I built Electra-Print's passive preamp using a pair of their PVA-2n audio transformers, following their circuit design, but with two switchable inputs and no subwoofer output:
Electra-Print.com PVA Passive Audio Pre-Amplifier
You Can DIY! Passive Preamp: Transformer Implemented | audioXpress
I used a Galaxy 1U 124mm x 170mm Alu case from diyaudiostore.com with customized drill holes for an ALPS 10k pot and a DPDT on-on toggle switch on the front panel, and three sets of RCA jacks on the back panel. I drilled out a few of the vents on the bottom panel to accommodate mounting screws for the trafos.
With the PVA-2n based passive preamp replacing a Schiit SYS passive preamp (10k audio taper pot with switchable inputs), my system sounds amazing. My perception is that digital sources (a Sony CDP-302 and a RaspberryPi with a AD1868 DAC HAT card) sound much cleaner, with more instrument detail and better levels (frequency response). Listening fatigue I experienced with the CDP-302 completely disappeared last night, and albums with challenging levels to my ears, like U2's The Joshua Tree, suddenly sound way better balanced. I much prefer the sound of this preamp to my Korg NuTube B1 as well.
The only real downside was sourcing parts from multiple vendors and the cost of the customized case. Being my first build completely from scratch, I'm satisfied with how it turned out. Hope you enjoy the pictures.
Electra-Print.com PVA Passive Audio Pre-Amplifier
You Can DIY! Passive Preamp: Transformer Implemented | audioXpress
I used a Galaxy 1U 124mm x 170mm Alu case from diyaudiostore.com with customized drill holes for an ALPS 10k pot and a DPDT on-on toggle switch on the front panel, and three sets of RCA jacks on the back panel. I drilled out a few of the vents on the bottom panel to accommodate mounting screws for the trafos.
With the PVA-2n based passive preamp replacing a Schiit SYS passive preamp (10k audio taper pot with switchable inputs), my system sounds amazing. My perception is that digital sources (a Sony CDP-302 and a RaspberryPi with a AD1868 DAC HAT card) sound much cleaner, with more instrument detail and better levels (frequency response). Listening fatigue I experienced with the CDP-302 completely disappeared last night, and albums with challenging levels to my ears, like U2's The Joshua Tree, suddenly sound way better balanced. I much prefer the sound of this preamp to my Korg NuTube B1 as well.
The only real downside was sourcing parts from multiple vendors and the cost of the customized case. Being my first build completely from scratch, I'm satisfied with how it turned out. Hope you enjoy the pictures.
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Yes, but that was more about capacitive coupling, than an ohmic connection.
Your source will already have an ohmic connection between the left and right commons.
There's no need for a redundant such connection in the preamp, especially if you use
monoblock power amps. Then you will have no audio ground loops in your system at all.
Your source will already have an ohmic connection between the left and right commons.
There's no need for a redundant such connection in the preamp, especially if you use
monoblock power amps. Then you will have no audio ground loops in your system at all.
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Thanks for the tip rayma. I measured the center-to-center capacitance and resistance across the left and right channels, on both sets of inputs. Since the input primaries are tied together at ground, there is a left channel to right channel center-to-center circuit that passes through both primaries in series. I measured 74-80pF (different inputs, likely well within the measurement error of my cheap Cx/Lx meter and measurement setup) and 65 Ohms center-to-center. Unless I'm missing something, that should behave as a low-pass filter which roles off at 30.6MHz. I'm not worried.
It's not described in terms of inherent impedance. it's got an ~1:8 turns ratio, so the impedance ratio is ~1:64, which is very close (virtually identical) to the ratio you listed above.
Hi Ranshdow, I built that passive transformer preamp too. I built it a few years ago and put it back in my bedroom set up powered by a DynaST35. I would love to talk to you as opinions are rare. I have some good pics I'd like to show you if I can learn how to post them. I'm 66 and live in Old Orchid Beach Maine.I'm up all hours too.Call anytime 207-632-1648 .....kordamark@gmail.com
Hi Dawkus, I'm happy to continue the discussion here, if that works for you, that way everyone can participate. It's easy to post pictures, you click on the little square icon that looks like it has two peaks on it- when you hover over it, it will say "insert image (Ctrl-P). Click that, and you can add pics from your computer.
I've done a bit with these PVA-2n's since the time of my last post in this thread in late 2011. I tried to wire them to generate "balanced" output, unsuccessfully- I got weird phasing issues depending on where the volume knob was set. I also tried putting the volume pot on the primary, which did odd things to the sound, and finally I wired them back up exactly as Jack specified, with a 20k ohm pot on the secondaries, as shown in the picture below.
I've used them with a variety of sources and in a few systems. They lack in bass, and they add a sort of fullness and resonance to the treble, which can be desirable or over the top depending on source and power amp. I wonder often if they would benefit from a nice buffer up front, to reduce the load on the source and feed the primary with however much current the reflected impedance asks for.
I'm learning to use an oscilloscope. I fed these with a range of sine waves from 1-3 Vp-p, from 1kHz to 20kHz, and the output waveform looked clean to my eye- but it was inverted relative to the input, something I'd noticed previously when attempting to use them to make an unbal. A 1kHz square wave showed "damped, symmetric ringing", a 20kHz square wave had a "rounded" appearance. I was playing with some Edcor transformers at the same time and was impressed by the relative waveform fidelity of the PVA-2n's.
I've done a bit with these PVA-2n's since the time of my last post in this thread in late 2011. I tried to wire them to generate "balanced" output, unsuccessfully- I got weird phasing issues depending on where the volume knob was set. I also tried putting the volume pot on the primary, which did odd things to the sound, and finally I wired them back up exactly as Jack specified, with a 20k ohm pot on the secondaries, as shown in the picture below.
I've used them with a variety of sources and in a few systems. They lack in bass, and they add a sort of fullness and resonance to the treble, which can be desirable or over the top depending on source and power amp. I wonder often if they would benefit from a nice buffer up front, to reduce the load on the source and feed the primary with however much current the reflected impedance asks for.
I'm learning to use an oscilloscope. I fed these with a range of sine waves from 1-3 Vp-p, from 1kHz to 20kHz, and the output waveform looked clean to my eye- but it was inverted relative to the input, something I'd noticed previously when attempting to use them to make an unbal. A 1kHz square wave showed "damped, symmetric ringing", a 20kHz square wave had a "rounded" appearance. I was playing with some Edcor transformers at the same time and was impressed by the relative waveform fidelity of the PVA-2n's.
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Hi Rranshdow, thanks for that info.I am getting thru to you on a tablet.My desk top won't let me thru without the pass word which I'm uncertain of.I'm waiting to hear from DIY to clear this up.My pictures of the passive transformer preamp are on my desk top. I have a pile of questions I'd like to ask you and show you tiny differences in our builds.Thanks again for that great letter of info you sent.....Mark Korda......kordamark@gmail.com 207-632-1648
Ranshdow, I'm going to try a picture on my tablet. I am at the cross roads with the Passive Transformer and the FX-01 Chinese tube buffer.I used a Dyna PAM-1 preamp for my chassis.All the holes are there already drilled and ready to be filled.I hope to get my desk top going when they give me the password I forgot....but did write down....somewhere....Mark Korda.....Dawk.
Hi Ranshdow, I think I got the problem solved with logging on.I'm on a tablet for this test but the pictures I want to send you are on my computer. Let me try sending you a couple picks until I get on my computer where the transformer passive build pics are.....thanks....Mark Korda..Dawkus
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hi Ranshdow, I built this after reading the article in AudioXpress. I used a Dyna PAM-1 chassis, which already has the right size holes for jacks already there. I used Goldpoint stepped pots,silver wire,gold jacks. The front are Dyna PAM-1 knobs and a piece of walnut from the hobby shop that I used amber shellac coats on, all hardware stores have it. I have this hooked up in my bedroom with a Dyna-35 amp and Dyna A-25 Mark 2's from 1978. I hope these pics go thru. I am getting real good bass but am really liking this tube buffer,FX-01 too. Need any info from anybody about how good these buffers are vs. the transformer passive.One thing I can't get out of my noggin is a quote from Mark Levinson.....keep the transformers out of the signal path? Anyway,I built this after my original passive build,I'll show that later.....favorite test cd is Sammy Davis Live at the Coconut Grove,1962. Thanks for all the info and patience....Mark Korda
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Nice! Yes I can see your pictures fine. That's an interesting chassis, it looks like it could be used for quite a few things.
I think transformer passive vs. buffer probably comes down to impedance matching between source, preamp, and amp. The 1:8 turns ratio of the PVA-2n will tend to reflect a hard, low impedance load back onto the primary and hence the source. Whether that source handles it well or not is probably guesswork, a muddy or very distorted sound seems to be one marker of an overloaded source.
I think transformer passive vs. buffer probably comes down to impedance matching between source, preamp, and amp. The 1:8 turns ratio of the PVA-2n will tend to reflect a hard, low impedance load back onto the primary and hence the source. Whether that source handles it well or not is probably guesswork, a muddy or very distorted sound seems to be one marker of an overloaded source.