The gerbers would be published to everyone. If a few friend in close locale order, they can save a bit on shipping. Nothing more complicated than tat. Gerbers will be available to anyone who wants them.
The circuit design, including PCB layout, are Wyn's and he can decide how he wants to distribute them. I'm just the middleman...(and happy to keep it that way).
I've made a small circuit change to improve the protection for when the AC plug is pulled out during operation (or the AC mains goes down).
This shows the line output change (yellow plot), occurring about 200ms after the plug is pulled (not shown). The blue plot is the internal -15v supply that triggers the protection. The protection relay is tripped about 30ms after the -ve supply starts to change.
The unit is in MC mode, no extra gain boost.
Under normal operation multiple on-off cycles using the on-off switch is essentially inaudible.
The final board is now being completed.
The prototype will be put in a case and sent out for listening.
This shows the line output change (yellow plot), occurring about 200ms after the plug is pulled (not shown). The blue plot is the internal -15v supply that triggers the protection. The protection relay is tripped about 30ms after the -ve supply starts to change.
The unit is in MC mode, no extra gain boost.
Under normal operation multiple on-off cycles using the on-off switch is essentially inaudible.
The final board is now being completed.
The prototype will be put in a case and sent out for listening.
A fully functional prototype has been constructed in a less-than-ideal box.
Next will be to listen and see how it does.
Next will be to listen and see how it does.
I have measured the noise of the boxed prototype stage in MC mode 54dB gain, with the input shorted.
The A weighted value, relative to the nominal 6dBv output is c. 94dB. This is very close to what was expected.
Note that the mains pickup is a very low c. 120dB below rated output.
It should also be noted that the short is at the end of c. 6" of phono cable.
The converter noise is at -100dBVA and the hum is at -140dBVA with its input shorted.
Now, 69dB gain (+6dB at the input and +9dB at the output) with the input shorted.
All seems as it should be.
This should be inaudible with even the lowest output cartridges.
The A weighted value, relative to the nominal 6dBv output is c. 94dB. This is very close to what was expected.
Note that the mains pickup is a very low c. 120dB below rated output.
It should also be noted that the short is at the end of c. 6" of phono cable.
The converter noise is at -100dBVA and the hum is at -140dBVA with its input shorted.
Now, 69dB gain (+6dB at the input and +9dB at the output) with the input shorted.
All seems as it should be.
This should be inaudible with even the lowest output cartridges.
Listening has very positive first impressions. No sub-woofer pumping, very quiet with no apparent noise, even at very high listening levels.
All the functions work, no audible impairments when in warp mode, however switching from MC to MM or vice versa when the unit is powered up is a big no-no as the calibration needs to be redone for each mode.
Also, I'd probably wait for a minute or so after powering up before operating the mono/warp switching as the DC levels need to completely stabilize.
Channel matching c. 0.3dB, imaging excellent.
Next is a get together with the local audio club for a listening session.
All the functions work, no audible impairments when in warp mode, however switching from MC to MM or vice versa when the unit is powered up is a big no-no as the calibration needs to be redone for each mode.
Also, I'd probably wait for a minute or so after powering up before operating the mono/warp switching as the DC levels need to completely stabilize.
Channel matching c. 0.3dB, imaging excellent.
Next is a get together with the local audio club for a listening session.
I added a mute switch that should be used each time a function switching occurs. It uses the same control port as the power on/off and supply protect function.
This is a 3D representation of what is intended to be the final board(s).
The board can be split into two sections for those who wish to put a divider between the PSU and the preamp, or to have a completely separate external supply.
Please note that nothing so far suggests that either of these two alternatives seem necessary. Measurements and listening with the board intact and an external 18vAC wall-wart and a grounded metal box (the box connected directly to the PSU ground and the outer ring of the AC plug) indicate that the hum is effectively zero, and the contribution of the noise from the supply is both inaudible and unmeasurable.
The design seems to be very stable, with no detectable sensitivity to RF interference from local Wi-Fi nodes, and no HF peaking.
No problems were found with 4m long phono runs from the output to a Benchmark DAC3 L.
When used with LPs that have warps and embedded rumble the "warp filter" seems to be effective in reducing the woofer excursion to near invisibility while not having noticeable effects on the LF response.
The board can be split into two sections for those who wish to put a divider between the PSU and the preamp, or to have a completely separate external supply.
Please note that nothing so far suggests that either of these two alternatives seem necessary. Measurements and listening with the board intact and an external 18vAC wall-wart and a grounded metal box (the box connected directly to the PSU ground and the outer ring of the AC plug) indicate that the hum is effectively zero, and the contribution of the noise from the supply is both inaudible and unmeasurable.
The design seems to be very stable, with no detectable sensitivity to RF interference from local Wi-Fi nodes, and no HF peaking.
No problems were found with 4m long phono runs from the output to a Benchmark DAC3 L.
When used with LPs that have warps and embedded rumble the "warp filter" seems to be effective in reducing the woofer excursion to near invisibility while not having noticeable effects on the LF response.
I have attached what should be the final schematic, and what is in the board currently being assembled.
The prototype is actually at an audio dealership for evaluation and will be passed on to SoTa once it's complete.
The prototype is actually at an audio dealership for evaluation and will be passed on to SoTa once it's complete.
Wynn I'd be happy to do a GB of pcb for anyone in the UK and make them available for cost + p&p for anyone interested.
Bill Hirsch requested that a transimpedance style MC design should be investigated, based on the voltage in/voltage out one previously deigned/built.
Requirements: <1uA input current, cartridge operation from 2 ohm to 40 ohms, able to use the voltage stage RIAA /gain/filter section.
Comparable distortion, noise, power supply rejection to the voltage gain unit.
Above is what I came up with. High open loop gain (c. 100dB at 1kHz). 57dB closed loop gain with a 2 ohm source (about 40dB feedback factor), 45dB closed loop gain with a 15 ohm source, 37dB with a 40 ohm source. Equivalent input noise R about 22 ohms (typical). With the prior RIAA etc. stage the RIAA compliance 20-20kHz is +/- 10mdB, nominally. The channel is inverting, rather than non-inverting. +/-15v supplies as was the case with the prior design.
No giant caps other than the power supply filtering units, as was the case for the prior design.
Comments? Observations? Criticisms?
Requirements: <1uA input current, cartridge operation from 2 ohm to 40 ohms, able to use the voltage stage RIAA /gain/filter section.
Comparable distortion, noise, power supply rejection to the voltage gain unit.
Above is what I came up with. High open loop gain (c. 100dB at 1kHz). 57dB closed loop gain with a 2 ohm source (about 40dB feedback factor), 45dB closed loop gain with a 15 ohm source, 37dB with a 40 ohm source. Equivalent input noise R about 22 ohms (typical). With the prior RIAA etc. stage the RIAA compliance 20-20kHz is +/- 10mdB, nominally. The channel is inverting, rather than non-inverting. +/-15v supplies as was the case with the prior design.
No giant caps other than the power supply filtering units, as was the case for the prior design.
Comments? Observations? Criticisms?
Dropbox links for the schematic, BOM, Gerbers, of the V4.
Schematic:
https://www.dropbox.com/scl/fi/9qxa...ey=nsb2le30dz8dpyfl4a0thg8sq&st=kn10oah8&dl=0
BOM:
https://www.dropbox.com/scl/fi/fr9q...ey=s32zg5hzvdh0ntho6eo0qho06&st=c08o0jlj&dl=0
Gerbers:
https://www.dropbox.com/scl/fi/omlj...ey=rfzl5p9ccu46ephfbxndo8vrw&st=abwof9re&dl=0
Schematic:
https://www.dropbox.com/scl/fi/9qxa...ey=nsb2le30dz8dpyfl4a0thg8sq&st=kn10oah8&dl=0
BOM:
https://www.dropbox.com/scl/fi/fr9q...ey=s32zg5hzvdh0ntho6eo0qho06&st=c08o0jlj&dl=0
Gerbers:
https://www.dropbox.com/scl/fi/omlj...ey=rfzl5p9ccu46ephfbxndo8vrw&st=abwof9re&dl=0
The V5 has a layout, courtesy of Bill Hirsch.
I see no comments on the V5. Surely there must be some interest/questions. It's hardly the most common approach/design.
I see no comments on the V5. Surely there must be some interest/questions. It's hardly the most common approach/design.
I have PCBs for V4 if anyone trolling this thread wants to build this pre. I love the V3 version and have it up against several other fantastic preamps—most are projects here at diyaudio...fun to play with different carts and preamp combos.
Send a PM for PCB arrangements. No cost other than shipping. (I also have V3 PCBs). (the real build details and tips/tricks etc. are over on Audiokarma)
(Thank you @wynpalmer2 !!)
Send a PM for PCB arrangements. No cost other than shipping. (I also have V3 PCBs). (the real build details and tips/tricks etc. are over on Audiokarma)
(Thank you @wynpalmer2 !!)
OPA202 replace with OPA192, 5 x 2SK209 with single JFE150
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