Grid to plate and grid to cathode on a Telefunken ECC83 is under 2pf. Not sure if this would actually cause problems? Input resistance is dominated by the cartridge load, not the tube.
Could you please elaborate? Thanks. The most discussed use for the filter, at least from the days of analog and as I remember it, was removing non musical LF crud from the amplification chain which would a) keep your amp from working needlessly and b) keeping your woofer from pumping back and forth when the amp amplifies the 'subsonic' crud. Is this what you are referencing?The most important feature of the high pass filter, though it is not often mentioned, is to remove the output from the cartridge below 2x its natural frequency which, in a seismic transducer, is wrong in both amplitude and phase...
C'mon, stop beating about the bush and say what you really mean.;-)i fucking hate tubes
Is rumble really an issue anyway, except for a really cheap TT?The most important feature of the high pass filter, though it is not often mentioned, is to remove the output from the cartridge below 2x its natural frequency which, in a seismic transducer, is wrong in both amplitude and phase. Removing any rumble generated by the turntable is a less important side benefit, though it is the thing it is mostly mentioned for.
Now, if only someone would send you a Pro-Ject Phono Box S2 Ultra. I'd love to see how it compares with the Cambridge Duo.This is a review and detailed measurements of the Pro-Ject Tube Box S2 phono preamplifier. It is on kind loan from a member. The S2 costs US $399 on Amazon including Prime shipping.
I must this say this is the cutest tube audio product I have seen:
A nice set of controls let you pick one of six (6) different gains plus a useful subsonic filter.
Power is provided through an external switcher, a bit larger than a typical USB charger:
View attachment 60442
Sorry, don't know what tube is in there. Perhaps the owner can chime in.
Phono Preamplifier Audio Measurements
My standard dashboard is a 1 kHz tone at 5 millivolts simulating a moving magnet cartridge. Here is the output with 40 dB gain setting:
View attachment 60443
SINAD is mainly determined by the "tube 2nd harmonic distortion" to the tune of -72 dB. Add a bit of noise to it and you arrive at our SINAD of 69 dB. This naturally ranks near the bottom of our rankings:
View attachment 60445
One of the most important tests of a phono preamplifier is the proper implementation of RIAA equalization and the S2 does well here:
View attachment 60447
Other than tiny bit of emphasis at low frequencies the rest is pretty flat. Subsonic filter (dashed purple) does what it is supposed to do to get run of LP rumble.
Signal to noise ratio is not great by our standards but likely better than what the format (LP) can do:
View attachment 60448
Distortion versus input level is again "tube like" with proportional rise and without hard clipping until the end:
View attachment 60449
Distortion+noise versus frequency shows good behavior:
View attachment 60450
It gets a bit upset at 20 Hz and rises a bit at highest frequencies. For the most sensitive part of our hearing (2 to 5 kHz), it is the lowest at -70 dB.
Conclusions
Most of the time when a tube is put in some audio product the result is a disaster. It is as if they think stuffing the tube in there is all they need to do, performance to be damned. Not here. The Pro-Ject Tube Box S2 seems to have been designed well to do what people expect a tube to do: produce a gradual rise in distortion with level.
Personally I have no use for a tube audio product. When I have listened to them in the past, they either do nothing (i.e. distortion is below audibility) or obscure detail due to higher distortion. To the extent you do, the Pro-ject Box S2 scratches that itch well and looks adorable to boot!
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As always, questions, comments, recommendations, etc. are welcome.
You all know how addicted I am to money and shopping. I thought I see if I can shake off the habit and stop buying things cold turkey. Well, it didn't last but a few hours before I went on Amazon and bought something!!! Can't help it. Until I figure out the method to kick the habit, I need to rely on your money. So please donate what you can using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
A squid eating dough in a polyethylene bag is fast and bulbous.Thanks for sharing, now would anyone else in the group like to share their thoughts ?
THanks. Forgot to mention and show a picture of dip switches underneath that sets the capacitance.Some useful adjustability...
Input impedance10 ohms, 100 ohms, 1 kohm, 2 kohms
Input capacitance/impedance 47pF, 147pF, 267pF, 367 pF, 487 pF and 587 pF* / 47k ohms
Input gain 40 dB, 43 dB / 50 dB, 60 dB und 63 dB
THanks. Forgot to mention and show a picture of dip switches underneath that sets the additional capacitance.
... but only if the tubes are in the first amplification stage. Do we know this is the case?FTFY. With a starting point likely to be a minimum of 150pF, that throws those numbers off significantly.
... but only if the tubes are in the first amplification stage. Do we know this is the case?
Reading elsewhere, it seems the input stage is FET. <https://www.project-audio.com/en/product/tube-box-s2/#features>... but only if the tubes are in the first amplification stage. Do we know this is the case?
Of course. It wasn't just for reliability and durability that transistors replaced valves (tubes).I love audio but most of what's on this site is WAY over my head. But I read enough of I think, the Audio Critic years ago to know that Tubes do introduce some distortion. Glad to know Amir's basic stance on tubs confirming this.
Also from there, manufacturer's specReading elsewhere, it seems the input stage is FET. <https://www.project-audio.com/en/product/tube-box-s2/#features>
Noise floor 80 dB (A weighted) at 40 dB input gain, 75dB (A weighted) at 50 dB and 63 dB input gain
THD <0.02% at 40 dB input gain <0.05% at 50 dB and 63 dB input gain
RIAA-equalisation curve accuracy +/- 0.4 dB/20 Hz - 20 kHz
Subsonic filter at 20 Hz with 18 dB/octave
But, if you wire them in series, you get the Internet.i fucking hate tubes
Best case it's then a hybrid preamp, and there is a good chance all the heavy lifting is done with solid state components and the tubes are there either as a final stage amplification and an excuse to call it a "Tube" preamp or just for eye candy .Reading elsewhere, it seems the input stage is FET. <https://www.project-audio.com/en/product/tube-box-s2/#features>
Well, audio gear does not come with such an EQ. EQ is a linear process whereas second harmonic is a non-linearity.What is the point of tube amplifiers, if you want to add colour why not just EQ to your taste...probably with less 'noise' and more customisable...tubes seem like the love of vinyl, just sounds like pawn!