Upss i am sorry Salas... Myself had way to many weissbeer's yesterday, along with this Restina; no more than looking at newyears skijump it will be today i think!
Garmisch-Partenkirchen - New Years Skijump - Enjoy the flight into the New Year!
Jesper.
Looking at Vienna new year Waltzes concert now on TV
Hey guys, Happy New Year! I have a couple of questions as I have zero experience with the headphones. I am not sure I will be using DCG3 as a head amp, but who knows (I should have AT-55x somewhere around). Should I put 7.5R or 12R for higher bias? (These are two values Tea suggests in the kit), or should I put 10R as smh in between (if I put 7.5R for pre use as Tea suggests, will it work as a head amp?)? What RZ I should put for 55x headphones? Thanks!
In general, low impedance headphones (like yours) want current (more bias), where high impedance headphones want voltage. If it was me I'd bias it as high as you are comfortable with and your heatsinking allows. That will theoretically sound best for pre and phones. Although 150ma ish bias is extreme overkill for pre use.
For RZ I'd start with a jumper. It's best on paper although some output impedance on the headphone side sounds better to some people...it sounds looser and less dry. But a jumper is technically the best...I would experiment in 5 ohm increments if you feel the sound is too tight and dry with the jumper. It's kind of headphone dependent.
For RZ I'd start with a jumper. It's best on paper although some output impedance on the headphone side sounds better to some people...it sounds looser and less dry. But a jumper is technically the best...I would experiment in 5 ohm increments if you feel the sound is too tight and dry with the jumper. It's kind of headphone dependent.
Thank you, got it!
Another thing, I was planing to use a stepped attenuator with R_out in the range 6Ohm-3.2kOhm (depending on position), will that work with the pre? If so I need around 9-12Vdc(150mA) to power it. Is there any way I can tap on the PSU board maybe to get this voltage without losing anything in performance of the preamp of course.
Another thing, I was planing to use a stepped attenuator with R_out in the range 6Ohm-3.2kOhm (depending on position), will that work with the pre? If so I need around 9-12Vdc(150mA) to power it. Is there any way I can tap on the PSU board maybe to get this voltage without losing anything in performance of the preamp of course
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Another thing, I was planing to use a stepped attenuator with R_out in the range 6Ohm-3.2kOhm (depending on position), will that work with the pre? If so I need around 9-12Vdc(150mA) to power it. Is there any way I can tap on the PSU board maybe to get this voltage without losing anything in performance of the preamp of course
I wouldn't recommend so low an impedance in the attenuator because the bandwidth of this preamp will be very wide with such. There is danger of RFI, buzzes, and/or underdamping leading to harsh transients. So if you don't have lab equipment to check its all stable and clean better stick with the 20K-50K recommended range. On the other hand you could just try listen and experience if all seems working smoothly and sounding good if you already got it in hand. It won't be a destructive experiment. You can tap off raw DC from a reservoir capacitor's legs on the DCSTB and regulate with an LM317 or 7809 on some small perfboard and a little sink for it. If its a success I would still recommend to subjectively compare it with some good 20K-50K pot or switcher in this preamp at a point though. Making an easier load on the source equipment. In any circumstance any metal part of any of those attenuators/pots should be referenced at the same potential as the signal's zero return side.
Can't afford to get some decent shielded transformers at the moment but what I have got is two multitapped EI transformers with the required 18v tap out of each.
Possible problem is that they are of different power ratings - one has a power rating of 60VA and the other is only 18VA.
Will the smaller one's power rating (18VA) be big enough and if so, does it matter that they have different VA ratings as above?
I do have a third EI transformer rated at 60VA but this only has a 17.5v tap out.
Any thoughts if I can use any of these transformers together to get the preamp working?
Thanks
Possible problem is that they are of different power ratings - one has a power rating of 60VA and the other is only 18VA.
Will the smaller one's power rating (18VA) be big enough and if so, does it matter that they have different VA ratings as above?
I do have a third EI transformer rated at 60VA but this only has a 17.5v tap out.
Any thoughts if I can use any of these transformers together to get the preamp working?
Thanks
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It is very easy to work out the maximum current capabilities of your mains transformer.
VA = Vac * Iac
for an 18VA 18+18Vac transformer the maximum continuous AC current output is 18/{18+18} = 500mAac
You need to de-rate this when the transformer is feeding into a capacitor input filter.
Divide by 2 is close enough for a de-rating factor. The manufacturers do give information for their transformers.
After derating the maximum continuous DC current from the smoothing capacitors will be ~250mAdc
Use this continuously and the transformer will run hot.
Therefore I suggest you use <50% for cooler operation.
That results in 125mAdc continuous and lots more for short term transient peaks.
That's why Salas said
For cool operation divide your Iac by 4 to get a DC max continuous current.
Yes !!! No more smoke
What's the plan? To make an extra preamp for another system, to add a headphones preamp for this system, or to only substitute the tube line preamp section of the Viva amp?