lgreen the amp looks real nice by the way.
Just noticed that this person got fake Sankens from MCM:
http://www.diyaudio.com/forums/soli...r-high-dc-adcom-gfa-555-a-45.html#post2138651
Anyone know of a reliable source?
Just noticed that this person got fake Sankens from MCM:
http://www.diyaudio.com/forums/soli...r-high-dc-adcom-gfa-555-a-45.html#post2138651
Anyone know of a reliable source?
Great, something new to worry about -fake Sankens!
To provide an update- I am still waiting for someone else to build one of these so we can compare data. I have received a few emails off-line so I know people are working on them. I have also received emails off-line from others concerning interactions with and the personality of the original poster, but I'll not get into that here.
To provide an update- I am still waiting for someone else to build one of these so we can compare data. I have received a few emails off-line so I know people are working on them. I have also received emails off-line from others concerning interactions with and the personality of the original poster, but I'll not get into that here.
Sander, do you have pictures of how it should look, so as other builders can get it right?
GK posted this on another forum and I thought it might be of help:
I noticed that you resurrected the "ExtreemA" thread. I haven't the stamina to read through it all, but has anyone asked Lgreen what kind of preamp/source or signal generator he is using?
The reason I ask is that the amplifier uses shunt feedback. What this means is that if the source is disconnected from the input, the amplifiers input resistors are un-terminated, and the amplifier reverts to a closed loop gain of unity. Unless the amplifier is frequency compensated for unity closed loop gain (very unlikely) that will turn it into an instant oscillator.
Also, a lot of test bench audio signal generators have an output impedance of 600 ohms. The ExtreemA's input/feedback resistors are 1k.
600 ohms in series with that would result in a substantial closed loop gain reduction of 1.6
times. That could very well cause the oscillation that he is seeing.
He also mentioned:
There are a few things with that design that are a bit suspect; The cfp VAS buffers (making these with to-92 BC5** parts in my experience often makes an oscillator), no zobel or output inductor.
I noticed that you resurrected the "ExtreemA" thread. I haven't the stamina to read through it all, but has anyone asked Lgreen what kind of preamp/source or signal generator he is using?
The reason I ask is that the amplifier uses shunt feedback. What this means is that if the source is disconnected from the input, the amplifiers input resistors are un-terminated, and the amplifier reverts to a closed loop gain of unity. Unless the amplifier is frequency compensated for unity closed loop gain (very unlikely) that will turn it into an instant oscillator.
Also, a lot of test bench audio signal generators have an output impedance of 600 ohms. The ExtreemA's input/feedback resistors are 1k.
600 ohms in series with that would result in a substantial closed loop gain reduction of 1.6
times. That could very well cause the oscillation that he is seeing.
He also mentioned:
There are a few things with that design that are a bit suspect; The cfp VAS buffers (making these with to-92 BC5** parts in my experience often makes an oscillator), no zobel or output inductor.
To answer the questions-
The preamp is a Krell KRC-2 and source is Wadia 301 (through preamp or not, results are the same). Also tried with my X-CCS-BOSOZ (same results).
The test bench signal generator is a Tektronix FG-501A.
Is it thought a zobel would correct the issue? What zobel values should be tried? Would you put in two zobels to ground or one zobel from + to - output?
To summarize for everyone so you don't have to reread everthing, under normal circumstances the amp is fine, no oscillation with no input or short circuit or even any input other than one sufficient to cause the signal to approach the rail voltage. So unloaded there are no issues (despite the theory above). There are no issues unless you are very near clipping. As the rail voltages are neared an oscillation slowly forms.
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I wouldn't worry too much if the behavior is only at clipping as one shouldn't operate there most of the time!
As for getting distortion mesurments try using a computer! something like the creative SB24bit can be purchased for 15$ and has crazy low distortion:
Buy Creative Audigy SE | Creative Labs Online Store (UK)
Couple that with software like rightmark and a voltage divider you have a relativly easy to use high resolution mesurment card.
As for getting distortion mesurments try using a computer! something like the creative SB24bit can be purchased for 15$ and has crazy low distortion:
Buy Creative Audigy SE | Creative Labs Online Store (UK)
Couple that with software like rightmark and a voltage divider you have a relativly easy to use high resolution mesurment card.
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You are correct. I am simply amazed at how good the DX sounds, its really incredible. I know I've said this before but its good to restate every couple of years.
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Yes, I know. I mean, an amateur with good ears can make such an amp while experts can only show numbers and when the market do not want to use their products the experts say that the market prefer distortion or don't like hi-fi
This is confusing
because1) Is it true that "hi-fi" can be represented by THD (and a few other numbers) alone? Because nobody like to be judged that way, I mean tube lovers wont be happy to be judged preferring distortion than hi-fi.
2) We listen to music because we enjoy it, so why we have to listen to something perfect that we don't enjoy?? If perfection cannot be achieved, I prefer imperfection that I can still enjoy.
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I made the chasis (most of it anyhow) and made a pcb for the power supply - I've designed a CLC floating power supply
The amplifier pcb was made but I'm not quite happy with it (inadequate heat-sinking for the driver, and I want plenty of driver current). So I have been waiting to re-make the pcb and keep getting distracted!
My friend and I have purchased the PCBs and I have started my build. My PSU is complete and working and I've just started the amplifier PCBs. I'm not worried about the Sanken since I've bought them at Digikey.
I'm about to order a Modushop 5U, 400mm chassis for this amplifier and a SumR 1500VA encapsulated power transformer with four secondaries to supply the two PSUs in dual mono.
I'll post some pictures later
Ciao!
Do
I'm about to order a Modushop 5U, 400mm chassis for this amplifier and a SumR 1500VA encapsulated power transformer with four secondaries to supply the two PSUs in dual mono.
I'll post some pictures later
Ciao!
Do
…great pictures!
I was also in the process of building ExtremA amps, - two of them! However, other projects and issues interfered and forced me to put this project on hold. Now, I am not sure when, if ever, I may go back to it. I still have 2 sets, for 2 stereo amps, of circuit boards. If anyone wants them, I’ll let them go for a reasonable cost.
Vadim
I was also in the process of building ExtremA amps, - two of them! However, other projects and issues interfered and forced me to put this project on hold. Now, I am not sure when, if ever, I may go back to it. I still have 2 sets, for 2 stereo amps, of circuit boards. If anyone wants them, I’ll let them go for a reasonable cost.
Vadim
Hi Vadim,
Please PM me the board rev. # and your asking price in CAN$ per set. I might have some friends interested in building it.
Thanks
Do
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