Goldpoint SA4M-47 passive 'preamp' winging its way to Marco Towers...

[The Black Adder]

how cool... It's great having little nuggets of information like that, Nick...

[Firebottle]

Yes there's nothing new in analogue electronics, it has all been mastered with valve designs many decades ago. By some very talented design engineers to boot

[Arkless Electronics]

probably the first application which crude valve op amps were put to was in electronically aimed ack ack guns in conjunction with early radar in WW2

[Marco]

Aaanyway, Marco moochacho, hows the Goldpoint sounding after today?

Sounding great, mate, but still going through some light tweakage. Dunc is adjusting how the stepped attenuators operate, in terms of attenuation, in order to optimise their use within the gain structure of my system

Marco.

[Marco]

Ok, just a little update on the above... As the unit has effectively been changed from a series to a shunt type (as it sounds markedly better that way), so that the signal, at any position on the dials, now only goes through one resistor in each channel, the value of those two resistors, as well as their inherent quality, is therefore critical.

In that respect, it's been rather interesting playing around with those resistor values (initially using inexpensive but decent quality metal-film types), in order to tailor the gain structure of my system to the volume levels available, at various positions on the controls of the Goldpoint, where it became obvious that the 50K value of the resistors originally fitted on the stepped attenuators were the reason for why I wasn't getting enough volume available on the early steps [e.g, 0-8 was virtually silent]...

Therefore, changing the value of the two resistors, initially to 10k, completely cured that problem, but made it too loud, so we changed them to 22K, which was just about right, but not quite, so I've now settled on 20K, which is perfect. It now means that normal listening levels, for me, occur at the 8 to 9 o'clock positions on the dials, and not the 11 to noon positions previously, which I found unnatural and somewhat counter-intuitive.

What this means now is that there is an opportunity to experiment with some 'audiophile quality' 20K resistors, and to that end I'm going to order from Hi-Fi Collective two each of the following:

Charcroft Z-Foils, AudioNote Tantalum (non-magnetics), Caddocks, PRPs, and for something a bit different, Amtrans AMRG carbon films, just to see what carbon sounds like compared with metal... All will be either 1 or 2W versions. You can read all about the various resistor types here: http://www.hificollective.co.uk/catalog/-c-61_62.html

The resistor 'bake-off' will be taking place on Tuesday this week, and the results of that will be posted here later on that evening, so it'll be very interesting hearing what happens and what turns out to be the winner!!

Marco.

[Firebottle]

It certainly will Marco, thanks for taking the time to do this.

[Marco]

No worries, Alan. I have to admit to finding all of this fascinating, with the ability to fine-tune things to suit your system. Ok, so the unit is no longer standard (although the mods are easily reversible), but then neither is any of the other kit I use, so I guess it was only a matter of time before the Goldpoint was similarly modified!

The fact is, it sounds markedly better now that it did when I first got it, and I still have the flexibility of all 47 different volume steps, together with the superb quality of the Goldpoint switches themselves, as well as that of the whole unit. If things can move forward, sonically, even more by fitting some audiophile quality resistors, as mentioned, then this little device will really be something special!

My report on the resistor comparisons may help others considering upgrading the resistors in their equipment, as it's always a rather unknown quantity (and somewhat of a lottery) choosing these things, so I'll do my best to describe what Duncan and I heard before each changeover of resistors, and will takes notes to that effect, so that I don't forget anything.

At the end of the experiment, I'll also have some cut-price high-quality resistors for sale, so folks can keep an eye out for that, too!

Marco.

[Barry]

I'm more concerned that Goldpoint chose to employ a series attenuator circuit topology, rather than shunt.

Regarding the setting for 'normal' listening levels, I find that if the angular range is centred around 12 o' clock (say minimum level at 7 o' clock to maximum at 5 o' clock), then I try to arrange things (output voltage from the individual sources) so that my normal listening level is at 12 o' clock.

That way you are sufficiently out of the noise floor, but have ample room to encompass the required dynamic range.

I should of course add that I assume the volume control has a logarithmic 'law'.

[struth]

Been using metal films in my wad when changing values too. They are great for very little money.

[Marco]

Regarding the setting for 'normal' listening levels, I find that if the angular range is centred around 12 o' clock (say minimum level at 7 o' clock to maximum at 5 o' clock, then I try to arrange things (output voltage from the individual sources) so that my normal listening level is at 12 o' clock.

That way you are sufficiently out of the noise floor, but have ample room to encompass the required dynamic range.

We're obviously different in that respect then, Barry. I've always been used to my normal listening levels (say, 75-80db) to be achieved at around 8-9 o'clock on the volume knob of my preamp. We only measured 50db at that point on the dials of the Goldpoint, using white noise to test with (and an app on Duncan's iPhone), when the unit was standard.

Also, music reproduced, with the unit as standard, although good, sounded somewhat limp and 'weedy', in comparison with how it is now, which mirrors my experience in other areas whenever that effect has happened - and I don't like it.

For me, it's about optimising the gain structure in your system, and finding the 'sweet spot' where everything sonically clicks into place. In my system, that's achieved with the use of 20K resistors, and it gives me ample room to encompass the required dynamic range with all recordings.

Marco.