LCR Phono using 6C45P

the road not taken.
reVintage
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Post by reVintage »

Got rid of the extra caps and resistors. D3a at its max ratings. Seems like the LCR doesn´t care what impedance it is fed with as long as the endtermination is is right. It sims good with a 1:1 (looking forward to a bifilar there). Overload 1%THD at ca 100mV rms. Gain ca 12dB incl. LCR.
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Lars
dave slagle
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Post by dave slagle »

Hey lars,

Now make it a 7K3 LCR and double the inductance of the IT.

an extra 12dB of gain and less distortion :-)

Then drop your frequency to 100hz and explain the results to me. ???

dave
reVintage
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Post by reVintage »

dave slagle wrote:Hey lars,

Now make it a 7K3 LCR and double the inductance of the IT.

an extra 12dB of gain and less distortion :-)

Then drop your frequency to 100hz and explain the results to me. ???

dave
Was lazy so I went for a 6k. Sims even better on all points.

Remember to change both .tran and .four expression when changing frequency.
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izzy wizzy
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Post by izzy wizzy »

Hi Lars and Dave,

Are stepdown transformers a problem? With a 2:1 stepdown, the 1k5 circuit gains 6dB in gain. But I'm guessing that's not for free; must be a catch.

cheers,
reVintage
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Post by reVintage »

Hi guys,
My guess is that 1,5k with 1:1 is the way to go. Think its better to keep resistances low. You will need a second gainstage anyway. With more output you have the risk to overload the second stage.

With a second gainstage like a D3a triode with 4:1 you´ll get 350mV out. Low compared to CD, but on par with the semipro-standard -10dBU.
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dave slagle
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Post by dave slagle »

izzy wizzy wrote:Hi Lars and Dave,

Are stepdown transformers a problem? With a 2:1 stepdown, the 1k5 circuit gains 6dB in gain. But I'm guessing that's not for free; must be a catch.

cheers,
that depends who you ask :-)

I still find it so cool that you could use a 2:1 stepdown to double the gain. With my sims of the d3A and 225V on the plate 150 on the SG i found 12K was the best looking but the problem with reflecting back larger valued loads is that you then need the appropriate inductance to work against that load. (a 6K load needs 4X the inductance of 1K5 load). I am also not a fan of low ratio transformers and a 2:1 that can handle the DC and have enough L for acceptable low end is going to be compromised on the top end.

the 1:1 bifilar lets you get away with murder since as you add more turns to keep the bass the top end doesn't become compromised anywhere near as quickly as it does with other transformers.

dave
dave slagle
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Post by dave slagle »

reVintage wrote: Was lazy so I went for a 6k. Sims even better on all points.
Yeah... I saw that... WHY????

(the higher load makes sense, but why would the distortion be lower at 100hz than at 1Khz?)

dave
reVintage
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Post by reVintage »

dave slagle wrote:
(the higher load makes sense, but why would the distortion be lower at 100hz than at 1Khz?)
dave
Must be that input signal is lower due to the rev-RIAA.
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Lars
dave slagle
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Post by dave slagle »

ahh good thought... but when I increase the drive to 600mv @ 100hz distortion drops :shock:


dave
reVintage
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Post by reVintage »

Spice errors :? ?
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izzy wizzy
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Post by izzy wizzy »

I asked earlier about small step down tx and wondered why it wasn't a great idea or not finding much favour - loked like it was being avoided.

Have since been digging around here and found this http://www.intactaudio.com/forum/viewto ... c&start=30 last post at the bottom which explains Dave's reasons.

Sometimes what looks like gain for free may not be :wink: Sims and real life experience can be at odds sometimes it seems. Thing is, I don't really need that much gain so maybe squeezing more out may not be a good idea.
dave slagle
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Post by dave slagle »

Hey Stephen,

Sorry to not be more clear. I was possibly still thinking how cool it was that using a 2:1 actually gives more gain. I also thought the bulk of the people here know of my distaste for small ratio transformers. I did do a pair of 2:1's and 3:1's for steve bench's LR phono and got 70Khz bandwidth, buth they only had 30hy's or so of inductance and doubling that number would cause substantial loss in the HF behavior. Typically people want a 2:1 to increase drive and in my experiences a 4X increase in drive with compromised frequency and phase behavior just isn't worth it. I'll take the bifilar 1:1 and bandwidth out well past 100Khz.


dave
PET-240
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Post by PET-240 »

Curiosity, did this end up anywhere?

Thanks,

Drew.
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