Intact Audio

Generally speaking, you can only use a transformer input for a phono cartridge if that cartridge is a moving coil type. Moving magnet types have a source impedance of some 1500 ohms, and it's a reactive source as well, which makes it basically impossible to use a transformer with them. Thus, if you ...

But yeah, you're right, these are probably too difficult to make with wide bandwidth. They have significant phase shift, for example.

You may be reading the schematic too literally. See the coil winding they use in this reference: http://nees.buffalo.edu/pdfs/lvdt.pdf

Also, since we only need attenuation, then we only need one secondary coil.

OK thanks.

Alibaba lists a few suppliers of mu metal rod:
https://www.alibaba.com/product-detail/ ... 9602Un1lLc

I have no idea right now how to do the math needed to determine if this could be practical for audio. Obviously, the moveable core would have to be high perm metal like mu metal or nickel/iron. There would have to be a lot of turns of wire in each coil as well, but the good part is that it's easy to...

Hello David, have you ever considered the Linear Variable Differential Transformer as an audio attenuator? It seems to me that this is something that could be really great. No steps. You would need two for stereo obviously.

Hi everyone, Anyway, I had a chance last night to compare it directly to a Nagra PL-L and, while the AVCs were by far preferable (the Nagra is cold, steril and just lifeless with no PRAT or musicalty), the Nagra did present loads of detail and texture that the AVC simply did not. Especially in the ...

There's no such thing as "break in" time when it comes to magnetic devices. There is simply no relevant feature or quality of the device that would require any kind of "break in". The voltages are far too low to make any difference to anything. The magnetic circuit does not chang...

Hello Dirk! You state that the source impedance of the oscillator is about 600 Ohms. In this case it is no wonder that there is less ringing. The 600 Ohms damps the TVC quite good. But what when you drive it with abot 200 Ohms or even 50 Ohms? Then you see the truth :wink: You can do this while dri...

I'm not concerned with ringing, so I'm not going to do the test you describe, thanks. I checked it with a digital generator that has very low source impedance and it performed very well as I recall. It's not an issue for me. What is an issue is DC balance for the following gain stage after the AVC. ...

Hello Dirk! Very nice measurements! But as such results much depends on the source impedance would you please tell us what was the source impedance of you function generator and what was the schematic for measurement? Was this device loaded? Thanks! Docali the circuit is the AVC as an input, with a...

10kHz square response. Input set to 2Vrms, attenuation is -6dB. Really nice! Inductance is 218H @ 100Hz.

And here is the FFT for the full lam stack, this time only -6dB attenuation but the input signal is the same as before @ -18dBFS (-3dB is 2Vrms). Distortion is zero. That little pip @ 2kHz was not a harmonic since it was just part of the noise floor. I just happened to hit "print screen" w...

Frequency Response with full inductance lam stack. Much better bass response. Only down 0.3dB @ 20Hz! Rock on!

I checked the input/output linearity @ -18dB attenuation and it looks perfect to me. So, I'm excited about using these in my headphone amps.

I think you might find this pleasing. Zero distortion @ -18 dB input level @ -18 dB attenuation. 0dB is 2Vrms in this case. Noise is in the basement. Very nice!

Yeah, I don't think the TCR of the copper windings is critical to an AVC. I would be curious about the VCR though, which is the change in resistance with changes in applied voltage. A typical metal film resistor is 5ppm, for example, which is very low. So, for an AVC, the relevant value would be a c...

The TCR of copper is 3.9x10^-3, which is 3900ppm. That's terrible for a resistor, but may not be important because this is an AVC.

Any ideas on the temperature coefficient of resistance for this AVC? What about the voltage coefficient of resistance? In other words, how much does the resistance change with changes in temperature or applied voltage?

I did a loop back on the L (red) channel in this screen shot. As you can see, the oscillator adds 2nd and 3rd harmonics, so we subtract that from the blue trace and see that the 2nd and 3rd added by the AVC is actually lower than shown. I can't figure out yet how to subtract the left from the right ...

OK, here is the FFT for -3dB input level (0dB is 2Vrms, so -3dB should be 1Vrms), with attenuation set to mid level, -18dB. Performance is still excellent. Noise is extremely low, as expected. I like this a lot. What seems to happen is that as the level goes up, the harmonics multiply, but that coul...

Here is the FR, at -18dB attenuation. Note the scale. The AVC is down only 1.5dB or so at 10Hz. That's really great!

Hello Dave, sorry for the delay but I have been very busy lately. Here is one of several screen shots of FFT's of your AVC with a unity gain op amp buffer on the output. The performance is very good. I am impressed enough that I think I want to use these in one of my products. Input was set at 2Vrms...

I ordered the boards over a week ago. I'll post results when I get them. thanks.

This is where I'm at with the board now. Almost done.

I don't see any flying leads in this photo. It's not a big deal, but I'll have to wait until I have the attenuators in hand before finishing the test boards.

http://www.intactaudio.com/images/Atten ... AVC_Lg.jpg

dave slagle wrote:Where in the headphone amp are you planning on using them?

dave

At the input, after a blocking capacitor, just like a normal volume control. The AVC is DC coupled to the + input of an opamp (probably a DOA).

You can send me an invoice via Paypal if you want to.

OK! great! That's low enough that I think I want to use these in my headphone amp product. I need to order a pair of them for testing first. How do you want to be paid?

How do you identify pin 1 on your attenuator? Is there are mark on the bobbin? Is that image from the top or bottom of your attenuator?