The Marco-boy main system, as of August 2020

[Marco]

Good post, Gaz - shows how you've learned from your experiences and used that info to your benefit (and that of your system). I also think it's no 'happy accident' that you've got into CD again after getting a decent transport, which for me is the key to really enjoying what CD has to offer, and a properly designed dedicated transport makes a big difference

It's not just about the DAC, and 'any old transport' will do, off of a DVD player or whatever. For me, that's bollox and simply doesn't tally with my experience.

Unlike you, I've never 'fallen out of love' with CDs, despite embracing streaming (although not to anywhere near as high a standard as you), and of course have never stopped enjoying vinyl, and that's because I've been using the same (top notch) Sony CDP and DAC for the last 11 years, which really shows what the format can do.

So continue enjoying those sliver discs mate, along with everything else. You've got a nicely assembled system going on now, by paying close attention to the details and making properly informed choices, and long may that continue!

Marco.

[Beobloke]

Marco, out of interest, why are you using nylon bolts on your cartridge? Is this a recommendation to do with the Houdini?

[Marco]

Hi Adam,

Yes, it's because of how the Houdini is designed. The bolts/screws have to be cut to fit (reduced in size) in order only to penetrate the Houdini far enough to secure the cartridge, but not so far as to upset its suspension.

Plus it also reduces mass, should that be a consideration

Marco.

[Light Dependant Resistor]

Interesting idea, and one that could work. This is far from an urgent project though (just floating some ideas about, really), so I won't be rushing into anything. As usual, when I've decided to go ahead, extensive research will be undertaken, and the processing of as much relevant info as possible will be carried out before a choice is made.



Yes, so they say, and in certain circumstances that may be true.

However, I've used umpteen different passives in my system with the Copper amp, which is even more sensitive than a Quad 306, and high-efficiency speakers (95db Tannoys), and where on paper a passive should thrive, yet (aside from LDRs), when used the soundstage collapses and they *always* sound soft/veiled/'padded out'/lacking in 'drive' and dynamics (even receiving a 2v digital signal), *in comparison* [that bit is crucial] with the best active designs.

Therefore, given the above and the type of system I've tried passives in, I'm struggling to see what the 'compatibility issues' would be?

Don't get me wrong, the sound isn't dreadful or anything like that, with passives, just not up to the high standards I'm used to from top-notch active designs. You have to remember the benchmark I've got as an active preamp...

My modded Croft, in today's market, would likely retail for around £8-10k - it's a very capable, highly-optimised design, which allows serious insight into recordings, and a truly wide-open window onto the music, so that's what any passives are up against.

Interesting though, that LDRs, some of them despite not sounding anywhere near as good as the Croft, don't suffer from a lack of said 'drive', and consequently don't sound soft, so there must be something in their design that negates this.

They're powered by the mains supply, so perhaps that's part of it?

Marco.

Hi Marco
LDR's are capable when properly powered to present music exactly as it was recorded. They neither add or subtract from presenting every bit of detail, dynamics that the recording has preserved.

Properly powering them has been my passion and interest for over 13 years. The type of LDR firstly is the encapsulated type NSL32SR3 . The SR3 has the best properties for audio as well as capability of highest resistance range.
The circuit formed on the signal side is a passive L pad, however with a distinct difference, to simply being just variable resistance ( achieved by more or less light intensity ). The difference is the enormous hold or grip which LDR's have on the entire grounding of all audio equipment, that it attaches to. The benefit is a black silence in a unbalanced audio system, that even balanced systems cannot achieve. To make this occur the LDR anodes needs to receive ideally 8 volts or more and have its cathodes not directly grounding, rather far better forming active current drive for the circuitry.

If we think of the most outstanding amplifier circuits that preserve bandwidth such as the cascode and common gate, and we apply those forms to what is ostensibly a DC circuit, we find we suddenly are confronted with added audio properties
occurring on the signal side. Some might say DC circuitry does not need high bandwidth as it is form, is the exact opposite, however if we read manuals such as Designing with Field Effect Transistors 2nd Edition reference is indeed made to using cascodes in DC circuitry. I regularly inform audio forums who muster all sorts of opposition to LDR's, that they simply relay how well or how poorly they are powered, power them well if we speak in positive terms and that is what you hear.

Comparison then to other passives that do not have this grounding grip as we are calling it , has LDR's in a area all of their own. Other passives use ideally or represent approximately 15 k of resistance at mid volume in usually equal halves as a potentiometer, variations are those with log curves meaning there is usually a taper in the volume curve . The benefit with LDR's is they emphatically do NOT have to follow potentiometer set curves and forced restrictions.

We are thus free with LDR's to have total control over where the shunt pair becomes active vs the series pair. Another is that we can have total silence at zero volume, simply by arranging a voltage reference pushing appropriately against the series cathodes. Which begins to ask, what is ideal resistance of the potentiometer used in LDR's and what is its best positioning. In my circuits I can proudly say there are NO resistors on the main board - none at all ! Rather I have solved all need of resistors, with semiconductors. Most of the semiconductors used therefore are very close internally to exactly half the potentiometer resistance value, so the potentiometer used for attenuation is just seen as yet another semiconductor resistance value and in effect semi disappears as a device. The potentiometer is placed between the series cathodes volume UP, and shunt cathodes volume down. When measured we find some really good impedance characteristics for matching to source components and to power amps. Typically 1k3 on the shunt pair at half volume and 2k to the series pair. If we compare this to a stepped attenuator or a potentiometer passive it is losing badly in terms of connecting the source component and power amp, as it has much higher resistance in order to function. LDR's therefore connect not only all your grounding paths with grip, but also connect to the source component and power amp in near perfect relationship.

I hope that helps to answer some of the mysteries. Please let me know if I can help further.

[Marco]

Hi Chris,

Thanks for that, much appreciated. I think this part kind of suns up what you're saying, especially the emboldened text, in reference to what I was describing earlier:

Rather I have solved all need of resistors, with semiconductors. Most of the semiconductors used therefore are very close internally to exactly half the potentiometer resistance value, so the potentiometer used for attenuation is just seen as yet another semiconductor resistance value and in effect semi disappears as a device. The potentiometer is placed between the series cathodes volume UP, and shunt cathodes volume down. When measured we find some really good impedance characteristics for matching to source components and to power amps. Typically 1k3 on the shunt pair at half volume and 2k to the series pair. If we compare this to a stepped attenuator or a potentiometer passive it is losing badly in terms of connecting the source component and power amp, as it has much higher resistance in order to function. LDR's therefore connect not only all your grounding paths with grip, but also connect to the source component and power amp in near perfect relationship.

Do you think that the higher resistance you've outlined, together with the lack of "grounding paths with grip", explain why with the passives I've used to date in my system (despite it on paper being 'ideal' for incorporating such a device), music reproduced sounds 'subdued' and lacks 'life' [best way I can describe it] compared with when done by a good active preamp or LDR?

For me, what you say makes sense and confirms my listening experiences in that respect. I'm convinced that a) I'm not imagining the effect, and therefore it's real, and b) that it isn't due to the artifice of an active preamp (in this case my Croft) making the sound appear as superficially 'more exciting', and therefore creating a false effect.

To my ears, it's definitely the other way round, and in fact the passive device robbing the sound, and subsequently the music, of elements that should *actually* exist!

Marco.

[Light Dependant Resistor]

Yes that nails it, passives other than LDR's, alter the ideal source to power amp relationship by using too much resistance, just when less is needed. In effect as you say, robbing us of the life in music that is actually there in abundance.

The fact that LDR's solve other passives failings, in their unique way, connecting us so well with the music, is why I have been so excited about them, all these years.

[Marco]

Yes, your current Stereo Coffee is the best LDR I've heard, and which no doubt will become even better when fitted with the latest boards!

It certainly pisses all over any other 'passive preamp' I've heard.

Marco.

[Marco]

Btw, just an addendum to the 'which preamp to partner the 306 with' conundrum.... After having carried out some research, I've decided to go for a late (grey-version) 44, and have it modded/upgraded by Redhill or similar - the full monty, with off-board PSU!

So if anyone sees or knows of any for sale [only minty examples would be of interest), let me know!

Marco.

[Marco]

I use these voltage regulator tubes in my Croft preamp, and I've been wanting this one for a while, as it's a special (and rare) military spec version, from the 1950s, of the 85A2:





I've rolled these VR tubes before, and the best ones always make a nice difference, so will be interesting hearing what this one does!

For the Croft's line stage, I've also just bought a rather nice matched Pair of 1940s Raytheon 6SL7GTs in gray glass:



Looking forward to hearing those, too!

Marco.

[Marco]

I haven't used one of these in the Croft for years, but had very fond memories of it, so decided to take the plunge and treat myself to one, which as you can see has been fully tested and is conforming to spec, courtesy of AnthonyTD of Tube Distinctions:









It'll be interesting comparing it with my current favourite ECC83/12AX7 type, which is my rather rare and superb sounding La Radiotechnique, of a similar vintage, as shown here where I bought it from (read the description): https://reverb.com/item/4913765-la-r...d-1967-vintage





It'll be interesting seeing if the Mullard can better it!

Marco.