Got a hair-brained idea this morning and wanted to get some feedback. Most audiophiles know the sonic benefits of a transformer-based passive preamp. Kits and complete units cost a fair amount of money, but I've noticed that wall-based transformer volume controls are under $100, and some even half that. Has anyone ever tried making a passive preamp with something they carry at say, Home Depot, Lowes, or Parts Express? It looks easy enough to do and is tempting to try.
FM
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I believe those transformers you refer to are intended to contrtol the volume of a speaker running off a 70V or 100V sound reinforcement amplifier or "P.A." system.
They're the wrong impedance for line level, by a long shot. And they are not even close to "hi-fi." The uber high end ones (not the ones at Home Depot) have a claimed frequency response of typically 70-20,000 Hz.
They're the wrong impedance for line level, by a long shot. And they are not even close to "hi-fi." The uber high end ones (not the ones at Home Depot) have a claimed frequency response of typically 70-20,000 Hz.
Actually I have a few of these that I picked up at the Parts Express tent sale and at Radio Shack and they are not designed for 70V systems. They are for nominally 8 ohm systems, tho they do have taps for other impedances.
Here's the problem. I've tried to use them as you want to, a line level transformer volume control. Yeah, they kinda work, but they also kinda suck. The transformers just are not of high quality. Limited frequency response, bad phase, lack-luster sound.
Sure wish I could get this to work and sound good, but I have not, so far, been able to. 🙁 OK for background music speakers, not good for Hi-Fi.
Here's the problem. I've tried to use them as you want to, a line level transformer volume control. Yeah, they kinda work, but they also kinda suck. The transformers just are not of high quality. Limited frequency response, bad phase, lack-luster sound.
Sure wish I could get this to work and sound good, but I have not, so far, been able to. 🙁 OK for background music speakers, not good for Hi-Fi.
I've never noticed these, probably because I never concieved of a use for them. Do you have a quick link?*
Since some of us like to use "passive" preamps, there would be a modest market for a "hi-fi"stepped line level transformer. There are some advantages to using a stepped transformer over a potentiometer for a passive preamp.
Absolutely. Typical "elevator" music is distributed through 70 volt speaker level transformers.
*Edit: I did see a transformer based speaker level volume control at Menards. I never gave it a second thought, because I assumed that it sucked.
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I have a number of high-power 8 Ohm L and T reostat pads for a wallmount application. I never used them after I realized what the did to the amlifer damping. They are OK though for "casual" listening situations. E
No, what I bought was on close out or surplus. But I'll look around. I could post photos, I suppose.
I thought impedance and the overall quality of the transformers may be issues. Seems the proper transformers are expensive to experiment with, so I'm just surprised someone hasn't come up with a cheap DIY solution. I think I read a post about someone making one with a standard, cheap transformer from Radio Shack, but it hummed like crazy.
The Parts Express model I have is very similar to this:
http://www.parts-express.com/pedocs/installation-guides/182-303-parts-express-installation-guide.pdf
It's actually a dual autoformer. I can test it again, if you are interested.
Give me an idea of the impedance of your source and the impedance of your load so that I can get the tests close to your conditions.
http://www.parts-express.com/pedocs/installation-guides/182-303-parts-express-installation-guide.pdf
It's actually a dual autoformer. I can test it again, if you are interested.
Give me an idea of the impedance of your source and the impedance of your load so that I can get the tests close to your conditions.
A passive pre-amp does not need any power supply.
An active pre-amp does need a power supply.
An active pre-amp can be a buffer without any gain, or it can be an amplifier with some gain. If you go for gain then I recommend that it be switchable, +0dB, +6dB +12dB gives you a lot of flexibility for various source output levels. Use the MINIMUM gain to get to the volume levels you listen at.
An active pre-amp does need a power supply.
An active pre-amp can be a buffer without any gain, or it can be an amplifier with some gain. If you go for gain then I recommend that it be switchable, +0dB, +6dB +12dB gives you a lot of flexibility for various source output levels. Use the MINIMUM gain to get to the volume levels you listen at.
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