Not on this amp. The shield bypassed the chassis and went straight to the amp pcb to some magic ground plane !! It was a magnet for shield induced noise. The owner even wanted to mod my preamp and disconnect pin 1 from the chassis on the balanced output board in order to float the ground on the preamp. Go figure !
cheers
david
blink
blink blink
That is so impressively wrong headed it could be taught in EE courses as "What Not To Do". I can count at least three reasons why this is madness, one of which is deadly.
Wow. Just... wow.
Regarding the ESS reference design balanced outputs, I can see how there could be problems with it and always thought it was probably a bit of a shortcut. Probably better if the filtering on the unbalanced output was also available on the balanced outputs, and if any common mode noise from the dac itself was removed.
It turns out many pro audio products use a two opamp unbalanced to balenced
line driver circuit as shown below. Might not be a bad idea to make the balanced outputs that way from the filtered unbalanced signal. Or, maybe jumpers on the board to select one or the other balanced output option depending on needs.
Just a thought.
Attachments
Last edited:
We have completely re-designed the post DAC processing to take into account the higher current requirements of the 9038PRO DAC. The changes also result in cancellation of the common mode noise from the DAC so it should no longer be an issue on amplifiers with crappy balanced input stages
cheers
david
cheers
david
And a poor attempt at legitimizing this practice with those "Cheater" mains adapters which disconnected the earth from the proceeding appliance that it was connected to
Yes, and providing a chassis earth via the interconnect shielding - somehow, we survived this idiocy - I remember some of the TT motors/electronics having the 240v figure 8 leads, and no earth connection at all
Do you think you will have the development of the dsp pre completed and begin production by the end of the year?
Do you think you will have the development of the dsp pre completed and begin production by the end of the year?
Yes I’m still here. Sorry for the lack of updates recently
Recently have been dealing with what I would classify as the customer from hell who owns a poorly designed power amplifier with an equally poorly implemented balanced input stage basically providing little or no immunity to ground induced noise and common mode noise produced by the DAC used in the Preamp. This dude has caused me no end of grief and has thrown road blocks in front of me so it has become impossible to resolve the problem by dealing directly with him ! [Snip...]
regards
David
Ii feel for you man. Been there and done that to many times to count. And it's always the fault of the person who actually knows what they are doing of course!
Nothing can be made idiot proof. They keep on inventing better idiots!
I have a strange question that probably shows my ignorance but would the overall sound of the preamp change very much if you were to use the AK 4497 dac chips instead of the Sabre 9038s?
Does each different brand of dsp product have a specific 'sound' built in? (that couldn't be compensated for by using internal program freq adjustments, I mean)
Sorry for the 'dumb' question but I've not heard much about this aspect of these dsp units
Does each different brand of dsp product have a specific 'sound' built in? (that couldn't be compensated for by using internal program freq adjustments, I mean)
Sorry for the 'dumb' question but I've not heard much about this aspect of these dsp units
I do not believe so (Tranquility Base may be different). I have heard a number of products using ESS9028 and AK4497/4490 chips, good implementations (eg RME, Benchmark and Gustard) sound basically the same. They were sighted tests so not rigorous, but there were no glaring differences. I suspect that how the IV converter, power supply, clock, and, say how intersample overs are implemented or handled have a much larger contribution to the sound of a complete DAC than the actual DAC chip used.
Last edited:
How is this for a kludge ?
Radio Parts - Electronics & Components - TORTECH ISO300ES-240V 300VA ISOLATION TRANSFORMER MAINS ELECTROSTATIC SCREEN
And the smoking gun in the specs for this device ! Just what a good amplifier designer recommends for his great well designed power amplifiers !
Last edited:
I agree and regarded it suspiciously, ie sub optimal and bad engineering/app note advice to rely on downstream stages to cope with HF CM without consequences.
David, I would treat the time spent resolving this issue as time well spent and actually fortuitous......once a product is out in the wild it can be sunk by one bad review due to a 'non compatible' amplifier.
If the likes of Stereophile et al did some further investigation and determined that excess HF CM is the root cause, then it's curtains for your product's future.....much better to stop the problem before it starts.
What about fully differential opamp ic to provide filtered buffering and balanced output drive ?.
For single ended DAC chip output there are of course several balanced line driver chips available with internal precision resistors and 600ohm capable output stages.
While you are at it I would provision polarity inversion function, preferably via remote control.
Ideally this should be done in DSP prior to DAC/OPS, but at the OPS would be better than none.
Dan.
The new IV stage has already been done and is different to the existing ESS reference design. The noise should not be present in this design. The funny part about it is the noise does not show up in the measurements on my external sound card. It's as clean as you can get. But when you look at the schematic of the front end of this device then you can see how well it is designed for maximum common mode rejection.
As well some DAC designers use audio line transformers to eliminate the common mode noise from the DAC but this is an expensive alternative especially for 8 channels.
Also some pretests on the Ncore hypex modules also produces minimal noise which is only detectable with a tweeter right up to your ear and disappears at 6 inches away
cheers
david
As well some DAC designers use audio line transformers to eliminate the common mode noise from the DAC but this is an expensive alternative especially for 8 channels.
Also some pretests on the Ncore hypex modules also produces minimal noise which is only detectable with a tweeter right up to your ear and disappears at 6 inches away
cheers
david
Yes I’m still here. Sorry for the lack of updates recently
Recently have been dealing with what I would classify as the customer from hell who owns a poorly designed power amplifier with an equally poorly implemented balanced input stage basically providing little or no immunity to ground induced noise and common mode noise produced by the DAC used in the Preamp. This dude has caused me no end of grief and has thrown road blocks in front of me so it has become impossible to resolve the problem by dealing directly with him !
It's a long story but basically my Preamp has been blamed for every noise problem in his system whilst his mates flawed amp design gets let off the hook. I have repeatedly requested that he sends me his amp or similar amp for evaluation so it could help me diagnose the problem and rectify any possible issues in future designs but so far, no amp has materialized. He has scoffed at the AES48 standard for balanced interconnect system saying in his own words that it is "unsafe" and a "dubious standard", so instead I have done the next best thing and through some detective work have found a similar schematic of this amp and entered it into a circuit simulator and have simulated all possible contingencies and have found that this amp has some serious design flaws. To summarize it has more holes in it than Swiss cheese when it comes to suppressing unwanted noise in the system !
Just a warning to young players. Please be careful of amplifiers that have balanced inputs. A lot of them appear to be poor implementations and provide little or no noise immunity. In particular ask the manufacturer whether their balanced inputs or outputs conform to the AES48 standard. One way of testing this is by measuring the resistance between pin 1 on the XLR connector and chassis ground. It should be a near short circuit and no more than half an ohm. If it is 1 ohms or more then this signals a potential problem with this equipment. Move onto the next vendors equipment if this is the case ! I don’t want to have to go through this crap again ☹
I have written up a white paper on the subject which you can download from here.
http://www.analog-precision.com/Downloads/Docs/Not_all_balanced_inputs_are_created_equally.pdf
I wasn’t going to get involved in amplifier design at this stage but because of this less than satisfactory experience along with requests from another customer for a custom designed power amp, the gloves have come off and I have decided to join the fray of amplifier builders ! I am now engaged in producing a custom multi-channel amp design for a stereo 4-way active speakers, which like the Preamp also doubles as a no-compromise high-quality, high-powered stereo power amplifier ! Will have more to say about this later.
regards
David
Hell Customer here
Is all good, the Professional System is back in action again able to provide some bread and butter as well as be used.
Will say emphatically though at no point was entertaining the idea of even removing the lid from my new DSP, let alone modifying any of it's grounding/shielding.
After discovering over 1.6 DC volts on the balanced outputs through, the lid needed to be removed and then the product disassembled to remove jumper pins. Glad this was found, as after inhibiting all the power amplifiers DC Protection systems could have led to the destruction of every speaker coil in the photo, which is 18 drivers in total. True dat.
Anyway, you can't win them all and I'm just glad I found a workable solution and in my position find I am left wanting for my hard earned money, with something I cannot use.
Photos of poor quality system, which has proven to entertain well 500 people venues several times a year. Last thing I need is problems during these events and moving right along.
Regards
Matt
Operations Manager
SOLAR TASMANIA
Attachments
Last edited:
Yes and you conveniently forgot to add the photo with that pesky mains isolation transformer in it, otherwise your mates amplifiers make too much noise without it. Wonder why ? And speaking of lifting lids how long did you have your mates amplifiers in pieces whilst you were building them up from scratch, but it was such an effort for you to remove 8 screws and the lid from my preamp just to remove a few jumpers so you could drive DC coupled power amps of all things. Give me a break will you !
And I am still waiting for you to send me your mates amplifier but don't worry I simulated it anyway and it's got more holes in it than Swiss cheese when it comes to noise immunity. I would have found this out if I had the amp in front of me. You can read about it here if you like
http://www.analog-precision.com/Downloads/Docs/Not_all_balanced_inputs_are_created_equally.pdf
Have a nice day comrade.
And speaking of lifting lids how long did you have your mates amplifiers in pieces whilst you were building them up from scratch, but it was such an effort for you to remove 8 screws and the lid from my preamp just to remove a few jumpers so you could drive DC coupled power amps of all things. Give me a break will you !And I am still waiting for you to send me your mates amplifier but don't worry I simulated it anyway and it's got more holes in it than Swiss cheese when it comes to noise immunity. I would have found this out if I had the amp in front of me. You can read about it here if you like
http://www.analog-precision.com/Downloads/Docs/Not_all_balanced_inputs_are_created_equally.pdf
Have a nice day comrade.
Last edited: