I think the production variability would have been 1 dB for these types of EQ amps - ok for the day. If the active devices were selected and 1% components used in critical places it would have been manageable.
Looking back, the best way to have tested these things would have been with a square wave and inverse RIAA - but as I mentioned earlier, it never crossed my mind in 1979. I want to also make it clear my original design was a real hack - breadboard, scope calculator affair and the conformance measurements were done by injecting an input signal and looking at the output level on a scope at 10 or 15 points on the responose. It ended up on a PCB and I used it for about 10 yrs.
Looking back, the best way to have tested these things would have been with a square wave and inverse RIAA - but as I mentioned earlier, it never crossed my mind in 1979. I want to also make it clear my original design was a real hack - breadboard, scope calculator affair and the conformance measurements were done by injecting an input signal and looking at the output level on a scope at 10 or 15 points on the responose. It ended up on a PCB and I used it for about 10 yrs.
I’m a bit amazed that we take the 3 to 4 dB deviation for granted.
I still have three amps from those days, Accuphase, Sansui and B&O.
All three Riaa’s measure with margin within +/- 1dB.
So those large deviations are probably for cheap TT’s with integrated (tube) amps like my wife had in the sixties.
Hans
I still have three amps from those days, Accuphase, Sansui and B&O.
All three Riaa’s measure with margin within +/- 1dB.
So those large deviations are probably for cheap TT’s with integrated (tube) amps like my wife had in the sixties.
Hans
The 3~4 dB figure was quoted by Lipshitz. I agree it is a big spread but +- 1 dB from the era was I think quite the norm on good products - bit like 0.1% distortion being acceptable whereas now we tend to feel we can do better than that.
I have an old Pioneer receiver (from 1967) with a MM phono input under my bench I want to restore. It will be interesting to see what that is. I am not expecting anything better than 1-2 dB
I have an old Pioneer receiver (from 1967) with a MM phono input under my bench I want to restore. It will be interesting to see what that is. I am not expecting anything better than 1-2 dB
I guess that input impedance is far below 47kOhm due to neg feedback resistor to the input base. With the quite low output impedance of your reverse RIAA-network certainly this will not show up.
I'm pretty sure we had SPICE at SUNY Buffalo in '79 - input was hollerith punch card. You'd hand your deck to the lady through a window, then wait for your printout to be placed in a cubby. I vaguely remember someone was doing speaker crossover sims at the time. I wonder what ever happened with that?
Unfortunately, I didnt recognize the significance right then and just stuck with programming the EE class examples. I'd use it off and on over the next 40 years in my career.
In a couple-few years we'll literally say "Computer - create an electronic filter, 10k input impedance, 1k output impedance, low pass 3 db down at 20Hz, high pass 3 db down at 18kHz. Use discrete transistors. Use component values you can actually buy; provide a BOM from Digikey". A bit of an upgrade, from handing someone a punched card deck.
Unfortunately, I didnt recognize the significance right then and just stuck with programming the EE class examples. I'd use it off and on over the next 40 years in my career.
In a couple-few years we'll literally say "Computer - create an electronic filter, 10k input impedance, 1k output impedance, low pass 3 db down at 20Hz, high pass 3 db down at 18kHz. Use discrete transistors. Use component values you can actually buy; provide a BOM from Digikey". A bit of an upgrade, from handing someone a punched card deck.
@jjasniew "In a couple-few years we'll literally say "Computer - create an electronic filter, 10k input impedance, 1k output impedance, low pass 3 db down at 20Hz, high pass 3 db down at 18kHz. Use discrete transistors. Use component values you can actually buy; provide a BOM from Digikey". A bit of an upgrade, from handing someone a punched card deck."
I have to say, that reminds me of the 1960's song by Zager & Evans "In the year, 2525"
We've (well, a lot of humans) have gotten to the point of barely using our mouths and limbs.
Just sit there, and tell that tabletop Alexa gadget what you want to do.
God forbid you'd have to use your own brain and limbs to do something.
Try to tell me that's a normal way to live..... try.
I have to say, that reminds me of the 1960's song by Zager & Evans "In the year, 2525"
We've (well, a lot of humans) have gotten to the point of barely using our mouths and limbs.
Just sit there, and tell that tabletop Alexa gadget what you want to do.
God forbid you'd have to use your own brain and limbs to do something.
Try to tell me that's a normal way to live..... try.
b & o use jfet and that is not good!!!!!!!!!!!!@Baldin...... right, but if your aim is to make a $20 riaa just for the fun of it, it´s quite OK.
Remember Bang & Olufsen?? They got away with using the same 2-transistor riaa in all their products......... for decades
Perfect example of "If it works, don´t fix it".
We're not there yet but we are well on the way... if you don't mind opamps
It's not much of a leap to have something like this recognise speech.https://tools.analog.com/en/filterwizard/
The answer of ChatGPT:
To design an electronic filter with the given specifications, we can use a combination of a high-pass filter and a low-pass filter, connected in series. We will use a discrete transistor circuit for each filter stage.
Here's the circuit diagram:
Low-Pass Filter Stage
For the low-pass filter stage, we can use a common-emitter amplifier configuration with a capacitor in the feedback path. The cutoff frequency of this stage is determined by the value of the capacitor.
The required cutoff frequency is 20Hz and the input impedance is 10kΩ. Using the formula:
Cutoff Frequency = 1 / (2 * π * R * C)
We can calculate the value of the capacitor (C) needed as:
C = 1 / (2 * π * R * Cutoff Frequency)
Plugging in the values, we get:
C = 1 / (2 * π * 10kΩ * 20Hz) = 795 nF
We can use a 820nF capacitor (Digi-Key Part Number: 493-11343-1-ND).
The transistor used for the low-pass filter stage is a NPN transistor (2N3904). The resistor values can be determined by assuming a quiescent collector current of 1mA and a collector-emitter voltage drop of 5V.
Using the formula:
R = (Vcc - Vce) / Ic
We can calculate the value of the resistor (Rc) needed as:
Rc = (12V - 5V) / 1mA = 7kΩ
We can use a 6.8kΩ resistor (Digi-Key Part Number: 311-6.8KFRCT-ND).
The bias resistor (Rb) can be calculated using the formula:
Rb = (Vcc - Vbe) / Ib
Assuming a base-emitter voltage drop of 0.7V and a base current of 10μA, we get:
Rb = (12V - 0.7V) / 10μA = 1.13MΩ
We can use a 1MΩ resistor (Digi-Key Part Number: 311-1.0MFRCT-ND).
The input coupling capacitor (Ci) is used to block DC and prevent the input signal from being affected by the DC bias at the transistor base. We can use a 10μF capacitor (Digi-Key Part Number: 445-1308-1-ND).
High-Pass Filter Stage
For the high-pass filter stage, we can use a common-base amplifier configuration with a capacitor in the input path. The cutoff frequency of this stage is determined by the value of the capacitor.
The required cutoff frequency is 18kHz and the output impedance is 1kΩ. Using the formula:
Cutoff Frequency = 1 / (2 * π * R * C)
We can calculate the value of the capacitor (C) needed as:
C = 1 / (2 * π * R * Cutoff Frequency)
Plugging in the values, we get:
C = 1 / (2 * π * 1kΩ * 18kHz) = 8.83 nF
We can use a 8.2nF capacitor (Digi-Key Part Number: 399-1427-1-ND).
The transistor used for the high-pass filter stage is a PNP transistor (2N3906). The resistor values can be determined by assuming a quiescent collector current of 1mA and a collector-emitter voltage drop of (That's the end).
To design an electronic filter with the given specifications, we can use a combination of a high-pass filter and a low-pass filter, connected in series. We will use a discrete transistor circuit for each filter stage.
Here's the circuit diagram:
Low-Pass Filter Stage
For the low-pass filter stage, we can use a common-emitter amplifier configuration with a capacitor in the feedback path. The cutoff frequency of this stage is determined by the value of the capacitor.
The required cutoff frequency is 20Hz and the input impedance is 10kΩ. Using the formula:
Cutoff Frequency = 1 / (2 * π * R * C)
We can calculate the value of the capacitor (C) needed as:
C = 1 / (2 * π * R * Cutoff Frequency)
Plugging in the values, we get:
C = 1 / (2 * π * 10kΩ * 20Hz) = 795 nF
We can use a 820nF capacitor (Digi-Key Part Number: 493-11343-1-ND).
The transistor used for the low-pass filter stage is a NPN transistor (2N3904). The resistor values can be determined by assuming a quiescent collector current of 1mA and a collector-emitter voltage drop of 5V.
Using the formula:
R = (Vcc - Vce) / Ic
We can calculate the value of the resistor (Rc) needed as:
Rc = (12V - 5V) / 1mA = 7kΩ
We can use a 6.8kΩ resistor (Digi-Key Part Number: 311-6.8KFRCT-ND).
The bias resistor (Rb) can be calculated using the formula:
Rb = (Vcc - Vbe) / Ib
Assuming a base-emitter voltage drop of 0.7V and a base current of 10μA, we get:
Rb = (12V - 0.7V) / 10μA = 1.13MΩ
We can use a 1MΩ resistor (Digi-Key Part Number: 311-1.0MFRCT-ND).
The input coupling capacitor (Ci) is used to block DC and prevent the input signal from being affected by the DC bias at the transistor base. We can use a 10μF capacitor (Digi-Key Part Number: 445-1308-1-ND).
High-Pass Filter Stage
For the high-pass filter stage, we can use a common-base amplifier configuration with a capacitor in the input path. The cutoff frequency of this stage is determined by the value of the capacitor.
The required cutoff frequency is 18kHz and the output impedance is 1kΩ. Using the formula:
Cutoff Frequency = 1 / (2 * π * R * C)
We can calculate the value of the capacitor (C) needed as:
C = 1 / (2 * π * R * Cutoff Frequency)
Plugging in the values, we get:
C = 1 / (2 * π * 1kΩ * 18kHz) = 8.83 nF
We can use a 8.2nF capacitor (Digi-Key Part Number: 399-1427-1-ND).
The transistor used for the high-pass filter stage is a PNP transistor (2N3906). The resistor values can be determined by assuming a quiescent collector current of 1mA and a collector-emitter voltage drop of (That's the end).
I asked for an other image:
Here's an alternative circuit diagram for the filter:
This circuit diagram shows a Sallen-Key topology for the filter, which is a common topology for active filter circuits. This topology uses an operational amplifier (op-amp) and two resistors and two capacitors to form a second-order filter. The op-amp provides high input impedance and low output impedance, which meets the specifications given in the question.
The low-pass and high-pass filter stages are combined into one circuit using this topology. The cutoff frequencies of the low-pass and high-pass filters are determined by the values of the resistors and capacitors.
The resistors and capacitors can be chosen to meet the given specifications of a 10k input impedance, 1k output impedance, low-pass 3 db down at 20Hz, and high-pass 3 db down at 18kHz. Here are some possible component values:
Here's an alternative circuit diagram for the filter:
This circuit diagram shows a Sallen-Key topology for the filter, which is a common topology for active filter circuits. This topology uses an operational amplifier (op-amp) and two resistors and two capacitors to form a second-order filter. The op-amp provides high input impedance and low output impedance, which meets the specifications given in the question.
The low-pass and high-pass filter stages are combined into one circuit using this topology. The cutoff frequencies of the low-pass and high-pass filters are determined by the values of the resistors and capacitors.
The resistors and capacitors can be chosen to meet the given specifications of a 10k input impedance, 1k output impedance, low-pass 3 db down at 20Hz, and high-pass 3 db down at 18kHz. Here are some possible component values:
- R1 = R2 = 10kΩ (Digi-Key Part Number: 311-10KFRCT-ND)
- C1 = C2 = 1.5nF (Digi-Key Part Number: 399-1465-1-ND)
- R3 = 1.82kΩ (Digi-Key Part Number: 311-1.82KFRCT-ND)
- R4 = 100Ω (Digi-Key Part Number: 311-100FRCT-ND)
Ignoring the irony in your comment for now. I think it all went wrong with electric start and synchromesh gear boxes. My Grandfather had an austin seven. Hand cranked and 3 speed non-synchro box. You actually had to drive that unlike modern cars.
While we are on about AI I had a genuine question I asked ChatGPT on how to configure LTspice to generate noise source. The results were impressive reading but didn't actually work. As I kept saying in the LT thread years ago, a lot of knowledge is assumed and that is where many resources fall down. It took me a while to figure out (using the web generally) that you needed to use a Behavioural Voltage Source. This was over a week ago but I saved one of the sessions.
Anyhooo:
Anyhooo: