captouch
Addicted Member
Cool, I already have one pair of 49990's on a DIP adaptor for another amp, so I'll pick up another.
About increasing gain. . .which resistor/s should be replaced with 100ohms?
Thanks again.
Another Super High End Phono Stage! No expense spared...
- Thread starter Fasterdamnit
- Start date
Cool, I already have one pair of 49990's on a DIP adaptor for another amp, so I'll pick up another.
About increasing gain. . .which resistor/s should be replaced with 100ohms?
Thanks again.
skrodahl
Active Member
My CNC with variable gain PCBs turned out nice:
Edit:
A word about the variable gain.
Using 150R and 300R for the gain resistors, you can choose between 36, 40 and 44dB gain (at 1kHz). 40dB is the gain of the standard CNC circuit.
The resistor values can of course be changed. Change them to 120R and 220R, and the selectable gains will be 38, 42 and 46dB. Another example: 100R and 300R gives 36, 44 and 48dB.
Edit:
A word about the variable gain.
Using 150R and 300R for the gain resistors, you can choose between 36, 40 and 44dB gain (at 1kHz). 40dB is the gain of the standard CNC circuit.
The resistor values can of course be changed. Change them to 120R and 220R, and the selectable gains will be 38, 42 and 46dB. Another example: 100R and 300R gives 36, 44 and 48dB.
Attachments
Last edited:
alleenchecke
New Member
Are there any measurements of this phono amp?
ghazzer
Senior Member
Hello, and welcome to AudioKarma!
Yes, there are several posts with parameters of boards. Use the search function in this thread and you can find them easily.
If you are specifically asking about the PCB that skrodahl just posted about, ask for measurements of his board, or you can send him a PM.
Yes, there are several posts with parameters of boards. Use the search function in this thread and you can find them easily.
If you are specifically asking about the PCB that skrodahl just posted about, ask for measurements of his board, or you can send him a PM.
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skrodahl
Active Member
The dimensions of the board that I had made are 4x3 inches, but I suspect that you are asking for gain, THD/noise, frequency response, RIAA response, THD etc.
I have not done any serious measurements, but the praise shown for the CNC in this thread gives a clue about real life performance. The gain is easily calculated (at 1kHz), and is shown in my previous post. The frequency response depends on the opamps, and the RIAA curve is very decent thanks to a tried and true passive RIAA filter.
Rod Elliot's P06 RIAA stage uses an active low frequency filter and a passive high frequency filter. It is otherwise quite similar, being a two gain-stage opamp circuit. He is providing some performance numbers in his article.
Apart from that, it all depends on the components you choose, the input impedance/capacitance, enclosure/shielding, interconnects, pickup, turntable etc.
I have not done any serious measurements, but the praise shown for the CNC in this thread gives a clue about real life performance. The gain is easily calculated (at 1kHz), and is shown in my previous post. The frequency response depends on the opamps, and the RIAA curve is very decent thanks to a tried and true passive RIAA filter.
Rod Elliot's P06 RIAA stage uses an active low frequency filter and a passive high frequency filter. It is otherwise quite similar, being a two gain-stage opamp circuit. He is providing some performance numbers in his article.
Apart from that, it all depends on the components you choose, the input impedance/capacitance, enclosure/shielding, interconnects, pickup, turntable etc.
Grainger49
Old Fart
CNC phono
Hi, every body of this groups,
I jointed Ak for very long time ago, but i had several posts only.
Some weeks ago, i had the board from local audiophile. I found that is the same cnc phono board what you have been discussing.
IMO this is wonderful phono stage i have heard vs with many phono stage i have. Therefore base on this one, I would like to upgrade to MC phono by add more opam... because of I had several MC carts.
Could you please support me by the circuit?
Sorry i don't known how to post a picture.
Many thanks and regards
Hi, every body of this groups,
I jointed Ak for very long time ago, but i had several posts only.
Some weeks ago, i had the board from local audiophile. I found that is the same cnc phono board what you have been discussing.
IMO this is wonderful phono stage i have heard vs with many phono stage i have. Therefore base on this one, I would like to upgrade to MC phono by add more opam... because of I had several MC carts.
Could you please support me by the circuit?
Sorry i don't known how to post a picture.
Many thanks and regards
Grainger49
Old Fart
There are two different phono stages from the same group you should look at. First is HypnoToad's LOMC phono stage:
http://www.audiokarma.org/forums/showthread.php?t=387121
The other is HypnoToad's variable gain phono stage:
http://www.audiokarma.org/forums/showthread.php?t=501186
http://www.audiokarma.org/forums/showthread.php?t=387121
The other is HypnoToad's variable gain phono stage:
http://www.audiokarma.org/forums/showthread.php?t=501186
skrodahl
Active Member
How about a smaller PCB, and variable gain?
Two layers for reduced interference:
In addition:
Size is 97x53mm (3.8x2.0"), Eagle files attached. When opening the board view in Eagle, click Ratsnest to create the ground fill.
Two layers for reduced interference:
- Bottom: Audio path + ground fill
- Top: Power, anything outside of audio path + ground fill
In addition:
- Much shorter tracks
- An extra GND pad for turntable ground at input
- Power input pads much closer together, and away from audio out
- Audio in and out pads positioned so that three-lead shielded cable can be used
Size is 97x53mm (3.8x2.0"), Eagle files attached. When opening the board view in Eagle, click Ratsnest to create the ground fill.
Attachments
Last edited:
Looking good! It would work, but I think it's time to think better grounding scheme now. Now I am inspired from Pass Pearl-2 phono PCB. [emoji39]
It implements star ground where all ground current run towards central connection of PS filter caps.
Sent from my iPad using Tapatalk
It implements star ground where all ground current run towards central connection of PS filter caps.
Sent from my iPad using Tapatalk
skrodahl
Active Member
Thanks omishra,
I may very well be absolutely wrong on this, but...
It doesn't seem to me that removing copper from the ground fill will improve anything. The ground will remain grounded anyway, it wouldn't run anywhere.
Isn't it better, from a shielding point of view, to keep the liberal amount of ground on the top and bottom layer?
This is all guesswork from me, I'm open for suggestions. The Eagle files are there to be edited and improved as well.
If there's any interest, it would be very easy to turn it into a single layer as well. The power input would end up between the right and left audio output, but there will be no other side effects on the layout.
Please don't take my comment as criticism. You have already made nice artwork. But was mentioning what I learned from my experience while designing PCB for that pearl-2 phono. Initially I made PCB for this too. But you must agree, improvement is always thought of.
Btw this PCB will work as it should be.
Sent from my iPad using Tapatalk
Btw this PCB will work as it should be.
Sent from my iPad using Tapatalk
Okay, see this! Please follow link.
Here you will find thick track between R13 & R26, left side of blue preset. That is centre point where power supply ground references are coming from + and - sides are connected, see unused golden solder pad. For input circuit all ground lines from input, load setting resistance and grounds from RIAA passive components are connected separately to this central ground sink without any cross talk of ground currents. This may be minute current but for mV levels it makes low noise floor, enhances accuracy.
Btw I will try to make one similar for CNC too, will take some time , may be 2-3 days.
Sent from my iPad using Tapatalk
Here you will find thick track between R13 & R26, left side of blue preset. That is centre point where power supply ground references are coming from + and - sides are connected, see unused golden solder pad. For input circuit all ground lines from input, load setting resistance and grounds from RIAA passive components are connected separately to this central ground sink without any cross talk of ground currents. This may be minute current but for mV levels it makes low noise floor, enhances accuracy.
Btw I will try to make one similar for CNC too, will take some time , may be 2-3 days.
Sent from my iPad using Tapatalk
Last edited:
skrodahl
Active Member
Thanks for the explanation. So what you're saying is that there might be variations in the ground potential with such a huge ground area? Would an extra ground pad, one that connects to a central star ground within the chassis, make any difference? ...or am I missing the point?
It will be really interesting to see, because I still have problems picturing it. A picture of the bottom side of the PCB would perhaps clarify things a bit better.
A single layer version of my previous Eagle design might interest those who etch their own boards. No difference, except that the signal output and PSU input has to be routed in another way. Same board size with variable gain:
I also made the traces a bit wider, which helps when etching at home. Very little copper needs removing, so it should be much easier to etch.
Eagle files are attached. Again, in board view, click the Ratsnest button to create the ground fill.
Attachments
imdocjas
Well-Known Member
hey i have had the CNC board for a while and just now getting to the project. Digikey is out of all the panasonic metal film resistors and the 1uF 50v low noise stacked metal film cap. anyone in the states have extra of these i could buy? i ordered all the remaining parts they had in stock.
in addition to the 1uF 50V cap the 1/4w 1% panasonic resistors needed are:
-8.2 kohm x1
-100 ohm x4
-150 ohm x4
-18 kohm x2
-2.2 kohm x2
-200 ohm x2
-27 kohm x2
-33 kohm x2
-47 kohm x2
-62 kohn x2
-750 ohm x2
thanks in advance! looking forward to a battery powered phono stage as a Xmas gift to myself
in addition to the 1uF 50V cap the 1/4w 1% panasonic resistors needed are:
-8.2 kohm x1
-100 ohm x4
-150 ohm x4
-18 kohm x2
-2.2 kohm x2
-200 ohm x2
-27 kohm x2
-33 kohm x2
-47 kohm x2
-62 kohn x2
-750 ohm x2
thanks in advance! looking forward to a battery powered phono stage as a Xmas gift to myself
