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

[Marco]

Yes I know what you mean, Martin, and to a degree you're right.

However, at this stage the only extra costs I've incurred are about £1 for the two series metal-film resistors installed. Once the Z-Foils (or whatever) are fitted, then I'll be out a bit more money (those, for example, are £15 each, so £30 for the Z-foils alone).

That's still piss all, in the grand scheme of things, in the context of a £30k system.....

If before I had embarked on this journey, with a passive preamp, someone had said to me 'Marco, spend £600-odd quid and you'll end up with an utterly stunning sound, and better than you've ever had before', I'd have snapped their hands off!

Remember too, that the Goldpoint now, 'as is', is outperforming the Croft, on line-level! So you've got a £600 passive (including import duty and tax) sonically outperforming a £4k valve preamp. I'd call that a result, no? If that's not high SPPV, what is?

Marco.

[Marco]

I do certainly, some previous description could be mis-interpreted as only one shunt resistor in play at any time, not the case as Nick also understood.

Not sure what you mean, Alan. As I understand it, there *is* only one resistor (per channel) in play at any time...

Marco.

[Macca]

Remember too, that the Goldpoint now, 'as is', is outperforming the Croft, on line-level! So you've got a £600 passive (including import duty and tax) sonically outperforming a £4k valve preamp. I'd call that a result, no?

Marco.

No question about it - this is what I have been saying about passive pre amps for ages. If you don't have thousands to spend on a pre (or even if you do) it is the way to go.

[Marco]

Indeed, but it has to be done right, whilst preserving system synergy. That clearly wasn't the case with the majority of passives I've heard in the past.

Marco.

[sq225917]

Any chance of a pic Marco. I owned a Goldpoint and cant imagine how it could be made a true shunt without a serious rewire. Though I can easily understand how swapping the actual shunt resistor for a different value would affect the voltage divider to give a completely different attenuation at each point of the switch.

[Marco]

Also remember, Martin, that if I had gotten Duncan to build me a passive from scratch, I'd still have wanted to use Goldpoint dual-mono steppers and a Goldpoint selector switch, so those alone (with knobs fitted) come to a total of $395, not much less than the cost of the whole unit itself - and that's before you buy a case, high-quality internal wiring, and quality RCA sockets!

So, in reality, how much would I have saved by just getting Duncan to build me one?

Marco.

[Marco]

Hi Simon,

Any chance of a pic Marco. I owned a Goldpoint and cant imagine how it could be made a true shunt without a serious rewire. Though I can easily understand how swapping the actual shunt resistor for a different value would affect the voltage divider to give a completely different attenuation at each point of the switch.

Sure, I'll do that when the resistor 'bake-off' is taking place and post the pics later along with my report

In terms of the bit in bold, that's one of the reasons why the whole exercise was worthwhile!

Marco.

[User211]

Q. Why did Mr Ohm marry Mrs Ohm?
A. Because he couldn't resistor...

Sorry, couldn't resist

[Firebottle]

Not sure what you mean, Alan. As I understand it, there *is* only one resistor (per channel) in play at any time...

Marco.

OK I'll try to elucidate. A basic attenuator has two 'arms', shown here by resistors Z and Y:



The Z resistor is the series part, this is the resistor that you are going to experiment with.
The Y resistor is the shunt part but in your case with the Goldpoint is made up from a string of resistors on the Goldpoint pcb. The 47 way switch now selects how many of these resistors makes up the Y arm.

The resistors in the Y arm are connected in series, that is through one to the next, then through that one to the next and so on. This can be seen clearly on the picture from the Goldpoint website:



So at position 47 on the dial (max volume) there will be 47 resistors in series making up the Y arm of the attenuator. Each click down from max will remove one of these resistors from the chain.

Clear?

[Marco]

Yup, I think so, and am pretty sure that's what is going on. However, I'll show your post to Duncan and ask him to confirm

I think his view is that the effect of the resistors in 'Y' can't be heard, as they're going to ground. In reality, I guess that they'll have a small influence on the sound. The main thing you're hearing, however, is the sonic effect of the series resistor.

Regardless, I'm more than happy with the current arrangement, which has effected a massive step-up in performance on the unit, compared with how things were originally!

Marco.