Some interesting snippets taken from the Goldmund technical notes
The question has been asked multiple times in this thread about transistor matching, and it seem the design has engineered this factor out.
No wonder your previous breadboard clones were not blowing up Nagys 😉
The question has been asked multiple times in this thread about transistor matching, and it seem the design has engineered this factor out.
No wonder your previous breadboard clones were not blowing up Nagys 😉
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"All in all, it probably has more than 1000 parts, all crammed into a chassis of only 1.75" in height."😕😕
All this is more reason to build the modules exactly as Goldmund did. It is perhaps possible they knew what they were doing.
Certainly Nagys experience of this amp besting all the other high end brands attest to that.
Certainly Nagys experience of this amp besting all the other high end brands attest to that.
Nagys: If we use a single transformer with dual windings (1 for 80V+, 1 for 80V-) we still don't have a separate winding for the 65VAC required for the VA section. What are your recommendations for that transformer?
The transformer should have dual secondary windings of 60VAC in parallel, or 120VAC in series.
You can certainly use just a single transformer for each channel. If you take the voltages after the bridge, you'll have +/- 85VDC (formula: 60X1.414=84.84) to feed the outputs, which is perfect. Then just feed the input stages with 60VAC that you can take before the bridge.
You can certainly use just a single transformer for each channel. If you take the voltages after the bridge, you'll have +/- 85VDC (formula: 60X1.414=84.84) to feed the outputs, which is perfect. Then just feed the input stages with 60VAC that you can take before the bridge.
Can you confirm what Goldmund use in the 9.2?
You will be doing everyone a disservice if they put in a smaller transformer than what Goldmund use.
The transformer is one of the key ingredients.
Thanks Mosfets
Specs state the following
Max power is 400W rms into 3Ohm load.
Max Voltage swing 60V peak
Max Current swing 40A peak
Maximum power consumption 1000W
60V x 40A = 2400W peak or 1200W average.
This suggests they use a transformer rated at somewhere between 1000VA and 2000VA.
Most likely 1000VA based on the last spec. However I wouldn't be surprised if they used a 1500Va (1.5kVA) transformer per channel (or two 750VA transformers per channel).
Specs state the following
Max power is 400W rms into 3Ohm load.
Max Voltage swing 60V peak
Max Current swing 40A peak
Maximum power consumption 1000W
60V x 40A = 2400W peak or 1200W average.
This suggests they use a transformer rated at somewhere between 1000VA and 2000VA.
Most likely 1000VA based on the last spec. However I wouldn't be surprised if they used a 1500Va (1.5kVA) transformer per channel (or two 750VA transformers per channel).
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Thanks for the link. An interesting observation is that the Japanese guy who made the original chip amp also used low value reservoir caps and the sound was claimed to be stunning. I never heard one but so the reports say.
But if one look at it closely small capacitors discharge quickly and the amp gain compresses at high volume levels (peaks) in that it sounds louder because the average power increases which could be perceived by a listener as being more dynamic. Could this be partly responsible for their characteristic sound apart from all the mechanical stuff. It is more or less in contrast what most DIYers do, bigger reservoir caps are better, punchier fuller bass etc.
I have been a member here for a few years and notice that we strive to be technically correct maybe musically we miss the boat or maybe it is a case of different strokes for different folks.
This is only an observation from what I read in the pamphlet.
But if one look at it closely small capacitors discharge quickly and the amp gain compresses at high volume levels (peaks) in that it sounds louder because the average power increases which could be perceived by a listener as being more dynamic. Could this be partly responsible for their characteristic sound apart from all the mechanical stuff. It is more or less in contrast what most DIYers do, bigger reservoir caps are better, punchier fuller bass etc.
I have been a member here for a few years and notice that we strive to be technically correct maybe musically we miss the boat or maybe it is a case of different strokes for different folks.
This is only an observation from what I read in the pamphlet.
I cannot confirm how powerful Goldmund's transformers are because I don't own the Mimesis 9.2, nor do I have access to one. And even if I did, the transformers are completely potted so I wouldn't be able to look.
Any suggestion that Goldmund Mimesis 9.2 uses, or that this amp needs transformers in the 1000+VA range, is completely ridiculous.
For Mimesis 6, Goldmund used approximately 300VA (5"X2") transformers per channel. That amp has a max power rating of 200 watts at 3 ohms. Perfectly falls in line with this simple basic formula: 200 X 1.414 = 283 watts.
Here's a picture that shows the tops of the transformers:
For Mimesis 3, Goldmund used two transformers per channel. They are very small (3.5"X1.5"), therefore I'm guessing they are 150VA each. Mimesis 3 also has a max power rating of 200 watts at 3 ohms. Which again corresponds with this basic simple formula: (150 + 150) X 1.414 = 283 watts.
I conclude with certainty, that Goldmund Mimesis 9.2 uses two 300VA transformers per channel, totaling 600VA. Mimesis 9.2 has a max power rating of 400 watts at 3 ohms. 400 X 1.414 = 566 watts.
I agree that using good transformers is very important. So may I suggest the Hammond and the Plitron.
Any suggestion that Goldmund Mimesis 9.2 uses, or that this amp needs transformers in the 1000+VA range, is completely ridiculous.
For Mimesis 6, Goldmund used approximately 300VA (5"X2") transformers per channel. That amp has a max power rating of 200 watts at 3 ohms. Perfectly falls in line with this simple basic formula: 200 X 1.414 = 283 watts.
Here's a picture that shows the tops of the transformers:
An externally hosted image should be here but it was not working when we last tested it.
For Mimesis 3, Goldmund used two transformers per channel. They are very small (3.5"X1.5"), therefore I'm guessing they are 150VA each. Mimesis 3 also has a max power rating of 200 watts at 3 ohms. Which again corresponds with this basic simple formula: (150 + 150) X 1.414 = 283 watts.
I conclude with certainty, that Goldmund Mimesis 9.2 uses two 300VA transformers per channel, totaling 600VA. Mimesis 9.2 has a max power rating of 400 watts at 3 ohms. 400 X 1.414 = 566 watts.
I agree that using good transformers is very important. So may I suggest the Hammond and the Plitron.
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Nico Ras - The capacitor size does not make a Goldmund amplifier sound incredible. Simply because Mimesis 9.2 uses 4700uF, Mimesis 6 uses 6800uF, and Mimesis 3 uses 15000uF. They all sound fantastic, but they all have different capacity power supply capacitors. I think the excellent quality of sound is due to the circuit and the construction.
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Nagys,
It still baffles me.......where does 1.414 come from, which text book is this from? I must have missed something in engineering school is it related to two divided by the square root of two?
Usually when desingning you calculate for worst case load and add a margin for losses and account temperature rise and regulation.
Judging from what you are telling us, the Goldmund power supply is extremely "spongy" and I assume would produce a fair amount of lower harmonic distortion under high drive conditions maybe this is the magic Goldmund sound.😕
My tests found the amp lacking into low impedance loads granted I have a preference for electostats and ribbons so it is nowhere near a Pass Labs or Krell in that regard. I have to say Goldmund is very vague in stating their specs. I would like to know for instance power into eight ohms and the power into four ohms or two ohms (if possible) to gauge the current dilivery of the amp.
Jam
It still baffles me.......where does 1.414 come from, which text book is this from? I must have missed something in engineering school is it related to two divided by the square root of two?
Usually when desingning you calculate for worst case load and add a margin for losses and account temperature rise and regulation.
Judging from what you are telling us, the Goldmund power supply is extremely "spongy" and I assume would produce a fair amount of lower harmonic distortion under high drive conditions maybe this is the magic Goldmund sound.😕
My tests found the amp lacking into low impedance loads granted I have a preference for electostats and ribbons so it is nowhere near a Pass Labs or Krell in that regard. I have to say Goldmund is very vague in stating their specs. I would like to know for instance power into eight ohms and the power into four ohms or two ohms (if possible) to gauge the current dilivery of the amp.
Jam
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I think there is no contrast or disagreement there. Bigger reservoir caps do bring punchier fuller bass etc. But to consider "better", you have to wait. We know that bigger caps have limitation. At least the high impedance issue.
One reason why I don't like bigger amp is because then I have to use bigger cap while power supply along with the caps is very critical. It is very expensive to have a high quality caps in thousands of uF. If you use "cheap" cap, then you will have the problem.
It is not uncommon that people parallel caps with smaller one, and use the highest quality for the smaller ones (look at those yellow caps in Mimesis85?). And many others parallel small caps to achieve bigger capacitance. I think 20000uF generic caps just don't work well with high frequency? You (and of course salas) know better what might be the issue.
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Sounds realistic.
Lateral MOSFETs sound better with lower value source resistors, and best without them.
But using no source resistors carries the risk of blowing the outputs, one way to mitigate that problem is a powersupply that runs out of oompf for suspended periods in a low impedance load.
Long enough for the protection circuit, cq thermal switch on the heatsink, to cut in.
Basic rule for that overhere in the '80s-'90s was sizing the transformer smaller or at max equal to total Pd of the output devices.
Also in-line with the mains fuse value, 5A slow at 220Vac is 1100VA, fat chance the total transformer VA was way more than half that value.
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IMHO, this project would require a MAX 500VA XFMR per channel(and that is too much) but who cares anyway. Strap a couple 2000VA's down and get yer freak on. To each is own.
300VA to 400VA per channel would deliver the goods.
Now if somebody would proto these Goldmund board(s) and run it through some paces...then you may end up with another "Krell KSA50 Clone" type thread...but who ever did finish THOSE K50 builds anyway?
He he...wink wink ...
Carry on as ye were...
300VA to 400VA per channel would deliver the goods.
Now if somebody would proto these Goldmund board(s) and run it through some paces...then you may end up with another "Krell KSA50 Clone" type thread...but who ever did finish THOSE K50 builds anyway?
He he...wink wink ...
Carry on as ye were...