• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Is this a good phono preamp circuit to build?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.

6L6

Moderator
Joined 2010
Paid Member
fig7.png


This is the arrangement jack suggested for heaters and I wholeheartedly recommend it! It's easy to elevate and because the tubes are heated from a bipolar source across the filament, much of the (minimal) noise becomes common-mode, and becomes silent.

Also, as it's not shown exactly on this schematic, the heater PSU is set up to give half the voltage per phase, so if you used 12AX7 and 12AT7, you could make the heater supply +6.3 GND -6.3, and wire the tubes across the V+ and V-

If you were using all 6.3v tubes, example 6DJ8 ECC88, then set the heater PSU for +3.15 GND -3.15, and again wire across v+ and v-.
 
Last edited:
Funny you should mention this, it's actually a dynaco PC6 ( phono from PAS3)
made for shure.
PC6 boards ( or clones ) are available at several places.
But i thing the thread starter want's to build by himself, thus a ready made
card is considered "cheating".

Actually the Shure M65 is not the same as the Dyna PAS phono. It's very similar to be sure, but not the same. My point in mentioning the M65 was not to say the OP should buy a Shure or a PAS for that matter, or even a PC6 board for building a phono circuit; instead I was just suggesting the circuit itself as a very simple, cost-effective, all-tube design that could be easily built with point-to-point wiring. I did that myself a few years ago and the end result was very nice sounding especially given the minimal effort required. I did use different RIAA eq values and a tube-rectified power supply with CLCRC filtering, and I used a DC heater supply instead of the AC used in the M65.

Unfortunately my version of M65 just gathers dust because my primary phono preamp is heads and shoulders better sounding, but it's also a lot more expensive and complicated to build than the M65, plus it doesn't use 12AX7s so does not meet the OP's criteria.
 
I recently built a phono stage using three dual triodes where I allocated one half of each triode to the left channel and the other to the right channel. I see some designs where both halves are kept to the same channel excepting of course if the design has a third valve which must be shared between both channels. I'm thinking here that matching both halves of a triode valve is easier than matching pairs of valves. Any thoughts?
 
I recently built a phono stage using three dual triodes where I allocated one half of each triode to the left channel and the other to the right channel. I see some designs where both halves are kept to the same channel excepting of course if the design has a third valve which must be shared between both channels. I'm thinking here that matching both halves of a triode valve is easier than matching pairs of valves. Any thoughts?

That makes sense to me. Not only are your channels likely to be well-matched, but this gives you the option of using different brands of tubes in the various spots. For example, you might want a Mullard in the first valve spot and a Siemens in the second, that sort of thing. If you have both halves devoted to just one channel, you will always need a pair of identical tubes so the channels sound the same.
 
I'm thinking here that matching both halves of a triode valve is easier than matching pairs of valves. Any thoughts?

It depends on the circuitry in use. In the case of RCA style setups, with passive EQ, matching across channels in each of the gain block positions is required. OTOH, providing open loop gain is great enough, setups employing active EQ (via NFB) don't require matching, as the feedback network defines the closed loop gain.

The 'X7 triode is a VERY poor driver of loads, including NFB networks. Active EQ setups are less overload resistant than passive EQ setups. Both active and passive EQ have yeas and nays. TANSTAAFL will forever be with us. :boggled: "Name your poison."
 
Hello, i'm interested about phono preamp.
I want to built my own unit from a simple schematic to learn.My power supply's voltage is 250 v.
I founded this schematic who is à Dynaco Pas2 like.
But please, what's is doing this R10 22 Ohm resistor wired to chassis here ?
Regards
An externally hosted image should be here but it was not working when we last tested it.
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.