Bottlehead Forum
General Category => Technical topics => Topic started by: Dyna Saur on November 27, 2011, 10:46:59 AM
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I know, it's been quite a few months since I've posted on the forum.
Friend of mine has a rather extensive collection of vintage (what other kind is there) 78 RPM records, and he is looking for a "decent" sounding setup. One channel, one speaker system, no "soundstage" needed.
As I recall, there was no set standard for equalization or compensation for the myriad variety of 78s, other than a very simple resistor / capacitor sombination, usually up front where the ceramic / piezo pickup signal encountered the first stage's control grid. I presume that a magnetic cart would require something better. than that
I suggested that he find a decent quality monaural magnetic cartridge, with a stylus made of something other than sharpened steel or cactus spines ;-)
What I'm looking for is some advice on designing a decent and functional phono stage for a decent quality mono cartridge. It doesn't have to be top end Bottlehead's finest quality, just something which can make a 78 sound as good as it can, without "cheating", no unnecessary bass or treble tweeking, to give it frequency response that it never had in the first place.
And, what would be a good, even decent, but not " boutique audiophile" quality mono cartridge, these days?
thx
I'm hoping to do something, just a bit more technically advanced than this finely crafted example of paleolithic technology, which was spotted at a flea market in Egypt several years ago:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fpictures.insulators.info%2Fpictures%2F94%2F297302346.jpg&hash=f6214753faa8cd85eae65781bcc411bed0565d55)
/ed B in NC
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Off the top of my head, I seem to remember that LPs were also known as "microgroove" recordings - the grooves are smaller, which means the cartridge tip size is larger. If I recall correctly, some manufacturers (including Shure) make needles specifically for 78RPM recordings.
I have an antique Harmon-Kardon mono receiver which has I think seven equalization settings. They are much like the RIAA in that there are usually three turnover frequencies, they are just not the same frequencies. It should be possible to make a modified mono Seduction, using the space of the second channel for a set of equalization switches.
Hopefully someone who knows more will have an idea of what the desired equalizations are, or were.
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I found this link, maybe you have seen this already. there are some schematics, but not with tubes. Good luck and please report on your progress.
http://www.lencoheaven.net/forum/index.php?topic=4660.0
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First let me say that I have no financial or busines interest in this company. I have only been a customer. You can purchase a well designed and well made printed circuit board sold as a half kit from HAGERMAN TECHNOLOGY: WEB SIGHT IS www.hagtech.com
The circuit board was originally for a stereo phono amp, but can be used to build a single channel line stage and phono stage pre. for 78rpm recordings. It will come with a schematic with the proper equalization for 78rpm recordings. I still have it all in my archives, but have not gotten around to building the amp, as I too have several 78rpm recordings. I believe the PCB is around $100.00 I hope this information will help.
Bernie.