Hi Folks,
Back by popular demand... I am starting a GB2 thread for another RTR batch of this amp.
https://www.diyaudio.com/forums/gro...3255-reference-class-amp-gb2.html#post6306343
Back by popular demand... I am starting a GB2 thread for another RTR batch of this amp.
https://www.diyaudio.com/forums/gro...3255-reference-class-amp-gb2.html#post6306343
Just placed my order on the GB list 
Question... I run LX521 speakers. I presently run the woofers in parallel, which presents a 2 ohm impedance. Therefore requiring PBTL. Alternatively I can run them separate as BLT... which option would be best for this amplifier?
Also, the initial design showed a greater number of bulk caps on the PCB, where as now you just seem to have two larger ones... what was the rational?
Thanks
Question... I run LX521 speakers. I presently run the woofers in parallel, which presents a 2 ohm impedance. Therefore requiring PBTL. Alternatively I can run them separate as BLT... which option would be best for this amplifier?
Also, the initial design showed a greater number of bulk caps on the PCB, where as now you just seem to have two larger ones... what was the rational?
Thanks
Hi Stretchneck,
Thanks for your order of 5 amps! As I will be configuring these as stereo BTL, I would say that BTL is best. But it’s also more cost effective as you get double the channels. The LX521 is a fine speaker and I have always wanted to hear one. The image you see with 6 bulk caps shows what the amp looks like when configured for 4 ch in and 4 ch out SE mode. This requires coupling caps for the outputs. BTL mode is balanced drive so doesn’t need the caps and only 2 bulk caps for the input DC voltage supply is needed. What’s interesting is that according to the data sheet, the amp can drive 2ohm loads up to 120w in SE mode. So if you have 4 woofer cones, each could be independently driven (cap coupled though) up to 120w each (1% THD without PFFB). But in BTL, they only show 4ohms as lowest impedance load. For a woofer though, being able to drive them to max headroom of 250w into 4ohms in BTL seems to be the most attractive to me.
Thanks for your order of 5 amps! As I will be configuring these as stereo BTL, I would say that BTL is best.
But it’s also more cost effective as you get double the channels. The LX521 is a fine speaker and I have always wanted to hear one. The image you see with 6 bulk caps shows what the amp looks like when configured for 4 ch in and 4 ch out SE mode. This requires coupling caps for the outputs. BTL mode is balanced drive so doesn’t need the caps and only 2 bulk caps for the input DC voltage supply is needed. What’s interesting is that according to the data sheet, the amp can drive 2ohm loads up to 120w in SE mode. So if you have 4 woofer cones, each could be independently driven (cap coupled though) up to 120w each (1% THD without PFFB). But in BTL, they only show 4ohms as lowest impedance load. For a woofer though, being able to drive them to max headroom of 250w into 4ohms in BTL seems to be the most attractive to me.
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Thanks - well it looks ideal for active speakers... great price, low heat, small form factor, balanced input, no need for input buffers (Unlike ncore / purifi) as my DAC does 5v over XLR. Plus performance of optimised TPA3255 that is reportedly in the same league as ncore, and not too far off the sound of your Alpha Class A amp... good second harmonic profile.
I was going to go class AB for upgrading my LX521 amplification, but the cost of feeding it 6-8 channels of quality class AB is very high. Heatsinks for dealing with high bias cost a lot!
Looking forward to building it!
Any ideas on classic linear power supply that could feed all these modules in one chassis... most only have dual outputs... I’d like to stick with ideal rectifier like SLB. Large traffo plus multiple All Cee’s Class AB PSU‘s perhaps?
I was going to go class AB for upgrading my LX521 amplification, but the cost of feeding it 6-8 channels of quality class AB is very high. Heatsinks for dealing with high bias cost a lot!
Looking forward to building it!
Any ideas on classic linear power supply that could feed all these modules in one chassis... most only have dual outputs... I’d like to stick with ideal rectifier like SLB. Large traffo plus multiple All Cee’s Class AB PSU‘s perhaps?
xrk, I just yesterday ran into this thread. Interesting class D amp. I didn't look through the entire thread (67 pages!) but I saw numerous harmonic distortion plots. Did you by chance to any output impedance vs. frequency plots?
Should be able to get the data with REW or similar. Just do a voltage level sweep with no load and with some low resistance load. Postprocess is (at each frequency):
Rs = Rload* (Vopen/Vloaded - 1) .
I'd be curious how it differs with and without the post-filter feedback
Should be able to get the data with REW or similar. Just do a voltage level sweep with no load and with some low resistance load. Postprocess is (at each frequency):
Rs = Rload* (Vopen/Vloaded - 1) .
I'd be curious how it differs with and without the post-filter feedback
Hi Bwaslo,
No, I never did that - it sounds like a lot of work and I just finished taking some data and put all the gear away before I saw your post. I wonder if Texas Instruments would have a plot of ouput impedance vs frequency. It's probably low in any event as the BTL amp is designed to drive 4 ohm loads. Yo really should not run a sweep without a load on Class D amps (at least at higher powers) as that can fry the chip with the excessive back EMF from the inductor. I have done it once when I forgot to connect the second channel to a dummy load during a power test.
I just took another distortion measurement using my new BTSB Buffer:
Same as with THAT1646 in terms of overall THD, but now with 20dB gain built into the buffer and the profile doesn't have higher freq grass. More info in the BTSB thread here:
BTSB Buffer - SE/Bal to SE/Bal Buffer GB
No, I never did that - it sounds like a lot of work and I just finished taking some data and put all the gear away before I saw your post. I wonder if Texas Instruments would have a plot of ouput impedance vs frequency. It's probably low in any event as the BTL amp is designed to drive 4 ohm loads. Yo really should not run a sweep without a load on Class D amps (at least at higher powers) as that can fry the chip with the excessive back EMF from the inductor. I have done it once when I forgot to connect the second channel to a dummy load during a power test.
I just took another distortion measurement using my new BTSB Buffer:
Same as with THAT1646 in terms of overall THD, but now with 20dB gain built into the buffer and the profile doesn't have higher freq grass. More info in the BTSB thread here:
BTSB Buffer - SE/Bal to SE/Bal Buffer GB
A thought is that with all the emphasis on distortion, such very low levels could easily become irrelevant for an amplifier having much output impedance getting its output affected by the usually rather nonlinear (distortion-wise) load impedance of speakers. Speaker impedances (not being like pure resistance, inductance and capacitance combinations) can generate distortion products in their back emf that can appear on the amp's output if the amp can't hold it stiff enough. I mean not just a variation in speaker frequency response due to impedance (the usually mentioned concern), but nonlinear products.
One of the issues with pre-filter feedback is that the output impedance can climb at high frequencies due to the series inductor. Post filtering can bring the impedance back down, provided there's enough loop gain at high frequencies. Ability to drive low impedance loads doesn't really say a lot about it, as you can drive a 4 ohm load with a transimpedance (sky-high output impedance) amplifier too!
Not really too much work to measure if you're handy manipulating data in spreadsheets. --Pull the measured data in from it's saved files and process with a little math from there, then have the spreadsheet graph it. It can also be calculated using two different resistive loads instead of with one resistive and one open. (Or drive into the measured amp's output from another power amp through a resistor.... another way). Without spreadsheet, though, I'd agree that it's not so easy since typical measurement software doesn't inherently provide that measurement. It seems a measurement that DIY amps tend to gloss over. Added distortion from it might be well below audibility, but then so would be the kinds of nonlinearity normally measured.
One of the issues with pre-filter feedback is that the output impedance can climb at high frequencies due to the series inductor. Post filtering can bring the impedance back down, provided there's enough loop gain at high frequencies. Ability to drive low impedance loads doesn't really say a lot about it, as you can drive a 4 ohm load with a transimpedance (sky-high output impedance) amplifier too!
Not really too much work to measure if you're handy manipulating data in spreadsheets. --Pull the measured data in from it's saved files and process with a little math from there, then have the spreadsheet graph it. It can also be calculated using two different resistive loads instead of with one resistive and one open. (Or drive into the measured amp's output from another power amp through a resistor.... another way). Without spreadsheet, though, I'd agree that it's not so easy since typical measurement software doesn't inherently provide that measurement. It seems a measurement that DIY amps tend to gloss over. Added distortion from it might be well below audibility, but then so would be the kinds of nonlinearity normally measured.
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Pretty much done! Just some minor cleanup / finishing touches to do. Definitely like soldering more than finishing a case, heh.
Love the sound! I think my favorite part is how it does kicks / bass. Very punchy clean and deep on my elac dbr 62s. Since they are 6 ohm I'm running 53.5v. It definitely likes the extra juice. I can hear no hiss from my speakers sitting at 3 feet and have to put my ear right up to the tweeter to find the slightest hiss.
Thanks x, jps64 and jhofland!!
Love the sound! I think my favorite part is how it does kicks / bass. Very punchy clean and deep on my elac dbr 62s. Since they are 6 ohm I'm running 53.5v. It definitely likes the extra juice. I can hear no hiss from my speakers sitting at 3 feet and have to put my ear right up to the tweeter to find the slightest hiss.
Thanks x, jps64 and jhofland!!
Attachments
I'm just going straight from my topping dx3 pro DAC RCA -> RCA to XLR cable. The ones you see are star quad cables which actually eliminate my PC -> DAC -> amp ground loop. My listening space is very small so I don't really need all that much gain. Might upgrade to a XLR DAC in the future... or there's just enough room for the SMT BTSB board at the rear right wall which I still might do
X,
Am I reading your plot right? Is that the spectra of the Class D design (with your BTSB buffer) at 10V RMS into a 10 ohm load? At 10 watts RMS?
Thanks,
Anand.
.....@redjr,
Your sweet build and fine review swayed me to get in on GB2
Thanks Vunce. I'm sure you will enjoy the new build with the TPA3255. Simply a great sounding class D amp!
I see you've sign-up for shaan's new preamp too.
I'm using the meanwell epp-500-54. I have a small / hot listening room I use this in so wasn't too big on power but more efficiency (not that I'm able to push this thing very hard without the BTSB buffer). The total draw of the amp while idle is only 10 watts (7 TPA / 3 SMPS). Even leaving it on all day it's just vaguely warm to the touch.
Hi folks,
I decided make THAT1646 board and BTSB buffer on one board with extenal PSU for them. It is only remix from XRK an JH work's, so don't expect something new. It is only because I prefer it on one PCB. PSU is designed for BTSB buffer and for my DAC (Topping D50s). If you want it, just write me here and I with permission from XRK and JH I can upload gerbers.
I decided make THAT1646 board and BTSB buffer on one board with extenal PSU for them. It is only remix from XRK an JH work's, so don't expect something new. It is only because I prefer it on one PCB. PSU is designed for BTSB buffer and for my DAC (Topping D50s). If you want it, just write me here and I with permission from XRK and JH I can upload gerbers.
Hi Rtep,
What’s the purpose of having the THAT1646 balanced line driver if the BTSB already has a balanced line out via the LME49724 already?
Since this is my GB thread, it wouldn’t make any sense for you to post your Gerbers here. But you are free to start your own thread - just don’t call it the BTSB, and if you do use the BTSB design, please attribute it to Jhofland and myself. Thanks.
What’s the purpose of having the THAT1646 balanced line driver if the BTSB already has a balanced line out via the LME49724 already?
Since this is my GB thread, it wouldn’t make any sense for you to post your Gerbers here. But you are free to start your own thread - just don’t call it the BTSB, and if you do use the BTSB design, please attribute it to Jhofland and myself. Thanks.
I got my power supply from connex electronic, the SMPS600RS last week. It was a long wait but I finally have it now. It was well packed and the built looks professional. And as for the performance I can say that before with the huge laptop brick and the buck converter I could hear the hiss from 3-4 inches from the tweeter, now with the SMPS600RS I literally have to put my ear 1 inch from the tweeter to hear the hiss. I would say a pretty good improvement.
