[jules]

Hugh,

I'm [back] in the process of building my GK-1 M and unable to resist the temptation to do things slightly differently [though I won't subject you to the details].

I've been looking at the phono stage and I have to ask this question ... What is the point of the single banded 0 Ohm resistor? Is this a little audio expert prank just waiting for someone like me to ask the Q? Why isn't a piece of wire used? Anything to do with the current rating/limit of the resistor?

Jules

[gerchin]

What is the point of the single banded 0 Ohm resistor? Is this a little audio expert prank just waiting for someone like me to ask the Q? Why isn't a piece of wire used? Anything to do with the current rating/limit of the resistor?

Jumper wires that can be handled by an autoinsertion machine that normally grips the body of a resistor.

[jules]

yes ... that makes sense but in this case we're looking at a circuit board that's designed for DIY/manual construction.

Jules

[AKSA]

Jules,

A 0R resistor is, ummm, how you say, a tosser's exercise in pcb layout elegance, no more.  It is an acceptance of defeat that on a single sided board the designer was unable to do it without a link.....

And just as Gerchin says, it's a convenient way of using an insertion machine to install a link without human intervention.

Besides, it is amusing, no??   

Cheers,

Hugh

[jules]

I like it a lot 

Jules

[andyr]

Why isn't a piece of wire used?

Jules

Well, IMO, when you use links made from the gold-plated lead cut-offs from those Japanese Riken Ohm resistors, they look much nicer than a 0R "resistor"!   

Regards,

Andy

[Joules]

Sooo ... I suppose, Hugh Your amplifiers are ANR, Active Negative Resistance, less than zero resistance? 

[gerchin]

Jules,

Besides, it is amusing, no??   

Years ago I worked in Component Applications Engineering at Collins Radio.  One of my colleagues was asked by a design engineer to source some zero-Ohm resistors.  He had never heard of such a thing, and thought that the design engineer was pulling his leg.  Continuing the joke, he asked, "What tolerance?"

Greg

[AKSA]

Jules,

One of the peculiarities of the AKSA is that when you load it down the output very slightly increases;  from 50Vpp to 52Vpp into an 8R resistive load in fact.  This is effectively negative resistance!!   

Greg,

I love a tongue-in-cheek response.  But he failed to specify wattage - very important.  I always use half watt 0R resistors because the voltage rating is MUCH higher!   

Cheers,

Hugh

[ginger]

Laugh if you like - I'm like Jules, as I'm building stuff I think "what might work better in this position?" In the case of the GK1-M Phono Stage Input 0R resistors, the answer was some RF beads.
Cheers,
Ginger

[jules]

ferrite beads eh ... interesting idea. I'll resist the temptation to ask if they come in a string. That could take the humour of this thread into quite a different place.

Since you've mentioned RF Ginger, that's precisely what's been on my mind although my electronics is minimal and my approach is more, ummm, mechanical I suppose.

What I've been thinking of doing, is to excise the phono stage from it's pcb thus detaching it from the various tendrils that snake around that board. It will also allow me the freedom to place it away from the trafos and with short leads to pretty much everything. I'll also do away with the HT bypass and replace the Lorlin with an Elma fed by shielded wire ... but that's getting far too hard to explain in words where a picture would be easy.

jules

[andyr]

Laugh if you like - I'm like Jules, as I'm building stuff I think "what might work better in this position?" In the case of the GK1-M Phono Stage Input 0R resistors, the answer was some RF beads.
Cheers,
Ginger

Hi Ginger,

Can youse please hexplain (for us non-hexperts) what benefit "RF Beads" will provide in this position?

If we have used caps between the phono RCA input earth tags and chassis earth, shirley we have sorted out RF?

Regards,

Andy

[andyr]

What I've been thinking of doing, is to excise the phono stage from its pcb thus detaching it from the various tendrils that snake around that board. It will also allow me the freedom to place it away from the trafos and with short leads to pretty much everything.

jules

Mmmm, hi Jules,

I don't think just "excising" the phono stage section of the GK-1 Relay board (or the 'M' board, depending on which version you have) will necessarily allow you to "place it away from the trafos".   

I suggest what is a better thing to do is put your trafos near each other (oriented at 90 deg) and then have a metal "case divider" between them and all the GK-1 PCBs.  Thus minimising AC "noise".   

I myself decided to use two phono stage boards to give me a dual-mono phono setup ... ie. two op-amps, one powered by the R channel trafo and serving the R channel and the other powered by the L channel trafo and serving the L channel.  In my system, the R channel is the phono stage which is integral to the GK-1 Relay PCB and the L channel consists of just the phono stage section of a GK-1M PCB.  The unused input of each op-amp is shorted to ground.

All leads to and from are very short.

Regards,

Andy

[ginger]

Andy said

"Can youse please hexplain (for us non-hexperts) what benefit "RF Beads" will provide in this position?

If we have used caps between the phono RCA input earth tags and chassis earth, shirley we have sorted out RF?"

The caps from Phono RCA input earth tags to chassis earth will definitely help. What that does is effectively connect the shield of the cable to the metal case (chassis) at RF and therefore extends the shielding action of the box back along the input cable. There will still be unshieled bits of wire back at the cartridge itself or in the connections between the cartridge and the shielded cable. RF can get in there.  Not everyone has fitted the cartridge loading capacitor across the input (to 0V) but the cable itself is a "distributed" capacitor. That capacitance not only provides a more ideal load to the cartridge but also gives some RF protection. The Ferrite Beads are effectively a tiny inductor and they act to make any shunt capcitance to 0V the preferred path (lower impedance) for any RF on the input. That keeps the RF out of the opamp input. Its one of those "everyone knows" things (and therefore maybe wrong) that RF does nasty things to amplifier front ends. In an RIAA amp the high frequency end is boosted for ever and so the only thing limiting its RF response is the Gain/Bandwidth product of the Op Amp itself. (Andy, note that the extra 3.183us timeconstant roll off we added is after the opamp and so won't help here).To get best performance out of the phono section Hugh chose an Opamp with really good Gain/Bandwidth product so its best to do everything possible to keep RF out. Did I try it with just links before? - no, so I don't really know if it made a difference or not. I just satisfied my philisophical bent if you like.
If you want to try it you can purchase small ferrite beads which slip over the straight through piece of wire or you can do what I did and use Murata BLR01RN1-A62. These are 20 cent components which are just as described and are usually used for applications like tying the Analog and Digital grounds together in a Digital to Analog Converter to keep the digital noise out of the analog section.
The Murata part specs are as follows (which give you an idea of what they are doing):
DC resistance 0 Ohms (well 0.005 ohms or similar)
Impedance at 10MHz 38 Ohms
Impedance at 100 MHz 65 Ohms
Impedance at 1000 MHz 130 Ohms
Cheers,
Ian   

[jules]

Thanks Ian,

very useful in the quest to take some of the guesswork out of anti-hum design.

Jules

[andyr]

The Ferrite Beads are effectively a tiny inductor and they act to make any shunt capcitance to 0V the preferred path (lower impedance) for any RF on the input. That keeps the RF out of the opamp input.

If you want to try it you can purchase small ferrite beads which slip over the straight through piece of wire or you can do what I did and use Murata BLR01RN1-A62.

Cheers,

Ian   

Hi Ian,

Thanks for the explanation.  Presumably, the effect of RF getting into the phono stage opamp would be harshness in the highs?

I would certainly like to put some into my GK-1 phono stage but, having just put it all together after taking it apart to put in the 3.183us time-constant roll off mod, I dooo not want to take it apart again! 

However, it is relatively easy to get at the phono input RCAs ... so am I correct in thinking I could just unsolder the input wires from the phono input RCA pins, thread each wire through a ferrite bead and then solder them back again?

Secondly, you emphasised that the phono stage opamp has a wide bandwidth, so doing everything to limit the entry of RF is a good thing.  Does the same argument hold good for a discrete-component phono stage (ie. one not based around an opamp)?

And where do I buy ferrite beads?  My friendly local Dick Smith shop?   

Regards,

Andy

[jules]

Andy,

sorry I can't find the thread this came from but it's an earlier post from Ian on the ferrite beads. I've checked the RS sight and the RS part no. doesn't exactly correspond with the Murata part no. but I'm assuming that the RS part no. is ok. You'll notice that these arn't so much slip-on as solder in.

Quote ginger:

"If you look at your board you will see that the left and right channel Phono Amp inputs go thru' a couple of 0R resistor links. These 0R links can be replaced by ferrite bead inductors such as the Murata BL01RN-1-A62 (Radio Spares 239-589) @ 44 cents each. This will block any Radio Frequency (RF) picked up by the input cables."

Hope this isn't superfuous ....

Jules