• Disclaimer: This Vendor's Forum is a paid-for commercial area. Unlike the rest of diyAudio, the Vendor has complete control of what may or may not be posted in this forum. If you wish to discuss technical matters outside the bounds of what is permitted by the Vendor, please use the non-commercial areas of diyAudio to do so.

Commercial Gainclone kit- building instructions

I got a 3875 standard kit and was wondering if I could use some 1000uF Panasonic caps instead of the provided ones that are 2700uF. I saw in the opening posts that C1/C2 were specified to 4.7uF-100uF and wanted to know what lead to higher capacitance in between back then and today.
Ragards, Stefan
 
Yes, no problem using 1000uF Panasonic caps.
C1/C1 are not recommended to be used any longer.

The main caps, Panasonic FC 1500/50, are sometimes on backorder, and then I need to substitute them with something else not to further delay order shipment.

Some people tried those 2700uF Chemicons in the past and claimed they sounded better then stock caps.
 
Yes, no problem using 1000uF Panasonic caps.
C1/C1 are not recommended to be used any longer.

The main caps, Panasonic FC 1500/50, are sometimes on backorder, and then I need to substitute them with something else not to further delay order shipment.

Some people tried those 2700uF Chemicons in the past and claimed they sounded better then stock caps.

Hi,

I'm in the process of building a second LM3875 kit right now; Hope you have time for a few questions:

- Should I now leave C1/C2 empty, not even use the 10uF caps?

- How would you recommend adding more capacitance nowadays if need be, only directly on the amp board?

- Is there any downside to mounting the led on the psu board since it is only driven by one of the rails, any risk for asymmetry between the rails somehow?

/M
 
Yes, leave those empty, or if you like, put some small caps there and listen if it makes any difference.
You can install big caps on rectifier board as per attached pic.
No problem with LED being powered from one of the rails.
 

Attachments

  • b3.jpg
    b3.jpg
    128.8 KB · Views: 277
Yes, leave those empty, or if you like, put some small caps there and listen if it makes any difference.
You can install big caps on rectifier board as per attached pic.
No problem with LED being powered from one of the rails.

My ambition is to make this one better in terms of hum and noise. I am improving the wiring and ground handling significantly this time around. What should I do to improve hum and noise and achieve a more 'black' background?

Can the cap selection on the rectifier board and amp board somehow be made to improve this?
 
Ok, so I tried to build an stereo amp based on Peters kit and unfortunately I'm afraid that for whatever reason I have fried one of my chips, One of the channels went up in smoke for whatever reason and the smell and the sparks came from the chip. I have no idea if I can source another chip, but I would be interested to know if anybody would make an educated guess as to what went wrong:


49728002223_f5cc652d31_z.jpg


49728550766_c02b1146f3_z.jpg


On the back one can see the 3 black coloured pins of the chip



Thank you,
Stefan
 
Last edited:
On the channel that did not went up in smoke I measure 25V on input and on output with nothing connected to the amp - can that be ?!? Somehow I am seriously puzzled by this project of mine. P.S.:I did not use any insulation when fixing the chips to the aluminum profile used as cooling.

No need for insulation when mounting the chip, as the case is self insulating plastic package.

It could go in smoke because the supply voltage was reversed, or you had some sort of short circuit? Can you post picture of your rectifier board?

25V at the input could be caused by bad solder joints or resistors mixed up?
 
I just recently found this site, and been reading about this kit.

Would this be a good kit to mod an existing speaker set into a couple active speakers, primarily used as keyboard monitor ? since its designed as a mono block.

Also where would I find info about using 2 in either paralell or bridged mode ?
 
Yes, no problem using 1000uF Panasonic caps.
C1/C1 are not recommended to be used any longer.

The main caps, Panasonic FC 1500/50, are sometimes on backorder, and then I need to substitute them with something else not to further delay order shipment.

Some people tried those 2700uF Chemicons in the past and claimed they sounded better then stock caps.

Do you mean that C1 and C2 on the rectifierboard no longer are required?
If so for what reason and should i remove them from my assembled kit ?

Kind regards
Edwin
 
I've been successfully using AudioSector LM3875 kits for several years with stepped attenuator VCs but would now like to re-site the amps, shorten the perhaps over-long speaker leads and use longer leads between the VC and the amps.

The snag is that, when I try longer signal leads, the amps oscillate in an, er, lively manner. I'm reasonably sure a buffer circuit would fix the issue but I'd prefer (also) to try and fix the oscillation.

The signal leads use a quad-core geometry that, as you know, is rather more capacitive than alternatives. I omitted the 1K input resistor R1; the SA's serial resistor in on the low side (5K6). (I accept that low-value resistors do not help stability but the amps' sound quality is noticeably better than it is with higher values.)

Any suggestions as to what I might do?

TIA,

Dave