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Old 18th October 2005, 08:27 AM   #121
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Richard Murdey
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Hi BT,

The tonearm cable earth connects to the chassis of the VSPS/ultra which is further connected to the COM pad of the PCB, as per the connection diagram for the regular VSPS. That the battery charger does not have a third "earth" connection is not a concern here - you wouldn't connect it to the VSPS ground even if it did.

/R
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Old 18th October 2005, 09:36 AM   #122
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Tose, show us some work in progress pics please
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Old 18th October 2005, 10:12 AM   #123
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Hi Tazzy,

I don't have a camera with me at the moment, so I'll try to take some tomorrow.

Regards BT
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Old 18th October 2005, 05:35 PM   #124
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Default Filter cap wiring.

My phonoclone has two large filter caps in the box with the transformer and diodes. The smaller caps on the board should be decoupling, the lead in four feet long and 20 ga to give some resistance and inductance.
I do not have a scope, but do have a VOM that measures to 0.0 mv AC. This should tell if there is an ac component riding the rails.
Are there any downsides to running a wire from the cap ground to COM? Such as RFI.
The boards are finished, hate to remove them and replace the caps.


George
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Old 19th October 2005, 02:39 AM   #125
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The filter caps in the power supply reduce the ripple and the charging currents in C8-11, so the shared ground connection will have less effect. I would leave the PCB as it is.

At least give it a few weeks to break in and for you to become familiar with the sound. If you start thinking that its a little soft, or slow - giving everything a vintage tint, like - then perhaps its time to start tweaking.

If your power supply voltages are over 18V, you might try adding 7815/1915s as pre-regulation. I'd do that before re-wiring the caps, at any rate.

The harmonics seen in the FFT spectrum are so low that the difference in the measured AC output voltage would most likely be below the measurement threshold. Your ear is a better detector: the ripple is a triangle wave, and sounds like buzzing. If you can clearly hear the buzz above the background hiss with the volume turned all the way up, then the harmonics are present. Dont forget you have to have your cartridge attached or a dummy load on the input before making any measurement.

I have 2 or 3 remaining sets of replacement 100uF/25 caps for those who bought phonoclone PCBs and want to do the mod. I will send these out free to the first people to email me to ask for them, but in return you are required to post your results here.


Since people have said the Phonoclone works better at lower voltages, and since I only have 15V DC on my power supply I plan to replace my 7812s with 7809s (or whatever I can find in that range) on the PCB and use the 7812s to pre-regulate the power supply. See how that flies.

Note that theres no need to go overboard on the preregulator. 20-40dB of ripple rejection is more than sufficient. Its temping to just add filter capacitance to get there, but this has its own set of problems. MOSFET series regulator? CRC filter? All kinds of options to play around if you want to.

/Richard
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Old 21st October 2005, 09:07 AM   #126
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Hi Tazzy,

Here is a picture of my battery powered VSPS Ultra.
Power wiring loom nearly complete.
Boards sans ICs.

Just need to solder signal and power wires into boards
and check power and connect sign wires to phonos.


Regards BT
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File Type: jpg 102_0286.jpg (40.5 KB, 1546 views)
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Old 21st October 2005, 10:48 AM   #127
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Nice work! I've been thinking about building the same setup with a normal VSPS
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Old 25th October 2005, 07:53 AM   #128
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Thumbs up Lower Gain on Phonoclone

Hi all,

I promised to report back on my results when lowering the phonoclone gain for use with my Ortofon Kontrapunkt b cartridge, unfortunately just after making the mods I picked up an ear infection which left anything sounding like it was playing through a 1/2" tweeter with a torn dome!

I was actually quite worried for a while but mercifully my hearing is well on the way to recovery although not yet up to really critical listening.

I'm pleased to report however that dropping the gain setting resistors to about 1K did the job fine and at least through my left ear which is recovering faster than the right it now sounds truly wonderful and every bit a match for a $700 commercial unit I compared.

Thanks RJM for a great board and your help with the gain issue.

Best Regards,

Dave.
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Old 25th October 2005, 11:35 AM   #129
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Default Novel idea

Read the idea about using another cartridge in the feedback loop. How would this work on the input of the phonoclone? I have another cartridge that has the cartilever broken off. It should match closer than the resistors already used.
Once mine new phonoclone is working properly I may try to evaluate. The two resistors I used are more usefull than my broken cartridge.
I did not follow the datasheets for the LM320/340 regs or the sage advice given by one here. The bypass caps on the output of the regs are 100 ufd ultra low impedance type. And guess what, the regs are acting up.
The unit had about 3 mv of ac on the output with no cartridge attached. I assumed this would go away once loaded with a 14 ohm load. Guessed wrong again.
One novel thing found. Disconnected the ground wire from the turntable to try and reduce the noise. Started picking up radio with the phonoclone. Not bad quality. First phono stage I have tried that did this. Usually grounding issues just give hum.
The noise I am getting is not hum. It is grittier. Got some 10 ufd ultra low impedance caps in the closet. Gunna install and some Onsemi 7812/7912 too. The specs show much less voltage noise than others of this type. Thanks for the tip!

George
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Old 26th October 2005, 01:04 AM   #130
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Two posts, one phonoclone project looking good, the other obviously having some teething trouble.

Thus, some (more) comments about noise vis. the phonoclone:

HUM is the presence of sinusoidal line frequency (60Hz or 50Hz) AC on the output. It gets on the output most often by coupling of the magnetic fields produced by power transformers or the turntable motor into either the cartridge coils or some other part of the input stage. Moving magnets are more prone to this than moving coils, but inproperly connecting (or not connecting) the turntable ground wires can produce hum on a MC setup, too. I've never had any problem with hum in my setup. (Sheilded external power transformer, shielded wires, turntable grounds connected to the chassis of the phonoclone unit, which is itself connected to the phonoclone circuit ground.)

BUZZ is heard when some of the AC ripple riding on the DC power rails gets into the output. The ripple has the line frequency as its fundamental, but since its a triangle wave contains lots of higher order harmonics as well. It is not a pleasant sound. Fortunately the PSRR of the OP27 is high, and together with the ripple rejection of the voltage regulator this means only a tiny fraction of the unregulated DC ripple finds its way onto the output in normal circumstances. (Example: my stock phonoclone, gain 70dB, has an output ripple of about -72dB, or about 250uV rms. After the mod to change the ground layout, its reduced to 100uV- this together with over 1mV of broadband output noise, so its barely audible even with the volume turned up.) This is with only 100uF x4 of filter capacitance, and generic LM7812s. As hinted in the example, extra ripple can get into the output for all kinds of subtle and not-so-subtle reasons related to the grounding layout.

HISS/HUSH is most likely noise originating from the opamp itself, in normal operation. The OP27 is 3.2 nV/rtHz, and the Phonoclone is designed such that the circuit adds no significant noise above this. At 70dB gain, there will be about 1mV of broadband noise, mostly at frequencies below 100Hz. This is intrinsic to the design of the op-amp.

CHMR 101.3fm: Since the ripple rejection and PSRR both cease to be of much use at frequencies of 100kHz and above, high frequency noise (RFI/EMI) on the power supply cable or any of cables running into the box can be a problem in cases where significant amounts of it are present and no steps are taken to prevent it from getting to the phonoclone PCBs. I as said before, the phonoclone PCB has no defense against RFI, and moreover the bipolar-input OP27s are a little more prone to demodulating RF signals than FET types. So, yes, it will become a nice little FM radio if you give it a suitable antenna, as some of you have discovered. I've never had a problem with this myself.

Richard
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