And to show how beautiful a Technics Turntable can be:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Super Economic
Thanks RJM,
I assembled a VSPS with cheapest, not "audio" devices, due to unavailable. Ceramic obsolete caps, cheap diodes, 10%(!!) tolerance resistors,
and cheap 4,7 uF bipolars. The OP is the OPA 2134, load resistors at 1K. Original circuit running with Ortofon TM7. It works well, but I want to change:
C3 to 5uF x 250 MKP Caps (these are available);
C1, C2 Ceramic to Oil;
Do the Kuei / Carlosfm improvements.
This changes will improve the sound? What do you think?
Thanks RJM,
I assembled a VSPS with cheapest, not "audio" devices, due to unavailable. Ceramic obsolete caps, cheap diodes, 10%(!!) tolerance resistors,
and cheap 4,7 uF bipolars. The OP is the OPA 2134, load resistors at 1K. Original circuit running with Ortofon TM7. It works well, but I want to change:
C3 to 5uF x 250 MKP Caps (these are available);
C1, C2 Ceramic to Oil;
Do the Kuei / Carlosfm improvements.
This changes will improve the sound? What do you think?
Sure they will. Also think about the quality of the power transformer, and maybe build a dual mono version... there are lots of little ways to tweak the circuit.
rjm,
What were the exact values you got for the feedback caps and resistors from your calculations?
ran
What were the exact values you got for the feedback caps and resistors from your calculations?
ran
RIAA values pt 2
... and second the response for the following numbers
R2 220 ohms
R3 780 ohms
R4 33k ohms
R5 229.8k ohms
C1 3.2nF
C2 9.57nF
where I tweaked the values manually until the response converged on the modified RIAA.
-rjm
PS: the red curve labelled "RIAA" is the simulated VSPS. The dotted line "Modified RIAA" is the Allen Wright response I'm aiming for.
... and second the response for the following numbers
R2 220 ohms
R3 780 ohms
R4 33k ohms
R5 229.8k ohms
C1 3.2nF
C2 9.57nF
where I tweaked the values manually until the response converged on the modified RIAA.
-rjm
PS: the red curve labelled "RIAA" is the simulated VSPS. The dotted line "Modified RIAA" is the Allen Wright response I'm aiming for.
Attachments
Thanks rjm!
The 2nd graph with modified RIAA values looks great minus the dip in the lower frequencies and around 5kHz from the 1st graph using the original values.
Is the difference noticable with listening?
The 2nd graph with modified RIAA values looks great minus the dip in the lower frequencies and around 5kHz from the 1st graph using the original values.
Is the difference noticable with listening?
Those graphs are 1dB full scale. The worst deviation on the first is only 0.25dB. So, no, honestly I doubt you'd hear a difference.
But, if you are selecting caps from a large lot, or have a wide range of precision resistors available, you might try choosing ones closer to the values from the second chart.
-r
But, if you are selecting caps from a large lot, or have a wide range of precision resistors available, you might try choosing ones closer to the values from the second chart.
-r
TLE2426
Hopefully no one thinks I'm to silly for posting this simple modification to the schematic, I'm not even shure it will work, not really knowing to much about electronics. Anyone wishing to assist, it would be greatly appreciated. 🙂
Naz
Hopefully no one thinks I'm to silly for posting this simple modification to the schematic, I'm not even shure it will work, not really knowing to much about electronics. Anyone wishing to assist, it would be greatly appreciated. 🙂
Naz
An externally hosted image should be here but it was not working when we last tested it.
Also I would like to add a PCB I layed out and see what people have to say about it. 🙂
naz
naz
An externally hosted image should be here but it was not working when we last tested it.
The reason for doing this being ... to use the VSPS circuit with a single supply voltage, I suppose?
Bear in mind that a split supply is not that hard to obtain and build, and it would perform better than the rail-splitter solution being proposed here.
If you insist on using your +24V wall-wart, however, then please consider the following points re. your layout.
Unless the power supply is regulated, you'll need to put in a LM7824 someplace. Also, since you've made the star ground point on the PCB - sensible enough - you need to return the input and output signal grounds to that point too so add in 4 extra pads. (maxw seems to have a blind spot for these, too) Last, if you figure you need two 220uF caps in parrallel, save yourself some money / space and just use a single 470u.
I had 220uF on each rail, but one was before the regulator and one was after, remember.
-r
Bear in mind that a split supply is not that hard to obtain and build, and it would perform better than the rail-splitter solution being proposed here.
If you insist on using your +24V wall-wart, however, then please consider the following points re. your layout.
Unless the power supply is regulated, you'll need to put in a LM7824 someplace. Also, since you've made the star ground point on the PCB - sensible enough - you need to return the input and output signal grounds to that point too so add in 4 extra pads. (maxw seems to have a blind spot for these, too) Last, if you figure you need two 220uF caps in parrallel, save yourself some money / space and just use a single 470u.
I had 220uF on each rail, but one was before the regulator and one was after, remember.
-r
Just a quick question.Is this circuit going to work with non unity gain opamps?
I remember building the Slone opamp phono for a friend but the opa 637 would not work at all and I spent hours trying to look for mistakes until I replaced them with opa 627 which sounded great.
With this complex feedback network it is hard to see whats happening .
I remember building the Slone opamp phono for a friend but the opa 637 would not work at all and I spent hours trying to look for mistakes until I replaced them with opa 627 which sounded great.
With this complex feedback network it is hard to see whats happening .
I think you have to subtract the value of R2 2.2K from 10K to get the value of R3=(10K-2.2K=6.8K). At least, thats how I understand the building instructions. See Component description. Also I have a question: the caps C1 and C2 is causing some confusing. In the BOM, C1 is the smaller value, but on the drawing and pic's, C1 the outermost cap, is the biggest to look at! Could you please clarify this rjm?
Steen🙂
I was trying to keep things simple and was thinking of putting the phono preamp in the same chassis as a pimeta headphone amplifier. I was also thinking of using the steps powersupply from tangent soft as the supply for both phono preamp and pimeta headphone amp. Essentially I was trying to figure out a easy way to use that setup to power the phono preamp.
Thanks to everyone for the advice on my project.
🙂
Naz
Thanks to everyone for the advice on my project.
🙂
Naz
ericpeters said:
Not only that one.
That's a rule, you will ALWAYS have better results that way.
ericpeters said:
Seriously? 😀
Hey, at least somebody was paying attention!
You're right. The pairs R3-C1 and R4-C2 should be reversed on the layout. And, yes its technically 10k-R2, but I let it go since the difference between 10k and 6.8k isn't huge.
Maybe. The high frequency gain flattens out about 30dB below the midband gain. That's touch and go for a 40dB midband gain setting, when used with something like the OP37. If you run into trouble try raising the gain first before switching opamps.
If the headphone amp's ground is the same virtual ground as the phono preamp, fine. If not, that's not gonna work.
-r
Sorry, but I'm just not seeing what your talking about when it comes to the R3-C1 and R4-C2 reversal. Maybe I'm just being dumb 😕 , someone care to explain it again? The reason for the 220uF 63V caps in the schematic and the pcb is based on the fact I have few Panasonic FC caps of that value not going towards any project at the moment.
Naz
Naz
C1 is 330pF and C2 is 1000pF (1nF) in the BOM. From that you can
count on C2, being the biggest part in real life can't you? Being 3 times the value of C1. But on the Layout drawing, C1 is drawn bigger than C2 and that doesnt make sense in real life
The only question left is, why did rjm put the biggest cap in C1's place? See the photos on the homepage😉 At least, it looks that way.
All the best
Steen.🙂
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