|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
||Thread Tools||Search this Thread|
|14th October 2003, 08:15 PM||#11|
Join Date: Jun 2003
> Can I use one as the volume control in a passive pre-amp.
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.
|Thread Tools||Search this Thread|
|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 06:39 PM|
|Supravox 215-2000 EXC OB, Tribute autoformers and Visaton TL16H for sale on Ebay||ligascon||Swap Meet||0||24th February 2009 03:04 PM|
|MC 352 Autoformers||Jai||Solid State||1||10th July 2006 03:34 PM|
|Is this statement about autoformers correct?||Saurav||Parts||2||30th September 2003 06:06 PM|
|Can you tell me about these zero autoformers?||JZatopa||Parts||6||23rd June 2003 03:42 AM|
|New To Site?||Need Help?|