I only use speaker protect circuits with solid state relays now.
A little more expensive but what price do you put on a decent set of speakers ?
There is no consensus on such design parameter. When I built and measured the P101 amp using Rod instructions I got a much slower slew rate than specified and Rod confirmed to me that he may have made a mistake on this parameter. By the way any design can be challenged. If you look in your thread I am not the only one saying that you should use a higher bias current....
It is just a recommendation to help so feel free to not change your bias...
Fab
It is just a recommendation to help so feel free to not change your bias...
Fab
SSR is a great solution to disconnecting speakers during a fault because of the high interrupting current of the mosfets. I use CSD18537NKCS. There is no spark gap, at least there isn't supposed to be
. I also like rail switches in addition to the relays too, with delay on, fast off for DC det, OC det, and other fault conditions like excessive heat build up! This has saved me a lot of damage when I go to experimenting with different operating parameters.
Lat FETs are not immune from the decrease in Gm as Id decreases below a few hundred mA. Although the transfer sure looks alot more geared towards analog; inverse sq. The switching vertical FETs also have a significant decrease in Gm as Id falls below a few hundred mA, despite the extraordinary possible conductance. Without enough bias the missing Gm at current crossover requires a lot more dV/dt at the gate to mitigate this and provide a "linear Gm" within the global loop.
This must come from the previous stage which may be limited in SR to compensate. A bias greater than 100mA helps to fill in this missing gap in Gm, per say.
One exception to the rule is HEC drive but I have never seen it applied to Lat FETs. I am using an enhanced version of that arrangement with planer stripe FETs, they are super rugged
, bias about 25mA. The slope of the error signal is very steep at current crossover but there is no crossover distortion at the output or indication of missing Gm at the input.
This must come from the previous stage which may be limited in SR to compensate. A bias greater than 100mA helps to fill in this missing gap in Gm, per say.
One exception to the rule is HEC drive but I have never seen it applied to Lat FETs. I am using an enhanced version of that arrangement with planer stripe FETs, they are super rugged
, bias about 25mA. The slope of the error signal is very steep at current crossover but there is no crossover distortion at the output or indication of missing Gm at the input.
Thanks for sharing your experience. I too want to hard-wire some Exicons to the Elliott P101 boards, but using a Hafler 200 chassis and power supply. The board will be mounted very close to the heat sink so my wires will be even shorter than the ones you show in your photo. Based on your experience I have more confidence there won't be issues.
The rail voltage in the Hafler is +/- 60, but there are 2 pairs per side, so I will be using 4x each of the Exicon ECF10P20 and ECF10N20 (TO-3)
Ron
Good that you are satisfied with the sound. I am not surprised that you can not hear difference between 20ma and 50ma bias current because both values are too low...
Normally most lateral mosfet amps have about 130ma bias current per pair (where the temperature coefficient is nullified). For double die, that would be about 260ma. Personally I use even more bias current to have higher power in class A... but for that you need sufficient power heatsinks....
Also 560 ohms gate resistors with double die is an unusual high value.
Fab
Hi FAB ,
a question about the parallel of the lateral mosfets.
I have paralleled three pairs of mosfets (old hitachi sk135 and sj50). 60 volts stabilized for the voltage amplifier and 68 unstabilized for the lateral mosfets. I left the gate resistors at r 560.
The amp runs smoothly on DC the bias is about 200 MA but the sound is very low in volume I have to turn the preamp up to maximum volume to hear equally low.
I think maybe the MJ350 driver is weak to drive six mosfets. or that the gate resistors need to be lowered to R 220 or so and I would try raising the input amp voltage from 60v to 65v.
Any ideas? Has anyone played the ESP101 with six mosfets yet?
Thanks for your interest and answers.
Giubos.
Normally most lateral mosfet amps have about 130ma bias current per pair (where the temperature coefficient is nullified). For double die, that would be about 260ma. Personally I use even more bias current to have higher power in class A... but for that you need sufficient power heatsinks....
Also 560 ohms gate resistors with double die is an unusual high value.
Fab
Hi FAB ,
a question about the parallel of the lateral mosfets.
I have paralleled three pairs of mosfets (old hitachi sk135 and sj50). 60 volts stabilized for the voltage amplifier and 68 unstabilized for the lateral mosfets. I left the gate resistors at r 560.
The amp runs smoothly on DC the bias is about 200 MA but the sound is very low in volume I have to turn the preamp up to maximum volume to hear equally low.
I think maybe the MJ350 driver is weak to drive six mosfets. or that the gate resistors need to be lowered to R 220 or so and I would try raising the input amp voltage from 60v to 65v.
Any ideas? Has anyone played the ESP101 with six mosfets yet?
Thanks for your interest and answers.
Giubos.
The Tandberg design is far more sophisticated than the P101. It is not a million miles away from the design of the Michell Alecto, which is a great sounding amp.
I built a P101 quite a few years ago. I swapped it in out out of the same chassis and PS as my Leach amp several times. (Sorry to say that) the Leach provided markedly superior sound.
In the past, speakers tended to be higher impedance. 8 to 16 ohms was usual. Nowadays they are somewhere between burger-all and 8 ohms. Single or double die depends on your speaker impedance, efficiency and SPLs required.
By the way, I would have thought you needed some ventilation holes/slots for airflow past the heatsinks in your amp. As soon as you put the lid on, the heatsinks will only be acting only as heat spreaders and you will have to rely on convection cooling from the external surfaces of the chassis.
Hi giubos
Not sure I understand what you mean by “very low in volume” (I suppose you mean low amplitude of voltage) so the 6 mosfet (3 pairs) drive instead of 2 should not create that specific issue. Gate resistor value will not have an effect on the overal gain of the amp at audio frequency. It must be something else.
Outside of your issue the MJ350 drive crurent?
Fab
Not sure I understand what you mean by “very low in volume” (I suppose you mean low amplitude of voltage) so the 6 mosfet (3 pairs) drive instead of 2 should not create that specific issue. Gate resistor value will not have an effect on the overal gain of the amp at audio frequency. It must be something else.
Outside of your issue the MJ350 drive crurent?
Fab
gate resistance?
Hi FAB,
thanks for the suggestion,
I solved the low volume problem, you were right it was a stupid pcd error.
But I take this opportunity to reveal some doubts, the gate resistor, what influence does it have on the sound?
Maybe it affects the bandwidth, the slew rate?
Maybe to increase the mosfets from two to three pairs it is better to decrease the gate resistances to increase the gate current, even if in reality the mosfets are driven more by voltage than by current. What do you think? In the meantime I can assure you that I like the sound of the amp with three pairs of mosfets much more detailed, with less colouration and the heat is better distributed than with two pairs of mosfets.
Thanks for the support
GIUBOS
Hi FAB,
thanks for the suggestion,
I solved the low volume problem, you were right it was a stupid pcd error.
But I take this opportunity to reveal some doubts, the gate resistor, what influence does it have on the sound?
Maybe it affects the bandwidth, the slew rate?
Maybe to increase the mosfets from two to three pairs it is better to decrease the gate resistances to increase the gate current, even if in reality the mosfets are driven more by voltage than by current. What do you think? In the meantime I can assure you that I like the sound of the amp with three pairs of mosfets much more detailed, with less colouration and the heat is better distributed than with two pairs of mosfets.
Thanks for the support
GIUBOS