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In the Forum: Melquiades Amplifier
In the Thread: Valve Preamplifier for Macondo/DSET
Post Subject: Oh, low voltage sources...Posted by anthony on: 4/21/2019
 rowuk wrote:
How many sources do you currently have? If you are building a phono corrector, make it for 4 volts output. If you have a PC for digital playback, there are good DACs with more than 2V output. That would leave a tuner to pimp - certainly less risky than a new preamp.


Yes, Rowuk, it is important to specify this:

Dac:  My dac outputs about 2VRMS but it never sounds its best unless attenuated slightly.  I always run it at -6dB into the Placette and use the Placettes volume control, which is why I said the dac outputs 1WRMS.  At the moment I do not listen to this dac and have just been streaming from my computer through a soundcard which only outputs 2VRMS, and if I want loads of volume I add a SUT.  I can talk with the manufacturer about increasing the output of this dac.  It has zero feedback in the IV stage but I think the stages can be "stacked" to give more voltage.

Tuner:  TU-X1 which puts out plenty of voltage from memory, certainly it was a lot louder than all my other sources.  Unfortunately the cockatoos have ruined the cable on the FM antenna and I need to get on the roof to rewire and better protect it from birds.  I am reasonably sure this source will put out 4VRMS.

TT:  One of the valves I am looking at using in a valve phono is a cascoded 6S3P which should give about 56dB of gain from two stages after RC RIAA filter losses.  30pF-50pF input capacitance.  Add a SUT before and I may have as much as 32dB more gain which would give a total of 88dB which should squeak 4V from my 0.2mV MC cartridge.  The SS phonos that I have here will give 76dB (1.3VRMS output including 32dB SUT) and 63dB (0.25VRMS without SUT - not sure if I can run a SUT before this phonostage, but if I can that is 95dB gain).  One complication here is that I would like to run balanced from cartridge to phono which would reduce those total gains by 16dB at the SUT:  72dB for the valve phono; 60dB for the first SS; 79dB from the second SS).   86dB total gain is 4VRMS.  Then if I go for an LCR RIAA filter I may lose more gain...not sure how much.

Bluray/DVD:  I've been hoarding some DVD's of various orchestral performances with intention of adding visual capability to my listening room after everything else is up and running.  Every decent disc player with modern video these days only outputs 2VRMS and I do not know of any that output more.

Computer:  Streaming youTube or Tidal from my PC via a sound card such as Focusrite Scarlet 2i2 or RTX-6001 Audio Analyser only gives the equivalent volume of about 2VRMS output.  Note that my computer streaming is different to using my Dac (above).  The Dac has its own dedicated and optimised computer whereas streaming, as we are talking about here, happens from my work PC through a random soundcard.


Hence my case for a pre-amp with some gain, ideally about 12dB or 4x.

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