These are to be used on a discrete buffer for nulling DC offset, any suggestions as to which brands are reliable?
I would rather say "It's hard to find good parts in these days"
the follow versions offers good quality:
http://www.bourns.com/ProductLine.aspx?name=trimming_potentiometers_military_quality
Bourns 3296W, three wire, in line, vertical 25T adjust.
Don't use the Chinese knockoffs, often they do not engage with the adusting screw.
Hugh
Don't use the Chinese knockoffs, often they do not engage with the adusting screw.
Hugh
If you have spare money, use any of these
http://www.texascomponents.com/pdf/vpot.pdf
I changed to use (10R) 1260 on my Erno's 320 phono preamp and it produces more details VS the stock supply which is already a good one from Japan. Adjusting the zero offset is a piece of cake since the voltage does not go up and down with small turn. The price could be a concern because it is over $30 each but you can also consider a cheaper alternative such as 1280 if your PCB allows.
http://www.texascomponents.com/pdf/vpot.pdf
I changed to use (10R) 1260 on my Erno's 320 phono preamp and it produces more details VS the stock supply which is already a good one from Japan. Adjusting the zero offset is a piece of cake since the voltage does not go up and down with small turn. The price could be a concern because it is over $30 each but you can also consider a cheaper alternative such as 1280 if your PCB allows.
Thank you for this advice. Also a wide range of their other devices about
http://www.texascomponents.com/
are of interest, e. g.
http://www.texascomponents.com/pdf/tx221.pdf
and
http://www.texascomponents.com/pdf/zseries.pdf
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Sheesh, looks like it is possible to spend some big bucks on small components!
While we're on that topic, what is an audio grade DPDT switch to use for toggling between two inputs?
While we're on that topic, what is an audio grade DPDT switch to use for toggling between two inputs?
A double pole double throw switch - ie stereo, switching between two inputs. The ones sold by Jaycar are excellent quality and quite suitable. Don't bother spending any more.
goldpoint is good, but that is more of a rotating switch.
Look deep into the specs of the given devices and look for high copper alloys and small area (cubic size) where there is little to no shape change throughout the length of the contacts, and they should run out of the chassis of the switch and also be the solder or board mount pin. Ie, the only moving part is the throw contacts themselves, and they need to also be of a high copper alloy.
Basically, all the same metals -throughout, and no shape or volumetric change for the signal to pass through.
This does not mean money spent, it merely means spending the time investigating switches. They should also be mechanically stable and solid with not too long of a paddle as this can be source of mechanical vibration that would feed back into the electrical contact points.
For example, to make cheaper audio equipment sound better these days without spending the farm... the chassis/board mount switchcraft RCA jacks are just about the best and cheapest..as they are the just about the ONLY high copper alloy contact units left out there to be found.
http://www.switchcraft.com/products/535.html
For many years, sliding rather than simply closing contacts have been preferred for low level switching - sometimes also referred to as dry switching. That can include audio line level.
You would think that those RF style ceramic wafer rotary switches on eBay would be a shoe-in. Maybe they are if you have the space and are happy to perform a little occasional maintenance. The alternative of ugly slider switches with dubious quality has always been frowned on, even if some old Stackpole designs did work well.
I think the best ideas come from the design of sealed line level switching relays which are often faced gold over siver alloy and, like most relays, have a small (self wiping) movement on closing due to overshoot with the flexible fingers.
For plain manual types, we don't have the choice retail. I have used inexpensive C&K pattern miniature toggle switches and copies for as long as they have been available. They are not really suitable for audio but their contact resistance is low at 10 mohm. However, putting the CRO probe across the terminals carrying the signal can be interesting when the switch faces have oxidised a little and the mechanism is loose (often). This can be true of any unsealed construction types.
Experience with 80s and 90s style equipment where miniature alternate action push buttons were used is much worse. Some silver plated contacts pass zero signal when unused, as most amp controls were. Similar types for logic level may also be grouped with tactile switches.
In local catalogues, I note that contact resistance spec. is now quoted. This tells you how they will perform initially. Look at how high some expensive types are quoted and vice versa. Note the figures for a good sliding alternate action push button types is about 10% of a big solid floor stomper for guitar use. Whilst the actual resitance is unimportant, any variation whilst in use is detrimental. That is the real issue. If it starts low, you might hope that variation will be likewise.
What I think mach 1 is referring to is also the miniature toggle type and this is about the only retail choice, dinky as they look. Check after a while with a sensitive ac measurement though, some actually do become faulty and show odd contact behaviour. There is an excellent kit milliohm adaptor for DMMs locally which can also test switch contact resistance. They are cheap so replace them at the first sign of inconsistent behaviour.
You would think that those RF style ceramic wafer rotary switches on eBay would be a shoe-in. Maybe they are if you have the space and are happy to perform a little occasional maintenance. The alternative of ugly slider switches with dubious quality has always been frowned on, even if some old Stackpole designs did work well.
I think the best ideas come from the design of sealed line level switching relays which are often faced gold over siver alloy and, like most relays, have a small (self wiping) movement on closing due to overshoot with the flexible fingers.
For plain manual types, we don't have the choice retail. I have used inexpensive C&K pattern miniature toggle switches and copies for as long as they have been available. They are not really suitable for audio but their contact resistance is low at 10 mohm. However, putting the CRO probe across the terminals carrying the signal can be interesting when the switch faces have oxidised a little and the mechanism is loose (often). This can be true of any unsealed construction types.
Experience with 80s and 90s style equipment where miniature alternate action push buttons were used is much worse. Some silver plated contacts pass zero signal when unused, as most amp controls were. Similar types for logic level may also be grouped with tactile switches.
In local catalogues, I note that contact resistance spec. is now quoted. This tells you how they will perform initially. Look at how high some expensive types are quoted and vice versa. Note the figures for a good sliding alternate action push button types is about 10% of a big solid floor stomper for guitar use. Whilst the actual resitance is unimportant, any variation whilst in use is detrimental. That is the real issue. If it starts low, you might hope that variation will be likewise.
What I think mach 1 is referring to is also the miniature toggle type and this is about the only retail choice, dinky as they look. Check after a while with a sensitive ac measurement though, some actually do become faulty and show odd contact behaviour. There is an excellent kit milliohm adaptor for DMMs locally which can also test switch contact resistance. They are cheap so replace them at the first sign of inconsistent behaviour.
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