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Old 13th December 2011, 02:49 AM   #31
EUVL is offline EUVL  Europe
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> I was wondering if the circuit is flawed to start with. any idea what it might be?

No. I have done this many times.
10 FETs in parallel are more quiet than a single, if anything.
120R gate stopper is OK. Bias is a bit lean for Grado (low impedance?).

I bet your noise is from the power supply.
Try powering it with 2x 9V battery first.

It won't last too long, but enough to tell you whether the noise is from the supply or not.


Patrick
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Old 13th December 2011, 02:37 PM   #32
Fenris is online now Fenris  United States
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In the original circuit, I use a pair of DC-DC converters to give me +/- 9v. They operate in the megahertz range and with a good low ESR solid electro and tant cap for bypass, I have no audible noise. When I use a similar circuit (using MOSFETs instead of JFETS, but otherwise the same) and a linear power supply, I always have noise.
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Old 13th December 2011, 04:28 PM   #33
routhun is offline routhun  United States
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Hello Fenris,

What is the output FET of the schematic given in post #23? It can't be 2sk170 I guess?

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Routhu
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Old 13th December 2011, 04:44 PM   #34
Fenris is online now Fenris  United States
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I'm using an IRF520 IIRC, but just about anything should work in the role of a basic source follower.
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Old 13th December 2011, 07:07 PM   #35
pidesd is offline pidesd  Canada
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concerning the noise i have, i havent tries the battery yet, but when i connect the amp to a portable media player the noise seems to disappear. but when i connect i connect it to my dac which is not very well ''laid out''(made to experiement), i get a low level distortion as i mentioned, a bit like when you cant tune a radio. so the power supply issue seems very plausible. thanks all i ll try to give a confirmation later that this is indeed the issue.
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Old 13th December 2011, 07:23 PM   #36
pidesd is offline pidesd  Canada
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BTW, i damaged one of my grado drivers by accident and i m only listening with one ear, but this buffer really rocks from what i can hear one eared . it might even be better than my DAO. One thing for sure, it shows details in the recording to say the least. at least with my grados which are 32r(as far as i know all grados are 32r...). just makes me wonder what the amp would sound like with 2sk372,369,bf862, etc.

also, i took a batch of 50 k170bl and even though the pairs are not all below 1% idss i get total around 1 mV or even less dc offset with thermal coupling. so probably thermal coupling and close idss match is not really necessary with more than a few fets in parallel...

Last edited by pidesd; 13th December 2011 at 07:37 PM.
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Old 13th December 2011, 08:03 PM   #37
Fenris is online now Fenris  United States
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I don't think there will be any discernable difference between different JFET types, the source follower is pretty transparent and not too dependant on part types. The front end is in the "sweet spot" for the average 2sk170 (but could vary based on your particular one of course). Good to hear you got it working and are happy with the sound.
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Old 13th December 2011, 08:31 PM   #38
pidesd is offline pidesd  Canada
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from what i know, jfets in the source follower with higher transconductance will lower the output impedance. maybe EUVL can comment on the sound? i believe he played a lot with source followers.

by the way, just in case, i m not using a gain stage, just the follower and also i m not expert enough to comment on the importance of the parts in the front end so ill give you the benefit of the doubt .
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Old 25th December 2011, 03:10 PM   #39
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Default Sennheiser HD600

This is the correct schematic to drive Sennheiser HD600 300 ohms?

LED's value?
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File Type: gif Nelson Pass headphone amp Sennhs HD600.GIF (19.2 KB, 1001 views)
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Old 21st April 2012, 10:36 AM   #40
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