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Old 5th August 2011, 02:15 AM   #1
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Default Can you help me to chose my D amps ?

I want to change my 2X150w passive filtered system to an active one (based on DCX 2496).

My loudspeakers are high efficiency (~100db/w) with a 30cm (12") and a 1" JBL motor behind a wooden horn, 24 db/oct crossover at 1000hz.
Each loudspeaker is 6 ohm near flat impedance curve (motion and self compensated)
Click the image to open in full size.

My actual amplifier is a home made 2X150w current-feedback with power mosfets (sound great) 10-3Mhz at full power with 200V/µs of slew rate and very low thd+imd.

I would like to bring two *cheap* D amps inside the enclosures.
I'm absolutely lost with all those models and the lack of complete documentations, from china or well known D amps spécialists (41hz, ice, etc...)and have no ideas of the sonic qualities of the different chips (tripath, IR, Philips etc.)
.. Not so easy when you cannot listen to them and compare...

I would like to use a symmetrical power supply between +- 60V and +- 70v in order to can use my actual amps for the JBLs if i'm not satisfied with D amp treebles. Would like to get a good stereo board (or two monos each channel) able to deliver something around 200W (rms low thd) each unit .
I do not care about the quality of the filtering cores (hf) on the board: i will change them for better ones (big air ones?) and will tune the rollover frequency.
I like *solid*, dynamic and transparent sound, do not care too much about audiophile subtle details (it is to listen to music, and not to listen to my system ;-) As an old sound engineer i'm used to studio big monitors, see what i mean.

My questions.
1- What would be the best value for money kits and/or chips for bass and treeble amplifiers (may be differents). I would like to achieve very high damping factor for Bass, and to get solid and natural trebles. (no ribbon or domes 'pss pss' like sounds.)
2 -If i use two different board/ amplifiers on the same power supply, any problem to fear if different HF carriers frequencies on the two boards and, if yes, any way to lock them together ?
3- Did-you think i will have a *big* sound difference between those D amplifiers and my actual one for hgh medium / trebles ?
(My actual amp goes to 1Mhz power bandwitch with >200V/*s, but so huge, 500ma of quiet current and so, so hot)
4- Did a bridge mounting on each channel with D amps improove audio results (reducing impair harmonics) like on AB amps ?
Thanks in advance for your help, i'm lost, as i said...
And, please, apologize for my poor English.
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Old 5th August 2011, 03:03 AM   #2
trevmar is offline trevmar  United States
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Remember that an astronomical "damping factor" becomes technically hard to justify when there are no crossover networks connected to the output Speakers themselves present a pretty consistent load, and have an effective series resistance which is quite easy to define.

I have just tested a number of amps for my own new system, and I chose TDA7293 analog amps for my tweeters, these from Ebay:
2Pcs TDA7293 Mini amplifier board | eBay
New TDA7293 Amplifier Amp Board DIY assembled finished | eBay
I tested both of these types to work well, but I did replace the power supply bypass capacitors on both boards with Low ESR 470uF 35V versions. Two surface-mount 0.1 bypasses across the rails of the smaller board may not be necessary, but I put them there anyway You will also want to remove the 0.2 ohm series speaker resistors on the smaller boards. The larger double board can be connected in bridge mode, and gives a lot more power that way.

For woofers I tested a number of switching boards. The T2 from HifimeDIY is well designed and well-built, but stretching to provide the power you need. That supplier does have other amps in their range you might look at, as does Connexelectronics (both post on this forum). But I selected the L20D amps from ljm_ljm with a +/- 70V rail capability, and lovely clean performance, for my woofers. they will be be struggling to drive the full 70V into your 6 ohms, you might look further into the issues there. I bought mine from Ebay:
2pcs L20D IRS2092 200-250W X 2 Class D amplifier sc | eBay
The soldering flux hadn't been removed, but quality of parts was good and performance was excellent at extremely high power levels into both 8 ohm and 4 ohm loads.

These amps all cost next-to-nothing, I suggest you try the most likely candidates for yourself. Your mileage may vary
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Old 5th August 2011, 03:49 AM   #3
trevmar is offline trevmar  United States
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Let me point out something I saw immediately, but you may not notice it. The L20D from the Ebay source I linked you above has 63V bypass capacitors on the supply rails. The board is labelled as handling 60V to 80V. You may want to change those bypass caps if you intend to run the board much above +/-60V, or at temperature

When testing amplifiers the first thing I look at is the bypassing. At least the L20D had ceramic bypasses on the supply rails (100V rating) (so many don't), But the main capacitors measured 0.12 ohms ESR and so were headed to the junkheap as soon as they crossed my doorstep, as I draw the line at about 0.05 ohms right now But you might be more interested in their low voltage rating

Incidentally, my two boards needed about 45 volts to start operating properly, there is an under-voltage cutout on the L20D.

Ljm's description thread is here: MY DESIGN L20D IRS2092+IRFI4020H 200W8R

Last edited by trevmar; 5th August 2011 at 03:50 AM. Reason: typo
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Old 5th August 2011, 03:55 AM   #4
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you can always check hypex modules , they are expensive but they should be very good

click on amplifier modules

https://www.hypexshop.com/
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Old 5th August 2011, 04:45 AM   #5
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Quote:
Originally Posted by trevmar View Post
Remember that an astronomical "damping factor" becomes technically hard to justify
High (around 1000 ) is not what i call astronomical ;-) Just i like to keep my boomers by the guts when they run in bass reflex enclosures.

I will not go for any other analog A or AB amp other than mine. Unless it is current feedback based or, at least, with the same kind of slew-rate. I have never found any unit as transparent than this Mark Alexander design. And all my analog preamps are using OP260 (Analog Design curent feedback too) .

I believe you feel that theTDA7293 you had chosen sound better than your Class D for treble ?
The only class D amplifier i've heard (tripath based) had impressed me very much in medium and treble, ( despite i had a bias against the bias leaks ;-) i felt-it very close to the kind of transparency and separation i love (but it was not in my place, so no way to compare by switching this D amp and mine on the same speakers) . Does your choice means i have to forget to use D amp for trebles ?

Thanks a lot for your " 200-250W X 2 Class D amplifier " link. Exactly what i was looking for (power, supply voltages, performances), and much cheaper that i was hoping.
Don't worry for the current i will ask them. I have hight efficiency speakers, and will not be often at more than 10watts. Just some 15 db transient margin.
Thanks again.
Btw, my compression drivers have a 110db efficiency, so i can use a 25 watts units for them, but that means an other power supply ;-(

Did-you have any idea of the switching frequency of your D kit and if the feed-back loop returns before or after the filtering coil or the both ?
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Old 5th August 2011, 05:08 AM   #6
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Quote:
Originally Posted by trevmar View Post
L but you may not notice it.
I use to bypass any capacitors by series of 1/100 values from the original value to 10pf, electrolitic for high values, mylar or polyporo for nf, ceramics for pf and change electrolytics for good ones with enough capacity and tension margin i can use them for years. That the first thing i always look at and a kind of religion.

lduarte1973: Thanks for your link. Don't you think the difference between those two boards, regarding sound quality, can be mainly the quality of the output coil ?
Indeed, this hypex board look like very better designed, with good Rf protections. But 4 time the price means that difference in listening pleasure ? Regarding the measurements, and if i had understood well class D i'm not so sure, under 1Khz ?
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Old 5th August 2011, 12:30 PM   #7
AP2 is offline AP2  Italy
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Hi,
To Esperado:
I've seen your room and of course your speaker (very nice) so I decided to propose a new model of amplifier AudioPower. This is the DPA-400, developed specifically for the needs of the beloved. (not suitable for PA amps)
It certainly is not easy to explain the actual performance (now all class D amp. .. They say very good, very nice so I would not have the right words to describe the high resolution on high-frequency sound, or speed of response with to an innovative on-board psu.
I do not sell this amp, I can give you information that you can request samples by email at info@audiopower.it form requestor. After the compilation is possible to have the trial DPA-400 for 30 days (without pay).
I enclose a photo of the version / F,. this is also full of PCB input with XLR + RCA inputs. you just need the mounting with 6 screws (included).
Some features are on the site.
(photo refers to a prototype).
You can see a FFT on DPA-600 ->"more" button
this is a important result of innovation.

Best regards
Roberto P.
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File Type: jpg DPA-400-F.jpg (84.0 KB, 393 views)
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Old 6th August 2011, 12:41 AM   #8
trevmar is offline trevmar  United States
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Quote:
Originally Posted by Esperado View Post
Thanks a lot for your " 200-250W X 2 Class D amplifier " link. Exactly what i was looking for (power, supply voltages, performances), and much cheaper that i was hoping.
I am very happy with mine, ljm_ljm has done a good job. My dummy loads give up before I get to 250W, so I haven't tested it much above 160W sinewave into 8 ohms, which is what each of my SEAS woofers is rated at (max long-term power)(which means 1min on, 2min off, duty cycle). The amplifier heatsink doesn't even get warm. The average switching frequency is around 500KHz. The feedback is before the filter, as is most common these days, as it is very tough to deal with the phase shift in the output filter. However, it is a simple resistor pathway, so you could always add in some AC component from the speaker output terminals, if you want to play around a bit. I suggest it is not worthwhile though - analyze the electrical equivalent of the woofer, and you are faced with 3-6 ohms of series resistance which just won't go away. No point in getting too high a damping factor IMO. With passive crossovers, the damping factor is important, but not when using bi-amped drivers (IMO).

This L20D uses the IRS2092 Delta-sigma controller chip, which, IMO, sounds the best of all the digital conversion chips. But I am biased, I did many designs in the 1970s and 1980s based on delta-sigma (synthesizers, audio-delay,etc) and know how good the technology can sound. The L20D don't disappoint, and , as you say, the price point can't be beat.

I selected the TDA7293 for the tweeters as cleanliness is paramount above 1KHz, and I just don't need as much raw power as I do for the 30Hz pipe organ notes. This is a good, rugged chip, which just works well...

Enjoy!

Last edited by trevmar; 6th August 2011 at 01:02 AM.
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Old 6th August 2011, 01:21 AM   #9
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Thank-you AP2. if i understand well, you are part of the Audiopower company ?
I would like to read more datas (any white paper ?) about your board. (and an idea of it price ?)

Let-me introduce myself. I had began my professional life in the research and development departure of the first French Hifi manufacturer company, and was the chief of the electro acoustic department. After some years, i began a 25 years career as a freelance sound engineer for music, big live concerts and tour, TV and movie and was the technical manager of a numeric post-prod studios company.
I has been involved at a time in the design of the well known Akaďe DD1500, a numeric 16 track recorder and virtual editing system and owned my own studio.

Well, now, i'm a young retired, and want to return back to my passion, with this project : explore the world of digital amplification and publish on a future dedicated web site the results of my researchs, listening comparisons, technicals innovations and DIY, and create a community, as i had done for photography http://www.street-photo.fr

First, i have to explore more in order to learn deeply this domain, mostly to correlate measurements and listening experience, work on career's filtering and their auditive impact and experiment some ideas i have on listening improvements and active filtering.
That's why i want to begin with low price stuffs.

I have some work on my system to get a good base, before to accept your nice proposal and be able to listen, compare and measure numeric amps in a useful way for both of us.

Did your proposal will be available in one or two months ?

If you are not part of Audio-power company, can you tell your listening feelings of this board, comparing to some others D class amps ?

Thank in advance.
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Old 6th August 2011, 02:20 AM   #10
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[QUOTE=trevmar;2662230]No point in getting too high a damping factor IMO.[/QUOTE
First, thanks for your precisions, trevmar. I have the same experience (and feelings) about the delta sigma, my favorite on my fists discreet DAC designs before oversampling DAC ICs appears. After that, i was working on the analog stages and the clocks instead.

Will try to play with frequency on D amps too, triyng to increase to their limit to see how it turns for sound an heat and work with an idea i have about adding some linear parallel active filtering of the career.
Will try too with inceasing passive filtering poles and see how it sounds.
I remember, on analog amps, how adding a low level high frequency signal can change the audio feelings, some times in a positive way, and want to explore more that point.

About damping factor, just short-circuit your boomer and hear how it change when you hit the cone, specially around the resonance of a good tuned (equal impedance peaks) bass reflex enclosure.
And try parallel motion impedance compensation (calculated with hp in free air) . Amazing improvement IMHO. And if you measure how it change the curves around 200hz, transients and damping, it is obvious.
Agree with you for treble compression motors, air coupling is better and motion charge is enough. But, here too, it helps and you can measure the waterfall changes.
But some people like to let their speakers play their own music, and,with full range speakers, it can indeed sound better ;-)
Anyway, it is so easy to add a low value serial resistance in the output to reduce damping factor (and dynamic ;-).
( Oh, man, i feel so stupid with my poor English ;-(
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