Pass X250 concept ? - Page 2 - diyAudio
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 15th February 2006, 12:08 PM   #11
diyAudio Member
 
Join Date: Sep 2005
Send a message via MSN to ANALOG GUY
Default Some concept coming soon

I used ACAUDIO & MY & DAVID BERNING design concept for a new PCB layout, it's quite good result with simulation and now I designing this schematic (I don't use 2SK389, 2SJ109, ZVN3310, ZVP3310, ZTX450, ZTX550) but I used 2N5458/5461, IRF610/9610, BC550/560, so I have to change parts value for best frequency response with 220uF coupling IN/OUT, UNBALANCED/BALANCED.

Maybe I have a wrong schematic but I don't care because it's only DIY project.

Best regard

analog guy
Attached Images
File Type: jpg untitled.jpg (85.4 KB, 3191 views)
  Reply With Quote
Old 15th February 2006, 02:55 PM   #12
diyAudio Member
 
CheffDeGaar's Avatar
 
Join Date: Feb 2003
Location: Safe and sound
Default Mysterious Poster...

Well, as you guys seem to be full of ideas, here's the version I use :

Pretty close to acaudio's one, but I made some cosmetic changes :

- Higher bias for the input jfets (3.8 mA)
- BJT cascode for the first stage
- Choose Zetex mosfets (lower capacitance)
- Added "McMillan magic resistors" to stabilize the differential offset, as done in the Aleph X

Straight from the box, it already shows a ridiculous absolute offset (+/- 5mV).

But with matched mosfets (M1 matched with M2 and M3 matched with M4) I can go under one mV. In free air, the offset still wanders a bit, but I lately added a little thermal coupling with aluminium bars for all the active devices, and the absolute offset stays under 1 to 2 mV for hours. The relative offset is always ridiculous and typically under 0.5mV.

Now for the sound... All I can say is : Wowwww
It easily blows away my BoSoZ. A perfect match to my AXs. It's a rocket : fast and stratospheric. Added depth and width, so quick on transients. Marvelous highs, no part of the spectrum is privilegied. Widens the scene, reveals every aspects of the sound. It was the first time I heard a noise gate shutting so clearly...

And dead silent... Even if I made PCBs for them, the whole thing is breadboarded with thin wires, low quality volume pots at the output... And despite of that, absolutely no noise...

Made some measurements for what it's worth. Absolutely flat response from 5Hz to 20 kHz, mainly H2 distorsion (-70/-75 dB), but I will remake the measurements with the final version.

I'll try to post some pics on Friday (I'm having hard times finding time ), showing the breadboarded horror

All I can say is : Thanks, Mr Pass

Cheff
Attached Images
File Type: gif schemgus.gif (20.7 KB, 3663 views)
__________________
/Cheff - Falling feels like flying, until you hit the ground
  Reply With Quote
Old 15th February 2006, 03:02 PM   #13
diyAudio Member
 
CheffDeGaar's Avatar
 
Join Date: Feb 2003
Location: Safe and sound
And the PCB I use.

This one is temporary. I'm currenly making a double sided one, mainly for aesthetic purposes More seriously, I want to add some compensation caps, since I detected very little oveshoot on square signals. Very layout dependent, since I didn't have this problem on the very first prototype...

Cheff
Attached Files
File Type: pdf ugs-1.pdf (35.8 KB, 987 views)
__________________
/Cheff - Falling feels like flying, until you hit the ground
  Reply With Quote
Old 15th February 2006, 03:34 PM   #14
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
Hi Cheff,

How is th offset? Do you need coupling caps?

Jam
  Reply With Quote
Old 15th February 2006, 04:05 PM   #15
diyAudio Member
 
CheffDeGaar's Avatar
 
Join Date: Feb 2003
Location: Safe and sound
Hi Jam, nice to see you rambling around here

No coupling caps were necessary

With thermal coupling, absolute offset is under 1 to 1.5mV, with slow variations due to home wind . But the whole setup has no casing, so I thing it overestimates the offset variations. It's mainly a thermal problem, since I clearly saw the differences before and after the thermal coupling. Before, the 0.1mV digit on the DMM changed at each reading, and after, the same digit stays stable for 5 to 10 seconds, even longer in case of fair weather conditions . BTW, if people want to use it without coupling caps, I think it's better to leave it on all the time. At cold startup, the offset begins at 20-25 mV, and rapidly stabilize to its nominal and almost null value.

Anyway, even without thermal coupling, and with matched mosfets, the offset very seldom rises above 5mV...

Differential offset is always below the mV (0.2 to 0.5mV max typical)

Well it's only at prototyping stage for the moment, so specifications may change without notice

Cheff
__________________
/Cheff - Falling feels like flying, until you hit the ground
  Reply With Quote
Old 15th February 2006, 04:31 PM   #16
gl is offline gl  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Sierra Foothills - California
Hi Cheff,

A very nice piece of work indeed. Thank you for sharing it. I particularly appreciated your comment about the circuit sounding better than other simpler circuits like BOSOZ. It is a concern of mine when things start becoming too complex.

Cheers,
Graeme
  Reply With Quote
Old 15th February 2006, 04:57 PM   #17
diyAudio Member
 
CheffDeGaar's Avatar
 
Join Date: Feb 2003
Location: Safe and sound
Hi Graeme,

Thanks for your kind comments. But also thank Nelson
Indeed it outperforms my heavily biased (65mA/Fet) BoSoZ, especially in the area of high frequencies. The BoSoZ seem to cast a veil on this part of the spectrum, while the UGS reveals it. But no harsh, just silk
And it also goes very low, without any boomy aspect. Everything is where it should be...
But the main thing is that it seem to widen the scene in a spectaculay way... I dunno where it comes from... And all of this without any special or audiophile component... Black magic, or am I just another proud father ?

And looking closer, it's not that complicated. Not more than my CCSed BoSoZ...
__________________
/Cheff - Falling feels like flying, until you hit the ground
  Reply With Quote
Old 15th February 2006, 05:07 PM   #18
gl is offline gl  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Sierra Foothills - California
Hi Cheff,

Yes you're right. I thank the man every chance I get. You're right too about the simplicity if you look at the overall component count. What I was referring to is the number of stages. There's something about the elegance of a single transistor line stage that is very compelling - unless it's a zero transistor line stage.

We could probably toss this back and forth all day.

Graeme
  Reply With Quote
Old 15th February 2006, 05:15 PM   #19
zinsula is offline zinsula  Switzerland
diyAudio Member
 
zinsula's Avatar
 
Join Date: Mar 2004
Graeme

Some remarks:

- it seems to me that you have positive feedback. Your circuit is not inverting (like Cheff's), so you have to feed back the + output to the - input and vice versa

- turn Q7, drain must be attached to the negative rail, not to output

- with R38 and R29, do you want some "current feedback"? For offset reduction?

Success
Tino
  Reply With Quote
Old 15th February 2006, 05:36 PM   #20
gl is offline gl  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Sierra Foothills - California
Hi Zinsula,

Yes you are right about the number of inversions. I realized this after re-reading may notes last night. The inside ends of R39 and R31 should be swapped. R38 and R29 return to a common point so they're fine. Without the followers this is actually a single gain stage amp. I have not used current mirrors in this way before and was intending to sort all this out experimentally before posting.

Correct on Q7. Thank you.

R38 and R29 are the "MacMillan" resistors used to help stabilize absolute offset. They are taken from the X2 preamp ver 2 schematic.

Thank you for the input.

Graeme
  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
Pass X250.5 right channel hum problem georgehifi Pass Labs 4 1st October 2014 05:24 AM
Pass X250+ Wadia martev Pass Labs 4 6th August 2009 09:44 AM
Lower the gain on a Pass X250.5? aljordan Pass Labs 10 8th January 2009 09:26 PM
pass x250.5 a little defect... kyrochan Pass Labs 10 31st May 2006 12:19 AM
Pass X250.5 question for Nelson georgehifi Pass Labs 4 15th March 2005 08:37 PM


New To Site? Need Help?

All times are GMT. The time now is 04:47 AM.


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