A rotary switch for phono playback that presents three positions: mono, mute, and stereo.
Seems it comes with a selection of values in the kit.
Best guess is to derive the value on thephoto and start with that and figure it out from there...
Seems it comes with a selection of values in the kit.
Best guess is to derive the value on thephoto and start with that and figure it out from there...
Says "Glassware" on it.
A rotary switch for phono playback that presents three positions: mono, mute, and stereo.
Would have been sweet to save us all a Search.
Doesn't Broskie put instructions in his kits? If not, he has generally been responsive to email.
He doesn't have a recommendation regarding type. One can purchase either metal film or carbon film so that's why I'm asking for recommendations. There is also an option for 1% resistors but then you lose the option of type. Confusing to me.
The value is also in question.
I apologise for not linking to the unit. I thought it was a basic question or two.
The value is also in question.
I apologise for not linking to the unit. I thought it was a basic question or two.
A mono/stereo switch in a preamp could in some cases be simply a SPDT which either connects the two channels at a suitable point or not. It was unclear to me why someone might need a separate PCB for such a trivial role. The fact that it is a phono preamp tells us nothing much at all.
In this case it appears to be a more complicated setup meant to go after a preamp. The resistors are just there to avoid shorting the output - although a good design of preamp would probably already incorporate these internally. The value is not too critical: a little higher than the output impedance, a lot lower than the load impedance. The type does not matter too much; by design they do not do very much so they cannot do much harm either.
In this case it appears to be a more complicated setup meant to go after a preamp. The resistors are just there to avoid shorting the output - although a good design of preamp would probably already incorporate these internally. The value is not too critical: a little higher than the output impedance, a lot lower than the load impedance. The type does not matter too much; by design they do not do very much so they cannot do much harm either.
That.
It is the kind of question Broskie usually gives guidance on.... I'm surprised no clue comes with the kit. It is the kind of design balance that he pontificates well.
They should be high enough to "not hurt" the sound when in action. Your plan shows opamps with 47r resistor build-out; we can pencil this as 48 Ohms. However depending on the opamp it may not drive large level into 2k or 300r without rising THD or outright clipping.
The worst-case is out-of-phase L and R signals; however this is a rare event (sounds funny on most speakers; however this may be the case where mono is better).
The LOAD matters too. If you have one of those low-low-Z power amps with 1K input (there are a few) then 1K in series significantly hurts level. OTOH a 500K input hardly cares.
Taking an assumption that the preamp can drive 1K fine, and the power amp or line amp is 20k or more, 1k is a fine value. But if your preferred toasted-poppy-stem or OF-Zircon resistors only come in 789r or 1.567k, that will do too. If I had an overstock of 1k3 5% carbon-film, that's what I'd use.
Thanks to both of you for your help. I have a bunch of what I believe are carbon comp resistors - they have squared off ends on the cylinders. They look similar in form to ones I know are CC. Is that a defining feature of CC resistors? Also I have some carbon film ones in the same value.
The input load for the Cary SLP-98 line stage is 50,000 ohms.
I'll also fire off another email to GlassWare. Thanks for all the help!
The input load for the Cary SLP-98 line stage is 50,000 ohms.
I'll also fire off another email to GlassWare. Thanks for all the help!
Still don´t know the circuit schematic but guessing the MONO position links both Op Amp outputs together and amplifier has 50k input impedance, an excellent compromise is using 2 x 4k7 resistors.
Carbon or metal film won´t make a huge (or audible) difference here so use what you have or flip a coin.
Edit: forget carbon comp for any Audio use, it´s dated Technology in a bad way.
A carbon or metal film deposited on a ceramic substrate is WAY more stable and precise than ground graphite mixed with bakelite and clay and cooked in an oven.
Carbon or metal film won´t make a huge (or audible) difference here so use what you have or flip a coin.
Edit: forget carbon comp for any Audio use, it´s dated Technology in a bad way.
A carbon or metal film deposited on a ceramic substrate is WAY more stable and precise than ground graphite mixed with bakelite and clay and cooked in an oven.
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> so 10k 1%?
I can't read those things.
But assuming 10k, and 50k amps, in Mono the signal level drops 1.6dB. Enough to notice. I would tend to a smaller value.
I've used hundreds of Carbon Composition over the decades (from when there was no choice at the local shop) and with 99% satisfaction. Yes, had a couple go drifty, once very educational. However since Carbon Film arrived I have had NO trouble of any sort.
In this case I don't think Composition would be "wrong". The small increase of hiss is swamped by other impedances, and would only happen in Mono. 20% drift would be small mix-shift, and might not happen for decades (I have seen 90% drift in 20 years but that was a very hot chassis).
I can't read those things.
But assuming 10k, and 50k amps, in Mono the signal level drops 1.6dB. Enough to notice. I would tend to a smaller value.
I've used hundreds of Carbon Composition over the decades (from when there was no choice at the local shop) and with 99% satisfaction. Yes, had a couple go drifty, once very educational. However since Carbon Film arrived I have had NO trouble of any sort.
In this case I don't think Composition would be "wrong". The small increase of hiss is swamped by other impedances, and would only happen in Mono. 20% drift would be small mix-shift, and might not happen for decades (I have seen 90% drift in 20 years but that was a very hot chassis).
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