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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Re: some notes... posted by Stig on November 3, 1999 at 03:15:25:
Hi there,>>>I belive the AN trannie to be wound 1:3, which has partly been confirmed elsewhere. BUT, as Sowter winds their 1:18.7 There must be one hell of a difference in outputs??? Being a Maths student, I believe that there must be som algebraic formulae which could shed some light in this. Does anybode here have this formulae???<<<
It does. The term 1:3 and 1 : 18.7 refer to the degree of Voltage stepup.
So, if 1mV is presented to a 1:3 transformer the output will be 3mV.... If 1mV is presented to a 1:18.7 Transformer the output will be 18.7mV.
For the rest it is down to the way the I/V conversion Impedance is set. If one where to use the Sowter Transformer in the Audio Note Output Stage (with all other thing being identical with the AN Circuit) there would be way too much gain. If one uses a fundamentally different circuit it would likely be possible to bring the two set's of gain in line, but still, we are now talking about two fundamentally different designs again.
>>>Can anybody recommend some litterature, on this subject??
The Audio Note patent. The Application note on the sowter web-site.
>>>I am just about to equip my Denon DCD-3520 cd-player, with an all valve output stage, using a trannie(Preferably sowters, due to pricedifference between sowter and Audio Note), feeding a pair of E182CC, copying the circuit from Audio Notes DAC4. The E182CC´s do not amplify the signal as much as 6DJ8´s(so I have been told...please inform me if I am incorrect!!), so this setup might actually work.<<<
The difference in gain between the ECC88 and the E182CC is that the ECC88 has a gain of 33 and the E182CC a gain of 24.... As the E182CC has also got a lower Anode Impedance the loss of gain in the actual circuit will be a little les sthanthe difference between ECC88 and E182CC....
So the E182CC SRPP Stage will have about 3db less gain than the ECC88 version.... This is not substantially different. It might be worthwhile to look through the Sowter Catalogue for a suitable Microphone transformer having a 1 : 3 ratio (such exist) and use one of these.
I undertstand that the Sowter Transformer is aimed at stepping up the signal almost to line-level, to split the phase and to then drive balanced cathode followers to drive long balanced lines, possible with one of the Line "Bridge" Transformers. For such an application it seems eminently suited.
>>>I need only about 1v output from my cd-player.
Then just use the Transformer witout anything else.... You should get enough Output Voltage if you terminate the secondary using a 27kOhm Resistor. So as long as the load to the transformer (preamplifier) is resistive and at 27kOhm or higer you will get 1V....
Note - impendances are reflected through a transformer by the square of the winding ratio. So putting a 27k Resistor across the secondary of this transformer will mean that impedance reflected in the primary (which is coupled to the DAC) will 27k div 18.7^2 (square) or 27k div 350. So the "virtual" I/V Resistor seen by the DAC chip will be 27000/350=77 ohm....
BTW, the termination on the Audio Note transformer is 680 ohm and hence with a 1:3 Stepup transformer the reflected Impedance in the Primary is 680/9 or 75.5 Ohm. As can be seen, the load for the DAC is actually very similar.
Now, if we use a 1:3 transformer a'la AudioNote and a ECC88 SRPP Stage (gain around 24) we would for the +/-2mA swing of the PCM63 that AudioNote uses get a Peak full scale Output Voltage of:
2mA * 75 Ohm (DAC load)* 3 (Transformer Gain) * 24 (ECC88 SRPP Gain) = 10.8V peak or about 7.6V RMS
This is a bit high (though not higher some of the old Audio Alchemy Gear). Having noted that the AN DAC's are often slightly on the low, my guess at the transformer actually being 1:2....
For this case I believe the resitances shown in the patent actually omit a 200 Ohm primary side resistor. With that we get:
2mA * 92 Ohm (DAC load)* 2 (Transformer Gain) * 24 (ECC88 SRPP Gain) = 8.8V peak or about 6V RMS
This anyway can be seen as close to the usual CD Standard.
On the other hand the Sowter transformer is actually shown in the Application Note loaded with a 47 kOhm load.
If ten take this load we get a reflected 135 Ohm load that is relevant for the DAC Chip. Making the same Calculation as before we get:
2mA * 135 Ohm * 18.7 (Transformer gain) * 24 (SRPP Gain) = 121V peak or 85V RMS....
This obviously is totally out. As a result I would recon that the Sowter transformer and the Audionote unit cannot be identical.... Also, the Sowter transformer cannot be used at all in the Audio Note Circuit.
If it where to be used the Circuit to be used would have to be dramatically different.
Ciao Thorsten
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Follow Ups
- Re: some notes... - Thorsten 08:47:29 11/03/99 (2)
- Re: some notes... - Dave Ingels 11:40:09 11/03/99 (0)
- Re: some notes... - Stig 11:01:51 11/03/99 (0)
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