Hi and thanks for the valuable confirmation
The Dynaudios had some "variovent" on the back
The woofers were just as balky to move as to stop.
But the overall sound was quite clean indeed. Very natural.
And with classical music quite ok. But with ritmic music ... no way.
I am sure that the XL version you mention is much better.
Regards, gino
I've been too busy wasting time on this forum....also waiting for parts to build a balanced output preamp, and then I'll get back into the speakers and post some pics.
Sorry about that, Rome was not built in one day
.Dan.
Hi and thanks and sorry if this is OT.
But is it not always the case ?
I think that in commercial amps the savings start from maybe the most important element, the mains transformer, to go on with maybe the 2nd most important element, the PS caps.
I guess that a lot of the success of for instance Naim amps is due to their high quality power supplies.
Actually they provide the customers with an unpgrade path based on more powerful power supplies.
So i agree completely on the importance of the power supply.
Thanks again, gino
I've been too busy wasting time on this forum....also waiting for parts to build a balanced output preamp, and then I'll get back into the speakers and post some pics.
Sorry about that, Rome was not built in one day
Dan
Hi Dan and thanks a lot for your very interesting work.
From another discussion it seems that distortion measurements can be quite telling about a speaker sound quality.
Instead to check the effect of damping sheets on cabinet walls a member suggests the use of a stethoscope and a sweep generator.
He says that resonances of the panels are very easily heard in this way.
I am buying one.
Thanks again. Gino
I am not convinced that the transformer itself is particularly critical, that said there are transformer parameters that are reasonably important.
The things that are important are the power supplies and earthing arrangements.
In the bracket of power supplies is capacitance, and very importantly snubbing.
Lack of transformer winding snubbing allows rectifier caused HF ringing to pass straight through to the amplifier stage because of typical capacitor internal series inductance...ie the caps do not suppress HF junk coming from the rectifier/secondary.
Most amplifiers have degraded PSRR at higher frequencies, so expect PSU/Rect noise to cause MD in the amplifier.
Quieting/damping the supplies will quieten the amplifier.
Dan.
Hi Dan ! very clever system indeed. I did not think about it.
But if you look at the price ... i bought this one here
Professional Stethoscope Dual Head for Nurse or Doctor Stethoscope Color Black | eBay
i am curious to listen to a sweep through all the cabinet walls ... very curious
I am sure i will also listen the background noise ... even on equipment chassis.
I have also a weird idea ... maybe even wood for cabinets building could be selected by knocking on it and listen for resonance ... i know it is crazy but the more "dead" the material the better to build cabinet panels i guess .
Here i have a different opinion. For me the transformer is fundamental.
Both in terms of isolation from mains noise and more important in current delivery. Regulation is a key parameter for this.
Also the size is important. All the best amps have huge transformer.
I am listening now to what i think is a good little amp ... a cambridge audio 340 --- it is let down but its power supply mostly but it sound quite good.
Sorry i do not understand what you mean for transformer winding snubbing . Do you have a picture maybe ?
Thanks again, gino
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Snubbing. Good luck to those who try. Soft recovery diodes seem easier. Many just put 1 to 10 nF accross the AC in to the rectifier and hope for the best. The old 4 caps is now seen as the wrong choice. A snubber might be a resistor and cap in series accross the diode and then a cap directly accross the diode. The last capacitor mops up the problems snubber No 1 caused ( fat chance ). The inductance of the winding comes into it more than people would like to think. The big probnlem is to convert a very high frequency spike into a number of low amplitude lower frequency ripples. Puttting an AM radio near the rectifier will not help you. It can cure a problem you didn't have and now you do. As far as I can see the soft recovery diode has internal capacitance that being inside the device does a good job and has been determind by the maker. The spike is still high in frequency which helps. Try no snubber plus standard diodes and work from there. The law regarding compatability seems a bit odd. I never in my life had a diode cause something else to have a problem. A Sony AM tuner needed 4 inches between it and an amplifer I seem to remember. Schotkey have given me trouble. Whilst they work more like a MOS FET they still seem to store energy. They are N/metal rather than NP I think . I have never tried a group of MOS FET's as a rectifier. It could be the answer. They need a control circuit. In theory almost zero loss. If so almost zero noise ? As it is 50/60 Hz the dead band is not like class D.
Hi Gino.
It's called the 'knuckle test'.....like knocking on a door...ignore the initial sharp attack sound and listen for lower frequency hang ons.
With adequate/high PS capacitance, the transformer supplies the average power, and because typical music runs relatively low average power, transformer size does not need to be extreme, and smaller transformer VA can actually be a benefit. (typical consumer amps run smallish transformers which sag under amp max power delivery, reducing OPS dissipation and heatsink requirements. These typical amps/receivers/shelf systems have plenty of dynamic power, and limit during sustained overdrive conditions, saving cheap speakers from overdrive).
You may see the spec 'Dynamic Headroom'....this is really just a measure of how stiff the power supplies are.
An amp quoting eg 1dB of DH means that it has a huge, non sagging PS.
For sparse, dynamic type music, a soggy/saggy supply is entirely adequate.
For sustained organ/heavy metal/drum & bass/house music programme at high levels a stiff PS is required.
An amp with a stiff supply will play loud with whatever music you throw at it, with a saggy supply the max clean level is determined by the 'density' of the music programme.
For most domestic users the saggy version is adequate.
A larger transformer also means other parasitic behaviours, like higher energy resonances at diode turn off....this in turn requires more PS capacitance to absorb this energy.
The first solution is snubbing, and may yield better sound than going to oversize transformer/oversize caps, by eliminating PS resonance problems before they start.
http://www.diyaudio.com/forums/power-supplies/243100-simple-no-math-transformer-snubber-using-quasimodo-test-jig.html
Read the whole thread for full understanding.
Dan.
So the snubbing we look to is the transformer itself? Surely the very low inpedance of the mains is a snubber for that? In love the idea but to say the least I am dubious? Reminds me of the SME pick up arm damper. Great idea but ?
I guess what I refered to will do the same although cart before the horse working ? Damping the diodes or the transformer is nodal at the AC input to the rectifier. There is a very large word of warning. This snubber will work on the diodes also. You may well make new problems.
I guess what I refered to will do the same although cart before the horse working ? Damping the diodes or the transformer is nodal at the AC input to the rectifier. There is a very large word of warning. This snubber will work on the diodes also. You may well make new problems.
Good morning Dan !
as soon as i will receive this stethoscope i will "auscultate" the cabinets ... i am very curious about noise even without signal.
I really think that without a music speakers should be perfectly silent.
Thanks a lot this is very helpful. I would like to add some PS capacitance but it seems that when they design the boards they do everything to make this mod impossible
I am sure 2 better caps would be beneficial always
Some manufacturers actually propose a capacitance upgrade for their amps.
Perfectly clear ... no more question on transformer. Maybe on caps ?
Thanks again Dan and i will do it for sure.
But actually i would think another solution --- to take out the transformer to leave space for much much bigger caps.
I see someone doing that.
I would go with AC to the amp chassis, even if someone has advised me to go with DC to the chassis.
Kindest regards, gino
Gino, are you suggesting removing the power transformer from the chassis and mounting it externally to allow more room for caps?
If so don't do it. This will raise the inductive reactance scuing the results plus allowing rf noise to freely enter the circuit. What you want more than anything is a stiff shielded supply that has ultra low esr. Simply adding more caps will not help here there is a limit of what is effective and what is just throwing money at the problem thinking it will work better. It won't. This is so critical that the lead lengths, spacing, placement, is as critical as ESR and ripple current ratings. Have a read on this subject in the power supply forum.
If so don't do it. This will raise the inductive reactance scuing the results plus allowing rf noise to freely enter the circuit. What you want more than anything is a stiff shielded supply that has ultra low esr. Simply adding more caps will not help here there is a limit of what is effective and what is just throwing money at the problem thinking it will work better. It won't. This is so critical that the lead lengths, spacing, placement, is as critical as ESR and ripple current ratings. Have a read on this subject in the power supply forum.
Hi and yes ! exactly that !
Thanks a lot indeed. You have saved me to do something stupid.
Anyway some amps, like the Mission Cyrus Two and i think also some from Naim, provide the option of a super power supply connected with an umbilical to the amp.
Mission Cyrus 2,PSX Power Supply,and T Tuner Photo #286189 - Canuck Audio Mart
Thanks again, gino
I mostly agree with that. Did you ever find shielded cable made for a dull lifeless sound ? I have heard truly clean PSU's that don't sound that way.
Hi Dan !
i am using one of these ... Cambridge Audio 340a
honestly i am liking the sound quite a lot. Really.
I would like only a little more "rounded" sound. When pushed it becomes harsh and hard on voices particularly.
But i am surprised by the sound quality. It is one of the cheapest around here.
Regards, gino
P.S. now that i look better i think that two 15-20mF caps can be fitted in the PS at the place of the existing one ?
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I would be tempted to fit a larger size same voltage toroidal transformer, there seems to be space. I can not see how that can fail. The capacitors later. If you do the other thing sometimes it can sound worse.
Try 0.6 mm solid core speaker wires. It sometimes does what the system needs. One could say more the sound valve devotees like. Some will hate it. Very cheap to find out. Transformer wire is the best value.
Try 0.6 mm solid core speaker wires. It sometimes does what the system needs. One could say more the sound valve devotees like. Some will hate it. Very cheap to find out. Transformer wire is the best value.
Cambridge-Azur-340A-int-sm.pdf
Ok, looking at the pcb layout it's a mess, not dissing your choice in hifi.
What you have is an amp that should be ok generally, but has limited output, and expect it to get messy at higher levels.
Pretty hard to decide where to start...seriously.
Good amp performance depends on good earthing techniques...this pcb has hopelessly long earth traces with multiple components connected to the same earth line.
This all adds up to IMD, and is a cause of the harshness that you are experiencing.
Do you have a soldering iron...if so, there are plenty of kits available that will give you much better sound.
Dan.
That would probably be coming from SPiKe protection being
enabled. It severely distorts the signal and that can't be pleasing
at all.
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