Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Pass Labs This forum is dedicated to Pass Labs discussion.

First Watt F7 review
First Watt F7 review
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 15th July 2017, 03:42 AM   #1001
2 picoDumbs is offline 2 picoDumbs  Australia
diyAudio Member
 
2 picoDumbs's Avatar
 
Join Date: Sep 2013
Quote:
Originally Posted by oreo382 View Post
With matched 8 ma jfets you need 1 ohm on the k170 and 19 ohms on the J74 to get the same result(H2/H3).So unmatched jfets are probably beneficial.
I am using 11ma k170 and 13ma j74
Yes you precisely understood my reasoning.

I've decided to go lower Idss than your 11mA/13mA pair because I am intending to go with 28V rails (running 23V at the moment) when the new transformers arrive.
I have some heatsinks arriving for the jfets that are yet to be experimeted on, so we will see whether I can go higher.

I'm also using TO264 laterals biased around 1.7A, so my circuit values are bit different than other peoples.
__________________
"If you leave this point unattached to some circuitry, an ideal constant current source will emit a small lightning bolt which will travel until it connects to something." Nelson Pass

Last edited by 2 picoDumbs; 15th July 2017 at 03:52 AM.
  Reply With Quote
Old 15th July 2017, 12:27 PM   #1002
oreo382 is online now oreo382  Canada
diyAudio Member
 
Join Date: Jan 2013
Location: Winnipeg
Quote:
Originally Posted by 2 picoDumbs View Post
Yes you precisely understood my reasoning.

I've decided to go lower Idss than your 11mA/13mA pair because I am intending to go with 28V rails (running 23V at the moment) when the new transformers arrive.
I have some heatsinks arriving for the jfets that are yet to be experimeted on, so we will see whether I can go higher.

I'm also using TO264 laterals biased around 1.7A, so my circuit values are bit different than other peoples.
Cool, an F7 Turbo,that will grab a pair of speakers by the cojones.
  Reply With Quote
Old 15th July 2017, 05:53 PM   #1003
vdi_nenna is online now vdi_nenna  United States
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
First Watt F7 review Send a message via Yahoo to vdi_nenna
Quote:
Originally Posted by oreo382 View Post
Cool, an F7 Turbo,that will grab a pair of speakers by the cojones.
Yeah, but NP tried and went back to lower powered version.
__________________
I build, therefore I am.
  Reply With Quote
Old 15th July 2017, 05:55 PM   #1004
vdi_nenna is online now vdi_nenna  United States
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
First Watt F7 review Send a message via Yahoo to vdi_nenna
Quote:
Originally Posted by oreo382 View Post
Cool, an F7 Turbo,that will grab a pair of speakers by the cojones.
Yeah, but NP tried higher power and went back to lower powered version. Was it due to standard FW case and heatsinks?
__________________
I build, therefore I am.
  Reply With Quote
Old 15th July 2017, 06:04 PM   #1005
2 picoDumbs is offline 2 picoDumbs  Australia
diyAudio Member
 
2 picoDumbs's Avatar
 
Join Date: Sep 2013
Quote:
Originally Posted by vdi_nenna View Post
Yeah, but NP tried and went back to lower powered version.
That wasn't high powered with PCF.
That was high powered with cascodes and negative feedback. ie Conventional high powered amp with laterals, but it is very difficult to get the open loop gain required to get the feedback to generate decent damping factor using laterals in the selected amp topology, hence the reason to use PCF with the laterals.
Read over the F7 manual again, Papa explains the design process.
__________________
"If you leave this point unattached to some circuitry, an ideal constant current source will emit a small lightning bolt which will travel until it connects to something." Nelson Pass

Last edited by 2 picoDumbs; 15th July 2017 at 06:10 PM.
  Reply With Quote
Old 15th July 2017, 06:24 PM   #1006
oreo382 is online now oreo382  Canada
diyAudio Member
 
Join Date: Jan 2013
Location: Winnipeg
I can smell Vince's wood burning up here in Canada
  Reply With Quote
Old 15th July 2017, 06:35 PM   #1007
2 picoDumbs is offline 2 picoDumbs  Australia
diyAudio Member
 
2 picoDumbs's Avatar
 
Join Date: Sep 2013
I know it's a pain in the ars3 chasing that up so, here it is:

"Most of your “better” amplifiers have higher damping factors like 20 or 100, and this amplifier was only about 5 or so, typical of a simple Common-Source topology and low negative feedback.

The damping factor, which is the inverse of the output impedance, determines the flatness of the amplifier response when the load impedance varies and is important to the transient response of reactive loudspeakers, which is just about all of them. You could argue that single-ended tube amplifiers sound good and don't have much damping factor, and you would be right, but I'm not trying to duplicate single-ended tube amplifiers here – the First Watt SIT amplifiers, doing a decent solid-state emulation of Triodes, represent that genre nicely. I'm shooting more for the sound of The Beast With a Thousand JFETs but with obtainable parts.

I tried other Fets, varied the the feedback network values and tweaked the gain symmetry. These efforts delivered a little more warmth and dimensionality, and about a year ago I decided to go ahead and build a small pilot run in anticipation of a product release – after all, it was a perfectly nice amplifier. Still, I was not really satisfied, so I created new printed circuit board artwork, adding cascode operation to the input stage and doubling up the output devices.This version had a little more control, but still fell short.
So...

I went back to the original simple design. On the wall in my lab is a little box with a glass window labeled:
DANGER - POSITIVE FEEDBACK
I broke the glass. Inside was a single resistor."
__________________
"If you leave this point unattached to some circuitry, an ideal constant current source will emit a small lightning bolt which will travel until it connects to something." Nelson Pass
  Reply With Quote
Old 21st July 2017, 07:47 PM   #1008
vdi_nenna is online now vdi_nenna  United States
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
First Watt F7 review Send a message via Yahoo to vdi_nenna
Pico, do you know of a way to match laterals ? I tried the passdiy guide, but didn't work. Got .862 vgs.
Tried something Charles Hansen suggested, but got 14v readout.

Test setup is a 30v 5A lab supply set to 15v. 50 ohm resistor current source for .170A.

Thanks in advance

Vince
__________________
I build, therefore I am.
  Reply With Quote
Old 21st July 2017, 09:29 PM   #1009
2 picoDumbs is offline 2 picoDumbs  Australia
diyAudio Member
 
2 picoDumbs's Avatar
 
Join Date: Sep 2013
Quote:
Originally Posted by vdi_nenna View Post
Pico, do you know of a way to match laterals ? I tried the passdiy guide, but didn't work. Got .862 vgs.
Tried something Charles Hansen suggested, but got 14v readout.

Test setup is a 30v 5A lab supply set to 15v. 50 ohm resistor current source for .170A.

Thanks in advance

Vince
Have a look at Nelson's article on testing mosfets (not matching). Make his little test circuit. Mine is a simplified version.
http://www.firstwatt.com/pdf/art_mos_test.pdf


Are you trying to match Vgs threshold, Vgs at an operating point or Id vs Vgs curves?
Are you trying to match N to N or N to P?
If you're try to match N to N and P to P, I start by sorting them into Vgs threshold values. I do that with a component tester you can get them on ebay very cheap.
Then I start producing Id vs Vgs curves. Refer to Nelson's article. All you really need is a trimpot with wiper fed across a 1 Meg resistor into the gate of the mosfet.
I found on my parts that they match so closely (ie N to N, P to P), that matching for Vgs threshold ended up giving you perfectly matched parts.

You don't need critical matching for this amp though.
__________________
"If you leave this point unattached to some circuitry, an ideal constant current source will emit a small lightning bolt which will travel until it connects to something." Nelson Pass

Last edited by 2 picoDumbs; 21st July 2017 at 09:35 PM.
  Reply With Quote
Old 21st July 2017, 09:56 PM   #1010
vdi_nenna is online now vdi_nenna  United States
diyAudio Member
 
vdi_nenna's Avatar
 
Join Date: Oct 2000
Location: PA, USA
First Watt F7 review Send a message via Yahoo to vdi_nenna
Only trying to match same types n to n; p to p. Just 1 pair. I think trying to an operating point. I can only get to 30v max on the lab supply. Was just hoping to see a match at 15v, maybe at 30v. Repairing amp with 42v, class AB. I'm using the exicon "s" but just want to see how close they are. I have the red for n-ch and green for p -ch.

I thought they were the same articles in different places. Thanks, I'll check it out.
__________________
I build, therefore I am.
  Reply With Quote

Reply


First Watt F7 reviewHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
F7 F8 F9 F10 other planet sound from First Watt Soundhappy Pass Labs 56 14th November 2015 12:30 AM
First Watt F4 ,F5, F6, F7, F8 ? MikeW Pass Labs 10 6th June 2015 07:56 PM
2.3 watt x 4 or 5 watt x2 SET amplifier using DECWARE Zkit1 and Zkit4 schematics Redwolf92 Tubes / Valves 12 29th October 2014 10:19 PM
VFET for SONY TA-F7 2sj18 and 2sk60 ioschi2003 Parts 1 31st March 2009 03:35 PM
Wilson Watt Puppy Clone Design - Design Review Please soundengine355 Multi-Way 8 15th August 2008 02:07 PM


New To Site? Need Help?

All times are GMT. The time now is 11:25 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki