I have found these Series 10 resistors from Ohmite which I am thinking of for the O/P Mosfet source degeneration
https://www.farnell.com/datasheets/1851651.pdf
They claim to be non-inductive below 0.25R and TC seems to be less than 50ppm
I will be using 0.22R so the 5 watt version should be OK.
Can anyone suggest any alternatives that have given good results ?
Thanks
https://www.farnell.com/datasheets/1851651.pdf
They claim to be non-inductive below 0.25R and TC seems to be less than 50ppm
I will be using 0.22R so the 5 watt version should be OK.
Can anyone suggest any alternatives that have given good results ?
Thanks
Yes - I beginning to realise how useful these thermistors are when used like this.
Hello mikelm,
I have also used the Fukushima MPC74, MPC71 in a few of my builds as source-resistors with very good results. I have also used Ohmite Audio Gold - resistors (non magnetic). Also very good.
Some members here in the forum prefer MOX-resistors as source- or drain-resistors. To get a high enough W-rating often paralleled. Although up to 3W easy to get. Wire wound - resistors and their inductance...
Cheers
Dirk
I have also used the Fukushima MPC74, MPC71 in a few of my builds as source-resistors with very good results. I have also used Ohmite Audio Gold - resistors (non magnetic). Also very good.
Some members here in the forum prefer MOX-resistors as source- or drain-resistors. To get a high enough W-rating often paralleled. Although up to 3W easy to get. Wire wound - resistors and their inductance...
Cheers
Dirk
Thanks ACnotDC and Dirk,
I guess the holy grail here would be a metal strip or metal plate resistor with their simple signal path & low inductance combined with a TC below 50ppm.
The only resistors that have all these qualities that I know of that are actually stocked by any suppliers are SM devices and highest obtainable power seems to be 3W. If I were to go for multiples of something this would be top of my list but the problem is that I have not found one that quotes overload figures like the WW ones often do.
The Ohmite Gold look very nice but the non-inductive ones don't seem to be stocked by anyone, whereas the Ohmite series 10 are both low TC & non-inductive below 0.25 - these seem very interesting.
For starters I will try the 5W Ohmite series 10s & Fukushima MPS 71s and compare them to some 3W SM ones I have already.
I guess the holy grail here would be a metal strip or metal plate resistor with their simple signal path & low inductance combined with a TC below 50ppm.
The only resistors that have all these qualities that I know of that are actually stocked by any suppliers are SM devices and highest obtainable power seems to be 3W. If I were to go for multiples of something this would be top of my list but the problem is that I have not found one that quotes overload figures like the WW ones often do.
The Ohmite Gold look very nice but the non-inductive ones don't seem to be stocked by anyone, whereas the Ohmite series 10 are both low TC & non-inductive below 0.25 - these seem very interesting.
For starters I will try the 5W Ohmite series 10s & Fukushima MPS 71s and compare them to some 3W SM ones I have already.
At present I'm being entertained by Susumu RG2012s . . . . but not as source resistors
Sure, perhaps active devices make a bigger difference than resistors. JLH said a similar thing about amplifier topologies but still chose components carefully once he realised that they also make a difference . . . so why not make an informed choice ? 25 years ago I was happily using industry standard metal oxides which at the time I thought were greatHello out there,
I think, this is what Mr. Pass tries to teach us 'greedy boyz' for many years now - put your focus more on the 'active devices = transistors'?!
Cheers
Dirk
For the last few years I have preferred resistors made from metal films, strips, plates or wires. Susumu anneal the film on their RG2012s after it is spluttered onto the substrate and I have not found a better sounding SM thin film.After my posting here about resistor choice I found these:
https://fscdn.rohm.com/en/products/databook/datasheet/passive/resistor/chip_resistor/gmr-e.pdf
Look pretty ideal to me and they're also cheap !
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Actually I am using Vishay‘s VHP-3s that I bought in a surplus store. I paid 39 cents each and bought all they had 0.25 and 0.50 ohm 1%.
They were 50 bucks each custom parts new and they pop like fuses pretty easily. I cry when this happen. I got some of the Caddocks on eBay and think they would work very well as they appear to have a very tempco. I have used many Caddocks in feedback networks and they sound great. The TF020Rs are about s good as it gets. I bought my first Vishay bulk metal foils in the late 80s. The Vishay rep for Dallas wanted to know what I was using them for since has customers were NASA, Rockwell, and military weapons contractors. He got pissed off when I said they were going in my stereo. You are talking to one the early parts snobs in audio.
They were 50 bucks each custom parts new and they pop like fuses pretty easily. I cry when this happen. I got some of the Caddocks on eBay and think they would work very well as they appear to have a very tempco. I have used many Caddocks in feedback networks and they sound great. The TF020Rs are about s good as it gets. I bought my first Vishay bulk metal foils in the late 80s. The Vishay rep for Dallas wanted to know what I was using them for since has customers were NASA, Rockwell, and military weapons contractors. He got pissed off when I said they were going in my stereo. You are talking to one the early parts snobs in audio.
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Probably less the bond wire in the Mosfets and meaning less in low MHz amplifier circuit. PS I have done signal integrity design in digital telecom besides analog design. I worked with guys that worried about inductance of a via on a 15 mil pcb layer. I love the smell of RF in the morning but admit being more of a educated RF spectator Than real RF designers
https://www.americanbookwarehouse.com/2383692/?msclkid=b5afcba95f4d11ecadad7004ade43c9a
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There are actually some very good wirewounds and that is the type used in most audio amp. I and many other parts swappers have found tempco and voltage coefficient the two most important specs. I like to shoot for 50 ppm and less. Often over rating power size need helps reduce temperature effects. Substrate and lead termination matter as well I love the old Corning glass resistor. There plenty of very good resistors and I like to find Caddocks, Holcomb, PRP, and odd resistors networks like what I used in high reliability telecom. I got some Bournes 50 ohm analog line card surplus about the area of a postage stamp on both sides of a 20 mil substrate that sound very nice. I have played with resistors and caps for at least 30 years.I bought some surplus Tesla metal films from a guy in Bulgaria that I like and parallel for higher wattage in passive speaker crossovers. I am not not a parts snob but a parts enthusiast. I am going through my vintage interstage transformer phase now ( I blame you Nelson Pass) and am shocked the a 40 year old UTC transformer kind sound very nice. I bought a Siemens 600 ohm line level transform that I am waiting for from Germany. A lot of these vintage recordings we love went through lots transformers.
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O/P Stage AC Current Sharing & 2nd Harmonic Nulling
Have been looking at this in simulation and have a few questions.
I have the notion that in an ideal circuit balanced current sharing and 2nd harmonic nulling occur in the same place - is this generally agreed ?
However, I have noticed in spice that they do not in fact occur in the same place. A simple adjustment of the gain resistor trimmer can give one or the other but not both.
Is it possible to make adjustments to remedy this ? and if so is there an established procedure to do this ?
Many thanks
Have been looking at this in simulation and have a few questions.
I have the notion that in an ideal circuit balanced current sharing and 2nd harmonic nulling occur in the same place - is this generally agreed ?
However, I have noticed in spice that they do not in fact occur in the same place. A simple adjustment of the gain resistor trimmer can give one or the other but not both.
Is it possible to make adjustments to remedy this ? and if so is there an established procedure to do this ?
Many thanks
The F5 is actually two single-ended amplifiers connected in parallel. But the
series connected output devices, whether single or multiple, necessarily carry
the same total DC bias current for each of the two parallel amplifiers. That's why
there are two adjustments, one for the bias current, and one for the DC output offset.
Since the output devices are of different polarities, there cannot be a perfect cancellation
of the overall distortion, or even just the second harmonic, at any current level.
An amplifier like the F6 can use identical output devices because of the transformer drive
with a separate secondary for each device. With selected outputs of the same polarity,
the better symmetry of the F6 circuit can have lower inherent distortion, especially even harmonic.
series connected output devices, whether single or multiple, necessarily carry
the same total DC bias current for each of the two parallel amplifiers. That's why
there are two adjustments, one for the bias current, and one for the DC output offset.
Since the output devices are of different polarities, there cannot be a perfect cancellation
of the overall distortion, or even just the second harmonic, at any current level.
An amplifier like the F6 can use identical output devices because of the transformer drive
with a separate secondary for each device. With selected outputs of the same polarity,
the better symmetry of the F6 circuit can have lower inherent distortion, especially even harmonic.
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