Autoformers (again??!) - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

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 14th October 2003, 07:15 PM   #11
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: USA
> Can I use one as the volume control in a passive pre-amp.

No.

These are wound for use between a loudspeaker amp and a loudspeaker. Load impedance about 8Ω, source impedance very much lower. Probably the inductive impedance of the unloaded autotranny dips to 8 ohms at 20 Hz. Your CD deck's output impedance is more like 100Ω. Output level will be low and possibly distorted, and bass will be even lower.

Also as Dave says: the minimum useable attenuation setting is probably higher than you want as a main volume control. Steps may be larger than we'd really like too.

There are line-impedance tapped autoformers, but not at the $20-$60 level. Sowter has nice 10K:10K cores for 86.63, but you will have to find a 2 pole 24 position switch.

The main advantage of a transformer over a resistor attenuator is that it does not waste power. If you feed a 100 watt amplifier into an 8Ω pot to reduce speaker level, the pot burns up. With the autotranny, the transformer action reflects a higher load to the amplifier, drawing less power, and delivers 90+% of that power to the speaker. It runs cool.

At the 0.000,1 Watt levels that lines work at, overheated pots are not an issue. And pots are linear to DC and to high voltages and frequencies.

> What exactly is the z out of a cd player, and where would I find this out?

You could measure it. But the fact is: you never want to come close to loading most modern outputs in their actual source impedance. They have a rated load impedance, and you don't want to go lower than that. For hi-fi box line outs, usually 10K, though some will happily drive 2K or even 600Ω.

The internal impedance may be as low as 47Ω, but if you load them in 47Ω you will get half-output and probably gross distortion. The low output Z gives authoritative drive into long cables and no change in output level between 10K and 1Meg loads, but is not the load that the box can drive.
  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
Anyone compared electra-print SE:PP interstages to electra-print PSA-2 autoformers zobsky Tubes / Valves 0 11th June 2009 05:39 PM
Supravox 215-2000 EXC OB, Tribute autoformers and Visaton TL16H for sale on Ebay ligascon Swap Meet 0 24th February 2009 02:04 PM
MC 352 Autoformers Jai Solid State 1 10th July 2006 02:34 PM
Is this statement about autoformers correct? Saurav Parts 2 30th September 2003 05:06 PM
Can you tell me about these zero autoformers? JZatopa Parts 6 23rd June 2003 02:42 AM


New To Site? Need Help?

All times are GMT. The time now is 09:07 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