In setting up the GC I finished yesterday, I accidentaly connected a speaker between the 2 positive output poles of the 2 channels...
And it played? is this bridgeing? or is this just how to connect a subwoofer...
I would never have intentionaly tried this...lol
Sorry Peter, I just thought if anyone knew what I experienced there for the first time, it would be you.
And it played? is this bridgeing? or is this just how to connect a subwoofer...
I would never have intentionaly tried this...lol
Sorry Peter, I just thought if anyone knew what I experienced there for the first time, it would be you.
Just finished my 3875 premium and after a false start I have it working fine, it sounds far better than I had expected 
One slight issue is that with my 91dbm speakers there is some hiss, I can be heard within a few feet of the speakers and over the music and very low volumes. It does not increase with volume.
It happens with preamp connected or not, its an always present type hiss. It is much less with 87dbm speakers.
DC offset is very low, sub 40mv at least (can't remember off top of my head) The amp(s) are cased, wiring is short and twisted.
At present nothing is grounded bar the chasis,all components/jacks are isolated.
Is there anything I can do to fix this? Is it to do with me not hooking up ground?
I've also read about leaving R1 out, I assume I jumper this position? Is it worth doing?
One slight issue is that with my 91dbm speakers there is some hiss, I can be heard within a few feet of the speakers and over the music and very low volumes. It does not increase with volume.
It happens with preamp connected or not, its an always present type hiss. It is much less with 87dbm speakers.
DC offset is very low, sub 40mv at least (can't remember off top of my head) The amp(s) are cased, wiring is short and twisted.
At present nothing is grounded bar the chasis,all components/jacks are isolated.
Is there anything I can do to fix this? Is it to do with me not hooking up ground?
I've also read about leaving R1 out, I assume I jumper this position? Is it worth doing?
Does it hiss with inputs shortened? Than it is probably oscillating at high frequencies. All my Chipamps show only very little hiss, audible only with most of the speakers with my ears quite close to the tweeter.
I also would never leave out R1, in my experience this is an important part for stabilty, although i did not really find an evidence for that in the spec sheet. My Chipamps always seem to work better with R1 in place (but 150-220R not 1k).
I also would never leave out R1, in my experience this is an important part for stabilty, although i did not really find an evidence for that in the spec sheet. My Chipamps always seem to work better with R1 in place (but 150-220R not 1k).
lohk said:
Just testing it out now. With shorted inputs the hiss is tiny, well within acceptable limits.
As soon as I connect the preamp there is much more hiss.
With nothing connected there is hiss and hum, but I'm led to believe this is to be expected.
Groudning seems to make no difference to hiss.
So it looks like my preamp, which is a M³ headphone amplifier, is the cause. ( http://www.amb.org/audio/mmm/ )
Too much gain? The GC is a default of 33 and the headamp is 10, the volume does come up pretty quick, with max being about 10-11oclock.
I have 23mv / 14mv of DC offset on the GC with music playing and speakers connected (pretty much any volume)
I get no hiss on the headamp with my HD580s...nor when the speakers are directly connected to the headamp (it produces ~6 watts)
I have a simpler OPA637/BUF634 headamp I will try later as a preamp (Pimeta)
Yes, the hiss is from your preamp. If I fully open volume on my ML380S I also get some hiss.
You can reduce the gain of the amp. One way would be replacing 680R resistor with 1k2 resistor (or similar).
When no input connected to the amp, the noise and hum are normal, the input has to be loaded for proper operation.
You can try to short the input 220R resistor (I'm doing it presently with my amps). The advantage would be less coloration that this resistor inevitably introduces.
You can reduce the gain of the amp. One way would be replacing 680R resistor with 1k2 resistor (or similar).
When no input connected to the amp, the noise and hum are normal, the input has to be loaded for proper operation.
You can try to short the input 220R resistor (I'm doing it presently with my amps). The advantage would be less coloration that this resistor inevitably introduces.
Hello Peter,
It looks like you got a favorable review from 6moons again. They talk about running your amp as a mono-block off of a balanced xlr connector, one phase per amp. What are the sonic differences between the xlr method with the LM 3875 chip and using the LM4780 in balanced mode running off of an rca (se) input? Are there any load considerations in balanced mode with these two chips.
My apologies if this has already been asked, I can’t seem to find it, just point me to the page.
Leve
It looks like you got a favorable review from 6moons again. They talk about running your amp as a mono-block off of a balanced xlr connector, one phase per amp. What are the sonic differences between the xlr method with the LM 3875 chip and using the LM4780 in balanced mode running off of an rca (se) input? Are there any load considerations in balanced mode with these two chips.
My apologies if this has already been asked, I can’t seem to find it, just point me to the page.
Leve
If you check the summary here: http://www.6moons.com/audioreviews/47labs5/gaincard_3.html
this is how single ended vs. balanced compares:
Go out balanced from a pre into Peter Daniel's XLR-to-two-RCA adapter: presto, two 50-watt stereo chip amps turn 100-watt monoblocks, each with its own dedicated outboard power supply.
When I first acquired the Pateks, I felt that bridging them -- at the time necessitating the Bel Canto PRe2 for its balanced outputs -- overemphasized transients for too much sharpness at the expense of body or harmonic envelope. Perhaps due to further break-in; perhaps due to swapping out preamps for the Music First; perhaps due to different balanced cables (Analysis Plus Solo Crystal vs. Crystal Reference); I now feel differently. What I'm hearing is more meat especially in the midbass power zone, increased dynamic acceleration and a touch more image density, already a key point with the Pateks and chip amps in general.
Employing an unfair advantage is what sports are all about. If genetics made you 7'4", you belong on the basket ball court. The little white guy just has to put up with you and work harder for a goal. The Gaincard even in dual-mono mode was simply outmuscled, overrun and put in second place when I compared the four Canadian boxes in 100-watt bridged mode to the two Japanese cans plus aluminum postcard at 25 watts. The AudioSector quartet played beefier, with more excitement, harder-hitting attacks and, especially in the midbass-to-lower-midrange band, with more wallop and body.
Each monoblock consists of a stereo amp, which allows to run two halves of a balanced signal (per stereo amp). All you need is XLR --> 2 x RCA adaptor.
This applies to both LM3875 and LM4780. I still prefer the LM3875 chip as it has a bit more refinement especially in mid-to-upper treble which seem to be more refined
this is how single ended vs. balanced compares:
Go out balanced from a pre into Peter Daniel's XLR-to-two-RCA adapter: presto, two 50-watt stereo chip amps turn 100-watt monoblocks, each with its own dedicated outboard power supply.
When I first acquired the Pateks, I felt that bridging them -- at the time necessitating the Bel Canto PRe2 for its balanced outputs -- overemphasized transients for too much sharpness at the expense of body or harmonic envelope. Perhaps due to further break-in; perhaps due to swapping out preamps for the Music First; perhaps due to different balanced cables (Analysis Plus Solo Crystal vs. Crystal Reference); I now feel differently. What I'm hearing is more meat especially in the midbass power zone, increased dynamic acceleration and a touch more image density, already a key point with the Pateks and chip amps in general.
Employing an unfair advantage is what sports are all about. If genetics made you 7'4", you belong on the basket ball court. The little white guy just has to put up with you and work harder for a goal. The Gaincard even in dual-mono mode was simply outmuscled, overrun and put in second place when I compared the four Canadian boxes in 100-watt bridged mode to the two Japanese cans plus aluminum postcard at 25 watts. The AudioSector quartet played beefier, with more excitement, harder-hitting attacks and, especially in the midbass-to-lower-midrange band, with more wallop and body.
Each monoblock consists of a stereo amp, which allows to run two halves of a balanced signal (per stereo amp). All you need is XLR --> 2 x RCA adaptor.
This applies to both LM3875 and LM4780. I still prefer the LM3875 chip as it has a bit more refinement especially in mid-to-upper treble which seem to be more refined
Those boxes hold the batteries to power the shields on speaker cables: http://www.walkeraudio.com/speaker_cables.htm
Peter Daniel said:
Thanks Peter
How much gain would I be left with at 1k2 ?
Have to say this is the best amp I have ever heard, I am totally stunned how it sounds. I was expecting it to be a nice improvement but its been a massive step up for me. It is fast and punchy with vocals/midrange to die for, they really stand out.
Its been a long while since I've felt I've heard things I've never heard before but with this quite a few songs have revealed new details. I'm normally a headphone user too....
I've ended up having a two hour lunch break for the last 3 days because I simply have to listen to 'one more track' before I head back to work!!!
I'm using the stock config, with only a 10uf in the -v and an 80va toroid per channel, I have ample power and I'm not even using half of it most of the time.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.