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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Passive pre-amp for active speakers
Passive pre-amp for active speakers
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Old 15th January 2018, 09:51 AM   #21
sidlauskas is offline sidlauskas  Lithuania
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Quote:
Originally Posted by rmaudio View Post
Well I was considering the input Z of the active monitors that the OP has given as 10kOhm. I guess you could look at 1K0 pot at a push but it looks like quite a load for the source to drive min at - 909Ohm.

BUT the big problem - that I hadn't taken into account - is that the sources are 'Phono' by which I take it to be the bare output (before RIAA correction) of a cartridge - MM or MC is unstated.
If this is the case then the cartridge needs the correct loading and RIAA response before anything else. Definitely not a 1K0 or 2K0 pot with 10K off the wiper.
MM cartridge output is 2.5mV at 1kHz
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Old 15th January 2018, 10:44 AM   #22
rmaudio is offline rmaudio  United Kingdom
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Quote:
Originally Posted by sidlauskas View Post
MM cartridge output is 2.5mV at 1kHz
Okay but I wasn't questioning the signal strength.
I'm pointing out that MM cartridge needs correct loading / RIAA response before you can do anything else with it.
ie you need a Phono preamp as the 'first stop'.
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Old 15th January 2018, 11:15 AM   #23
sidlauskas is offline sidlauskas  Lithuania
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Originally Posted by rmaudio View Post
Okay but I wasn't questioning the signal strength.
I'm pointing out that MM cartridge needs correct loading / RIAA response before you can do anything else with it.
ie you need a Phono preamp as the 'first stop'.
As I mentioned in my previous posts I have two of them:

phono stage 1
Output impedance: 82 Ohms
Maximum output voltage: 9 V

phono stage 2
Output impedance: 200 Ohms
Maximum output voltage: 1.8 V
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Old 15th January 2018, 11:44 AM   #24
rmaudio is offline rmaudio  United Kingdom
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Quote:
Originally Posted by sidlauskas View Post
As I mentioned in my previous posts I have two of them:

phono stage 1
Output impedance: 82 Ohms
Maximum output voltage: 9 V

phono stage 2
Output impedance: 200 Ohms
Maximum output voltage: 1.8 V
Okay. So you already have phono preamps. I misunderstood.

Anyway - If you can't find what you want ready made I recommend DIY After all you're in the right place.
Cheers.
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Old 17th January 2018, 11:15 AM   #25
sidlauskas is offline sidlauskas  Lithuania
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Originally Posted by rmaudio View Post
Okay. So you already have phono preamps. I misunderstood.

Anyway - If you can't find what you want ready made I recommend DIY After all you're in the right place.
Cheers.
Something like B1 Buffer Preamp?
https://www.passdiy.com/pdf/B1%20Buffer%20Preamp.pdf
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Old 17th January 2018, 12:21 PM   #26
rmaudio is offline rmaudio  United Kingdom
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Originally Posted by sidlauskas View Post
That would fit the bill with added source switching - have a think about crosstalk / feedthrough from the non selected source if that is an issue for your application. And you'll need to provide the Power.
But it's a fair number of parts. Unless you want its particular sonic footprint the easiest way IMO would be to build simple op amp buffers after the pot using 'standard' NE5532 or NE5534 (compensated for stabilioty at unity gain) opamps or LM4562. For less current demand OPA134. Lots of options with same pinout.
Dual supply eg +/-15V would make simpler circuit but if only one rail you can split it to give a virtual ground.
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Old 7th February 2018, 09:15 AM   #27
miklos is offline miklos  Hungary
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The easiest way to find on ebay an audio switcher and build in a potentiometer to the output. These boxes exists most of them made in the seventies by major Japanese manufacturer like Sony etc. ,I have one from Akai.
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