Two speed Valhalla - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

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 9th March 2007, 06:10 AM   #1
tkwou is offline tkwou  Canada
diyAudio Member
 
Join Date: Feb 2006
Location: Vancouver
Default Two speed Valhalla

Well I finally finished my two speed Valhalla for my Linn and so far it works great and sounds even better. I had been wanting to play 45's on my Linn for quite sometime but I have always hated the adapter pulley so I've always played my 45's on an old Ariston RD-11S. 45 Singles have always been of mediocre quality so it really didn't matter. However very high quality 45 LP's are much more common now and I wanted to play these on the Linn. At the beiginning of the year my Valhalla suddenly died and I was forced to repair it. Not bad really considering it has been powered up since 1988. Thanks to the forum I was able to get a schematic. After realizing how simple the circuit it was, I decided to make a 45 rpm version. I purchased another Valhalla on eBay and mounted both boards externally in a separate case from my Linn. I wasn't very impressed with the power supply on the Valhalla. For 240V users it has a full wave rectifier filtered through two 47uF caps. For 110V user like myself it uses a voltage doubler circuit to obtain the 320V DC high voltage supply. Despite the low current requirements this is still not a very clean power supply so I built a separate power supply to power both boards using 110-240V transformer with rectifier bridge and 600uF filter cap. I also built a separate regulated 10V power supply for the low voltage circuit. I then added simple switching to allow easy changing for both speeds. I just finished it tonight and have been listening ever since. I think the better power supply has definitely helped with reducing motor vibration and the the sound stage has openned up and deepened. It reminds me of when I first heard a Lingo/Valhalla comparison but not nearly as dramatic. I am definitely happy with the improvment.
  Reply With Quote
Old 9th March 2007, 06:36 AM   #2
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Seems like a very inefficient way to utilise a second board. For 45 you just need a second oscillator. Maybe even switching to a different crystal will do the job.

A much cooler application for the second Valhalla will be to build a separate oscillator board, switchable between 33/45 and able to generate a second phase as well. Now you can use the second board to amplify the other phase and take out the motor phase cap.
  Reply With Quote
Old 9th March 2007, 07:04 AM   #3
tkwou is offline tkwou  Canada
diyAudio Member
 
Join Date: Feb 2006
Location: Vancouver
I tried that but switching to a different crystal changed the amplitude of the output signal of the square wave and I had to reduce the resistance to get the correct output voltage. The highest output voltage I could achieve was 72V at 45 rpm at the lowest resistor setting on the original Valhalla board. At 33 1/3 the same resistor setting produced 115V. Either way I needed to able to generate two differnet signals and adjust their output levels independently. It certainly is possible to build an add on board for the second signal and graft it in the original Valhalla board but with two simple part exchanges on another Valhalla board I had a fully functional 45 rpm output.
  Reply With Quote
Old 9th March 2007, 07:09 AM   #4
tbr is offline tbr  Switzerland
diyAudio Member
 
Join Date: Dec 2003
Location: Swiss Pampa
The filter after the crystal is caculated for a dedicated frequency, so you have to double the filtering circuit as well...
__________________
Thomas
  Reply With Quote
Old 9th March 2007, 07:22 AM   #5
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
It makes sense. I replaced the entire oscillator part with an 8515 AVR, two 8-bit dacs and very simple filters. Got less than 0.1% distortion of the sine wave which i guess is sufficient for this purpose.
  Reply With Quote
Old 10th March 2007, 09:00 PM   #6
tkwou is offline tkwou  Canada
diyAudio Member
 
Join Date: Feb 2006
Location: Vancouver
I can certainly appreciate there are much better modern techniques to generate sinewaves, but my goal was to get the second speed in a quick and easy fashion. Had I wanted to start from scratch I would probably want to use the new programmable MPU's to generate a clean sine wave with a minimum of filtering. They also allow you to accurately generate the second phase. What I am not clear on is the actual benefit of creating the phase shift actively through registers versus passively with a capacitor. The capacitor creates the 90° phase lag needed. Moreover I believe the the secondary windings on ac sychronous motors are designed to be impedanced matched with primary windings using the a specified capacitor so you would need to compensate for this also.
  Reply With Quote
Old 11th March 2007, 09:02 AM   #7
diyAudio Member
 
ticktock's Avatar
 
Join Date: Dec 2006
but why not using an Axis board?
separate stages for both speeds, matching switch and even torque sensing circuit like Lingo but cheaper.

Holger
__________________
SAY YES !!
Blaue Leuchtdioden machen blöd. (hb)
quod licet iovi, non licet bovi
  Reply With Quote
Old 11th March 2007, 05:34 PM   #8
tkwou is offline tkwou  Canada
diyAudio Member
 
Join Date: Feb 2006
Location: Vancouver
I actually bought a used Axis on eBay with that in mind. I rebuilt the ps to ensure full output first. First problem is mounting. I don't know that it can mount inside a LP-12 with that large heatsink. On the Axis there is a large slot cut out of the plinth to pass the heatsink through. The other thing I found out is that the power supply only generates 70V at startup and then drops down to about 25V at quiet mode. The platter on a Axis is considerably lighter than on an LP-12. The power supply will not free start the table loaded with my non-Linn record mat, you have to give it a boost to get it started. After that the load sensing circuit will adjust output voltage to maintain the correct speed. The other alternative would be the late model Valhalla used on both the Axis and LP-12 but you don't see those for sale very often. There is an after market version called the Hercules II which is basically a Valhalla board with two crystal generated signals that can be switched via the start button. It is about $375 though. Anyways when I put an arm and cartridge on the Axis it turned out to be a pretty decent sounding table so I it now replaces my old Ariston RD-11S with the noisy motor.
  Reply With Quote
Old 13th March 2007, 08:23 AM   #9
diyAudio Member
 
Join Date: Apr 2003
Location: Milan
Your sharing of this modification schematic would be a great help
to those linn users.
  Reply With Quote
Old 14th March 2007, 12:28 AM   #10
tkwou is offline tkwou  Canada
diyAudio Member
 
Join Date: Feb 2006
Location: Vancouver
Changing a Valhalla to run at 45 rpm is very simple. You need to change the crystal oscillator to 4.433 MHz. The original crystal is 3.2768 MHz. Then you need to change R13 from 22K to 15K to give a bit more output because the low pass filter is optimized for 50Hz. The Valhalla will now output 67.5Hz which will give you 45rpm.
  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
Need help with linn Valhalla repair ericpeters Analogue Source 29 20th August 2013 06:12 PM
Linn Valhalla - Value of R40 and D3 SPWONG Analogue Source 1 20th January 2008 12:01 AM
Linn Valhalla 6072a Analogue Source 5 15th October 2005 02:01 PM


New To Site? Need Help?

All times are GMT. The time now is 01:08 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