Greetings, Friend. Are you a Frugal Fi guy?
This is a Phono Stage built around a kit from ZeroZone. It's a clone of the Shure M65 circuit, using a pair of 12AX7s in a Class A configuration. PSU is on the board. A kit with all parts can be found on eBay or Ali for under $30, transformers cost about the same, and the PCB can be found for around $12.
I've read the threads on the EAR834p builds, and I see what can be done with $600, but let's consider a listener with a smaller budget. I don't know about the rest of you, but given the current economy, and the number of record-listening folks stuck home, out of work and bored, I think a project like this is due. I've only been messing with tubes since the beginning of the pandemic, getting time on the bench when my 2-year-old naps and researching when time allows, so this may be a tired subject already. Please feel free to steer me to any other M65-based projects, or share any advice you have.
The lack of the v3 tube and the lower power requirements (30VA, 100v@20mA , 14v@800mA ) bring the cost of all components well below $200, depending on options. The small size of the PCB (4x5.25", 100x135mm) allows the use of very small enclosures such as Hammond 1455Q2201BK (8.6x5x2")when the transformer is placed atop the chassis, under a steel cap, with a small amount of fabrication necessary so the tops of the tubes can stick out. If you don't want the tubes to show, the larger Hammond 1458VE3 (8x10x3") can accomodate transformer and PCB with very little fab work. Both of these options are under $50, as I'm sure are many other chassis from many manufacturers. I've been impressed with Hammond's quality and range of options so far.
For this build I swapped the film caps included with the kit with Orange Drops. C1 and C2 are 0.47uF, and the others are 0.047uF. This is the low value spec'd on the PCB itself, 0.47uF-0.047uF) and the caps included with the kit are 0.33uF. The preamp has a wonderful clear sound, especially in the range of the acoustic guitar, but the bass is lacking, and I wonder if the smaller 0.047 caps are responsible. Any thoughts on appropriate values for those caps?
Since each channel gets its own tube, both tubes should be high-quality V1 tubes, HG+ or similar, but TBH it sounds great with a cheap pair of matched JJs.
I've learned that the original M65 did not have a true RIAA de-emphasis, and that different parts in the feedback loop can address this, swapping the 470pF for a 680 Silver Mica and swapping the 100K for a 110K resistor, and swapping the 1800pF for a 2200pF polystyrene while leaving the 4M7 + 3M resistors in place.
In terms of off-roading, the PCB traces lead to pins 4&5 to heat the tubes at 12v, so a similar 30VA transformer with a 7v@1,6A (?) output could power a pair of 6N2P-EV tubes, for substantial savings. Perhaps different components would be called for in the PSU section? This part I'm just spitballin'
I have a PDF of the circuit here:
SHURE-PHONO-RIAA-SCH.pdf - Google Drive
And Here's the original BOM:
M65舒尔唱放 - Google Sheets
I've been working on a BOM of upgraded components from Mouser, and I'd appreciate any feedback on my selections.
M65 WORKSHEET - Google Sheets
This is a Phono Stage built around a kit from ZeroZone. It's a clone of the Shure M65 circuit, using a pair of 12AX7s in a Class A configuration. PSU is on the board. A kit with all parts can be found on eBay or Ali for under $30, transformers cost about the same, and the PCB can be found for around $12.
I've read the threads on the EAR834p builds, and I see what can be done with $600, but let's consider a listener with a smaller budget. I don't know about the rest of you, but given the current economy, and the number of record-listening folks stuck home, out of work and bored, I think a project like this is due. I've only been messing with tubes since the beginning of the pandemic, getting time on the bench when my 2-year-old naps and researching when time allows, so this may be a tired subject already. Please feel free to steer me to any other M65-based projects, or share any advice you have.
The lack of the v3 tube and the lower power requirements (30VA, 100v@20mA , 14v@800mA ) bring the cost of all components well below $200, depending on options. The small size of the PCB (4x5.25", 100x135mm) allows the use of very small enclosures such as Hammond 1455Q2201BK (8.6x5x2")when the transformer is placed atop the chassis, under a steel cap, with a small amount of fabrication necessary so the tops of the tubes can stick out. If you don't want the tubes to show, the larger Hammond 1458VE3 (8x10x3") can accomodate transformer and PCB with very little fab work. Both of these options are under $50, as I'm sure are many other chassis from many manufacturers. I've been impressed with Hammond's quality and range of options so far.
For this build I swapped the film caps included with the kit with Orange Drops. C1 and C2 are 0.47uF, and the others are 0.047uF. This is the low value spec'd on the PCB itself, 0.47uF-0.047uF) and the caps included with the kit are 0.33uF. The preamp has a wonderful clear sound, especially in the range of the acoustic guitar, but the bass is lacking, and I wonder if the smaller 0.047 caps are responsible. Any thoughts on appropriate values for those caps?
Since each channel gets its own tube, both tubes should be high-quality V1 tubes, HG+ or similar, but TBH it sounds great with a cheap pair of matched JJs.
I've learned that the original M65 did not have a true RIAA de-emphasis, and that different parts in the feedback loop can address this, swapping the 470pF for a 680 Silver Mica and swapping the 100K for a 110K resistor, and swapping the 1800pF for a 2200pF polystyrene while leaving the 4M7 + 3M resistors in place.
In terms of off-roading, the PCB traces lead to pins 4&5 to heat the tubes at 12v, so a similar 30VA transformer with a 7v@1,6A (?) output could power a pair of 6N2P-EV tubes, for substantial savings. Perhaps different components would be called for in the PSU section? This part I'm just spitballin'
I have a PDF of the circuit here:
SHURE-PHONO-RIAA-SCH.pdf - Google Drive
And Here's the original BOM:
M65舒尔唱放 - Google Sheets
I've been working on a BOM of upgraded components from Mouser, and I'd appreciate any feedback on my selections.
M65 WORKSHEET - Google Sheets
Moved to Tubes/ValvesThe output is at a small positive voltage from the cathode of the first stage trough NF network . Not good if you will ever use a direct coupled power amplifier . Normally there is a capacitor in series with the NF network if you look at some other designs .
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