National LM 1972 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 7th June 2001, 10:40 PM   #1
Herman is offline Herman  Germany
diyAudio Member
 
Join Date: May 2001
Location: Europe
Hi out there,
is there anyone who has experience with those LM1972 or LM1973 "precision pots" from National? The data sheet is quite promising, but I could not locate any real application reports or something similar.
Herman
  Reply With Quote
Old 13th June 2001, 04:55 PM   #2
mlloyd1 is offline mlloyd1  United States
diyAudio Member
 
mlloyd1's Avatar
 
Join Date: Feb 2001
Location: illinois
I have some of this but haven't yet used them (too many other projects - Spring and summer are too short!).

I wanted to build a few line stages with different mechanisms and parts (LM1972, CS3310, AD7112, discrete resistors and relays, etc.) to do the gain adjustment so I could compare and determine what I want to use in my next preamp design.

I have heard of no commercially available products that use the National part, but I have seen a few products that use the competitive part by Cirrus - the CS3310.

What were you planning to use for control: a micro controller like a PIC or AVR?

Michael
mlloyd1@enteract.com

  Reply With Quote
Old 5th September 2001, 06:03 AM   #3
hifiZen is offline hifiZen  Canada
diyAudio Member
 
hifiZen's Avatar
 
Join Date: May 2001
Location: Mountain View, CA
I'm also interested in the CS3310 and related volume control chips. I've been looking at doing a resistor and relay arrangement, but the cost is really prohibitive... please post updates on your results, or feel free to email me, and perhaps we can collaborate...
__________________
- Chad.
  Reply With Quote
Old 5th September 2001, 01:32 PM   #4
mlloyd1 is offline mlloyd1  United States
diyAudio Member
 
mlloyd1's Avatar
 
Join Date: Feb 2001
Location: illinois
OK, I have heard of a preamp that uses the National LM197X parts: allegedly the Souther Engineering preamp does.

No progress yet playing around - got hit by the "honey-do" for both the labor day holiday and vacation.

Oh well :-(
  Reply With Quote
Old 5th September 2001, 03:06 PM   #5
tsz is offline tsz  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Göteborg, Sweden
Send a message via ICQ to tsz
All Thule amps use LM1972.

see: http://www.thule-audio.com/technic.htm
  Reply With Quote
Old 5th September 2001, 08:12 PM   #6
diyAudio Member
 
Join Date: Aug 2001
Location: Kouvola, Finland
Is it necessary to add a current buffer after the CS3310 or can I drive a power amp directly (in my application: a NAD 214)? The data sheet claims the CS3310 can drive a 600 ohm load and it says the chip has a 20 mA short circuit current.

Janne
  Reply With Quote
Old 6th September 2001, 01:33 PM   #7
mlloyd1 is offline mlloyd1  United States
diyAudio Member
 
mlloyd1's Avatar
 
Join Date: Feb 2001
Location: illinois
Janne:

According to the data sheet, what you propose would work just fine. However, what the datasheet doesn't always tell you clearly is that the distortion will drastically increase with the lower impedance loads and also at higher frequencies. Using a buffer of some sort after the op amp helps minimize the effect. I use a buffer after all my op amp circuits and have NEVER gone back.

Michael
  Reply With Quote
Old 6th September 2001, 02:50 PM   #8
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
I've used an Analog Devices VCA circuit (I believe it was the SSM2018) with disappointing results. I get pops from AC line noise. When I traced it with a scope, I found that the VCA was actually amplifying the noise on its power supply rails to its output. Cleaning up the rails made it acceptable, but I'm now very leery of using electronic circuitry for a potentiometer.
  Reply With Quote
Old 7th September 2001, 10:09 PM   #9
hifiZen is offline hifiZen  Canada
diyAudio Member
 
hifiZen's Avatar
 
Join Date: May 2001
Location: Mountain View, CA
hmmm.. yeah, i'm very leery of it as well. On the upside, the newer devices (in particular the CS3310) actually implement a passive resistor ladder on the silicon, so in this regard it's just like a stepped attenuator. The questions in my mind are:

1. how good are these polysilicon resistors compared to say SMD metal film types?
2. how good are the FET switches they're using to select the tap point on the resistor ladder? ...are they linear enough?
3. how good is the output buffer?

I would imagine that the resistors are ok, if they can be sufficiently isolated from noise on the substrate. And, of course Crystal should be perfectly capable of making a sonically transparent output buffer (even if it takes some external circuitry to ensure this). The killer is these FET switches. They are basically the same thing used in IC analog MUXes... has anyone used an IC MUX for audio before? Opinions on their sound quality???
__________________
- Chad.
  Reply With Quote
Old 8th September 2001, 06:15 AM   #10
mlloyd1 is offline mlloyd1  United States
diyAudio Member
 
mlloyd1's Avatar
 
Join Date: Feb 2001
Location: illinois
For some useful commentary on the CS3310, see this link:
http://www.jeffrowland.com/dacs.htm

PaulB mentioned the SSM2018 VCA. I would never use a VCA as a gain control element in my preamp. Yes, I know about Dolby and the highly regarded Meitner preamp (of the 80's?). I just wouldn't use 'em in anything besides a homebrew analog synth. At least for now - THAT Corp has produced some parts that might be worth looking into.

I'm probably going to get shot even more for this, but I think FET switches are OK to use if carefully applied (correct layout, appropriate topology minimizing voltage swing across the switch, etc.). Some of the newer parts from Maxim and Analog Devices have VERY impressive specs on distortion, resistance variation, charge injection, etc. I'm thinking MOSFET switches suffer from some of the same early misapplication and bad press that OpAmps went through in the early days. Back in the day, LM741 parts were being used in some preamps, the preamps measured poorly and sounded bad. Consequently, ALL preamps using OpAmps were labelled as bad sounding. Slowly, Rowland, Levinson and others started properly using some of the "audio appropriate" devices, making some good sounding gear, but no reviewers ever really came back and said "OK, we forgive OpAmps".

My 2cents. Your mileage may vary ....

Michael

  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
RCA 1972 Basic amplifier MODS ostripper Solid State 110 1st August 2013 10:21 AM
jl hood 75w amp(1972) p robertson Solid State 2 4th September 2007 07:24 PM
1972 Luxman Sq-202 Schematic GJW Solid State 4 15th August 2006 10:44 PM


New To Site? Need Help?

All times are GMT. The time now is 11:05 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