How should Dick Olsher Blue Velvet measure?? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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 15th February 2007, 12:10 AM   #1
diyAudio Member
 
Join Date: Jan 2005
Location: S.C.
Lightbulb How should Dick Olsher Blue Velvet measure??

Hi, I built a Blue Velvet Preamp thatís posted be Dick Olsher http://www.blackdahlia.com/html/tip_44.html
My rendition uses a SS Shunt regulation but otherwise uses the same Audio schematic.
It sounds very nice but I a question on how much THD it shows.
On My distortion analyzer I get 1% at 3.00 volts out with a 100K load. I think this is kind of high. Its distortion looks more like a tube power amp. It does this through the entire audio spectrum.
With its design configuration what should I expect? Or should I just enjoy it.
I have a Lazarus Basic cascade that looks like a piece of wire as far as the distortion analyzer is concerned.
Thanks for your feedback, No pun intended.
Fred
  Reply With Quote
Old 15th February 2007, 01:13 AM   #2
mach1 is offline mach1  Australia
diyAudio Member
 
mach1's Avatar
 
Join Date: Sep 2004
Location: Brisvegas
QUOTE]With its design configuration what should I expect?[/QUOTE]

Intuitively, with 4.5k plate resistors on a 7k Ri tube I would have expected the THD to be through the roof. However, looking at the chosen operating point on the 6SN7 plate curves, the result appears to be pretty linear if the output is kept within moderate limits. The main result of the low value plate resistor appears to be low gain.

I would expect the local feedback loop to reduce THD to a pretty low amount. Probably lower than you are measuring. However, if the distrotion is mainly 2H and you like the sound I wouldn't be too perturbed. Maybe some tube rolling is in order.

It's an interesting design - using the second triode as an anode follower with local feedback to reduce output impedance instead of the usual cathode follower is a pretty novel approach.

pm
__________________
'Symmetrical equations are good in their place, but 'vector' is a useless survival, or offshoot from quaternions, and has never been of the slightest use to any creature.' Lord Kelvin
  Reply With Quote
Old 15th February 2007, 02:37 AM   #3
diyAudio Member
 
Join Date: Jan 2005
Location: S.C.
I have 3 differerent types of tube to toll
1. old raythyon
2. new EH
3. new sovtek
I like them in that order and #1 And #2 are very close.
The Sovtek should have been a mike . I can say Dam this sucks and hear it through my speakers.
Fred
  Reply With Quote
Old 15th February 2007, 06:43 AM   #4
aroS3 is offline aroS3  Greece
diyAudio Member
 
Join Date: Nov 2005
Send a message via MSN to aroS3
Default Re: How should Dick Olsher Blue Velvet measure??

Quote:
Originally posted by freddymac406
Hi, I built a Blue Velvet Preamp thatís posted be Dick Olsher http://www.blackdahlia.com/html/tip_44.html
My rendition uses a SS Shunt regulation but otherwise uses the same Audio schematic.
It sounds very nice but I a question on how much THD it shows.
On My distortion analyzer I get 1% at 3.00 volts out with a 100K load. I think this is kind of high. Its distortion looks more like a tube power amp. It does this through the entire audio spectrum.
With its design configuration what should I expect? Or should I just enjoy it.
I have a Lazarus Basic cascade that looks like a piece of wire as far as the distortion analyzer is concerned.
Thanks for your feedback, No pun intended.
Fred
I've made also the Blue Velvet following the original schematic. I only used VR105 instead of OA2. The BV gave me exactly the same THD measurements with 10k load.
1% at 3.00 V and 0.63% at 2.00 V.
THD looks huge but sonics are excellent. Tubes i used are NOS KEN-RAD. I'm waiting to check some RCA or SYLVANIA.
  Reply With Quote
Old 11th September 2015, 11:00 PM   #5
vilfort is offline vilfort  United States
diyAudio Member
 
Join Date: Feb 2010
Default Looking for a great 6sn7 cascade with 30X gain

Did anyone ever try messing with the resistor values on the Blue Velvet pre-amp?

I like the topology - but not the puny plate loads and puny B+ voltage. Something like 22K plate load seems worth a try...

Also: one could mess with the feedback voltage splitter. There is little DC difference there since both tube have identical operation points. But one could shift that around and then perhaps a 1:5 or 1:3 relationship between the two resistors forming the feedback splitter. More gain - but potentially higher output impedance. Worth a try...

D.
  Reply With Quote
Old 12th September 2015, 04:58 PM   #6
diyAudio Member
 
Mosquito's Avatar
 
Join Date: Sep 2009
Location: Santa Fe, Argentina
Quote:
Originally Posted by vilfort View Post
Did anyone ever try messing with the resistor values on the Blue Velvet pre-amp?
D.
Hi, I did... on LTSpice.
B+ 400V, 12AT7 tubes, keeping both triodes at the recommended DIYaudio sweet spot (200V on the plate, 3mA bias) R3 2K2, R4 5K6. Gain 2X.
It can even drive 10K at 2VRMS out, with moderate THD.
  Reply With Quote
Old 13th September 2015, 07:59 PM   #7
vilfort is offline vilfort  United States
diyAudio Member
 
Join Date: Feb 2010
Thanks Mosquito. I built a version yesterday. Here is what I changed:

320V B+
6SN7s with 33K plate loads.
15K feedback resistor from output tubes plate to a 100 ohm resistor to the input tubes plate.
Cathode resistors for both is at 390 ohm.
- So how does it sound? Very very nice! Great detail and bass slam. Think I like it better than the same 6SN7s in a grounded cathode and a cathode follower (which is such a standard) configuration. Also: although I do not like feedback, - here we have no loop feedback - just local feedback around the last triode. So it was worth a try. Never assume anything! - Build and listen :-)
Finally, you have to love the fact that the cascade here results in a pre-amp that does not invert signal polarity.
A great little weekend project.

D.
  Reply With Quote
Old 13th September 2015, 08:47 PM   #8
diyAudio Member
 
Mosquito's Avatar
 
Join Date: Sep 2009
Location: Santa Fe, Argentina
Hi, good to know. I think I'll hardly get my hands on SN7's but I do have some 6CG7 to try. So, R3 100R and R4 15K? (refer to the orig. D.Olsher schem)
Cheers
J.
  Reply With Quote
Old 14th September 2015, 04:53 PM   #9
diyAudio Member
 
Join Date: Jun 2010
Location: Croatia
hi all,
I also did it a few years ago,but never posted here.I dont have a measurement,but it is ded quiet and sound great.
Cheers,
Attached Images
File Type: jpg IMAG0059.jpg (828.8 KB, 95 views)
File Type: jpg IMAG0067.jpg (757.1 KB, 95 views)
File Type: jpg IMAG0063.jpg (921.9 KB, 87 views)
  Reply With Quote
Old 15th September 2015, 01:14 AM   #10
vilfort is offline vilfort  United States
diyAudio Member
 
Join Date: Feb 2010
Nice build misterno! Did you ever monkey with the values?

And yes, Mosquito: R3 is 100 ohm and R4 is 15K. Also tried 22K on the plates. 27K as R4 with 470 ohm on the cathodes. I am beginning to like this triode - no feedback + triode out with feedback design. Very versatile. Trick is to keep plate loads and cathode resistors the same it seems.

D.
  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
Samadi Ichiban or Magic Cube by Dick Olsher dsrviola Multi-Way 3 18th February 2014 08:10 PM
Alps Blue Velvet Bengali Parts 0 12th March 2009 10:12 PM
FS: All the parts needed for Dick Olsher's POLY-NATALIA DIY Speakers konstantin Swap Meet 2 9th July 2005 07:09 AM
Blue Velvet Preamp maynardg Tubes / Valves 1 26th May 2004 11:06 PM


New To Site? Need Help?

All times are GMT. The time now is 08:45 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright ©1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki