Explain this: Impedance matching transformer from DI into amp

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KVRist
92 posts since 15 Oct, 2010

Post Wed Jan 20, 2021 6:23 am

So.. I've been recording music privately at my own studio for decades and something odd (to me at least) happened a few years ago that I'm curious about, which I should probably be able to explain by now, but I'm actually still not extremely inclined in some of the more deep technical aspects of hardware.

That said, one day I tried this on a whim and it made my head do a 360 degree turn when I heard what came out of the amp:

Guitar -> small tube DI box -> Microphone Impedance matching transformer plug -> High gain input on amp

I should also note that the tube DI box was not 'starved plate' and used a transformer. The amp was also a 120 watt tube head.

Anyways, what I heard was an almost lifeless sounding tube amp - virtually turning into a raging, almost triple rectifier amp type sound. I just stared at the amp in disbelief for like 5 minutes scratching my head.

Technical explanation?

KVRAF
2067 posts since 15 Feb, 2006 from Berkeley, CA

Post Thu Jan 21, 2021 12:42 pm

Hard to say without knowing the input/output impedances and a little more info/specs about the gear. If it sounds good, it is good!

KVRer
7 posts since 21 Dec, 2020

Post Thu Jan 21, 2021 12:45 pm

It may relate to the changes in impedance over a wide frequency range.

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KVRist

Topic Starter

92 posts since 15 Oct, 2010

Post Fri Jan 22, 2021 6:06 am

Winstontaneous wrote:
Thu Jan 21, 2021 12:42 pm
Hard to say without knowing the input/output impedances and a little more info/specs about the gear. If it sounds good, it is good!
The DI was a Bellari ADB3 (the version without an input knob, three buttons per channel) and the adapter plug was a vintage Shure A95UF Line Matching Transformer. It was plugged into the high gain input on a Peavey VTM-120.

KVRAF
2067 posts since 15 Feb, 2006 from Berkeley, CA

Post Sat Jan 23, 2021 6:41 pm

Looking at the spec sheet for that Shure tranny, if you're going from low-Z input to high-Z output you're getting 20+ dB gain. There is internal wiring that can be changed depending on input impedance...whatever settings it's on seem to be working great for you! Also the more you slam a transformer with lots of level the more saturation you'll get. :party:

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KVRAF
5429 posts since 6 Jan, 2017 from Outer Space

Post Tue Feb 09, 2021 2:55 am

jp008 wrote:
Wed Jan 20, 2021 6:23 am
Guitar -> small tube DI box -> Microphone Impedance matching transformer plug -> High gain input on amp.
A DI box simply isn't made for this scenario and you definitely don't need it there.
https://www.soundonsound.com/techniques ... -impedance

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