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.

F5 Turbo Builders Thread
F5 Turbo Builders Thread
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 5th October 2019, 05:21 PM   #5781
thompsontechs is offline thompsontechs
diyAudio Member
 
Join Date: Sep 2019
Quote:
Originally Posted by AudioSan View Post
Any TO-220 NPN and PNP with the correct pin out can be used.

DO we need to do any matching on these? hFE maybe?


JT
  Reply With Quote
Old 5th October 2019, 05:58 PM   #5782
AudioSan is online now AudioSan  Norway
diyAudio Member
 
Join Date: Feb 2009
i have not testet. But as far as i remember, there was no matching of this devices.
  Reply With Quote
Old 6th October 2019, 01:40 AM   #5783
takitaj is offline takitaj  United States
diyAudio Member
 
Join Date: Apr 2012
Location: Maine
No matching of the cascodes is needed.

I wouldn't worry too much about the 100R from emitter to drain either, unless you find you have an oscillation issue and it can't be resolved by increasing C3 & C4 or increasing output gate stoppers. If you do decide to add them in then you'll have to cut traces.

I would recommend to spend a little extra $ and get .1% or .01% source resistors (inputs and outputs) - or - if you have an accurate enough bench dvm then match them.


TJ
  Reply With Quote
Old 7th October 2019, 06:50 PM   #5784
BigE is offline BigE  Canada
diyAudio Member
 
BigE's Avatar
 
Join Date: Aug 2008
Location: Toronto
Quote:
Originally Posted by takitaj View Post
No matching of the cascodes is needed.

I wouldn't worry too much about the 100R from emitter to drain either, unless you find you have an oscillation issue and it can't be resolved by increasing C3 & C4 or increasing output gate stoppers. If you do decide to add them in then you'll have to cut traces.

I would recommend to spend a little extra $ and get .1% or .01% source resistors (inputs and outputs) - or - if you have an accurate enough bench dvm then match them.


TJ
Hi Takitaj,

Either cut traces or add lands for the new resistor and connection from emitter to drain I suppose. I hate cutting traces, but in this case it's probably easiest.

Does a large difference in DC offset when biasing with/without shorted RCA jacks indicate presence of oscillation?

Would oscillation be visible on scope directly from the speaker outputs?

What value of Gate stoppers or C3/C4 would you use if you detected oscillation?
  Reply With Quote
Old 7th October 2019, 07:19 PM   #5785
nashbap is offline nashbap  United States
diyAudio Member
 
Join Date: Jul 2012
Location: New Jersey USA
Quote:
Originally Posted by takitaj View Post
If you do decide to add them in then you'll have to cut traces.IJ

No need to do that. Bend the relevant leg of the cascode transistor up 180 degrees, now solder one leg of the resistor to it and insert the other resistor leg into the PCB hole.
nash
__________________
F5TV3, AVC, BA3b pre, Salas DCG3b, OBL-15, SonyVfet2pair monos
  Reply With Quote
Old 7th October 2019, 07:33 PM   #5786
JeffYoung is online now JeffYoung  Ireland
diyAudio Member
 
JeffYoung's Avatar
 
Join Date: Jul 2017
Location: Ireland
F5 Turbo Builders Thread
Everyone should build at least one really simple dead-bug circuit. It'll give you a whole new perspective.

Click the image to open in full size.
Manhattan and Pittsburgh Electronics Prototyping Techniques — Parallax Forums
  Reply With Quote
Old 7th October 2019, 08:53 PM   #5787
BigE is offline BigE  Canada
diyAudio Member
 
BigE's Avatar
 
Join Date: Aug 2008
Location: Toronto
Quote:
Originally Posted by nashbap View Post
No need to do that. Bend the relevant leg of the cascode transistor up 180 degrees, now solder one leg of the resistor to it and insert the other resistor leg into the PCB hole.
nash
This also gives a good test point for measuring if the cascode is working.
  Reply With Quote
Old 7th October 2019, 10:21 PM   #5788
takitaj is offline takitaj  United States
diyAudio Member
 
Join Date: Apr 2012
Location: Maine
Quote:
Originally Posted by BigE View Post
Hi Takitaj,

Either cut traces or add lands for the new resistor and connection from emitter to drain I suppose. I hate cutting traces, but in this case it's probably easiest.
As mentioned you can bend a lead up (cascode emitter or JFET drain) and solder one end in the hole and solder the other end to the lifted leg or lift both and solder it across there. To each his own.

When I tried it I cut the traces on the top of the board, scraped some extra back for a place to solder to and used a 1/4w Dale. The tiny blue ones that are the size of other 1/8 watters. I didn't have an issue, I did it "just in case" but it seemed like it lost some sensitivity so I built a new FE board without it. The F5T v3 requires 2 sets of output boards and only one FE per channel so I already had the second set.

Quote:
Does a large difference in DC offset when biasing with/without shorted RCA jacks indicate presence of oscillation?
I wouldn't think a DC offset at the output would indicate an oscillation. Sounds more like a bias setting issue. When you set the bias you will most likely find the N channel and P channels won't match when the offset is at zero, it's ok and is expected. Just make sure the highest channel is where you want it (~350mv) and offset is as close to zero as you can get it when hot. Different ambient air temps will affect the bias and consequentially can affect the offset. You'll probably also see a big range of offset from cold to fully warmed up. I've seen as much as 200mv at turn on, cold, and it will settle back to near zero when fully warmed up. Even when the output devices are well matched. Most match them at some certain voltage/current/temp. While they are out of that range they can differ a lot and is why curve trace matching is the ultimate. What's important is the offset is set to near zero when bias is set and amp is fully hot. You should short the input when setting bias and offset.

Quote:
Would oscillation be visible on scope directly from the speaker outputs?
If there is an oscillation you 'should' be able to see it on the scope. May show up as a thick fuzzy trace instead of a nice crisp line. Ie: high frequency (MHz?) signal riding on the audio signal.

Quote:
What value of Gate stoppers or C3/C4 would you use if you detected oscillation?
I believe 6L6 had mentioned up to 680R. I personally increased them to 100R instead of 47R. Again, not that I had an issue, it was Just in case.


TJ

Last edited by takitaj; 7th October 2019 at 10:24 PM.
  Reply With Quote
Old 7th October 2019, 11:32 PM   #5789
takitaj is offline takitaj  United States
diyAudio Member
 
Join Date: Apr 2012
Location: Maine
Sorry, missed one.. C3 & C4 I used 1nf in all 4 positions. I believe that's what Nelson recommended in the F5T manual. He also mentions the same across feedback resistors R7,8 and R9,10. I didn't go that far, didn't need to.


TJ
  Reply With Quote
Old 8th October 2019, 02:09 PM   #5790
BigE is offline BigE  Canada
diyAudio Member
 
BigE's Avatar
 
Join Date: Aug 2008
Location: Toronto
Quote:
Originally Posted by takitaj View Post
What's important is the offset is set to near zero when bias is set and amp is fully hot. You should short the input when setting bias and offset.
Thanks for all the help!

The issue I had last time I tried to bias was that with input shorted, I got a certain offset. Without input shorted, I got a vastly different offset. Memory fails for an exact number.

The amp had been fully warmed up.

I am going to try to complete the amp shortly, so will keep an eye on this again.

I'll look at adding caps on the feedback as well.
  Reply With Quote

Reply


F5 Turbo Builders ThreadHide 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
B1 builders thread Bas Horneman Pass Labs 728 12th March 2018 06:45 PM
F5 Turbo is posted Nelson Pass Pass Labs 638 27th December 2017 06:12 PM
F5 Turbo Circuit Boards chchyong89 Pass Labs 2404 8th October 2017 07:14 PM
F5 turbo problems Rob Dingen Pass Labs 17 11th January 2013 08:38 PM
F5 Turbo ............. if only !!!!!! a.wayne Pass Labs 23 21st January 2012 02:24 AM


New To Site? Need Help?

All times are GMT. The time now is 06:14 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki