As a general statement, yes the DAC may care.
The DAC will have a spec sheet where it will state the minimum load. With out a sufficient impedance load, the amp (or whatever) may try to draw current. The DAC will not be designed for that. What you are looking for is a transfer of voltage not power.
Additionally, the DAC may have problems driving a capacitor (usually a necessary part of the the anti-aliasing circuit).
Have a look on the 'scope when the DAC drives a capacitor with and without a resistor. The signal may become very distorted ( I am not referring to the RC filtering).
Hi Bill,
BTW, thanks for pointing me to the Sescoms on eBay - fantastic value-for-money at $50. I will put a scope on them - as a noobie in scope use, do I want to output a sine wave from the laptop through the DAC & trafos, at what frequency, 200KHz?
I'm not using any series R yet so I'll try the 1K across primaries.
When I say shimmer, I mean in a good way like a crystalline clarity not a modulation. But I'm aware that odd order harmonics can give rise to a mid-range/HF forwardness that can seem like enhanced clarity. I'll scope the Slagles too!
Thanks Tarragon,
The PCM1793 DAC wants a minimum 1k8 load so I guess a 1-2K across the primaries would be a good starting point. Do I need to put some series R in there also? Just need to get the clock mod working on the unit before I can proceed
http://www.diyaudio.com/forums/digi...usb-spdif-24-192khz-asynch-5.html#post1973535
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Just put your signal gen across the primary with a 1K resistor in series with it and sweep the frequency.
The dac chip and the trafos both need some series resistance to operate properly. Looking from either direction, the series resistors are part of the load they see. The trafo sees the dac chip source impedence plus the series Rs as a whole, as a parallel circuit placed across the primary. The dac chip sees the trafo impedence and the Rs as a parallel load across it's outputs. Optimum values are probably not attainable, any workable value would be a compromise unless the trafo was designed expressly for the chip output.
The dac chip and the trafos both need some series resistance to operate properly. Looking from either direction, the series resistors are part of the load they see. The trafo sees the dac chip source impedence plus the series Rs as a whole, as a parallel circuit placed across the primary. The dac chip sees the trafo impedence and the Rs as a parallel load across it's outputs. Optimum values are probably not attainable, any workable value would be a compromise unless the trafo was designed expressly for the chip output.
Thanks Bill,
I'll be doing the signal gen on my PC & running this through this USB DAC which contains the PCM1793. So connecting the scope to the secondary trafo outputs & doing a freq sweep should do it.
I understand your second paragraph, thanks!
Hi, one thing to try if you're still getting hum on your TA2020 amp is to try powering it from a 12v battery (with fuse).
I have had humming issues when using different PSU's on a few of my TA2020 based amps, and having a battery handy is a nice way of eliminating the PSU from the suspects list!
I have had humming issues when using different PSU's on a few of my TA2020 based amps, and having a battery handy is a nice way of eliminating the PSU from the suspects list!
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Mike,
Thanks, the hum is very nearly gone, there's just a residual hum now which I think is coming from the laptop PS. I have to try running my laptop off batteries. Pity I can't use the ADUM USB isolator on hi-speed USB
Yes Lars, that's the idea but I haven't run it like this yet - I just ran it straight to the trafo at first. I'm going to put a scope on the secondary & begin experimenting with R values (& possibly RC values on secondary)
Thanks, the hum is very nearly gone, there's just a residual hum now which I think is coming from the laptop PS. I have to try running my laptop off batteries. Pity I can't use the ADUM USB isolator on hi-speed USB
Yes Lars, that's the idea but I haven't run it like this yet - I just ran it straight to the trafo at first. I'm going to put a scope on the secondary & begin experimenting with R values (& possibly RC values on secondary)
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After you have looked at it with a scope, run a listening test with two types of music, a very spare piano with a fair amount of fortissimo in the right hand, almost any Jessica Williams piece, and a lush and thick violin mass, or choral mass, with a piano playing counter point if possible. Step through those same resistor values while listening. You may find some surprising things when loading a wideband transformer with resistors, on either side of the device.
Bud
Bud
Thanks, Bud, do you want to give me a clue what to listen for or do you not want to influence my listening? It might be more interesting to do the later & see what I come up with
I have a laptop which does not hold charge, but there have been a few times I have had to use it away from the mains.Mike,
Thanks, the hum is very nearly gone, there's just a residual hum now which I think is coming from the laptop PS. I have to try running my laptop off batteries. Pity I can't use the ADUM USB isolator on hi-speed USB
I used a car-charger for my laptop which came to less than £20, and I wired it to a 12v 14Ah lead-acid battery....
It's a little bulky, but comes in handy when I need to use it away from the mains... If you happen to have these parts to hand then give this a try, but if not, it would be easier to get another laptop battery.
Nope, no expectations from me.
Just keep in mind that you are working with a reflected tuned circuit with LRC values within which the L changes according to frequency response. And, also keep in mind that a perfectly distortion free sine wave does not describe what occurs when the system goes non linear, which it does immeadiately upon application of music. And, all transformers initial half wave response is essentially unconstrained. The better the core material the steeper this rise time will be.
So, if your transformer is designed for the primary load to be met, with the inductance referred to the primary coil by the core, the designer will have built in enough "ballast" via distributed capacitance and leakage inductance to provide flat frequency and phase response on the top end. And, will have paid close attention to overshoot and subsequent ringing on a square wave input, both loaded and unloaded by a complex load.
Go right ahead and experiment, you cannot hurt anything. You will learn quite a lot too.
Bud
Just keep in mind that you are working with a reflected tuned circuit with LRC values within which the L changes according to frequency response. And, also keep in mind that a perfectly distortion free sine wave does not describe what occurs when the system goes non linear, which it does immeadiately upon application of music. And, all transformers initial half wave response is essentially unconstrained. The better the core material the steeper this rise time will be.
So, if your transformer is designed for the primary load to be met, with the inductance referred to the primary coil by the core, the designer will have built in enough "ballast" via distributed capacitance and leakage inductance to provide flat frequency and phase response on the top end. And, will have paid close attention to overshoot and subsequent ringing on a square wave input, both loaded and unloaded by a complex load.
Go right ahead and experiment, you cannot hurt anything. You will learn quite a lot too.
Bud
I have a laptop which does not hold charge, but there have been a few times I have had to use it away from the mains.
I used a car-charger for my laptop which came to less than £20, and I wired it to a 12v 14Ah lead-acid battery....
It's a little bulky, but comes in handy when I need to use it away from the mains... If you happen to have these parts to hand then give this a try, but if not, it would be easier to get another laptop battery.
As an aside from the main topic, I wanted to report this:
There are 2 Dell laptops in the house & when my battery pack in the Inspiron 6000 would no longer charge, I swapped over the battery pack from the Vostro 1000 laptop but OF COURSE it would not work so hey ho I thought, I'm still not buying another battery pack as I don't use this laptop way from mains.
Anyway, a couple of months later the other battery pack stopped working also. Just last week I decided to crack open both of these packs
. What do I discover - in the official Dell pack all the Panasonic Li-ion batteries are fully charged & working fine (3 sets of 3 batteries in each set). The pack isn't working because there is an id chip in either the pack or laptop that is no longer working. I consider this a scam perpetrated by Dell to make money! Check it out here for other Dell models DELL AC power adapter not recognized | The Laptop JunctionThe cheap battery pack I bought from ebay had 1 set of 3 batteries in the pack still fully charged & working, the rest not.
So I have 12 Li-ion 3.3V batteries in perfect working order.
I would recommend everybody to crack open their laptop battery pack before recycling it & checking them. I'll also be checking my local recycling center for free Li-Ion batteries when I need them
I'm going to post this in it's own thread over on Power Supplies to get wider exposure
Laptop batteries are the new printer cartridges!
I see you are using the lepai as an amp, which is TA2020 based. Your li-ion battery pack may be a good power source for it, see attached pic, this pack I ripped open tonight and is on charge right now - it should give 11.1v at around 8Ah when charged, which is a good amount for the Lepai. In fact I used the battery to power the Lepai TA2020 amp over a 1 week camping trip and it still was over 50% capacity after many days of listening. Just make sure you're familiar with li-ion cells, they need protection from discharging below 3v but I won't go into too much detail as this is not the thread to do so.
Sorry for going off topic, I'm slowly working thru this thread, and I've decided to have a go and try this transformer thing with a DIY DAC to TA2020 amp, once I find some reasonably priced transformers. Are there any good places to look for them apart from the usual online stores such as farnell and RS?
I wish I could say I'm surprised but I'm not, I've ripped open many laptop battery packs, not knowing if they would work as I only had the pack with no laptop to try out the battery. I've suspected the protection circuit limits the number cycles, which is a shame as I imagine many good packs are getting binned despite the cells being fine!So I have 12 Li-ion 3.3V batteries in perfect working order. I would recommend everybody to crack open their laptop battery pack before recycling it & checking them. I'll also be checking my local recycling center for free Li-Ion batteries when I need them
I see you are using the lepai as an amp, which is TA2020 based. Your li-ion battery pack may be a good power source for it, see attached pic, this pack I ripped open tonight and is on charge right now - it should give 11.1v at around 8Ah when charged, which is a good amount for the Lepai. In fact I used the battery to power the Lepai TA2020 amp over a 1 week camping trip and it still was over 50% capacity after many days of listening.
Just make sure you're familiar with li-ion cells, they need protection from discharging below 3v but I won't go into too much detail as this is not the thread to do so. Sorry for going off topic, I'm slowly working thru this thread, and I've decided to have a go and try this transformer thing with a DIY DAC to TA2020 amp, once I find some reasonably priced transformers.
Are there any good places to look for them apart from the usual online stores such as farnell and RS?Attachments
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