Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 23rd July 2012, 12:06 AM   #221
flg is offline flg  United States
diyAudio Member
 
flg's Avatar
 
Join Date: Jul 2005
Location: North East
Hi Mike, did you see my post #213. Is that correct? For instance; Higher gate Voltage (more -) on the R085 will cause a shallower slope ie; higher Resistance. Lower Vgate, (closer to 0V) will be lots of current change real fast, lower R.
__________________
"It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.
  Reply With Quote
Old 23rd July 2012, 12:22 AM   #222
www.audiohobby.com
diyAudio Member
 
Join Date: May 2001
Blog Entries: 4
I'm late to the party, so forgive me if I'm missing the context, but it sounds like you've got the right idea. Incidentally, I ran some curves for the R085 last summer over a more expanded range. I'll see if I can find them.
__________________
I'm not hanging around the forum these days but if you need help: Visit My Website | My YouTube Channel | Email Me | Wheaton's Law |
  Reply With Quote
Old 23rd July 2012, 12:29 AM   #223
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
Sweet. I am behind. Base don what you suggested, the Rds on my oroginal choice is about 10R. Does that sound about right.
__________________
...Shape the sound , Man!

Last edited by buzzforb; 23rd July 2012 at 12:31 AM.
  Reply With Quote
Old 23rd July 2012, 12:42 AM   #224
flg is offline flg  United States
diyAudio Member
 
flg's Avatar
 
Join Date: Jul 2005
Location: North East
RdsON is typically, the minmum resistance with a FET, with the gate slammed to 10V and the Vds will go almost to 0.0V. It is a parameter used for switching power supply design where you might have an inductor the FET and say 12V. You turn on the FET really hard and fast and current builds up in the inductor. Then you shut it off and the inductor still pulls current etc. etc. It might be analogous to Vcesat in a Bipolar.
It is not generally a parametor we care about because we operate in the resistive region between off and on.
Then there is Drain Resistance, that could actually be associated with RdsON but??? Then there is your load resistor on the drain???
__________________
"It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.

Last edited by flg; 23rd July 2012 at 01:00 AM.
  Reply With Quote
Old 23rd July 2012, 01:27 AM   #225
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
Sorry, incorrect thought made too big a hurry, as usual. 10r drain resistance.
__________________
...Shape the sound , Man!

Last edited by buzzforb; 23rd July 2012 at 01:32 AM.
  Reply With Quote
Old 23rd July 2012, 04:06 AM   #226
diyAudio Member
 
Loudthud's Avatar
 
Join Date: Nov 2007
Location: Near Dallas Texas USA
Quote:
Originally Posted by flg View Post
I am confused by these statements
If it is "an active component with an AC negative resistance" how can it's contibution be higher impeadance? It's negative, simply speaking, thats lower.
The negative impedance of the mu follower is in parallel with the 8 ohm load. To see it's effect on gain, remember to gain is roughly RL/(1/Gm).

The parallel combination of 8 ohms in parallel with -16 ohms is 16 ohms. Since RL is higher, the gain is higher. Using the conductace formula for parallel resistors, 1/8 + 1/(-16) = 1/16.

I built one channel using IRF640s, a 2N3904 and MPF102 (Idss=11mA). The only deviation from the ACA1 schematic was a 0.1 ohm resistor in series with the source of Q1. To measure open loop gain I just look at the gate of Q4 with a scope. Gain was 20 (26dB) with the 0.1 in place and 23.1 (27dB) with the 0.1 bypassed.

Looking at the IRF data sheet, the Gm is very non-linear at 1 amp. Isn't there a better part? This amp biases Q1 pretty hot, but that makes it more linear.
  Reply With Quote
Old 23rd July 2012, 04:00 PM   #227
diyAudio Member
 
Join Date: Jun 2002
Location: Italy
Default proto

A pic of the proto ACA I did build here .

They are in 2 sided board style , p2p , with IRF044 , works great .

s
Attached Images
File Type: jpg ACA.jpg (117.3 KB, 928 views)
  Reply With Quote
Old 25th July 2012, 12:52 AM   #228
diyAudio Member
 
Loudthud's Avatar
 
Join Date: Nov 2007
Location: Near Dallas Texas USA
Default Open loop gain vs distortion tradeoff

I looked at an IRF640 on the curve tracer using offset to get smaller steps around the (about) 1 Amp operating point. The second plot is the same part with 0.47 Ohms inserted in the source lead. The gain goes down but the linearity increases. I have no control over the camera shutter speed so some of the traces are fading out.

I replaced the MPF102 I was using with a PN4393. It gave slightly lower distortion numbers. Then I installed a 0.47 Ohm resistor between the Q1 source and ground and ran distortion plots with and without the source resistor. The distortion is higher above 4 Watts because of clipping, but at lower levels the distortion is lower inspite of the fact that the open loop gain is lower. Open loop gain measured 29.3 dB with the 0.47 shorted and 23.2 dB with the 0.47 enabled. DC operating point was adjusted to 10V at idle for each test.

Square wave response of the amp is very well behaved.
Attached Images
File Type: jpg IRF640_0R47_Rs.JPG (87.4 KB, 860 views)
File Type: gif ACA1_4.GIF (23.9 KB, 824 views)
File Type: jpg MVC-140F.JPG (77.6 KB, 834 views)
  Reply With Quote
Old 25th July 2012, 03:56 AM   #229
Variac is offline Variac  United States
diyAudio Editor
 
Variac's Avatar
 
Join Date: Dec 2001
Location: San Francisco, USA
Well here we are!

MAKE | My Day at Amp Camp
http://blog.makezine.com/2012/07/20/...arousel-224348
MAKE | MAKE magazine

Loudthud, that circuit is quite recognizable! Even with the monster resistors!

Last edited by Variac; 25th July 2012 at 04:17 AM.
  Reply With Quote
Old 27th July 2012, 05:59 PM   #230
diyAudio Member
 
Loudthud's Avatar
 
Join Date: Nov 2007
Location: Near Dallas Texas USA
Quote:
Originally Posted by Nelson Pass View Post
1) I wouldn't assume too much, as it depends on everything. There
generally will be a sweet spot where the 2nd nulls and where the total THD
is lowest, and on either side of that the 2nd comes back.
That was in reference to a question about R1, R2, R3, R4 and their ratios. (I'll just refer to them as R1 and R3.) I made a resistor string with a 0.12 ohm on each end and six 0.05 ohm resistors in between. Total resistance 0.54 ohms. The first attachment shows distortion plots. The comments are the two resistor values in order R1, R3. The surprising thing was that the lowest distortion was when R1 was zero! Looking at the analyzer output though, there was a lot of 3rd and higher harmonics. At any other position the distortion is a nice sinewave at 2x the frequency up to about 4 watts. (I didn't try R3 = 0.0 ohms.)

To investigate this I re-arranged the resistors so that all the 0.05 ohmers were on the Q2 source end and plotted three more curves in the second attachment. The third attachment is the same as the second but with three more curves with the 0.47 ohm resistor between the Q1 source and ground.
Attached Images
File Type: gif ACA1_9.GIF (31.3 KB, 756 views)
File Type: gif ACA1_7.GIF (22.2 KB, 105 views)
File Type: gif ACA1_8.GIF (25.9 KB, 99 views)
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Amp Camp Amp #1 Nelson Pass diyAudio.com Articles 32 17th April 2014 11:50 PM
Amp Camp! Jason Site Announcements 2 30th June 2012 02:57 PM
Best D camp config for Tweeter amp Zero One Class D 0 24th February 2010 04:57 AM
better the Pass camp? rick57 Tubes / Valves 6 26th March 2005 06:04 AM


New To Site? Need Help?

All times are GMT. The time now is 07:34 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2