Yes, very.
If you are interested in playing with the 7077, I have a few along with a pair of sockets. I don't know if the tubes are good, but if you have the time (I don't), it may be worth a shot.
John
If you are interested in playing with the 7077, I have a few along with a pair of sockets. I don't know if the tubes are good, but if you have the time (I don't), it may be worth a shot.
John
Scott - thanks for posting this comparison. I am rather baffled by how good the BF862 is noise wise at low freq as it is marketed as an RF JFET.
At what drain current did you run them?
Sigurd
At what drain current did you run them?
Sigurd
scott wurcer said:
1mA with a 4.7k drain resistor. I noticed last night that some of the low frequency noise was probably my pot. I stupidly set the drain current with a 10k pot (bypassed) in the source and with these FET's I'm at the end of the range and there's probably some excess noise that the bypassing doesn't catch at low enough frequencies. I want to set up the QuanTech circuit where you set current and voltage independently.
The BF862 is not a very good device for audio, because of excessive 1/f noise. It is NOT designed as an audio device, but is specified as an RF device for AM car radios.
Since the 2SK170 is still available, you will find it a better solution in almost every case, for a number of reasons, including noise and voltage breakdown.
Since the 2SK170 is still available, you will find it a better solution in almost every case, for a number of reasons, including noise and voltage breakdown.
I am going from measurements at the moment. You might check the spec sheet as well. I already know how to make A rated audio designs, evaluated by others, as well as myself.
This device is not appropriate without a cascode to buffer the voltage.
This device is not appropriate without a cascode to buffer the voltage.
A sample comparison between the BF862 and the 2SK170. Gate leakage with voltage.
Both devices 1ma operating point.
BF862, 1na 8V, 10na 11V
2SK170 1na 16V, 10na 21V
Of course, the low frequency noise is specified in the 170.
Both devices 1ma operating point.
BF862, 1na 8V, 10na 11V
2SK170 1na 16V, 10na 21V
Of course, the low frequency noise is specified in the 170.
8V who would do that? These are both short channel devices with a STRONG knee at just under 5V they both measure 1pA at well above Vp and well below the knee. Let's see, in a microphone 1nA and 5G Ohms thats 5V offset, hmmmm.
Scott, I just spoke to Ed Oxner on this. He looked at the spec sheet himself. PLEASE read the spec sheet and compare it to other well known audio quality fets. You are painting yourself into a corner.
For the record, you cannot run this device over 10V and hope for low noise or low gate leakage. Since I usually run +/- 15V to 30V, this device is almost useless. Two separate measurements of the BF862 states that it has uncontrolled 1/f noise makes it almost useless for any low voltage designs as well, where audio noise is important.
For the record, you cannot run this device over 10V and hope for low noise or low gate leakage. Since I usually run +/- 15V to 30V, this device is almost useless. Two separate measurements of the BF862 states that it has uncontrolled 1/f noise makes it almost useless for any low voltage designs as well, where audio noise is important.
john curl said:
Sorry I'll stop. I was helping some folks who don't have much money. The tip came from Jim Williams and the staff at LT. I have built circuits with them and they all worked fine and were not noisey. Maybe you might have to sort out a couple of bad players, so what. I never run FET's past the impact ionization knee, I cascode them with a more appropriate device.
http://en.wikipedia.org/wiki/Impact_ionization
![url]](/community/proxy.php?image=http%3A%2F%2F%5Burl%5Dhttp%3A%2F%2Fusers.ece.gatech.edu%2Fmleach%2Fheadamp%2Fcbamp2.gif%5B%2Furl%5D&hash=aa743edb6f3e12a19e58718048731ce8)
Scott, I hope that you are correct about the audio noise. I am independently getting it checked in Silicon Valley at this moment. However, you should have mentioned the need for cascoding, since many people here have little or no idea of what that involves, the added cost and complexity, and the need for it, IN THIS CASE.
john curl said:
Ok, I found a pile of BF862s and sent them to the boys in the lab over at Jensen along with your concerns about noise and other issues.
They made some modifications and sent me back a pile of these.
An externally hosted image should be here but it was not working when we last tested it.
😀
se
Hi PMA, good to see you here. I need a reasonable voice around here. These devices 'might' be OK for audio, but so far no real evidence, either from the spec sheet or really verified independent audio noise measurements have been brought forth. I hope to get independent verification through Jim Williams, or by way of Quantech measurements in future, if possible.
hitsware said:
Yup. That it is.
Here's Leach's page on moving coil head amps that feature this as well as some "tarted up" versions.
Moving Coil Cartridge Head Amps
se
- Status
- Not open for further replies.