Hi Peter!
I found out something quite interesting today about my slight low level hum problem (even though it's not really a 'problem' to me):
When I powered the amp on for the first time I used a 0,5m USB cable to connect my laptop (IBM T22 with PCMCIA USB 2.0 card, because USB 1.0 doesn't work with USB DACs) to the DAC. This cable has a ferrite ring on the end directed to the laptop. Today I tried a different cable, also of 0,5m length, which hasn't any ferrites. With this cable the hum increased quite a lot!
Then I tried another cable with ferrites on both ends of the cable, and with this one the hum was almost gone completely!
So I think with a high quality USB cable with large ferrites on both ends I can live with my grounding method easily without the urge to reconnect (and resolder!) everything.
Regards - martin
I found out something quite interesting today about my slight low level hum problem (even though it's not really a 'problem' to me):
When I powered the amp on for the first time I used a 0,5m USB cable to connect my laptop (IBM T22 with PCMCIA USB 2.0 card, because USB 1.0 doesn't work with USB DACs) to the DAC. This cable has a ferrite ring on the end directed to the laptop. Today I tried a different cable, also of 0,5m length, which hasn't any ferrites. With this cable the hum increased quite a lot!
Then I tried another cable with ferrites on both ends of the cable, and with this one the hum was almost gone completely!
So I think with a high quality USB cable with large ferrites on both ends I can live with my grounding method easily without the urge to reconnect (and resolder!) everything.
Regards - martin
And p.s.:
The first impressions about the sound after just two days of playing are that these units, dac, pot and amp, are playing together like one single unit! It almost sounds like a piece of wire, very neutral and direct, very open and with great soundstage. Very three-dimensonal, transparent sound. I just love it! It is so rhythmically involving, livelike and engaging!
I'm looking forward to a serious listening session when the whole thing has burned in for a few weeks ;-)
Very nice project, I'm happy!
martin
The first impressions about the sound after just two days of playing are that these units, dac, pot and amp, are playing together like one single unit! It almost sounds like a piece of wire, very neutral and direct, very open and with great soundstage. Very three-dimensonal, transparent sound. I just love it! It is so rhythmically involving, livelike and engaging!
I'm looking forward to a serious listening session when the whole thing has burned in for a few weeks ;-)
Very nice project, I'm happy!
martin
Hi,
even if I still have not a pre I could verify a dramatic improvement in the sound by my new monoblocks build with the Audiosector premium kit. Indeed, when connected to an ipod and to my self build Jordan MLTL speakers I get a far better sound than with my integrated commercial amp, a YBA Integrè (not a cheap amp, rated class A in the recommended component list of the Stereophile magazine).
I built these amps just for fun, I really did not expect a significant improvement in the sound since when I made some test in the past at home with different amps the differences I heard were minor. I had now to happily change the opinion on the influence of the amp.
Increased detail and "air" around the instrument are evident. The music is much more natural, in practice a significant step towards the simulation of the live performance in a concert.
As I wrote here in a previous post, I get a low noise which I can only hear with my ear near the speaker.
It is clearly a radio interference: classical music at very low level out of the speaker (my ipod is switched off, off course).
The intensity of the noise changes by changing the interconnect cable which works like an anthenna; no interconnect implies no noise. I get the lower noise with the more expensive cable I have (a cheap Kimber cable interconnect with twisted solid core wires).
I found in this thread a number of suggestions on how to eliminate or reduce this radio interference.
However since I almost irreversible damaged the pcbs when, after some errors, I desoldered some components on the pcb, I am afraid just to try.
I have now these possible solutions:
1) a small cap at the op-amp input (post #51); however I undesrstood that this solution is effective to avoid the "pop" when other electrical devices switch on-off in the house rather than to the rf interference;
2) to twist the input wires in the chassis (I did not);
3) to use a shielded input wire inside the chassis;
4) still better interconnect cable.
Please, can you suggest me the, probably, more effective solution?
Renato
P.S. forgive my English
even if I still have not a pre I could verify a dramatic improvement in the sound by my new monoblocks build with the Audiosector premium kit. Indeed, when connected to an ipod and to my self build Jordan MLTL speakers I get a far better sound than with my integrated commercial amp, a YBA Integrè (not a cheap amp, rated class A in the recommended component list of the Stereophile magazine).
I built these amps just for fun, I really did not expect a significant improvement in the sound since when I made some test in the past at home with different amps the differences I heard were minor. I had now to happily change the opinion on the influence of the amp.
Increased detail and "air" around the instrument are evident. The music is much more natural, in practice a significant step towards the simulation of the live performance in a concert.
As I wrote here in a previous post, I get a low noise which I can only hear with my ear near the speaker.
It is clearly a radio interference: classical music at very low level out of the speaker (my ipod is switched off, off course).
The intensity of the noise changes by changing the interconnect cable which works like an anthenna; no interconnect implies no noise. I get the lower noise with the more expensive cable I have (a cheap Kimber cable interconnect with twisted solid core wires).
I found in this thread a number of suggestions on how to eliminate or reduce this radio interference.
However since I almost irreversible damaged the pcbs when, after some errors, I desoldered some components on the pcb, I am afraid just to try.
I have now these possible solutions:
1) a small cap at the op-amp input (post #51); however I undesrstood that this solution is effective to avoid the "pop" when other electrical devices switch on-off in the house rather than to the rf interference;
2) to twist the input wires in the chassis (I did not);
3) to use a shielded input wire inside the chassis;
4) still better interconnect cable.
Please, can you suggest me the, probably, more effective solution?
Renato
P.S. forgive my English
Hi,
fit a 47pF direct across the audio input socket.
Twist the signal input pair (flow and return)
Fit RF suppression at the power amp input. 0.5us is about right. 1k0 and 470pF is close enough. You can adjust the 470pF from 330pF to 1000pF.
Fit a Thiele Network to the output. The Pi version is better than the L version. The first leg of the Pi (R+C) should be on the amp PCB and tied into power ground. The L//R can be between the amp PCB and the speaker terminals.
The last leg of the Pi (R+C) can be across the speaker terminals.
Mains borne interference is a different problem with different solutions.
Oh, get rid of (or switch off) all your RF transmitters in or near your house.
fit a 47pF direct across the audio input socket.
Twist the signal input pair (flow and return)
Fit RF suppression at the power amp input. 0.5us is about right. 1k0 and 470pF is close enough. You can adjust the 470pF from 330pF to 1000pF.
Fit a Thiele Network to the output. The Pi version is better than the L version. The first leg of the Pi (R+C) should be on the amp PCB and tied into power ground. The L//R can be between the amp PCB and the speaker terminals.
The last leg of the Pi (R+C) can be across the speaker terminals.
Mains borne interference is a different problem with different solutions.
Oh, get rid of (or switch off) all your RF transmitters in or near your house.
martinbls said:
If the hum changes with different USB cable types, you grounding is most likely fine. Please note that amp has relatively high gain (33dB or so) so any noises from the source are more audible.
thank you for your answers.
I just twisted the input wires and the noise further reduced. When I get the caps I am tryong them too.
Renato
I just twisted the input wires and the noise further reduced. When I get the caps I am tryong them too.
Renato
Notebook to USB-DAC connection
What a difference a cable can make...
In a previous post I reported about my slight low level hum problem, and that it went better with a usb cable with ferrite rings. Now, it goes like this:
Concerning hum and distortions
- with usb cable with NO ferrites low level hum is clearly audible
- with usb cable with ONE small ferrite the hum is much less audible
- with usb cable with TWO large ferrites the hum is nearly gone completely
Soundwise
- with usb cable with NO ferrites the sound is very open, transparent and speedy, with great detail and great micro dynamics
- with usb cable with ONE small ferrite the sound is quite nice, but lacks a bit of openness and transparency
- with usb cable with TWO large ferrites the sound becomes rather dull and a bit slow, less involving with less details all over the frequency range and a more boomy upper bass region
All tested cables are of the same length of 0,5m.
Seems that these ferrite rings are not only dampening the distortions from the computer but also dampening the sound in some way!
Don't know how this works, but I will certanly stay with the no-ferrite-solution.
martin
What a difference a cable can make...
In a previous post I reported about my slight low level hum problem, and that it went better with a usb cable with ferrite rings. Now, it goes like this:
Concerning hum and distortions
- with usb cable with NO ferrites low level hum is clearly audible
- with usb cable with ONE small ferrite the hum is much less audible
- with usb cable with TWO large ferrites the hum is nearly gone completely
Soundwise
- with usb cable with NO ferrites the sound is very open, transparent and speedy, with great detail and great micro dynamics
- with usb cable with ONE small ferrite the sound is quite nice, but lacks a bit of openness and transparency
- with usb cable with TWO large ferrites the sound becomes rather dull and a bit slow, less involving with less details all over the frequency range and a more boomy upper bass region
All tested cables are of the same length of 0,5m.
Seems that these ferrite rings are not only dampening the distortions from the computer but also dampening the sound in some way!
Don't know how this works, but I will certanly stay with the no-ferrite-solution.
martin
looks like you are confirming the advice given by the expert listeners/designers on this Forum.martinbls said:
Begins to show who deserves to be believed.
By the way: Recently I bought a Hagtech HagUSB USB-to-SPDIF converter for another project, and Hagtech also delivers a usb cable WITHOUT ferrites!
And I'm pretty sure that these guys did a lot of tests, too.
And I'm pretty sure that these guys did a lot of tests, too.
dear peter how is the value of the resistor that i need to use to use an led in the Rectifier Board of my LM3875 Kit?
DC offset
Hi guys, hi Peter!
I build the Gainclone/NOS-DAC unit presented on the ChipAmp Photo Gallery, page 44.
Today I measured DC offset at the amps output. I switched on the source (USB DAC), but didn't connect any speakers. With this configuration I measured 10,2mV on one channel and 10,4mV on the other channel (50k volume pot turned to 9 o'clock).
I think these are pretty good values, but the funny thing is, with the multimeter connected correctly to + and - of the speaker wire, I measured -10,2mV and -10,4mV! I don't know much about these things, but isn't this supposed to be +10,2mV here?
Thanks!
martin
Hi guys, hi Peter!
I build the Gainclone/NOS-DAC unit presented on the ChipAmp Photo Gallery, page 44.
Today I measured DC offset at the amps output. I switched on the source (USB DAC), but didn't connect any speakers. With this configuration I measured 10,2mV on one channel and 10,4mV on the other channel (50k volume pot turned to 9 o'clock).
I think these are pretty good values, but the funny thing is, with the multimeter connected correctly to + and - of the speaker wire, I measured -10,2mV and -10,4mV! I don't know much about these things, but isn't this supposed to be +10,2mV here?
Thanks!
martin
This is perfectly normal, chip can show either positive or negative offset, check this link for more info: http://www.diyaudio.com/forums/showthread.php?postid=1524877#post1524877
It will depend on type of LED and desired brigtness; start with 50k and adjust to your preference.
samsagaz said:
It will depend on type of LED and desired brigtness; start with 50k and adjust to your preference.
The values Peter suggests for LED resistors may sound high, but they are quite good. You only want a little bit of current (2-3 mA) on a standard 20mA LED otherwise it'll be way too bright. I used a 50k 25-turn potentiometer off board so I could adjust it to taste.
hello,
I think about building the LM4780 dual mono kit (paralel mode). I have 4ohms loudspakers.
I have a question regarding the transformer voltage. The diagram show on page 1, and recomendation in this topic is 2x18V, which would be 18x1,41=25V DC
this graph below is from the LM4780 datasheet. This suggests that 30V DC or even more is adequate. Is this correct ?
I think about building the LM4780 dual mono kit (paralel mode). I have 4ohms loudspakers.
I have a question regarding the transformer voltage. The diagram show on page 1, and recomendation in this topic is 2x18V, which would be 18x1,41=25V DC
this graph below is from the LM4780 datasheet. This suggests that 30V DC or even more is adequate. Is this correct ?