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Accession MM Capacitance/Loading Settings

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Graham Slee View Drop Down
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Post Options Post Options   Thanks (2) Thanks(2)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 05 Feb 2022 at 10:24am
The noise and signal gains of a non-inverting amplifier always differ, the signal gain is always +1. There is common mode distortion. The noise and signal gains of an inverting amplifier are equal. There is no common mode distortion.

In the early days of the single-valve preamplifier input stage, input resistance was in series. It was an inverting amplifier. All signals were small, except maybe a radio tuner, but tape heads and magnetic phono cartridge outputs were in units of millivolts. Valves were not "really noisy" as such, but the series input resistance contained resistor noise, which was amplified along with the signal.

All resistors exhibit noise at 4nV per square root of frequency at 1,000 ohms. There is no such thing as a lower noise resistor. The series input resistor of 47k ohms exhibited noise of 188nV per square root of frequency, which would be laughable if it were not for the RIAA EQ which is inverse to the cartridge's constant velocity response. The RIAA EQ is akin to an integrator such that the piercing higher noise frequencies are equalised along with the signal. The result was slight hiss. Quite acceptable at the time, and still is according to the valve renaissance.

The input stage of the Accession M is identical to the valve circuit but in solid-state. The exception being that it is a true single pole integrator giving constant loop-gain rather than the stepped loop-gain which causes phase shifts around the EQ turnover, which combined with the large gain, can result in audible distortions.

At that point the resistor noise is no different to that of the valved RIAA EQ preamplifier, and is actually slightly lower because of the lower noise solid state amplifier compared with the valve.

The second stage re-inverts the input stage inversion making use of the accuracy and zero common mode distortion of the inverting property, avoiding the need for empirical guesswork for the EQ. Due to it's additive nature it increases the noise from the preceding stage by +6dBu.

The measured noise is -66dB with CCIR quasi-peak rating at 20Hz - 20kHz. Unweighted it will be nearer -60dB, but the relative value is dependent on the cartridge output (lower equates to higher S/N because the volume is turned up). Even so, the old IBA specification was 58dB, and when the maximum velocity of 14dB is added, results in the dynamic range of 72dB, or 12 bit, which Elektor also established in the 1970's. Therefore, in play, the hiss level is at or below the noise floor for vinyl.

Unlike digital, analogue signals can be heard below the noise floor, and as such, even at -58dB, signals can be audible down to -64dB, and with vinyl headroom added, that corresponds to 13 bit.

The Accession was based on the forum's musings over "curve-in-curve" equalisation discussed more than 8 years ago. Having found a different and viable way of doing it, the details were then protected under patent law, enabling them to be discussed openly, and in 2014 to 2015, the prototype was demonstrated at three different public shows.
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Post Options Post Options   Thanks (2) Thanks(2)   Quote paulsmith048j Quote  Post ReplyReply Direct Link To This Post Posted: 05 Feb 2022 at 1:08pm
Graham and Jon,

Thank-you so much for your responses.
I do hope I didn`t (totally unintentionally!!) cause any offence Embarrassed.

The extra `hiss` did take me slightly by surprise to be honest. It will always be more noticeable for me compared to the overwhelming majority of your other Accession MM customers as all my listening is via headphones (tweaked Sennheiser HD600s) because of environmental (and marital!!) considerations.

For the avoidance of doubt, even after a brief listening session on an Accession that is nowhere near burned-in/fully optimised yet, I could never go back to the Reflex M now Clap

The general amount of extra musical detail; the tighter, `quicker` and more detailed bass performance, plus what also appears to be a general increase in transient performance/dynamic range clearly shows that I`ve made a very wise choice with the Accession. 
In short, it is superb, and I`m sure it will only get better in the ensuing weeks/months.

I was just seeking reassurance about the extra `hiss` which, from your comments, you seem to be suggesting is to be expected - so that is more than good enough for me Smile
Graham`s analogy of a racing car (Accession) versus, say, a saloon car (Reflex M) makes complete sense to me now. 

Again, gents, my sincere thanks to you both for your interest/support in my new purchase.

Best wishes, Paul


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Graham Slee View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 05 Feb 2022 at 5:01pm
Originally posted by paulsmith048j paulsmith048j wrote:

I do hope I didn`t (totally unintentionally!!) cause any offence Embarrassed.


Not at all, I was just explaining why. Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote paulsmith048j Quote  Post ReplyReply Direct Link To This Post Posted: 06 Feb 2022 at 5:51pm
A more lengthy listening session today.
In short, I think I`m in love! Clap

Where did all that extra detail and `musicality` come from?
Not to mention the extra space/separation between instruments.
The Accession MM has only been powered up since Wednesday afternoon so I know there is much more to come!

The hiss with no music playing is basically not an issue now as I have become fully `acclimatised` to the Accession MM.

The culprit is probably my Sennheiser HD600 headphones which have an impedance of 300 ohms and require a high volume setting on my Naim pre-amp to reach my desired level (which is probably louder than most people).

A headphone upgrade is on the cards this spring; maybe the Focal Clear which is much easier to drive (55 ohms) and will need a lower gain setting on the pre-amp to hit the same volume levels, so maybe less hiss evident?

One final question for Graham and Jon: I`m toying with upgrading my PSU1 to the `Enigma` but £385 is a lot of money. Would you guys accept a PSU1 as part exchange? I have the box and it is in mint condition.
Will the Accession MM take full advantage of the Enigma, or was it intended more to partner the Accession MC? I`m fully aware of the importance of the power supply in the hi-fi chain and was blown away by the difference that the `Radikal` MK2 PSU made to the performance of my L*nn LP12 Smile

Grateful for any suggestions/comments.


Edited by paulsmith048j - 06 Feb 2022 at 5:54pm
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Fatmangolf View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 06 Feb 2022 at 6:05pm
I have an Enigma PSU1 powering my AccMC and wouldn't go back. I haven't tried the Enigma properly with my Acc MM, just a quick go when my second Enigma (I don't go on expensive holidays!) came for the Majestic which sounds evn better for it. There are others here with Enigma PSU1's powering their Accession MM's, they would be better placed to answer than I am...

This posting from Kory may be helpful:

It is part of a longish thread about the Enigma PSU1 which may also be of interest Paul.

Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote ctalcroft Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2023 at 10:10pm
First post here. I start by acknowledging that I don't understand capacitance/load don't know how to calculate what is, at least in theory, best for my set-up. I've had an Accession MM for about a year and a half now and have been very happy with it and remain happy with it. I've got the switches on the back set to the recommended 100pf. I'm writing though because I've recently changed my turntable (to a Dr. Feickert Volare, previously a Rega Planar 6) and I'm auditioning a stylus change (contemplating going from the Ortofon 2M Black to the 2M Black LVB, which should be a step up.

However, I don't notice a huge difference between the two styli. I do notice a number of things though.
1. The LVB seems to suppress surface noise more than the regular 2M Black
2. The LVB seems a bit airier at the high end and a little better at presenting complex passages (notably, massed orchestral strings).
3. The LVB seems to dull down the lower frequencies.  

I'm wondering if changing the dip switch settings on the back of the Accension might be better with the LVB. I don't want to reject it because I'm not letting it do its best. 

Anyone have any thoughts on the subject?

To test my perception about the bass, I got out some of my old rock records (normally I listen almost entirely to classical music). I listened to The Who's "Who's Next" and the whole thing sounded a bit muffled and dull. Normally, I listen with the bass/treble controls on my Outlaw Audio rr2160 amp turned completely off but I have to turn them on when I listen to rock music and turn down the bass several notches because the bass is too much. With the LVB, bass did seem excessive with the controls turned off – as I say, it sounded reduced even, which I'm thinking confirms my perception that the 2M LVB somehow muffles the bass and enhances the highs relative to the plain 2M. 

So, again, would a change in switch position likely have a positive effect on the frequency presentation of the 2M LVB?

Thanks!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ctalcroft Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2023 at 10:12pm
Sorry, that should have read "With the LVB, bass did NOT seem excessive with the controls turned off..."
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