Hi,
another newbie question of mine to this thread.
I would like to put the 4.7 microF coupling caps at the input of my working LM3875 premium kit monoblock amps. I could not find the discontinued BG N non polarized caps suggested by Peter; for now I found cheap Rubycon caps with the same capacitance but polarized.
1. Can I use them?
2. If yes, what pin (+ or -) should I connect on the side of the RCA female?
(I think that I will be not able to put the cap on the place of R1 as suggested by Peter since the pcbs are now too populated so I intend to place the caps near the RCAs)
3. Aware of the opinion of Peter on the coupling cap placement, have you any suggestion for the brand of easy to find caps of good quality?
Thank you
Renato
another newbie question of mine to this thread.
I would like to put the 4.7 microF coupling caps at the input of my working LM3875 premium kit monoblock amps. I could not find the discontinued BG N non polarized caps suggested by Peter; for now I found cheap Rubycon caps with the same capacitance but polarized.
1. Can I use them?
2. If yes, what pin (+ or -) should I connect on the side of the RCA female?
(I think that I will be not able to put the cap on the place of R1 as suggested by Peter since the pcbs are now too populated so I intend to place the caps near the RCAs)
3. Aware of the opinion of Peter on the coupling cap placement, have you any suggestion for the brand of easy to find caps of good quality?
Thank you
Renato
Yes, it's correct, try connecting CHG to chassis through 10R resistor. Chassis should be connected directly to Earth ground.
Probably Rubycons ZA or ZL could be closest replacement for BGs (although not better): http://www.referenceaudiomods.com/M...Screen=CTGY&Store_Code=RAM&Category_Code=RUBY
You can use polarized capacitor in coupling without problem: +pin is usually on input side.
I have been reading this thread with interest and am going to be ordering a kit in the very near future.
I have a couple of questions....
I have an old Denon DRA550 receiver with a blown right channel. As it is expensive to fix it I thought I might use it for parts.... is there anything in there that I can pilfer for this project?
I also have some Yamaha gear that has been in storage and I was thinking of maybe reviving it - one unit is a DSP-1 Surround processor and an M35 power amp. What would I need to connect one of these little amps to the DSP-1? I have attached the 3 possible methods explained in the DSP-1 manual....
If none of this is possible, I will just build a standard unit and have a play
I have a couple of questions....
I have an old Denon DRA550 receiver with a blown right channel. As it is expensive to fix it I thought I might use it for parts.... is there anything in there that I can pilfer for this project?
I also have some Yamaha gear that has been in storage and I was thinking of maybe reviving it - one unit is a DSP-1 Surround processor and an M35 power amp. What would I need to connect one of these little amps to the DSP-1? I have attached the 3 possible methods explained in the DSP-1 manual....
If none of this is possible, I will just build a standard unit and have a play
Attachments
Just mt 2 cents here. Transformer is rated at 300VA. That's 300/120v for about a maximum 3.5 amps on the primary. Since you have dual secondaries I'll assume 150VA per secondary. At 22VAC each secondary should draw about 7 amps maximum. This is my semi-educated guess so I don't guarantee it's accuracy.
Peter usually recommends XLR connectors. I used them on my remote supply and although they worked very well they can get allitle pricey.
Regards,
Dan
Hi,
the smoothing capacitor charging pulses could be 10times the rms current.
The output current (=rail current) could be 5times the predicted current that a resistor will draw.
Applying these factors will produce pretty big numbers.
So What?
Short term peak currents will produce very little heating.
The biggest loss is voltage drop and a big terminal block or connector will not reduce this by much.
the smoothing capacitor charging pulses could be 10times the rms current.
The output current (=rail current) could be 5times the predicted current that a resistor will draw.
Applying these factors will produce pretty big numbers.
So What?
Short term peak currents will produce very little heating.
The biggest loss is voltage drop and a big terminal block or connector will not reduce this by much.
Thanks Dan.
In my case that means 2x160VA transformers,26V secondary.80VA/26V=3.1A.XLR's should be fine for that,but for 7A I'm not so sure.
Sikorel
What do you think about putting two pairs of Sikorels(two by he chip,and two on the rect. board) with 680uF?I can get them for very reasonable price.
What do you think about putting two pairs of Sikorels(two by he chip,and two on the rect. board) with 680uF?I can get them for very reasonable price.
An externally hosted image should be here but it was not working when we last tested it.
Wrong measurements
Hey guys,
I've been busy building my amp using Peter's kit for some time now. This weekend I've started assembling the amp and taking some measurements. The values between V+ and PG+ and V- and PG- (35.3V and -35.3V) seem fine, but the DC offset seems very high. Without any input I've measured 0.048V, with input and volume down 0.48V and with vol max 0.68V. Does anyone have an idea what could be wrong?
Here are some details about my amp:
- 2x250W, 25V torroids, dual mono, in a seperate housing
- Used the parts Peter supplied
- Used an old walkman as input
- Only one channel is assembled
- I didn't use a star ground as the housing of made out of wood. Only the heat sinks are metal (is this ok?)
I hope u can help me out! Also, any comments or recommendations are welcome
Thanks!
Erik
ps. Why isn't this thread sticky anymore?
See my pictures:
By erikdegier, shot with 6300 at 2009-09-09
Hey guys,
I've been busy building my amp using Peter's kit for some time now. This weekend I've started assembling the amp and taking some measurements. The values between V+ and PG+ and V- and PG- (35.3V and -35.3V) seem fine, but the DC offset seems very high. Without any input I've measured 0.048V, with input and volume down 0.48V and with vol max 0.68V. Does anyone have an idea what could be wrong?
Here are some details about my amp:
- 2x250W, 25V torroids, dual mono, in a seperate housing
- Used the parts Peter supplied
- Used an old walkman as input
- Only one channel is assembled
- I didn't use a star ground as the housing of made out of wood. Only the heat sinks are metal (is this ok?)
I hope u can help me out! Also, any comments or recommendations are welcome
Thanks!
Erik
ps. Why isn't this thread sticky anymore?
See my pictures:
An externally hosted image should be here but it was not working when we last tested it.
By erikdegier, shot with 6300 at 2009-09-09
you must create a star ground (=Audio Ground).
All the return cables and other return connections come together at the star ground.
This is the reference voltage that all the other stages require to amplify the signal with respect to reference.
The part that is not needed for Audio quality is the Safety Earth.
BUT,
for you and your families/visitors Safety all exposed conductive parts must be connected to Safety Earth and then to the PE (third wire in the mains supply cable).
This Safety Earth does not improve the audio performance of the amplifier, it usually makes it worse.
All the return cables and other return connections come together at the star ground.
This is the reference voltage that all the other stages require to amplify the signal with respect to reference.
The part that is not needed for Audio quality is the Safety Earth.
BUT,
for you and your families/visitors Safety all exposed conductive parts must be connected to Safety Earth and then to the PE (third wire in the mains supply cable).
This Safety Earth does not improve the audio performance of the amplifier, it usually makes it worse.
So I assume that you are adjusting the volume in the walkman. If offset doesn't go down with volume down, that could means that there is a buffer following the potentiometer and that buffer produces offset. The amp will amplify any such offset and that's why your readings are high.
What you measure without input connected is the offset produced by the amp itself and it's relatively low.
Use a different source with potentiometer directly at amp's input and your offset readings should be improved.
You do not need star ground running one channel only, just make sure that all metal parts are connected to Earth ground.
The thread is still sticky, but only in AudioSector forum section. I'm not sure if the change is for better.
of course you do need a star ground (Audio Ground) even when assembling a mono channel.
It can be any where that all the returns come together to obtain their reference voltage.
that makes more sense.
The Audio Ground is on the PCB.
Don't tell them they don't need one.
Putting it, as you have done, on the PCB removes the possibility of the assembler getting it all wrong.
I'm actually gonna say it again: you don't need external star ground in mono setup using my boards.
In case of stereo application, it's been already covered: http://www.diyaudio.com/forums/showpost.php?p=1518369&postcount=77
Just a quick post on the break-in of my gainclone. I'm pretty sure I've read somewhere in these forums to allow atleast three weeks for gainclone break-in. Well I am pleasantly suprised that this appears to be true. My first impressions were that my gainclone seem to be lacking treble extension and definition. Well, I am really happy to note that this appears to be changing and I'm starting to appreciate the gainclone's midrange warmth and detail.
Every day that I spend with this amp I seem to be more and more satisfied!
Regards,
Dan
Every day that I spend with this amp I seem to be more and more satisfied!
Regards,
Dan
Dear all
I now testing the LM3785 kit and have two problem as follow.
- The toroidal transformer for each channel is 250VA and at first use the 3A fuse. After several on/off for step by step checking the fuse blown. I had changed the fuse by other 3A then checked the DC off set 17/54mA at min/max volume. Next the fuse blown again at the time I switch on the amp.
I decided to check from beginning again and found even the transformer no load start the 5A fuse can be blown. The fuse blown after several time I did on/off the switch (waiting time between on/off around 1 minute). So which type of fuse and rating should I use for my amp.
- I had test the amp and its play without any hum and noise but just 1 second after I turned off the switch, there the explode sound from the speaker. How can I prenvent this explode sound.
I now testing the LM3785 kit and have two problem as follow.
- The toroidal transformer for each channel is 250VA and at first use the 3A fuse. After several on/off for step by step checking the fuse blown. I had changed the fuse by other 3A then checked the DC off set 17/54mA at min/max volume. Next the fuse blown again at the time I switch on the amp.
I decided to check from beginning again and found even the transformer no load start the 5A fuse can be blown. The fuse blown after several time I did on/off the switch (waiting time between on/off around 1 minute). So which type of fuse and rating should I use for my amp.
- I had test the amp and its play without any hum and noise but just 1 second after I turned off the switch, there the explode sound from the speaker. How can I prenvent this explode sound.
Are you on a 240Vac mains supply?
The T3A fuse is suitable for 750VA not 250VA.
You need a big fuse because all transformers draw a large current at start up.
A much smaller fuse can be used if you fit a soft start circuit to reduce the start up current surge.
You may find that a T800mA or T1A fuse will do the job of powering your amplifier.
The speaker noise at start up is due to a voltage surge from the amplifier output to the speaker.
This could be a DC surge or a slow and variable AC surge depending on how the internal circuits of the amplifier charge up and start operating.
The easiest way to eliminate the speaker noise is to fit a speaker relay that is delayed by anywhere between 500ms to 5seconds after powering up.
This same relay should have instant disconnect at power off/power failure.
The T3A fuse is suitable for 750VA not 250VA.
You need a big fuse because all transformers draw a large current at start up.
A much smaller fuse can be used if you fit a soft start circuit to reduce the start up current surge.
You may find that a T800mA or T1A fuse will do the job of powering your amplifier.
The speaker noise at start up is due to a voltage surge from the amplifier output to the speaker.
This could be a DC surge or a slow and variable AC surge depending on how the internal circuits of the amplifier charge up and start operating.
The easiest way to eliminate the speaker noise is to fit a speaker relay that is delayed by anywhere between 500ms to 5seconds after powering up.
This same relay should have instant disconnect at power off/power failure.
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