Intact Audio

Since you do not want to make the measurement I asked you for, I will tell you that the Z-in of a 600Ω LCR network above 1kHz is 600Ω independent of any terminating resistor. load it with 600Ω and the Z-in is 600Ω, load it with 1M5 and the Z-in is 600Ω. There is a small increase in Z below 100h...

Minimum input sensitivity is not a "thing". The firstwatt lists two different input sensitivities, one for full power (the accepted standard) and then one for 1W output which is not typical or traditional. I have been going by the traditional definitions and use of an autoformer and it see...

I have no need to attenuate below my amplifier sensibility

input sensitivity is the voltage input required to get to full power. If you have no need to go below that then you will be listening at full power all the time.

dave

I do not know the conditions of your test but it shows the output in the frequency domain and I asked you to measure the Z-in of the LCR with 1.5MΩ and 600Ω terminations.

dave

hello walter.... you are the one big on actual measured results in place of simulations so measure the input Z of a 600Ω LCR with and without the 600Ω termination and let me know if you want to change your above statement.

dave

I like and use the pentode as the first stage but the use of a 600Ω load which appears in parallel with the 600Ω input Z of the LCR presents a 300Ω load to the pentode which throws away precious gain. Granted a pentode loaded with 300Ω will have really low distortion but I only get around a gain...

Then tell me what the attenuation range and step size is and I'll wind them.

dave

OK... so you can't clip it... the next question becomes how loud do you listen and what range do you need. the 0.57V input voltage gives 1W out so the question becomes how loud do you listen with respect to that?

dave

it is possible and I will gladly do it for you but as far as I can tell is it will serve no purpose and render your system unusable since anything above 0.5V will clip your amps so your loudest setting should be -12dB and you should go down from there.

dave

The input sensitivity of the amp is the voltage input required to get to full power so you will need a minimum of 12dB attenuation to avoid clipping. Assuming the 30dB range I mentioned before, that makes the 42dB of attenuation of the $200 units at the edge and I suspect you will have "hair tr...

if you want all of your attenuation to be done with the autoformer you will need a 30dB range or more. What that range is becomes a function of your system gain.

dave

if you have access to digital attenuation through your dac then you can monitor the levels through several types of music and come up with a workable rage. I find I routinely use about 30dB from quiet to loud listening sessions. set the digital attenuation to -12dB and see it you ever feel the need ...

it can be but then you will not have a very practical range of attenuation.

dave

2V to 0.5V is only a 12dB range and will not be very effective for adjusting level.

are you looking to control overall system volume or match levels in a multi-amped situation?

dave

It is still unclear to me what you are trying to accomplish. 6dBv is 2V and 0dBv is 1V. That is not much of a range of attenuation.

dave

that is a custom taper on the basic $200 autoformers.

dave

Hey,

It is unclear what you mean by "6db is my max reduction". Do you want to be able to do some form of level matching and attenuate elsewhere?

dave

V! and V2 are just generic voltages and van be replaced by any biasing method that will give that voltage. I have used LED's in that position and like it. you will have to try a bunch of different types since they all sound and bias up differently. I think an unbypassed Rk is going to seriously effe...

well a nickel core goes a long way to getting better sound

dave

OK If the autoformer is not part of the filter network and is purely intended as a level match device then it is serving another purpose. a 4dB cut is a 1.6x voltage ratio and a 2.56 impedance ratio. This will make the 5mHy choke that follows it appear as a 12,8mHy choke and the impedance of the dri...

Hey,

I think you have answered all of your own questions and it is not my design so it is not my place to comment.

dave

I am not sure exactly what is going on in that crossover. I would need to know the inductance values of the autoformer to get a better idea since it is unclear if the autoformer is part of the filter or a simple attenuator.

dave

If I insure the package a signature will be required. Pop me an email and we can discuss the options privately.

dave

A shielded chassis doesn't hurt and a simple steel box will suffice.

dave

i just checked a pair and the crosstalk was less than 60dB @ 100hz

dave

you are correct that even though every attempt to minimize inductance is made, there is still a small amount that remains. The moral of the story is they are not linear and should not be used in filter circuits or as an unbypassed cathode resistor but once the resistance is bypassed, so is any resid...

yes that wiring diagram looks correct.

I don't have a quick source for that switch.

dave

hey, the wiring instructions are at the link below http://www.intactaudio.com/AVC_wiring.html as for the switch the wiper goes to the output RCA center pin and the taps get soldered in succession to the pins. Turn the knob all the way CCW and use a DVM to find which tap has continuity and solder the...

io

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