Comment on Differential Stage
I really like the quality of the craftsmanship. Comment on using a single opamp as an "instrumentation amplifier": The input impedance into the non-inverting input will always be R53 + R54 (188.2 K ohms). But, the input impedance into the non-inverting input will vary with the signal conditions. When the signal into the inverting input is equal to (R51/(R50 + R51)) times the voltage into the non-inverting input, the input impedance into the inverting input will tend to infinity.
Both R50 and R53 are in series with the signal and will add Johnson noise (actually, quite a lot of it). One approach to consider is the use of either a 2-opamp or 3-opamp instrumentation amplifier with a gain of 10 for MM or 100 for MC with the loading resistors (23.2K each for MM or 5-50 ohms for MC) to signal ground. This initial voltage gain overcomes the noise introduced in the following RIAA equalization stages. Splitting the RIAA equalization into 2 inverting stages (to produce overall non-inverting output) produces a better step response but at the cost of a slightly increased noise figure (compared to a non-inverting RIAA stage) because of the necessity of the "feed-in" resistors. Best Regards, tubewaller
I really like the quality of the craftsmanship. Comment on using a single opamp as an "instrumentation amplifier": The input impedance into the non-inverting input will always be R53 + R54 (188.2 K ohms). But, the input impedance into the non-inverting input will vary with the signal conditions. When the signal into the inverting input is equal to (R51/(R50 + R51)) times the voltage into the non-inverting input, the input impedance into the inverting input will tend to infinity.
Both R50 and R53 are in series with the signal and will add Johnson noise (actually, quite a lot of it). One approach to consider is the use of either a 2-opamp or 3-opamp instrumentation amplifier with a gain of 10 for MM or 100 for MC with the loading resistors (23.2K each for MM or 5-50 ohms for MC) to signal ground. This initial voltage gain overcomes the noise introduced in the following RIAA equalization stages. Splitting the RIAA equalization into 2 inverting stages (to produce overall non-inverting output) produces a better step response but at the cost of a slightly increased noise figure (compared to a non-inverting RIAA stage) because of the necessity of the "feed-in" resistors. Best Regards, tubewaller
Cool, Do not forget, you need a pair of LME49990's for the diff input, including some adaptor boards to Dip8. Note also that all resistors around these must be 0.1% (or better), otherwise CMRR will be compromised (badly).
One more thing let me know what cartridge you are going to use. I will have a look at the gain and the resistor values to be set (we need to optimize this for the cartridge).
P.s. Any comments on the boards?
Board look really good at first glance.
I will post loads more as I get along gold plating should be rely easy to solder to.
I like a lot the idea of using the screen between stages.
I am using a Goldring Elite at the moment.
From spec output is stated at 0.5 mV (but at what speed?) and resistance is about 10 Homs (I think)
On a cheap and nasty Project RPM Four with modified wire Loom
(Best thing ever to get rid of existing one) made for balanced 2 + 2 conductors and separate earth with pure single strand silver wire.
Silver Wire Global Online Supplies - Product Line AG5484
This is the real thing whit no price inflated by “FIFI shops”
It is Teflon coated I run the twisted pair strands on silicon tube and then screen.
I am finishing off the Pumpkin first as it has been on bench for last 2 months.
Once the preamplifier is done I will have a much better chance to really ear the Phono stage.
I am fan of Wyelvin RC55Y but if you have a favorite type I will be happy to try what you reccomend.
I will post loads more as I get along gold plating should be rely easy to solder to.
I like a lot the idea of using the screen between stages.
I am using a Goldring Elite at the moment.
From spec output is stated at 0.5 mV (but at what speed?) and resistance is about 10 Homs (I think)
On a cheap and nasty Project RPM Four with modified wire Loom
(Best thing ever to get rid of existing one) made for balanced 2 + 2 conductors and separate earth with pure single strand silver wire.
Silver Wire Global Online Supplies - Product Line AG5484
This is the real thing whit no price inflated by “FIFI shops”
It is Teflon coated I run the twisted pair strands on silicon tube and then screen.
I am finishing off the Pumpkin first as it has been on bench for last 2 months.
Once the preamplifier is done I will have a much better chance to really ear the Phono stage.
I am fan of Wyelvin RC55Y but if you have a favorite type I will be happy to try what you reccomend.
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while I get ready to build why not pick a few tracks
Reprise records RSLP 6356
Frank Zappa - Peaches En Regalia - YouTube
Hem that advent place has Mumetal in catalog I wonder.....
Reprise records RSLP 6356
Frank Zappa - Peaches En Regalia - YouTube
Hem that advent place has Mumetal in catalog I wonder.....
Yes, I do like those, they are very good and not to expensive. You can get them at Mouser.
Goldring Elite II MC-Cartridge
Technical data:
•Principle: MC
•Output voltage: 0,50 mV
•Tracking force: 1,7 g
•Impedance: 100 Ohm
•Weight: 5,7 g
•Mounting: 1/2 inch
•Microsection: Geyger II Super
•Stylus exchange: No
•Compliance: 18 mm/yN
The main points here are: 500uV 100Ohm
The gain, as set in the schema, if fine (the gain was calculated for 500uV).
The input impedance is also fine (it is 2 x 51 = 102Ohm in the schema).
For as far as I can see you should build with the values in message #2.
Regards,
Frans.
Making some progress (I bet you got the Paradise board too)
Just when one is planning on same fun the usual spanner drop in the works.
Was going to finish a preamplifier but ended up starting again from making new boards for that.
so it looks like a couple of weeks before I even dare take either boards out of box
There are no files in #82, sorry.
There are files in #81, I did test them and they are fine. If the question is if I have other files than the MultiSym files, then the answer is no I do not. But al the schema's are in post #1 and #2, just redraw using your own tool.
I used RC55's in my build (and I like them), there are no part changes (except for the LME49990 to be used for the input stage) http://www.diyaudio.com/forums/anal...all-dc-coupled-riaa-preamp-4.html#post2191425 you need a small adaptor board for these.
I can export a BOM from Multisim (but there are no actual/correct part numbers in there).
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