Hi Ryssen,
tell us how it sounded before and after.
Were the dual transformers used to minimise noise (hum) or to maximise other performance specs?
How did you interconnect the various grounds in this stereo amplifier?
Hmmm, no not hum,hmm..😉
Did not try it the other way around,used my "phase penn" to get the minimum noise (hum) from the core,and connected them in phase,will be connectd phase to phase from the "wall" to.Was heavelly😉 discussed in a swedish hifi forum.If it gets better I dunno..
Maximize other performance specs,again if it gets better I dunno..
They are connected as separate monoblocks in one chassie,only the mains protection earth is connected to the chassie.
Edit:So the only thing they have in common electrical is,the mains switch,fuse and mains cable.
Did not try it the other way around,used my "phase penn" to get the minimum noise (hum) from the core,and connected them in phase,will be connectd phase to phase from the "wall" to.Was heavelly😉 discussed in a swedish hifi forum.If it gets better I dunno..
Maximize other performance specs,again if it gets better I dunno..
They are connected as separate monoblocks in one chassie,only the mains protection earth is connected to the chassie.
Edit:So the only thing they have in common electrical is,the mains switch,fuse and mains cable.
Congrats Ryssen, bodywork certainly prettier than mine, I don't dare sharing a pic on how they are squeezed into the base of my active speakers...
Hmm, strange, so many PCB's sold but so few amps seem to have been completed... (or the builders are quiet about them).
Anyway in my amps I finally changed my low-hFE 2N5551 for >500 hFE BC550c since I have lower rails anyway (ca. 37V). Matching was easy, I got down to the last digit of the DMM matches. The result is a much reduced turnon thump, this had been plaguing my setup quite a bit. The sound seems to have become slightly mellower as well, can't quite explain why. Measured THD into 6R at 16 RMS is lower as well, -80 dB for the dominant 2nd HD on a soundcard with -78 dB THD by data sheet, in other words, below the limit of my measurement capability. 😉
Hmm, strange, so many PCB's sold but so few amps seem to have been completed... (or the builders are quiet about them).
Anyway in my amps I finally changed my low-hFE 2N5551 for >500 hFE BC550c since I have lower rails anyway (ca. 37V). Matching was easy, I got down to the last digit of the DMM matches. The result is a much reduced turnon thump, this had been plaguing my setup quite a bit. The sound seems to have become slightly mellower as well, can't quite explain why. Measured THD into 6R at 16 RMS is lower as well, -80 dB for the dominant 2nd HD on a soundcard with -78 dB THD by data sheet, in other words, below the limit of my measurement capability. 😉
Showing the result of the trafo coverup..
Better the I thought it would be..
Will do some RMAA later,and messaure the output power.(First time I do that.)
I have the bias at 75mv/resistor now,heatsinks are not so hot when in the chassie,could go higher.
Have any one doen any listening tests at differenct bias settings?
Better the I thought it would be..
Will do some RMAA later,and messaure the output power.(First time I do that.)
I have the bias at 75mv/resistor now,heatsinks are not so hot when in the chassie,could go higher.
Have any one doen any listening tests at differenct bias settings?
Hi,
is that 75mV across the output device emitter resistors?
That is no longer optimum ClassAB.
is that 75mV across the output device emitter resistors?
That is no longer optimum ClassAB.
Hi,
for optimum ClassAB output bias, the general opinion from those professional designers who cared to share their expertise is that Vre should lie between the limits of 15mV to 25mV. Possibly falling below the low end for very low values of Re. say 10mV to 15mV when Re~=0r1.
The aggregate voltage across both emitter resistors would normally be between 30mV and 50mV.
If measuring the quiescent current into the whole amplifier, then one must make allowance for the current drawn by the earlier stages and then calculate the output bias current to compare to the preferred value for that amplifier.
for optimum ClassAB output bias, the general opinion from those professional designers who cared to share their expertise is that Vre should lie between the limits of 15mV to 25mV. Possibly falling below the low end for very low values of Re. say 10mV to 15mV when Re~=0r1.
The aggregate voltage across both emitter resistors would normally be between 30mV and 50mV.
If measuring the quiescent current into the whole amplifier, then one must make allowance for the current drawn by the earlier stages and then calculate the output bias current to compare to the preferred value for that amplifier.
Yes, 24mv across the emitter resistors seems to be the value to have gm-doubling and unlinearity canceling each other.
BUT, with modern ring-emitter BJTs this might look different and the value might have become lower.
With the MJL0281, i measured lowest distortions at 20ma, ~4.5mv...
Mike
BUT, with modern ring-emitter BJTs this might look different and the value might have become lower.
With the MJL0281, i measured lowest distortions at 20ma, ~4.5mv...
Mike
Hi Ryssen,
I said"Lower heat is good too."
If you wanted an ultra low noise preamplifier, you what the circuit to run as cool as reasonably possible. Components may have minimum temperatures for operation though. Just in case you want to use liquid nitrogen in your next preamp project. 😀
-Chris
I said"Lower heat is good too."
It applies to all devices in audio. Heat causes an increase in thermal noise and reduces component life - all components.
If you wanted an ultra low noise preamplifier, you what the circuit to run as cool as reasonably possible. Components may have minimum temperatures for operation though. Just in case you want to use liquid nitrogen in your next preamp project. 😀
-Chris
Sommetimes i read about people maximazing the bias/heat/heatsink to get the best performance/sound out of it.Class A of cousre.
Liquid nitrogen is only to cool my computer (processor),wait now I have to poor some more..
Hi Ryssen,
Running the bias hotter may or may not help depending on the amplifier design. I found my bias setting by measuring the distortion at 10 KHz on an 8 ohm load while adjusting the bias current. If the distortion reading doesn't drop past that (I'm using a setup with a residual of 0.0018% THD), there is no reason to increase the bias current. Most of what people hear is in their head I think. I've also done listening tests with good sounding amplifiers and can not detect any difference either.
But, the fact remains. If you want to run high bias, increase the heat sink efficiency to lower the part temperature. Cooler is still better. It's not the heat sink temperature that makes an amp sound better at all.
-Chris
Running the bias hotter may or may not help depending on the amplifier design. I found my bias setting by measuring the distortion at 10 KHz on an 8 ohm load while adjusting the bias current. If the distortion reading doesn't drop past that (I'm using a setup with a residual of 0.0018% THD), there is no reason to increase the bias current. Most of what people hear is in their head I think. I've also done listening tests with good sounding amplifiers and can not detect any difference either.
But, the fact remains. If you want to run high bias, increase the heat sink efficiency to lower the part temperature. Cooler is still better. It's not the heat sink temperature that makes an amp sound better at all.
-Chris
Hi Ryssen,
-Chris
I was lucky. I have an HP 339A "Distortion Measurement Set". The lowest range is 0.01 % FS. I confirmed the residual by looping the output back in. This thing is pretty dead on for voltage level measurements. I am very impressed with it.
-Chris
Hi Ryssen,
One thing I did notice with the 339A is that I got higher distortion readings than my Leader LDM-171. The reason became clear when I started using the low pass filters on the 339A. If you don't have a high enough frequency response in your analyzer system, it will not read harmonics at their proper levels. Hence the lower readings. To give you an idea how bad it was, the 339A readings were very close to the LDM-171 when the 30 KHz low pass filter was engaged.
I do plan to run my sound card off the monitor output on the 339A so I can look at the residual noise and harmonics in greater detail. This will then provide all my input signal conditioning. Neat eh? The sound card would then have a more constant input level and be protected from damage (that's as long as I test the maximum output level of the analyzer to be safe).
-Chris
I did have a system running using a Creative XFI MusicExtreme. I didn't have the same issues earlier cards had. I am going to replace some op amps and try to install a shield to lower noise levels.
One thing I did notice with the 339A is that I got higher distortion readings than my Leader LDM-171. The reason became clear when I started using the low pass filters on the 339A. If you don't have a high enough frequency response in your analyzer system, it will not read harmonics at their proper levels. Hence the lower readings. To give you an idea how bad it was, the 339A readings were very close to the LDM-171 when the 30 KHz low pass filter was engaged.
I do plan to run my sound card off the monitor output on the 339A so I can look at the residual noise and harmonics in greater detail. This will then provide all my input signal conditioning. Neat eh? The sound card would then have a more constant input level and be protected from damage (that's as long as I test the maximum output level of the analyzer to be safe).
-Chris
They're done!
And after an hour they're holding a steady 25mv bias. I'll let them cook for a couple of days, reset the bias, measure DC offset, hook 'em up and provide a report on their sound and the highlights of Dummy's Epic Journey into Diyland.
And after an hour they're holding a steady 25mv bias. I'll let them cook for a couple of days, reset the bias, measure DC offset, hook 'em up and provide a report on their sound and the highlights of Dummy's Epic Journey into Diyland.
Connected my dummyload for some powermessurement..unfortunate
I to late noticed that the negative side of the load where connected together,so 8 and 4 ohms where fine,then 2 ohms the sinewave beacame some strange patterns on my scope.. smoke and a blown fuse,and...an output transistor had blown in one channel.
So if any one has one or more MJW0281A or even one or more MJW0302A for spare for sale,give me a message..
So I tested the channel that was still working.
8 ohms (8,3 ohms) = 75w
4 ohms (4,3 ohms) = 118w
2 ohms (2,3 ohms) = 140w
I thought it would be higher at 2 and 4 ohms but..
in 2 ohms the heat quickly built up in both load (should take at least 200w) and the amp infact I could see the heat rising from the amp(don´t think it was smoke)then shutdown.Hmm,what if I connect a speaker that has dips down to 2 ohms,will it be the same then?
I to late noticed that the negative side of the load where connected together,so 8 and 4 ohms where fine,then 2 ohms the sinewave beacame some strange patterns on my scope..
smoke and a blown fuse,and...an output transistor had blown in one channel. So if any one has one or more MJW0281A or even one or more MJW0302A for spare for sale,give me a message..
So I tested the channel that was still working.
8 ohms (8,3 ohms) = 75w
4 ohms (4,3 ohms) = 118w
2 ohms (2,3 ohms) = 140w
I thought it would be higher at 2 and 4 ohms but..
in 2 ohms the heat quickly built up in both load (should take at least 200w) and the amp infact I could see the heat rising from the amp(don´t think it was smoke)then shutdown.Hmm,what if I connect a speaker that has dips down to 2 ohms,will it be the same then?
Ryssen said:
Unless you are planning to play exactly that frequency where your speakers dip down to 2ohm for a long time, NO!
Mike