#26 pre amp - Page 61 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 18th August 2010, 08:07 AM   #601
diyAudio Member
 
i_should_coco's Avatar
 
Join Date: Dec 2003
Location: Surrey, UK
Hi Andy, it would be interesting to try one of Rod's supplies after an LC stage for the filaments. I was thinking about doing somehting like that for my next preamp project....
  Reply With Quote
Old 18th August 2010, 11:40 AM   #602
diyAudio Member
 
Join Date: Sep 2003
Location: London
Yes, absolutely. I know from experience how good Rod's supplies are - as you do! The LC stage for the filaments is a good idea. I have a pair of 280mH chokes for you if you wish. I feel like putting LC supplies right through my amp as well. The chokes annihilate LM1084 regs - and to think how long I was happily using those.

Heatsinking may be an issue with Rod's filament board, though as a final stage before the filaments for 10Y in filament bias it just needs to pass 1.25A and drop 4 volts or whatever it's happy with. What I didn't quite get was the surge at turn on with LC which shut down LM1085 regs - they're rated for 2.5A!! The LM1084 coped, and they're rated 5A. Don't know how this would affect Rod's board.

Andy
  Reply With Quote
Old 18th August 2010, 11:59 AM   #603
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
hi Andy

Nominal headroom for the boards is 5V, but that's to allow a raw dc which varies + or - 1V.

If you have a stable supply, 4V is enough. The first samples of the boards work fine even with 3.5V - but in most cases the higher voltage is better. THis is one improvement in the new design - full performance even with low voltage headroom.

With 1.25A in the 10Y, the transistors are dissipating only about 2.7 ... 3.3W each for 5...6V headroom. If you have some ventilation, a 5K/W heatsink like the little AAVID KM75 will suffice - it's only 75mm (3 inch) wide, and easily clips the transistors in place.

KM75 is in the picture, tested for 24 hours at 6V headroom in a 300B configuration, where the heatsink reached about 85 deg C in a 25 deg C environment.
Attached Images
File Type: jpg heatPCB1.JPG (181.2 KB, 750 views)
  Reply With Quote
Old 18th August 2010, 12:10 PM   #604
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
Quote:
Originally Posted by andyjevans View Post
Yes, absolutely. I know from experience how good Rod's supplies are - as you do! The LC stage for the filaments is a good idea. I have a pair of 280mH chokes for you if you wish. I feel like putting LC supplies right through my amp as well. The chokes annihilate LM1084 regs - and to think how long I was happily using those.

Heatsinking may be an issue with Rod's filament board, though as a final stage before the filaments for 10Y in filament bias it just needs to pass 1.25A and drop 4 volts or whatever it's happy with. What I didn't quite get was the surge at turn on with LC which shut down LM1085 regs - they're rated for 2.5A!! The LM1084 coped, and they're rated 5A. Don't know how this would affect Rod's board.

Andy

Andy, Sounds like the LM108x is unstable to me. It's quite possible it doesn't like the inductive large loop area of the filament as a load.

My design has been tested with large air-cored inductors as a LOAD
as well as with long supply cables and spaghetti-wired filament leads.

In all cases, the scope test, portable radio monitoring, and LTspice simulations show full stability, including during switch-ON and OFF transients.

THe testing programme is one reason the design took a while to appear.

The fact that only ONE component terminal connects to each filament terminal is a great help - just two outputs. There are no feedback loops connected to the filament at all. This sounds better than all other architectures, and is stable under any realistic load.
  Reply With Quote
Old 18th August 2010, 12:12 PM   #605
diyAudio Member
 
i_should_coco's Avatar
 
Join Date: Dec 2003
Location: Surrey, UK
Hi Rod, will yuo be publishing a schematic? Or will only boards be available?
  Reply With Quote
Old 18th August 2010, 12:22 PM   #606
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
Schematic will be available, as soon as I've finished all the build definitions & intstructions. Architecturally it's identical to the previous edition, but with a buffer for the CCS supply, adjustable current trimming, and wonderful low-voltage transistors.
  Reply With Quote
Old 18th August 2010, 12:29 PM   #607
diyAudio Member
 
Join Date: Sep 2003
Location: London
Just trying the difference in choke input between the Hammond 159ZC at 60mH and the other chokes I have at 280mH. It's the same generic sound. Sound is just a little less full and rounded. So bigger is better, though the sound is similar. Haven't tried switching them in the second choke position where Rod thinks it will make a difference.

It also occurred to me that with filament bias, the changes in filament supplies may well be more audible than when feeding filaments in the conventional way.

andy
  Reply With Quote
Old 18th August 2010, 12:49 PM   #608
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
Quote:

It also occurred to me that with filament bias, the changes in filament supplies may well be more audible than when feeding filaments in the conventional way.

andy
That is completely true.

A low ac impedance affects anode current (badly), whereas any power supply noise at the cathode resistor is the same as injecting noise into the grid.

Both these effects are nasty.
  Reply With Quote
Old 18th August 2010, 01:18 PM   #609
diyAudio Member
 
i_should_coco's Avatar
 
Join Date: Dec 2003
Location: Surrey, UK
Quote:
Originally Posted by andyjevans View Post
Just trying the difference in choke input between the Hammond 159ZC at 60mH and the other chokes I have at 280mH. It's the same generic sound. Sound is just a little less full and rounded. So bigger is better, though the sound is similar. Haven't tried switching them in the second choke position where Rod thinks it will make a difference.

It also occurred to me that with filament bias, the changes in filament supplies may well be more audible than when feeding filaments in the conventional way.

andy
Did you change both chokes or just the first one?

Quote:
Originally Posted by Rod Coleman View Post
Schematic will be available, as soon as I've finished all the build definitions & intstructions. Architecturally it's identical to the previous edition, but with a buffer for the CCS supply, adjustable current trimming, and wonderful low-voltage transistors.
Great stuff thanks Rod. I'm eagerly awaiting this.
  Reply With Quote
Old 18th August 2010, 01:49 PM   #610
diyAudio Member
 
Join Date: Sep 2003
Location: London
Did you change both chokes or just the first one?>>

Just the first one.

Andy
  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



New To Site? Need Help?

All times are GMT. The time now is 07:09 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