Finally made a LM1875 amp

[BrianGT]

Originally posted by korben69
Brian YGM

Alright, I am catching on mail, as I was away from my computer for most of the long weekend. (yesterday = us holiday)

[BrianGT]

Made a new thread for it here:
http://www.diyaudio.com/forums/showt...90#post1551690

[madisonears]

This is a compact layout with some nice features, but I think you missed an opportunity to implement a feature which would improve the performance of this amp. The importance of star grounding in this amp has been discussed many times on this board. I see that the power supply decoupling caps' ground path runs from C3/C4 THROUGH C5/C6. It would have been better to break the path between the C6 pad and the PSU ground pad, then run a separate trace from the PSU ground pad to a point BETWEEN C4 and C6, to the spot underneath the lettering "V+". This would also have served to separate the power supply decoupling ground path from all the other ground paths, providing something closer to the ideal of a true star ground.

Peace,
Tom E

[Leolabs]

Heatsink size/spec???

[rickmcinnis]

Would someone tell me how to configure this little board to use the minimal number of components?

I am having trouble with the optional components and whether they need to have jumpers or just be left out.

I want to use only the following: per AUDIOSECTOR
power supply bypass - BG N's one each for + and -
Feedback resistor to be attached to the chip
Feedback resistor to ground without a capacitor
Input resistor to non-inverting input
Input resistor to ground

Any help offered will be appreciated.

Thanks,

Rick McInnis

[BrianGT]

Originally posted by rickmcinnis
Would someone tell me how to configure this little board to use the minimal number of components?

I am having trouble with the optional components and whether they need to have jumpers or just be left out.

I want to use only the following: per AUDIOSECTOR
power supply bypass - BG N's one each for + and -
Feedback resistor to be attached to the chip
Feedback resistor to ground without a capacitor
Input resistor to non-inverting input
Input resistor to ground

Any help offered will be appreciated.

Thanks,

Rick McInnis

Rick,

As for the components, you only need to install one short circuit jumper, in the place of R6. Here is a minimized component listing for the amp board:

R1 - not used
R2 - 22k (input to ground resistor)
R3 - 1k (gain resistor , gain = 1 + R4/R
R4 - 22k (nfb resistor - on bottom of pcb)
R5 - not used
R6 - jumper (optional resistor between input ground and output ground)
C1 - not used
C2 - not used
C3 - not used
C4 - BG N
C5 - not used
C6 - BG N
C7 - not used

Note that you will wire your input to the top pad of C1. This avoids having to use a short for C1, and should be a cleaner wiring solution.

Let me know if you have any more questions,

--
Brian

[androuski]

Hi,

I've just order a LM1875 kit, and I wonder about a few things :

- can I use a 2X20v transformer without make the distortion grow, I would like to keep it at his optimum;

- What kind of potentiometer shall I use as passive preamp : 25, 50 100kohms ?

Thank

[Sparky OR]

Brian
I have 2 or your LM1875 boards up and running fine and I'm happy. I know this seems too simple to be necessary, but do you have a schematic diagram for the amp board itself, even without values. It helps me when I look back at some old project and have forgotten what I did. Thanks. (they sound great!!)

[madisonears]

Is anyone who has built this kit able to describe the sound quality, even in terms of comparison to a common standard such as a typical commercial amp (not a BestBuy receiver)? Is anyone listening to this amp as part of a quality system (not feeding computer speakers or sourced from an Ipod)?

Peace,
Tom E

[Sparky OR]

I have owned and listened to Harmon Kardon Cit I/II, Dyna ST35, tube amps, Marantz stereo SS receivers, I use a 6V6 SE tube (self made), and others. However, it would be hard to convey sound quality to someone else, unless there is something noticeably wrong. I can safely say I hear nothing detrimental in listening to Brian GT kit, and "Kit 50" available from various vendors. My source is an older Sony CD/DVD player, or a Panasonic portable CD player in the garage, and a mid range Marantz CD player in the house. My speakers are TB 4 ohm single drivers in 1/4 wave TQWTL speakers, in the garage, and a Mission 2 way, or an Optimus Lineum Pro LX-10 for testing single channels after they are first built. I'm satisfied, your actual smileage may vary. I listen at moderate levels, don't need huge bass. If I was set up to A/B test it against others with a switch, it would be more informative. In short, give them a try, not much expense involved.
Cheers!