#26 pre amp - Page 115 - 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 8th August 2011, 12:06 PM   #1141
Richard is offline Richard  Australia
diyAudio Member
 
Join Date: Apr 2005
Location: Melbourne
Quote:
These were the best sounding resistor types for me
Even better than the Welwyn wire wound you indicated in post 1117?

I recall someone mentioning that the old stock green Welwyn vitreous enamelled ww were pretty good. Have you tried these?

Rich
__________________
"A little learning is a dangerous thing"
  Reply With Quote
Old 8th August 2011, 12:29 PM   #1142
diyAudio Member
 
Join Date: Sep 2003
Location: London
Quote:
Originally Posted by Richard View Post
Even better than the Welwyn wire wound you indicated in post 1117?

I recall someone mentioning that the old stock green Welwyn vitreous enamelled ww were pretty good. Have you tried these?

Rich
Those dark green Welwyn resistors are fine. I never used them for filament bias because here we need about 50 watts. But anyway, the discontinued Dale ones are really good so I'd go for those. They are surplus supplies, so may be worth buying some. Don't know what remaining stock there is.

Andy
  Reply With Quote
Old 9th August 2011, 02:23 AM   #1143
Richard is offline Richard  Australia
diyAudio Member
 
Join Date: Apr 2005
Location: Melbourne
Thanks Andy, I'll give them a try.
__________________
"A little learning is a dangerous thing"
  Reply With Quote
Old 26th August 2011, 02:58 PM   #1144
diyAudio Member
 
Join Date: Sep 2003
Location: London
I have a question about the LL1660/5mA as preamp output. I've put this back in the circuit. A bit light on bass but transparent and clean sound. It's in 1:1 but may try 4.5:1 if I have enough gain.

Anyway, the question is what current can be put through this while allowing it to remain totally undistorted whatever the programme material. I have a feeling it's less than 5mA. Any comments on this?

Andy
  Reply With Quote
Old 26th August 2011, 03:03 PM   #1145
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Quote:
Originally Posted by andyjevans View Post
I have a question about the LL1660/5mA as preamp output. I've put this back in the circuit. A bit light on bass but transparent and clean sound. It's in 1:1 but may try 4.5:1 if I have enough gain.

Anyway, the question is what current can be put through this while allowing it to remain totally undistorted whatever the programme material. I have a feeling it's less than 5mA. Any comments on this?

Andy
Try it and find out I guess. The HA-133s in mine are rated 8mA and sound bad at this current and wonderful at 6mA..

I'd recommend using it at 4.5:1 as this will give you a very low source impedance for driving lines effectively and should give you about 4.5dB of gain. I find the 4dB of gain in mine more than adequate.. (5:1)
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 26th August 2011, 03:15 PM   #1146
diyAudio Member
 
Join Date: Sep 2003
Location: London
Hello Kevin! I was thinking along these lines that about 3/4 current would sound cleaner. That would make about 3.5 to 3.7mA. Listening to some choral music at the moment, which caused me to wonder - it can be tricky to get choral music to sound completely clean.

My whole system is CD player > 26 > 46 > 300b. All transformer coupled, no resistor loading or cathode resistors (except 300b). Filament bias on the 26 and battery grid bias on the 46. I have a little gain in hand but am about to switch to Jordan JX92 units, and those may swallow the gain.

Andy
  Reply With Quote
Old 26th August 2011, 04:55 PM   #1147
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi Andy,

when you talk about 'light bass' do you mean it has an early roll off? What is the -3dB frequency? What is the general behaviour in the bass, what was it in the circuit you compared it too?

How did you wire it? The 1660 does not offer exactly 1:1 did you put it 1:1.125 or 1.125:1 ? Worth trying if slight step up is better than slight step down.

The current depends on the signal swing you need. If you increase the current, you get less possible signal swing before saturation kicks in. Again this can be easily measured. When you change current the rp of the driver will change. So you will compare several effects. It might not be the impact of the current to the transformer you are hearing, but the different rp in conjunction with the transformer.

Also impostant, how is the B+ of this stage done? If it has it's own decoupling stage, the size of the decouplig cap also palys a role.

Best regards

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 26th August 2011, 05:24 PM   #1148
diyAudio Member
 
Join Date: Sep 2003
Location: London
Hi Thomas -

I don't use a scope alas - never learned. Just sounds like less bass than with the two Hammond 156c plate chokes - they take 8mA. Wiring - good point. I should at least make it 1.25:1. I'll look what I did. The Rp difference wouldn't make the sound congested, though. I've been looking again at the curves and I need 120v on the anode not 130v at present. Will swap that for starters. The B+ is decoupled with a 6.3K resistor and a 47uF cap. There are two chokes in the HT, which is choke input. I never did try ultrapath - run that by me again!

Comments?

andy
  Reply With Quote
Old 26th August 2011, 05:43 PM   #1149
diyAudio Member
 
Vinylsavor's Avatar
 
Join Date: Feb 2002
Location: Lindau
Hi Andy,

I recommend to do basic measurment checks when you try a new circuit, otherwise it is diffcult to understand what is going on and you easily draw false conclusions. A scope and signal gen are easy to use and you will learn a lot by using them.

Changing the B+ by 10V shouldn't make a big difference. If it does the circuit is marginal and I would rather make the whole circuit more stable rather than trying to find the optimum voltage.

Also note that your last B+ cap now is fully in the signal path while with LC coupling it was not.

Ultrapath is adding a cap from B+ to cathode. Many schematic on my blog show this. Does not make a huge difference with filament bias, but you could still try

Best regards

Thomas
__________________
http://vinylsavor.blogspot.com/
  Reply With Quote
Old 26th August 2011, 07:34 PM   #1150
diyAudio Member
 
Join Date: Sep 2003
Location: London
Hi - well, 10v difference on the anode means a difference between 3.5mA and 4.8mA. There isn't much of a margin with the LL1660/5mA. It's all very tight through the need to keep the Henries up for the 26. A LL1660/10mA would give a nice margin but then we lose the impedance headroom.

Why is there a difference between transformer output and a plate choke and cap output? I don't quite see this in terms of the last B+ cap being in the signal path - do explain!!

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 01:43 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