If you are making something like this project you will need to put a small BT type relay so that the output from the pre-amp is shorted to Gnd at power off.ie just connect normaly closed contacts to gnd from left and right out. Coil from supply + diode for back emf. Make sure the relay is switched directly from the on / off switch ..no capacitors to hold charge and stop it turning off quickly. This is because the HT turns off slowly this causes some noise on the o/p.
I think the highlighted Pre-amp answers your question this refers to a valve pre-amp section powered from the inverter..I guess you don't have one..LOL
The reason is because: At power off the inverter "winds down" ie the charge pulses reduce so you can get a whine through the output as it slows down. the Idea is to have a relay that powers off direct from the low voltage power "on off" switch that will drop out instantly and short the Preamp signal "out" to Ground ie an auto mute. Any charged caps in a power supply would slow the relay drop out and the mute may take to long to work so either a double contact power switch with one contact isolated at power off to the auto mute relay coil..
So in this case the contacts of the relay are just connecting the valve preamp out to Gnd via normaly closed contacts to mute the pre-amp signal output. Not switching any power
The coil of the relay is just switched from a separate contact on the same power switch so there are no charged power caps to hold it in when you switch off.
Regards
M. Gregg
I think the highlighted Pre-amp answers your question this refers to a valve pre-amp section powered from the inverter..I guess you don't have one..LOL
The reason is because: At power off the inverter "winds down" ie the charge pulses reduce so you can get a whine through the output as it slows down. the Idea is to have a relay that powers off direct from the low voltage power "on off" switch that will drop out instantly and short the Preamp signal "out" to Ground ie an auto mute. Any charged caps in a power supply would slow the relay drop out and the mute may take to long to work so either a double contact power switch with one contact isolated at power off to the auto mute relay coil..
So in this case the contacts of the relay are just connecting the valve preamp out to Gnd via normaly closed contacts to mute the pre-amp signal output. Not switching any power
The coil of the relay is just switched from a separate contact on the same power switch so there are no charged power caps to hold it in when you switch off.
Regards
M. Gregg
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Sorry was not very clear I guess.
I'm not trying to switch any of the power rails off but rather to disconnect the output of my passive pre-amp from the outputs to the power amp, As I don't want any pops at turn off. Probably not needed but may as well whileI'm at it.
So, would you think the reaction from a L7812 reguator would be qick enough?
Cheers
Dagwood
I'm not trying to switch any of the power rails off but rather to disconnect the output of my passive pre-amp from the outputs to the power amp, As I don't want any pops at turn off. Probably not needed but may as well whileI'm at it.
So, would you think the reaction from a L7812 reguator would be qick enough?
Cheers
Dagwood
As long as you dont get any noise from the circuit at power off its ok..If you want to use the auto mute its just a relay with one normaly closed contact per channel for left and right to Gnd from the signal input of the selector board (in your case) and power the coil from the power switch. So at turn off the relay drops out and the contacts (normaly closed) make up and connect the signal to Gnd.. this will mute any output to the selector board. I would think that the EM's will have no effect on the signal. If you do get any noise just use the auto mute relay...
So if its working OK as is...then its OK..
You don't need to disconnect the output its another break in the signal just short the OP to Gnd..no break in the signal..same as volume to Gnd.
Regards
M. Gregg
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Most of this would only apply to signal procssing valve circuits not passive....
Sorry just looking at your comment about the relay coil voltage...You could just take the regulated supply from the regulator through a second contact on the low voltage power switch to the relay coil, so when you switch off, the coil on the auto mute just loses its supply first.
Of course you could get technical and design a delay mute off at power up to ensure every thing was up and running first and instant mute at power off..LOL
But that would get you thinking design for fun again..LOL
Of course you could create a discrete monitor circuit that gave a mute out should anything happen to power supply as well and..and..LOL
Its all good fun!
Regards
M. Gregg
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It's all for fun
I have a fair bit of stock parts so my projects tend to grow and grow! I completed the re-design of the input and output PCB's last night, kept the mute relay in place but added a couple of jumpers so can try it first without adding the relay.
Cheers
Well when is the link to the box behind the amps from the selector, with speaker switching and dummy loads taking place then..LOL
I only jest because you would have to put some safety interlocks in place..
Remember you can just move the reset on the selector and put as many inputs as you like!
Regards
M. Gregg
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Ok, it's been a while.
Connected it all up as suggested, all works well thought there is a small amout of hum ( wiring not very tidy at this stage ) and cross talk on on 3 of the 4 outputs!
Planning to set the whole thing up in the case, that way I can run all of the wiring properly.
I also added a circuit so that when outputs 3 and 4 are selected it bypasses the volume control, this is for headphone amp connection.
Also went away from the inverter in favour of a little SMPS unit for the HT on the EM84's and the volume will now be controlled by a stepped attenuator that I completed over the weekend, used Dale RN60's.
Cheers
Connected it all up as suggested, all works well thought there is a small amout of hum ( wiring not very tidy at this stage ) and cross talk on on 3 of the 4 outputs!
Planning to set the whole thing up in the case, that way I can run all of the wiring properly.
I also added a circuit so that when outputs 3 and 4 are selected it bypasses the volume control, this is for headphone amp connection.
Also went away from the inverter in favour of a little SMPS unit for the HT on the EM84's and the volume will now be controlled by a stepped attenuator that I completed over the weekend, used Dale RN60's.
Cheers
The cross talk you have ? I would think if all unused OP's were at Gnd the the only cross talk could be between Left and Right which should be screened..?
Great that the project is evolving...
Could you post the small SMPS you are using..It gives people other options and can be quite interesting..
Regards
M. Gregg
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I guess,
Signal wire:
I should add that I prefer twisted pair (signal & Gnd) with aluminium foil covering + Drain wire (Connected at main Gnd end so this gives you a directional cable if used as an interconnect) and Heat shrink outer..This can work well for interconnects using silver plated copper flex and PTFE insulation... or any preferd wire... Or any wire run in equipment with just one signal wire and foil screen drain wrapped around it connect to Gnd etc..Sometimes with a driven cable the twisted pair on its own can be better...
Regards
M. Gregg
Signal wire:
I should add that I prefer twisted pair (signal & Gnd) with aluminium foil covering + Drain wire (Connected at main Gnd end so this gives you a directional cable if used as an interconnect) and Heat shrink outer..This can work well for interconnects using silver plated copper flex and PTFE insulation... or any preferd wire...
Or any wire run in equipment with just one signal wire and foil screen drain wrapped around it connect to Gnd etc..Sometimes with a driven cable the twisted pair on its own can be better...Regards
M. Gregg
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When I said the wiring was not very tidy at this stage I actually meant Spaghetti Bolognese! Working on the base plate of the case tonight so hope to run some screened cable to the outputs, I have used twisted pairs for both power and signal feeds on projects before with success but tend to mainly use them on power feeds.
Can you give me more detail on your cable like conductor size and type? Do you make your own using coaxial cable braid?
Here is the SMPS I used (http://www.ledsales.com.au/kits/nixie_supply.pdf), I up rated a few components and managed to get 250vdc out of mine ( note- 1 x fried inductor ! )
Can you give me more detail on your cable like conductor size and type? Do you make your own using coaxial cable braid?
Here is the SMPS I used (http://www.ledsales.com.au/kits/nixie_supply.pdf), I up rated a few components and managed to get 250vdc out of mine ( note- 1 x fried inductor ! )
The type of cable single core or stranded is personal choice also diameter (0.5mm)..
I dont use coax braid (screen) I dont think its good enough..
Type of cable I use is always PTFE insulated..This can be sleeving with bare singles or silver plated copper cable (solid or stranded) I think stranded creates more detail..
You can use silver wire (from a jewellery store) create twisted pair with PTFE sleeving..or use other standard PTFE cable..Then take a strip of aluminium foil the whole length of the twisted pair and fold it in half, put the twisted pair in to the fold then roll it around the cable so you get about two or three turns of double layer foil with the cable in the middle...Take a bare wire can be single or flex and wrap it around the foil about 20mm apart (between each turn) the full length of the cable this is the drain wire. Slide a length of heat shrink over the cable and shrink..so at one end you have the two conductors and the drain wire..at the other you have just the two conductors...you can make an interconnect with this using phono plugs remember to mark the drain wire end..If you use it inside equipment just ground the drain wire to chassis or star Gnd..and you have a shielded twisted pair or even just a single cable..there are variations on this using a mix of stranded and single core for each conductor used as just a single twisted pair, however the basic works well..
Regards
M. Gregg
I dont use coax braid (screen) I dont think its good enough..
Type of cable I use is always PTFE insulated..This can be sleeving with bare singles or silver plated copper cable (solid or stranded) I think stranded creates more detail..
You can use silver wire (from a jewellery store) create twisted pair with PTFE sleeving..or use other standard PTFE cable..Then take a strip of aluminium foil the whole length of the twisted pair and fold it in half, put the twisted pair in to the fold then roll it around the cable so you get about two or three turns of double layer foil with the cable in the middle...Take a bare wire can be single or flex and wrap it around the foil about 20mm apart (between each turn) the full length of the cable this is the drain wire. Slide a length of heat shrink over the cable and shrink..so at one end you have the two conductors and the drain wire..at the other you have just the two conductors...you can make an interconnect with this using phono plugs remember to mark the drain wire end..If you use it inside equipment just ground the drain wire to chassis or star Gnd..and you have a shielded twisted pair or even just a single cable..there are variations on this using a mix of stranded and single core for each conductor used as just a single twisted pair, however the basic works well..
Regards
M. Gregg
Ok,
I’m going for a twisted pair of silver wire in a PTFE sleeve. Thinking I might remove the screw terminals in favor of solder connections directly to the PCB
Progress is slow on the case work, had to wait for a plumber friend to fold the aluminum base and screening panel.
Progress so far-
· Ordered a few more phono sockets
· Sleeved up 1m of .5 solid silver ( think I will need more! )
· Machined up the chassis to support the EM84 pcb’s, this also acts as a bearing housing for the extension on the stepped attenuator.
· Assembled the stepped attenuator (100K)
· Drilled chassis
· Added fan to SMPS pcb (very hot)
Cheers
Dagwood
Photo's added
Pictures by Dagwood72 - Photobucket
I’m going for a twisted pair of silver wire in a PTFE sleeve. Thinking I might remove the screw terminals in favor of solder connections directly to the PCB
Progress is slow on the case work, had to wait for a plumber friend to fold the aluminum base and screening panel.
Progress so far-
· Ordered a few more phono sockets
· Sleeved up 1m of .5 solid silver ( think I will need more! )
· Machined up the chassis to support the EM84 pcb’s, this also acts as a bearing housing for the extension on the stepped attenuator.
· Assembled the stepped attenuator (100K)
· Drilled chassis
· Added fan to SMPS pcb (very hot)
Cheers
Dagwood
Photo's added
Pictures by Dagwood72 - Photobucket
Looking good!
Remember to use correct solder/eutectic for silver.....if you don't it goes black and creates a high resistant joint. You will probably find the sound will change over a few weeks with the silver. If you have used the wrong solder no problem desolder with a solder sucker and resolder.
I tend to make L shapped posts Stiff copper or silver for circuit boards and solder twisted pair to them. It can be a real pain if you want to change any connections and you have to remove the PCB to get at them.
Regards
M. Gregg
Remember to use correct solder/eutectic for silver...
..if you don't it goes black and creates a high resistant joint. You will probably find the sound will change over a few weeks with the silver. If you have used the wrong solder no problem desolder with a solder sucker and resolder.I tend to make L shapped posts Stiff copper or silver for circuit boards and solder twisted pair to them. It can be a real pain if you want to change any connections and you have to remove the PCB to get at them.
Regards
M. Gregg
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