Ultrasimple mm/mc RIAA preamp 2 - Page 21 - 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 12th December 2009, 05:04 AM   #201
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
18V and your model explains it. But mainly 10R answers it.
Too much CGS I would think, about 30 is nearer for it maybe gives you more THD in sim than in reality.
But the JFet model parameters and the actual Spice model for them aren't very reliable. If its Ok in the build, we are alright. And it seems OK from what you measure. Spencer matches are reported good in the long run too.
  Reply With Quote
Old 13th December 2009, 11:16 AM   #202
diyAudio Member
 
LucasAdamson's Avatar
 
Join Date: Feb 2009
Quote:
Originally Posted by Salas View Post
You can expect 7.6V at the drains, 51dB gain, and the curve in the attachment. The 6.8mA matched look pretty OK in this circuit. I used 30m beta in the sim for them. 51dB is good for 1mV cartridge.
Hi Salas,

My cart is a new-old-stock Shure M75 ED Mk2, the biggest selling cart of the 1970s, and considered at the time to be a bargain, though nothing special I guess.

It has 5mV output. 5 times what you say will be OK with my current circuit. How might I adjust the circuit to allow for that? Do MM carts go as low as 1mV output?

Many thanks
Lucas
__________________
Lucas
  Reply With Quote
Old 13th December 2009, 11:44 AM   #203
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
You can put 50R trimmers between each source pin and ground, get HFNRR test disc, play 3rd track -20dB pink noise, hook up the DVM set for AC RMS on each channel's output, and by starting at half point, get it to match 50mV for each output. That is 500mV 0dB i.e. 40dB gain on 5mV cart. See that the trimmers are producing about the same region DCV across drains and ground between channels and positions. Maybe you gonna end up around 27R for each trimmer with your Idss. Check the TT with the test disc while you are at it too. Good luck.
  Reply With Quote
Old 13th December 2009, 11:41 PM   #204
diyAudio Member
 
LucasAdamson's Avatar
 
Join Date: Feb 2009
Wow. That sounds complex. I was hoping to avoid all that kind of sorcery when I picked this RIAA. Maybe I should have got some GR fets after all.
__________________
Lucas
  Reply With Quote
Old 14th December 2009, 12:03 AM   #205
ra7 is offline ra7  United States
diyAudio Member
 
Join Date: Feb 2009
Blog Entries: 1
Salas,

Can you guide me to some good quality caps for this circuit? Anything from mouser and digikey, but not something that costs tons of money. I've heard the mkt (square ones) caps to be good.

Lucas,
I posted a circuit some posts ago which I modified for my 7.8mV cart. Maybe you could try that. I'm not guaranteeing success, but it worked for me.
  Reply With Quote
Old 14th December 2009, 12:43 AM   #206
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Quote:
Originally Posted by LucasAdamson View Post
Wow. That sounds complex. I was hoping to avoid all that kind of sorcery when I picked this RIAA. Maybe I should have got some GR fets after all.
Not sorcery, it is the simplest you can do without generator and scope. OTOH you may just up the source resistors to 27R and compare the level and the sound with the ones already installed for GR. If still loud enough, go 33R.
  Reply With Quote
Old 14th December 2009, 12:51 AM   #207
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Quote:
Originally Posted by ra7 View Post
Salas,

Can you guide me to some good quality caps for this circuit? Anything from mouser and digikey, but not something that costs tons of money. I've heard the mkt (square ones) caps to be good.
Look for Vishay and Wima polypropylenes, also Koa Speer resistors in Mouser.
  Reply With Quote
Old 14th December 2009, 06:47 PM   #208
diyAudio Member
 
LucasAdamson's Avatar
 
Join Date: Feb 2009
Quote:
Originally Posted by Salas View Post
Not sorcery, it is the simplest you can do without generator and scope. OTOH you may just up the source resistors to 27R and compare the level and the sound with the ones already installed for GR. If still loud enough, go 33R.
Thanks Salas. Duh! Which are the source resistors?

Thanks, Lucas
__________________
Lucas
  Reply With Quote
Old 14th December 2009, 06:49 PM   #209
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Under each fet to ground.
  Reply With Quote
Old 14th December 2009, 10:23 PM   #210
diyAudio Member
 
LucasAdamson's Avatar
 
Join Date: Feb 2009
ok, so could I trial and error it, starting with 27R? I don't have a test disc, or a good enough knowledge of test procedures to really trust myself without a guiding hand looking over my shoulder. If the spice suggests 27R, then I'd be happy to go with that. I'd only raise the alarm if it sounded awful I guess.

Many thanks
Lucas
__________________
Lucas
  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
Suggestions for RIAA preamp? coldcathode Tubes / Valves 17 7th March 2009 07:32 PM
tube preamp RIAA radiodieg Tubes / Valves 5 3rd September 2008 01:36 PM
Ultrasimple MM/MC RIAA Preamp mkIII GlidingDutchman Analogue Source 5 2nd July 2008 07:42 PM
RIAA Preamp Justcallmedad Solid State 4 2nd September 2005 01:52 AM
ultrasimple mm/mc riaa preamp Mad_K Analogue Source 109 31st July 2004 06:34 PM


New To Site? Need Help?

All times are GMT. The time now is 04:38 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