Hi. I tried unsuccessfully to copy the circuit of a known phono preamplifier.
I've captured it in LTSpice, but simulating it with reverse RIAA produces a graph that has nothing to do.
To simulate I have used ICs that are not real ones.
It's Pr. Je .. Phono B.x AC, dual mono that I got in garage sale at U $ S 5.
If someone suggests where the copy is wrong I thank you.
regards
I've captured it in LTSpice, but simulating it with reverse RIAA produces a graph that has nothing to do.
To simulate I have used ICs that are not real ones.
It's Pr. Je .. Phono B.x AC, dual mono that I got in garage sale at U $ S 5.
If someone suggests where the copy is wrong I thank you.
regards
> produces a graph that has nothing to do
What DOES it do?
But the "obvious" question is: why no other connection to U1 "- In" pin? We would expect the output of U1 to connect back to its "- In"; basic op-amp connection.
Suggestions: Lose U3 et al. This is a DC servo to correct real-world voltage errors. SPICE opamps have zero error. You do not need U3 to get it to "work" in SPICE. Lose the whole U2 stage. This IS needed to get the 500Hz+2KHz wiggle in the RIAA curve, but U1 alone will get a slightly-wrong but nearly-right response IF it is connected correctly.
What DOES it do?
But the "obvious" question is: why no other connection to U1 "- In" pin? We would expect the output of U1 to connect back to its "- In"; basic op-amp connection.
Suggestions: Lose U3 et al. This is a DC servo to correct real-world voltage errors. SPICE opamps have zero error. You do not need U3 to get it to "work" in SPICE. Lose the whole U2 stage. This IS needed to get the 500Hz+2KHz wiggle in the RIAA curve, but U1 alone will get a slightly-wrong but nearly-right response IF it is connected correctly.
Hi, PRR. I've listened to you.
I have removed the servo dc and have corrected errors in the copy.
I think now the frequency response agrees.
It is a Pro Ject Phono Box MM / MC preamplifier with AC power 16 volts.
Thankyou
I have removed the servo dc and have corrected errors in the copy.
I think now the frequency response agrees.
It is a Pro Ject Phono Box MM / MC preamplifier with AC power 16 volts.
An externally hosted image should be here but it was not working when we last tested it.
Thankyou
If I have correctly copied this circuit (components that convert it to MC are not included), can there actually be this response simulating with AT 440MLb cartridge, with that peak at 20khz ?. You can have that accentuation in low frequencies so important.
The peak at 20khz disappears if you remove the 22p capacitor that is in series with the 47k load resistor.
The peak at 20khz disappears if you remove the 22p capacitor that is in series with the 47k load resistor.
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.
I suspect the schematic in this article may be somewhat similar to your phonobox if not necessarily identical. It is at least a starting point. (Yours appears to be newer)
I'm not sure what to think of this design..
Here: http://www.angelfire.com/az3/dimitri/images/phonobox.pdf
I'm not sure what to think of this design..
Here: http://www.angelfire.com/az3/dimitri/images/phonobox.pdf
Kevinkr, almost identical. I was missing a resistor on U2. I put 47k parallel to 68n and the result is this. Thanks for the input.
For Osvaldo, greetings neighbor.
Anyway, it's just curiosity. In sound performance I will stay with VSPS 300 and with Muffsy Kit.
For Osvaldo, greetings neighbor.
An externally hosted image should be here but it was not working when we last tested it.
Anyway, it's just curiosity. In sound performance I will stay with VSPS 300 and with Muffsy Kit.
Hello again. I have successfully copied the circuit of Pro Ject Phonobox AC.
It is very similar to the circuit provided by Kevinkr.
I have made some modifications suggested by a circito that I found on the internet.
I show both circuits.
Of course I'm going to change the most beautiful aluminum pouna steel case, and I'll make a PSU with toroidal transformers + 15v 0 -15v / 50watts.
Sounds very nice.
It is very similar to the circuit provided by Kevinkr.
I have made some modifications suggested by a circito that I found on the internet.
I show both circuits.
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.
An externally hosted image should be here but it was not working when we last tested it.
Of course I'm going to change the most beautiful aluminum pouna steel case, and I'll make a PSU with toroidal transformers + 15v 0 -15v / 50watts.
Sounds very nice.
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Hello, searching the internet I found a circuit identical to that of Pro Ject Phonobox. It's apparently from a kit called Actidamp MK2.
I have already modified the Pro Ject based on the small variations shown in this circuit. Sounds great and reading the specs I found today on this page, it looks like it's good.
http://www.elektrolukis.estranky.cz/clanky/predzesilovac-pro-gramofon-actidamp-mk.ii.html
What will be the original circuit, Pro Ject or Actidamp MK2
I have already modified the Pro Ject based on the small variations shown in this circuit. Sounds great and reading the specs I found today on this page, it looks like it's good.
http://www.elektrolukis.estranky.cz/clanky/predzesilovac-pro-gramofon-actidamp-mk.ii.html
What will be the original circuit, Pro Ject or Actidamp MK2
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Calvin, you're right, the servo dc of this is badly connected. Does it influence the simulation ?. I show you the Actidamp MK2 circuit that is identical to the Pro Ject Phonobox circuit, or vice versa.
regards
regards
An externally hosted image should be here but it was not working when we last tested it.
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Hi,
that actidamp is a strange circuit.
beginning with C2 in series with the 47k R1 that normally defines the 47k input impedance .... and typically also forming a dc-path to bias the input transistors.
The small cap C2 blocks R1 over almost the whole audio range, so that the input impedance is very high.
So the cartridge is not loaded properly and this results in a HF-rise.
Since the dc-servo couples to the input via a 1M32 resistor, the input will see a large noise generating impedance.
The 220k R5 in the servo fb-loop also looks strange as it reduces the servo's gain to 1 while it reduces to 0 with typical servos.
The gain switch PR can be rightout dangerous for following equipment if it is not of a shorting type.
If its a common non-shorting type the gain of US2 will jump up to its openloop value at the moment of switchover.
Sounds like Big Bang Theory, ey?
The more I look at it the more my view changes from 'strange circuit' to 'ill designed'.
But then ... what do I know
jauu
Calvin
that actidamp is a strange circuit.
beginning with C2 in series with the 47k R1 that normally defines the 47k input impedance .... and typically also forming a dc-path to bias the input transistors.
The small cap C2 blocks R1 over almost the whole audio range, so that the input impedance is very high.
So the cartridge is not loaded properly and this results in a HF-rise.
Since the dc-servo couples to the input via a 1M32 resistor, the input will see a large noise generating impedance.
The 220k R5 in the servo fb-loop also looks strange as it reduces the servo's gain to 1 while it reduces to 0 with typical servos.
The gain switch PR can be rightout dangerous for following equipment if it is not of a shorting type.
If its a common non-shorting type the gain of US2 will jump up to its openloop value at the moment of switchover.
Sounds like Big Bang Theory, ey?
The more I look at it the more my view changes from 'strange circuit' to 'ill designed'.
But then ... what do I know
jauu
Calvin
Calvin, thank you for responding. This is the Pro Ject Phonobox AC circuit. I bought it in a garage sale at U $ S 5. As it is a well-known brand, from Austria I wanted to identify the diagram. I have found your "brother" the Actidamp. Diagram identical, with only slightly different values.
I do not understand how some components and their combinations work, since I'm just an audio and electronic enthusiast. My profession is Medical Doctor, therefore I only assemble circuits designed by others.
I have tried it and it does not sound bad. I actually listen to vinyl on my Marantz PM6006; Or with my Muffsy and VSPS 3000 preamplifiers. (I do not know which is closer to reality, since each of them has its particular sound). Pro Ject is no better.
Greetings.
I do not understand how some components and their combinations work, since I'm just an audio and electronic enthusiast. My profession is Medical Doctor, therefore I only assemble circuits designed by others.
I have tried it and it does not sound bad. I actually listen to vinyl on my Marantz PM6006; Or with my Muffsy and VSPS 3000 preamplifiers. (I do not know which is closer to reality, since each of them has its particular sound). Pro Ject is no better.
Greetings.
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