Electra Print -passive volume preamp. - diyAudio
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Old 2nd October 2007, 04:51 PM   #1
felixx is offline felixx  Romania
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Default Electra Print -passive volume preamp.

I like to know your thoughts about this design:
http://www.electra-print.com/pva.php
Electra Print has two variations of these trafos....one with silver for low power amps.
Wht do you think?
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Old 2nd October 2007, 08:31 PM   #2
Gordy is offline Gordy  United Kingdom
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Just thoughts in no particular order...

... a transformer can break ground loops so is good in that respect...

... also will have some form of in-built high frequency filter effect cutting line carried radio frequency interference to the next stage, because coupling from primary to secondary will naturally fall at some (higher-than-audible) frequency...

... I have no idea what he means when he says the silver version is 'better'... surely he must be able to back that up with R, L, C figures, etc., to prove it's not just hype...

... before you buy an expensive transformer just try the potentiometer on it's own at that position... you will not damage anything and it may work fine...
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Old 3rd October 2007, 02:58 PM   #3
felixx is offline felixx  Romania
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I'm thinking to use this design because I will have the preamp "close" to at list 2 meters from the amps (monoblocs) and I figure that those trafos give me output impedance that stays constant at any position of the attenuator on the same frequency response at any volume setting.

Another option will be this:
http://www.goldpt.com/
....or similar but don't give me the same constant impedance and maybe the poor sonic mark compare with trafos.

What do you think will be the best ideea ?
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Old 3rd October 2007, 03:42 PM   #4
Gordy is offline Gordy  United Kingdom
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I understand your thinking, however the Electraprint web page seems a little vague on the details.

If they do not supply the pot with the transformer I suggest that you get the pot first and simply try it. You can always add the transformer afterwards. Between a preamp with unknown output impedance and power amp with unknown input impedance, a pot of about 10 k Ohms would seem a good place to start. 2 M of cable is not so much really.

However, also note that the Electraprint web page says "Gain is sufficient to drive any amplifier." . The transformer is schematically shown with more turns on the secondary (output) side suggesting that it does indeed step-up the voltage. Actually I just noticed their page http://www.electra-print.com/specialuse.php which notes the gain. If you need gain then their transformer might be the best way to get it.
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Old 3rd October 2007, 03:55 PM   #5
felixx is offline felixx  Romania
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Gordy,...you are from England.
Sowter is an "englese" company.
They have some step attenuators:
http://www.sowter.co.uk/acatalog/SOW...UATORS_13.html

The taps topology on the trafos seems to be not much different, comparing with Electra Print trafos,right?....at list on the first view.
Too bad for Electra Print-because they don't have too much infos,but look what I find:

http://www.electra-print.com/techblog.php?blogid=1
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Old 3rd October 2007, 10:08 PM   #6
Gordy is offline Gordy  United Kingdom
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So now you have even more choice... !

However some of these components are relatively expensive, so I recommend that you buy a cheap 10k audio-taper (i.e. log scale) potentiometer for just a few for a very basic model. Try it at the desired position. If it works then replace it with a good quality model. If it is not so good then you can investigate the transformer option...

Good luck.
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