AudioSector-chip amp kits, dacs, chassis

[Colin]

I'm sure this will have been posted before but am I right in thinking the difference between the LM4780 and the LM3875 is that the former offers more power at the expense of a little transparency?

 

[PierreG]

Dual mono

I have a Dual Mono AudioSector LM3875 ChipAmp.

I need a schematic of the connections between:
- two (2) transformers -120VA (approx) transformers from Apex Jr. (Chia Yu Co Ltd).
Input: 2 X 120Vac
Output 42Vct 21V- 0 - 21V
- two(2) PS boards and the two (2) amplifiers boards

I searched here but I did not find. Sorry....

 

[Peter Daniel]

You will find guidlines for wiring LM3875 kit here: http://www.diyaudio.com/forums/showthread.php?postid=1108820#post1108820

And this is the modification for CT transformer: http://www.diyaudio.com/forums/showthread.php?postid=1196283#post1196283

BTW, at the bottom of this page you will find links to all important info on my kits and mods: http://audiosector.com/links.shtml

 

[Peter Daniel]

I'm sure this will have been posted before but am I right in thinking the difference between the LM4780 and the LM3875 is that the former offers more power at the expense of a little transparency?

If you use LM4780 in stereo configuration (2 channels from a single chip) you will not notice any loss in resolution.

Parallel connection affect resolution slightly, but if your aim is more current, it is rather negligable.

Overall, LM3886 and as well LM4780, has slightly less refinement in mids and highs. So if your goal is best sound quality, LM3875 could be preferred.

However, I was using balanced LM4780 in my main system for 6 months or so and I couldn't complain

 

[okapi]

peter,

do you have any photos of your balanced LM4780 amp you would be willing to post or have you already done so somewhere else?

is the signal balanced from the source or are you using transformers at the input of the amp to balance?

did you switch to LM4780 (2XLM3886) because the LM3875 was clipping when bridged?

i'm probably not alone in my curiosity for your latest design.

thanks,
Tim

 

[Peter Daniel]

It's pretty old amp and I was using it few years ago. It is still in use in my secondary workshop system. The balanced signal was provided by ML380S preamp.

I've built the amp to check the potential of LM4780 kit.

The amp was described here: http://www.diyaudio.com/forums/showthread.php?postid=636575#post636575


BTW, from kit ordering page you can get directly to forum discussion (on the particular kit) by clicking Applications Notes link, as below.

 

[Colin]

Hi Peter - thanks for the insight into the two amps. BTW, I'm sure I can't be the only waiting to see if you come up with an elegant active preamp design ...

 

[Giordano]

I've tried to search, but could not find, also in the datasheet I could not find that : what is the +-3dB (or whatever tolerance) bandwith if these chips ?
It will sound crazy, but beside a DC motor control for a turntable I'm seeking for a buffer for a 3 phase motor after tha generator and before the 24V motor. The problem is, I need about 8Hz to 60Hz bandwith. It is not a problem if all tree attenuates some, but with similar degree, but if one attenuates more than other, that is a problem because the torque will not be constant.

Sorry for the alien kind of question , Please let me know what you experienced as low freq point (actually I do not know the correct word in English for the low -3dB point). What about DC ?

Thanks,

JG

 

[Peter Daniel]

IIRC the freq. response (for my amps) was 5Hz - 250kHz (-3dB)

 

[Giordano]

Thanks,
JG

 

[t-head]

LM3875 with JX92?

Has anyone any experience in driving Jordan JX92S with the LM3875 chip? Thanks.

t

 

[Colin]

Not yet but my 20w Naim Nait 2 does the job fine with JX92s.

The LM3875 is, I think, the arrangement used by the original Gaincard and Konus Essence combination.

A review of the two used together is here.

 

[DaveM]

I heard the LM3875 gaincard used with the Jordan JX92S at the Montreal Hifi show several years ago. So, within the context of my memory several years later and the show where you hear 200 systems in a span of hours, that system was memorable. I won't speak to the exact details, but I have built Peters LM3875 kit and it is fantastic and I should be getting a pair of Jordans soon from the group buy.

In other words, I have heard it done to great success. and am on the road to doing it myself.

 

[t-head]

DaveM,

Thanks. Just what I was looking for. I have Jordans now (and another pair coming from the group buy as well). I have heard that GCs performance is dependent on associated source/load, so my question...I will be using Peters DAC and the Jordans. I was looking for confirmation, or not, that the combo worked.

Colin,

Thanks for the links.

t

 

[Colin]

The Jordans are a very easy 4 ohm load. Depending on cabinet design, you may elect to use a BSC circuit, which would make the load even easier.

I have done things the opposite way to DaveM - I've got the Jordans but yet to assemble Peter's kit.

 

[t-head]

Colin,

Cab is a 6x6x36 quarter-wave 3xfolded transmission line similar except in shape to the triangular design at Jordans site. Close to wall placement and a small sub precludes need for BSC. I have no idea how other designs compare, but am happy with the sound of the JX92S in this one...I am glad to hear others feel Peters amp design will drive the Jordans well as I am fond of the JX92Ss' off-axis presentation.

t

 

[audio1st]

LM3875 kit

Peter,

I don't no if this has been covered here before, but why do you not use 0.1 uF supply decoupling capacitors in your kits.
I guess you found they had a negative effect, yes?
Very pleased with the kit though, propulsive!!

regards..

 

[Peter Daniel]

I try to avoid parallel decoupling caps. Especially the small ones, like 0.1uF, do more harm than actual improvement: while you may notice that detail or presence is "artificially" brought forward, the effect is similar to using eqalizer in a system, the harmony and natural order of things is spoiled and personally I don't like it.

 

[SoNic_real_one]

I was looking to your site and was ready to by some PCB's for amplifiers, but then on the NS webpage I found this:
http://www.national.com/pf/LM/LME49830.html
Is there any interest for you in such an amplifier? PCB's layouts for your other amps are very nicely done so I would like to see if you will do one for the new chip.
Because now I am drooling over that one.

 

[Peter Daniel]

I believe there are some boards around already for that circuit.

Personally, I'm not really excited about such hybrid circuits and I don't think I will be persuing it in a near future.