off with headphones plugged in you could have a problem with too much DC getting to the phones as a lot of times the amp can have large DC offset while turning off.
If you have a pop on turn on then it could blow the headphones if they are plugged in when you turn it on. If you turn it off with headphones plugged in you could have a problem with too much DC getting to the phones as a lot of times the amp can have large DC offset while turning off.
Attachments
if 100r+1r gives too much attenuation (-40dB) then change to 100r+3r3 to give -30dB
Don't go and change the stability margins of the chipamp by reducing it's gain.
I can visualise 6 locations for capacitors around a chipamp implementation.
All will require selecting capacitors to suit the duty at that particular location.
Do you intend replacing all the capacitors with one type of Mundorf?
All will require selecting capacitors to suit the duty at that particular location.
Do you intend replacing all the capacitors with one type of Mundorf?
No. Just in place of the 2x 1500uf Panasonic FCs usually recommended on the amp board. Using same value of Mundorf Mlytic AG. I have them so will give them a try anyway - just curious about other's experiences of using them. Also going to try 10k Supertech caps + snubber on the rectifier board (but not at the same time 🙂)
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