DCAudioDIY.com

DC Area Audio DIYer's Community
It is currently September 17th, 2019, 10:49 pm

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 9 posts ] 
Author Message
 Post subject: Tape out volume control?
PostPosted: November 14th, 2016, 1:26 am 
Offline

Joined: July 15th, 2016, 10:02 am
Posts: 69
I have a Pioneer SA-6500 which I would like to add a remote volume control to. My plan is to buy one of the many kits available on eBay and put it in the tape monitor loop. For several reasons I'd rather do this than replace the volume pot that's in the unit. My question is: do I need to worry about impedance matching? I don't know what the typical output impedance of a tape deck is/was. The kit I'm looking at right now uses a 100K pot.


Top
 Profile  
 
PostPosted: November 14th, 2016, 1:38 am 
Offline
Site Admin
User avatar

Joined: February 28th, 2013, 10:38 am
Posts: 1124
That'll be fine....

Roscoe


Top
 Profile  
 
PostPosted: November 14th, 2016, 10:19 am 
Offline
User avatar

Joined: February 28th, 2013, 3:31 pm
Posts: 1155
Depends. The 100K pot should be no problem for the tape to drive but if you are going into a low impedance the taper of the pot can be affected. The lower the driven impedance the steeper the "slope" of the taper as you reduce the volume and the greater the deviance from an audio taper. That may be of no consequence for you.

Tom


Top
 Profile  
 
PostPosted: November 14th, 2016, 10:23 am 
Offline
Site Admin
User avatar

Joined: February 28th, 2013, 10:38 am
Posts: 1124
If he's going back into the tape loop in a receiver, the impedance should be plenty high enough not to be a problem...

Roscoe


Top
 Profile  
 
PostPosted: November 14th, 2016, 11:23 am 
Offline

Joined: July 15th, 2016, 10:02 am
Posts: 69
Quote:
Depends. The 100K pot should be no problem for the tape to drive but if you are going into a low impedance the taper of the pot can be affected. The lower the driven impedance the steeper the "slope" of the taper as you reduce the volume and the greater the deviance from an audio taper. That may be of no consequence for you.


Not sure if this is what you're getting at, but I will be using an audio (logarithmic) pot.


Top
 Profile  
 
PostPosted: November 14th, 2016, 12:55 pm 
Offline
User avatar

Joined: February 28th, 2013, 3:31 pm
Posts: 1155
You can think of it this way. Let's say the impedance of what you are driving is 1 meg ohm. If you turn the pot to the center of the resistance (which will not be the center of rotation with an audio taper) the voltage at the output will be just sightly less than 50% of the input voltage. If the impedance of what you are driving is 10K ohms at the same rotational position the voltage output will be around 14%. Therefore the audio taper will be greatly changed. What that means is with the high impedance the change in rotation will produce an output that was designed to match ear characteristics, ie. equal perceived changes in loudness that correspond to the same changes in rotation. As the impedance driven drops the rate of change in volume from loud to soft will drop much faster or conversely the change in volume from soft to loud will increase much slower. Again, that rate of change whatever it is may not be of any importance to you.

Tom


Top
 Profile  
 
PostPosted: November 14th, 2016, 1:05 pm 
Offline

Joined: July 15th, 2016, 10:02 am
Posts: 69
Quote:
You can think of it this way. Let's say the impedance of what you are driving is 1 meg ohm. If you turn the pot to the center of the resistance (which will not be the center of rotation with an audio taper) the voltage at the output will be just sightly less than 50% of the input voltage. If the impedance of what you are driving is 10K ohms at the same rotational position the voltage output will be around 14%. Therefore the audio taper will be greatly changed. What that means is with the high impedance the change in rotation will produce an output that was designed to match ear characteristics, ie. equal perceived changes in loudness that correspond to the same changes in rotation. As the impedance driven drops the rate of change in volume from loud to soft will drop much faster or conversely the change in volume from soft to loud will increase much slower. Again, that rate of change whatever it is may not be of any importance to you.


Got it. Looking at the schematic: after entering the tape return, the signal travels through a 6.8K resistor and then to the 250K balance pot and 100K volume pot (with associated loudness circuit), then is capacitively coupled to the first stage of the power amp. So I'm thinking I'll be OK.


Top
 Profile  
 
PostPosted: March 12th, 2017, 6:27 pm 
Offline

Joined: January 21st, 2017, 11:32 am
Posts: 8
The latests/greatest seem to use digitally-controlled analog stepped resistor chips. That's what's iside my new Emotiva preamp, and it's very nice.

I also have some cheap old vintage Kenwood add-on remote volume boxes that do exactly what you're describing, just remote volume via a tape loop or effects loop.


Top
 Profile  
 
PostPosted: March 12th, 2017, 7:13 pm 
Offline

Joined: April 4th, 2016, 4:07 pm
Posts: 16
Could use this- remote control, too!
http://www.mcmelectronics.com/product/50-8394


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 9 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group