I'm one of your viewers/subscribers Mr Beeny, thank you for your sharing!
Last time I ask the same question but for the 4.2 Ver and ljm_ljm didn't share the updated schematic, but he confirms my purchase was the real thing, not a copy cat. I guess we need to study this new version ( Of a Linn based circuit amp??) again to find out.
I bet he wouldn't share, ever. He always said he "lost the schematics". Believe if you want.
That's why he is here. He doesn't give a stuff.
But, this is what really matters, @michael beeny is among us. Welcome Michael, I am one of your steady Youtube channel members.
Hello Ljm,
Are these boards legit? How many watts is the transformer you recommend for 120+120w at 8Ohm load?
I just found this on AliExpress: ₪107.02 | L12-2 Dual Channel Amplifier Board 150W+150W HiFi Stereo Audio Power DC12V-55V
https://a.aliexpress.com/_oBPl8o7
Are these boards legit? How many watts is the transformer you recommend for 120+120w at 8Ohm load?
I just found this on AliExpress: ₪107.02 | L12-2 Dual Channel Amplifier Board 150W+150W HiFi Stereo Audio Power DC12V-55V
https://a.aliexpress.com/_oBPl8o7
Hi, I just mounted two L12-2 ver.4 boards, (without any modification) checking some data I found the following values V+V- 31VDC, (Trafo 2x22V) Offset on both channels 12mV, Voltage drop TP1 to TPOut 2mV equal on the two channels, other things everything seems regular.
At this point I ask if replacing the R19 1K with a 5K+1K5 trimmer I can solve the problem, I would like to bring the drop to about 6mV (40mA on each 0.15 Resistor).
Greetings to all, thanks in advance.
At this point I ask if replacing the R19 1K with a 5K+1K5 trimmer I can solve the problem, I would like to bring the drop to about 6mV (40mA on each 0.15 Resistor).
Greetings to all, thanks in advance.
Hi, Tolico but regardless of heat dissipation, (currently the final stages are practically frozen and I have not yet tested the amp sonically) then I wonder, why is it normally recommended around 40mA, when only 2mV/0.1=13.3mA can be enough? To increase it, R19 must be smaller than 1K ohm? Anyway, thanks for the answers
replace R19 with 1.5k, and solder 5k trim parallel to it. adjust the trim to maximal resistance before powering the board
Hi sergiog,
Some amplifiers work great at low bias currents, my Symasym runs at 5 mA with no improvement in distortion with increasing bias. Measuring at 10 KHz, 4R. Other designs improve performance as the bias is cranked to a point, then it's just heat. To ensure you get the performance stated, many manufacturers specify higher bias to make sure your get the performance you expect.
Still other designs are not very good, and performance improves as you increase bias. These can run quite hot. Normally, low to no feedback designs are like this, but a poor layout or design may also be the same.
In the audio world, poor designs are generally also heavy and run hot. They say it is a sign of quality (it isn't). It does cost more to do this, but that doesn't translate into better performance for you. Anyway, people came to expect hot, heavy things to be good. High bias also became an indicator of better sound by those who don't understand.
Example: Sadly, although Krell is a good sonic design, they chose to run it very hot to a point where it costs you more to own it in power and service requirements than it is worth. Too bad, it is a good basic design. You can't judge how much bias current an amplifier needs based on other designs.
Some amplifiers work great at low bias currents, my Symasym runs at 5 mA with no improvement in distortion with increasing bias. Measuring at 10 KHz, 4R. Other designs improve performance as the bias is cranked to a point, then it's just heat. To ensure you get the performance stated, many manufacturers specify higher bias to make sure your get the performance you expect.
Still other designs are not very good, and performance improves as you increase bias. These can run quite hot. Normally, low to no feedback designs are like this, but a poor layout or design may also be the same.
In the audio world, poor designs are generally also heavy and run hot. They say it is a sign of quality (it isn't). It does cost more to do this, but that doesn't translate into better performance for you. Anyway, people came to expect hot, heavy things to be good. High bias also became an indicator of better sound by those who don't understand.
Example: Sadly, although Krell is a good sonic design, they chose to run it very hot to a point where it costs you more to own it in power and service requirements than it is worth. Too bad, it is a good basic design. You can't judge how much bias current an amplifier needs based on other designs.
Very correct. One can compare the 6L engine of an old Chevrolet to the 2L of a Mitsubishi Lancer Evolution, and say that Chevrolet is more potent due to its volume, and fuel usage...
There is one single possibility, for judging circuit performance - measurements. There is a need (obligatory) to measure distortions at least, in some cases, there is a need to check that output devices are still in SOA.
Well, the GM 250 CID 6 banger wasn't a great engine. I had one. They were next to impossible to kill, like the Chrysler 225 (which had more power). Fuel economy wasn't a factor in design back then as much. The GM 327 or 350 (or larger) were far better engines, and the 350 got better fuel economy to add insult to injury.
Today's engines are designed to get far more power output, so you can't really compare the two. I had a 327 back in time (1979 or thereabouts). It was "fixed" to deliver 450 real horsepower, 331 CID when done. Throw some technology at a problem and you get better results. Just imagine how much power we could get out of that today!
Absolutely, you must measure performance of an amplifier to know where you are. If your outputs are anywhere close to their SOA, it is a bad design.
Today's engines are designed to get far more power output, so you can't really compare the two. I had a 327 back in time (1979 or thereabouts). It was "fixed" to deliver 450 real horsepower, 331 CID when done. Throw some technology at a problem and you get better results. Just imagine how much power we could get out of that today!
Absolutely, you must measure performance of an amplifier to know where you are. If your outputs are anywhere close to their SOA, it is a bad design.
I performed some measurements of my V4 modules, using 400W 4*37VAC transformer, and 6*22000uF caps. Signal source Yulong DA8 MK II, signal input Cosmos ADC grade 1. Both DAC and ADC connected to notebook, powered from its battery, to eliminate ground loop issues.
While noise looks good, and THD looks really great, IMD figures are not so great, but still in acceptable margins. The output power at 8Ohm, is 115W @ 0.05% THD, if one pair of secondaries of transformer used. Promised 120W possible if all outputs of 400W transformer connected to rectifier. So if one want to unleash full power of that amp, 500-600w single transformer, or 2*250-300W transformers should to be considered. The heatsinks sold on Ali for that amp, good in case you want to test modules, or drive some very sensitive loudspeakers only.
While noise looks good, and THD looks really great, IMD figures are not so great, but still in acceptable margins. The output power at 8Ohm, is 115W @ 0.05% THD, if one pair of secondaries of transformer used. Promised 120W possible if all outputs of 400W transformer connected to rectifier. So if one want to unleash full power of that amp, 500-600w single transformer, or 2*250-300W transformers should to be considered. The heatsinks sold on Ali for that amp, good in case you want to test modules, or drive some very sensitive loudspeakers only.
Normally tests are done into an 8 ohm load at 1 watt. The load is non-inductive. 1 KHz is the normal frequency for THD. IMD tests typically use 19 KHz and 20 KHz at equal amplitude, around the same total power.
It would be interesting to see that performance. I use a 96 KHz cutoff (192 KHz sampling).
It would be interesting to see that performance. I use a 96 KHz cutoff (192 KHz sampling).
load is 8-ohm resistor https://www.aliexpress.com/item/329...o.order_list.order_list_main.5.6d36180222sXYD
19+20k IMD test - a file called IMD CCIF 5W. At audiosciencereview.com IMD tests performed at 5W. But I can try at 1. I don't think it will change numbers dramatically.
19+20k IMD test - a file called IMD CCIF 5W. At audiosciencereview.com IMD tests performed at 5W. But I can try at 1. I don't think it will change numbers dramatically.
Regular behaviour of the snake oil sellers. Sell 500w ultimate fidelity amp, measured at 1W. Then I see reviews, about high-end gear, that claimed to be arc-welding capable, but missing energy at bottom registers, or even unable to carry vocals, for some reason. Normal test - power sweep, from either 0.1W to claimed output power. For 1W, there is no need power amp, some headphone amps, and most IC-based amps, are OK with it, while cost much less and take less space.
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Hi Tolik,
Measuring performance at 1 watt is a reasonable and standard way of doing things. I would worry about someone hiding noise by measuring at higher levels.
The industry standard dummy load is: Dale, 8R0 (4R0 optional additional loads) 250W, non-inductive 1% resistors mounted on suitable heat sinks. I have three sets mounted on proper heat sinks that I had milled flat (the milling cost what the resistor did, more actually). What you are using is passable, but you have to characterize them at higher frequencies since they may be inductive. Being wire wound, they probably are. The element also has to be wound with the correct wire type that doesn't increase resistance with temperature. Measurements are made with a true RMS responding meter good to at least 10X the test frequency. Harmonics being the issue.
There are specific reasons why we do things the way we do. If ASR wants to go out on their own, cool. But they or anyone else doing that is off-standard.
As for the IMD test. This is actually quite a good number. I have no idea why you might be disappointed with it. Correct me if I'm wrong, the measured figure is 0.00033%. Do you know what the accuracy of your equipment is? Just curious. I'm used to seeing dB numbers, not wanting to compute these. If you are using a sound card rather than an audio analyser the numbers may be optimistic, or pessimistic. Depends on the equipment and software.
Think about what you read. Not everything is a conspiracy. In audio sites there is a lot of talk and opinion from people not in the industry who simply don't understand the underlying reasons for why things are done the way they are. Also, a very important thing to remember is that our measurements originated from the telephone industry, and also the RF industry. This is all science based stuff done for good reasons and made repeatable by any lab with suitable equipment. Marketing people like to distort the truth, engineering people do not.
-Chris
Edit: Electrical connections to dummy loads is Kelvin, or four wire mode. You run the amplifier to the load. From the load resistor terminals you run direct to your test equipment.
Actually, no. Not at all. Many amplifiers perform worse at 1 watt, and it is also the average listening level. It is also the standard in the audio industry. Once you run at higher power levels all kinds of things come into the mix as well. Your AC supply for one, along with AC power distortion, and the DUT has to be on it's own circuit, same phase to avoid disturbing your test equipment. In addition, noise is more of an issue at the 1 watt level. So by measuring at 1 watt, we are being demanding on the equipment as well as being close to the average loud listening level. Also, most amplifiers can deliver 1 watt, so you can compare them on a level playing field. Remember too, average to peak levels can be 1 : 15. So a 1 watt average can be 15 watt peaks.
Measuring performance at 1 watt is a reasonable and standard way of doing things. I would worry about someone hiding noise by measuring at higher levels.
The industry standard dummy load is: Dale, 8R0 (4R0 optional additional loads) 250W, non-inductive 1% resistors mounted on suitable heat sinks. I have three sets mounted on proper heat sinks that I had milled flat (the milling cost what the resistor did, more actually). What you are using is passable, but you have to characterize them at higher frequencies since they may be inductive. Being wire wound, they probably are. The element also has to be wound with the correct wire type that doesn't increase resistance with temperature. Measurements are made with a true RMS responding meter good to at least 10X the test frequency. Harmonics being the issue.
There are specific reasons why we do things the way we do. If ASR wants to go out on their own, cool. But they or anyone else doing that is off-standard.
As for the IMD test. This is actually quite a good number. I have no idea why you might be disappointed with it. Correct me if I'm wrong, the measured figure is 0.00033%. Do you know what the accuracy of your equipment is? Just curious. I'm used to seeing dB numbers, not wanting to compute these. If you are using a sound card rather than an audio analyser the numbers may be optimistic, or pessimistic. Depends on the equipment and software.
Think about what you read. Not everything is a conspiracy. In audio sites there is a lot of talk and opinion from people not in the industry who simply don't understand the underlying reasons for why things are done the way they are. Also, a very important thing to remember is that our measurements originated from the telephone industry, and also the RF industry. This is all science based stuff done for good reasons and made repeatable by any lab with suitable equipment. Marketing people like to distort the truth, engineering people do not.
-Chris
Edit: Electrical connections to dummy loads is Kelvin, or four wire mode. You run the amplifier to the load. From the load resistor terminals you run direct to your test equipment.
0.00033%, you added extra zero.
Generally, I test the noise floor with short inputs. Here is the 1w IMD test. As I expected, there were no critical changes in numbers.
What bores me here else, is the 50Hz spike. Even 66000uF per rail isn't enough. On the other hand, caps are Chinese. Good Chinese, but it's still not Epcos or Kemet.
Oh, you was correct with .00033%. I’m sorry. It’s a bit difficult to count zeros after midnight))
Hi Tolik,
I'm having difficulty with your scale. I measure x dB from reference. In my case it would be 1 watt or 1 volt for signal stuff. Consumer gear is 0 dBu at 0.316 mV. I don't bother with +4 dBm, but I could with balanced gear.
What software are you running? I've seen it before but never asked.
About mains noise. It is next to impossible to eliminate mains pick up. I use isolation transformers for audio to look at supply stuff, they do have distortion. Your measuring equipment may introduce a ground current. Then you have your 50 Hz and harmonics show up. 60 Hz here. Additionally, it is extremely difficult to get the grounding perfect in equipment. If your noise is below 100 dB, it isn't normally audible. Not unless the system noise is also so high you can hear that plainly.
So if you are showing your mains frequency, that is normally stray pickup. 2X that may come from a normal full wave power supply. Capacitors will have some ripple, this is unavoidable. Going too large with capacitance is a very bad thing though. It creates higher frequency supply noise which is far more difficult to get rid of than the lower frequency stuff.
I'm having difficulty with your scale. I measure x dB from reference. In my case it would be 1 watt or 1 volt for signal stuff. Consumer gear is 0 dBu at 0.316 mV. I don't bother with +4 dBm, but I could with balanced gear.
What software are you running? I've seen it before but never asked.
About mains noise. It is next to impossible to eliminate mains pick up. I use isolation transformers for audio to look at supply stuff, they do have distortion. Your measuring equipment may introduce a ground current. Then you have your 50 Hz and harmonics show up. 60 Hz here. Additionally, it is extremely difficult to get the grounding perfect in equipment. If your noise is below 100 dB, it isn't normally audible. Not unless the system noise is also so high you can hear that plainly.
So if you are showing your mains frequency, that is normally stray pickup. 2X that may come from a normal full wave power supply. Capacitors will have some ripple, this is unavoidable. Going too large with capacitance is a very bad thing though. It creates higher frequency supply noise which is far more difficult to get rid of than the lower frequency stuff.