TDA5141's I/V with lightspeed
Hi guys,
Need your guidance again. I am in the mids of doing up the DAC using the TDA1541. The output is connect to a I/V and then to a 6x step-up output transformer. I was wondering if I can skip the buffer after the transformer before connect up to the Lightspeed, as there will be another buffer immediately after the Lightspeed.
Thanks and cheers.
KK
Hi guys,
Need your guidance again. I am in the mids of doing up the DAC using the TDA1541. The output is connect to a I/V and then to a 6x step-up output transformer. I was wondering if I can skip the buffer after the transformer before connect up to the Lightspeed, as there will be another buffer immediately after the Lightspeed.
Thanks and cheers.
KK
No response to my suggestion of using a double switch for mains powerup
First step for power supply and second for connecting the LDR curcuit
This way there are no current surge inrush at power up
Maybe even just use one of those thermistor
Can a CCS curcuit be configured to this very low current ?
Kits are rather expencive
But should be easy and simple to build
Or is it tricky with this low current
But if its dealt with by a simple resistor thats ok too
First step for power supply and second for connecting the LDR curcuit
This way there are no current surge inrush at power up
Maybe even just use one of those thermistor
Can a CCS curcuit be configured to this very low current ?
Kits are rather expencive
But should be easy and simple to build
Or is it tricky with this low current
But if its dealt with by a simple resistor thats ok too
I dont think the double switch is necessary as the resistor will absorb still not allow any extra mA through.
The CCS can be built with an LM334 for a few pennies and this is a CCS that will go far below mA level into uA and pA. Using this will work. Absolutely. It however is not temp stable even when using a temp compensation circuit in high heat. This wont matter in your regular home ambient temp so still a good choice. Inside an amplifier case I would use very stable pots with low low ppm. Right now when I test outside in 100+F heat amazingly the regular trimpots are more stable than the CCS circuit.
The CCS circuit allows me even higher resistance than the trimpots of 1MOhm. Crazy. You can use the LM334 with a pot as the Rset and you are good to go. You will need two of these circuits. One for series one for shunt. You will not have balance control this way but I am sure you could figure one to put in there. Or use 4 LM334. Nice thing is LM334 ONLY puts a max of 20mA so you can not damage your LDRs.
You can use LM317 but still this is not the most stable in the mV range and that WILL effect the stability of the LDR. I like LM2757T but it operates at 52kHz which might might maybe be audible. However it has some family members that operate at MHz range and that will never be audible. 52KHz wont be audible but there are some that would probably argue that. Anyway, the LM2575 is super stable even down at .0001V. All day long I might get from 4.9604VDC to 4.9601 drift.
On the other hand the LM317Z is a TO-92 package that outputs 100mA max and needs no sinking. It also costs pennies. For under $2 you could implement LM317Z and LM334 to control the LDRs. Maybe $4 if you use 4 LM334 and an extra pot to control output voltage so now you are in complete control
Easy circuits to implement as they are all outlined in their datasheets.
Uriah
The CCS can be built with an LM334 for a few pennies and this is a CCS that will go far below mA level into uA and pA. Using this will work. Absolutely. It however is not temp stable even when using a temp compensation circuit in high heat. This wont matter in your regular home ambient temp so still a good choice. Inside an amplifier case I would use very stable pots with low low ppm. Right now when I test outside in 100+F heat amazingly the regular trimpots are more stable than the CCS circuit.
The CCS circuit allows me even higher resistance than the trimpots of 1MOhm. Crazy. You can use the LM334 with a pot as the Rset and you are good to go. You will need two of these circuits. One for series one for shunt. You will not have balance control this way but I am sure you could figure one to put in there. Or use 4 LM334. Nice thing is LM334 ONLY puts a max of 20mA so you can not damage your LDRs.
You can use LM317 but still this is not the most stable in the mV range and that WILL effect the stability of the LDR. I like LM2757T but it operates at 52kHz which might might maybe be audible. However it has some family members that operate at MHz range and that will never be audible. 52KHz wont be audible but there are some that would probably argue that. Anyway, the LM2575 is super stable even down at .0001V. All day long I might get from 4.9604VDC to 4.9601 drift.
On the other hand the LM317Z is a TO-92 package that outputs 100mA max and needs no sinking. It also costs pennies. For under $2 you could implement LM317Z and LM334 to control the LDRs. Maybe $4 if you use 4 LM334 and an extra pot to control output voltage so now you are in complete control
Easy circuits to implement as they are all outlined in their datasheets.
Uriah
You can actually buy TO-92 heatsinks and this will help stabilize the LM334 by more than 3:1. On the other hand I suppose those sinks would just help it rise up to 100F a bit quicker if ambient was 100F, probably higher than the normal operating case temp of the LM334.
When I set the LDR with the LM334 to be at 21k at 75F and then stuck it out in 100F I ended up with 25k. Helping stablize that by a 3:1 difference would be nice. Using trimpots I started at 21k and ended up with about 22.4k. Resistor and heatsinked LM334 should be similar but neither are a great solution yet. So thats why thermistors are in the mail. I dont understand thermistors. If you read any papers on them you will find they are very very complicated devices. The math is anyway. So it will be plug and play til I find one or a combination that do the trick. Now if there were a trimmer pot that was in fact a variable thermistor I would like that very much.
Uraih
When I set the LDR with the LM334 to be at 21k at 75F and then stuck it out in 100F I ended up with 25k. Helping stablize that by a 3:1 difference would be nice. Using trimpots I started at 21k and ended up with about 22.4k. Resistor and heatsinked LM334 should be similar but neither are a great solution yet. So thats why thermistors are in the mail. I dont understand thermistors. If you read any papers on them you will find they are very very complicated devices. The math is anyway. So it will be plug and play til I find one or a combination that do the trick. Now if there were a trimmer pot that was in fact a variable thermistor I would like that very much.
Uraih
udailey said:
Resistor it is then, thanks
A stacked pot, if wanted
http://www.beyondeleven.com/Stacked...0K-with-Nut-p/500k-stacked-concentric-pot.htm
Other pots
http://www.voxhumanawebstore.nl/webstore/index.php?cPath=269_279_280&sort=2a
Bourns pots http://www.allparts.com/store/electronics-500k-pots,Category.asp
Pots http://www.warmoth.com/Potentiometers-C58.aspx
I dont know what a stacked concentric pot is. Tried to find out but could not find a schematic.
The balance pot moves left channel up and right channel down or opposite. So, you could use a low value one for exactly that. Or if you wired it differently you could use it for raising value of series resistors and lowering shunt or opposite. That would work.
But, I dont know where the center detent is at. If its in the middle of the total resistance or if it starts at 0 resistance and adds resistance when turned left or right.
www.tubesandmore.com has regular audio pots of 500k single and dual gang for good prices.
Uriah
The balance pot moves left channel up and right channel down or opposite. So, you could use a low value one for exactly that. Or if you wired it differently you could use it for raising value of series resistors and lowering shunt or opposite. That would work.
But, I dont know where the center detent is at. If its in the middle of the total resistance or if it starts at 0 resistance and adds resistance when turned left or right.
www.tubesandmore.com has regular audio pots of 500k single and dual gang for good prices.
Uriah
Nice site
And they have 2watt pots
Cant link directly, but look at PrecisionElectronicComponents, under Potentiometers http://www.tubesandmore.com/
Its audio taper, but I suppose that works too
btw, stacked concentric is just two mono pot driven simultaniously by the same shaft, and works just like a normal stereo dual gang pot, I suppose
And they have 2watt pots
Cant link directly, but look at PrecisionElectronicComponents, under Potentiometers http://www.tubesandmore.com/
Its audio taper, but I suppose that works too
btw, stacked concentric is just two mono pot driven simultaniously by the same shaft, and works just like a normal stereo dual gang pot, I suppose
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Re: TDA5141's I/V with lightspeed
You could omit a buffer if you use one after the output transformer if the transformer has lowish output impedance say below 300ohms or you could even try to omit the buffer and output transformer and try the I/V's output straight into the Lightspeed, again if it less than say 300ohms output impedance.
Also the newbies to the thread please don't forget to vote for our own Passive Attenuator preamp here
http://www.diyaudio.com/request/
And hey the finally Production Lightspeed Attenuator now has a website www.lightspeedattenuator.com please be gentile with it, I've found they are fragile things to maintain.
Cheers George
daredevil_kk said:
You could omit a buffer if you use one after the output transformer if the transformer has lowish output impedance say below 300ohms or you could even try to omit the buffer and output transformer and try the I/V's output straight into the Lightspeed, again if it less than say 300ohms output impedance.
Also the newbies to the thread please don't forget to vote for our own Passive Attenuator preamp here
http://www.diyaudio.com/request/
And hey the finally Production Lightspeed Attenuator now has a website www.lightspeedattenuator.com please be gentile with it, I've found they are fragile things to maintain.
Cheers George
"Passive Preamp"
As it encompasses all that's pure about passive pre's, no pre amplifing or buffers just to get the sources signal to the poweramps input with the least amount of electronics in the way, all passives, Pots, Tvc's, Lightspeed's, Switched resistors. All passive volume controls that have no electronics in the signal path.
Cheers George
As it encompasses all that's pure about passive pre's, no pre amplifing or buffers just to get the sources signal to the poweramps input with the least amount of electronics in the way, all passives, Pots, Tvc's, Lightspeed's, Switched resistors. All passive volume controls that have no electronics in the signal path.
Cheers George
My favorite sayings why would you want to add more gain with a pre amplifier only to take it away again When the source (cd player) has enough gain by it's self to clip nearly all poweramps out there.
Analogies:
It just doesn't make sense why drive with your accelerator pedal flat to the floor at but with you other foot pressing on the brake?
Or and I really like this one, why pour a bucket of water through a funnel to fill up a sink.
Cheers George
Analogies:
It just doesn't make sense why drive with your accelerator pedal flat to the floor at but with you other foot pressing on the brake?
Or and I really like this one, why pour a bucket of water through a funnel to fill up a sink.
Cheers George
I would say 75% of commercial and diy active preamps have gain yes, the ones that are unity gain are usually Diy ones opamp jobs that are using the opamps as buffers, they have their own set of problems with the sonic signature of the said opamp itself.
What is better than just sticking a buffer in to take care of mismatches between stages, is to address the mismatches itself so a buffer is not needed. That is to raise input impedances of poweramps and to lower output impedances of sources. So then there is no need to even have buffers.
Hell if I could drive the speakers with the output of a cd player I would, it would be even purer in sound.
Cheers George
What is better than just sticking a buffer in to take care of mismatches between stages, is to address the mismatches itself so a buffer is not needed. That is to raise input impedances of poweramps and to lower output impedances of sources. So then there is no need to even have buffers.
Hell if I could drive the speakers with the output of a cd player I would, it would be even purer in sound.
Cheers George
all sources use/need buffers to lower the output impedance to match the cables used to connect them to the next stage.georgehifi said:
If the source's own output buffer is inadequate for this duty (and many are totally inadequate) then additional active buffers are a necessary function that cannot be dispensed with.
The Lightspeed is an example of a source that cannot adequately drive the cables to a remote amplifying stage.
It must be located right at the input of the next stage, i.e. the next stage becomes Lightspeed's buffer (usually with gain) or the Lightspeed must have a buffer stage added on to drive longer cables.
In this last example the power amplifier is the buffer (with gain) that the Lightspeed needs to drive the speakers.