Electro~Harmonix Deluxe Memory Man Questions
Posted: 14 Jul 2018, 23:44
Hello everyone, I started to study the principle of operation of analog delay effects
I started to study the DMM scheme and it seemed to me that it looks very strange, in comparison with the BOSS scheme.
This forum has repeatedly helped me find answers to questions and I decided to ask a few more.
1) I am confused by the bypass operation mode, in this circuit we have not a true bypass. The gain controller will work even when the pedal is in bypass mode.
Why is it so?
2) The first stage is an inverting amplifier, so the input impedance is R2 or 100K, which is below the recommended 500K-1M, is it a design error or is there any advantage in this?
3) What is this cascade made for? If you look at the BOSS DM-2 scheme, there are no additional amplification stages at all, only 3 stages of filtering on BJT, 2 filters at the input and output, and also the input buffer, which looks much more logical.
4) After the first stage of amplification, we have a non-inverting amplifier (IC1B) with a flat frequency response, but giving an additional gain of 6dB, why so many amplification steps?
5) after each delay chip, we have inverting amplifiers (IC4A & IC4B). Why are these amplifiers added to the circuit? They create additional noise and take up additional space on the board along with the components. Again, in the BOSS DM2 there are no additional amplifiers after the delay section and the pedal works fine without losing any loudness.
6) After the first delay chip (IC6), the outputs are R41 & R42 resistors, although in all other delay effects there is a trimpot for fine-tuning the balance. Why did EHX put resistors, because they do not guarantee a tonal balance setting?
7) The offset scheme looks standard, but after it there is no buffer, and this adjustment will affect the input impedance, in contrast to the BOSS pedals.
Is this also a design error?
In addition to questions to the scheme, there are a couple of additional questions.
8 ) Repetitions in the DMM sound brighter than in other delay effects, Memory Boy, DM2, Carbon Copy give blurry repeats.
What is the reason? This is due to the power supply of 15V input to the circuit or with filters in the audio part? This is interesting, since I want to collect a copy, but the MN3005 chips seem too expensive and I want to buy the MN3205. The problem is that the MN3205 only works from 9V, which means that if the brightness of the repeats depends on the increased power (15V), then my idea does not make sense.
What is the reason for the brightness and readability of repetitions? Filtration or increased power?
9) The NE570 chip remains a mystery to me. I understand that it works in compressor / expander mode, compresses the signal to the delay section and returns it to its original state after the delay section. But I do not understand what components affect, in Datasheet I did not find the information, where can I read it?
I will be grateful to your answers.
I started to study the DMM scheme and it seemed to me that it looks very strange, in comparison with the BOSS scheme.
This forum has repeatedly helped me find answers to questions and I decided to ask a few more.
1) I am confused by the bypass operation mode, in this circuit we have not a true bypass. The gain controller will work even when the pedal is in bypass mode.
Why is it so?
2) The first stage is an inverting amplifier, so the input impedance is R2 or 100K, which is below the recommended 500K-1M, is it a design error or is there any advantage in this?
3) What is this cascade made for? If you look at the BOSS DM-2 scheme, there are no additional amplification stages at all, only 3 stages of filtering on BJT, 2 filters at the input and output, and also the input buffer, which looks much more logical.
4) After the first stage of amplification, we have a non-inverting amplifier (IC1B) with a flat frequency response, but giving an additional gain of 6dB, why so many amplification steps?
5) after each delay chip, we have inverting amplifiers (IC4A & IC4B). Why are these amplifiers added to the circuit? They create additional noise and take up additional space on the board along with the components. Again, in the BOSS DM2 there are no additional amplifiers after the delay section and the pedal works fine without losing any loudness.
6) After the first delay chip (IC6), the outputs are R41 & R42 resistors, although in all other delay effects there is a trimpot for fine-tuning the balance. Why did EHX put resistors, because they do not guarantee a tonal balance setting?
7) The offset scheme looks standard, but after it there is no buffer, and this adjustment will affect the input impedance, in contrast to the BOSS pedals.
Is this also a design error?
In addition to questions to the scheme, there are a couple of additional questions.
8 ) Repetitions in the DMM sound brighter than in other delay effects, Memory Boy, DM2, Carbon Copy give blurry repeats.
What is the reason? This is due to the power supply of 15V input to the circuit or with filters in the audio part? This is interesting, since I want to collect a copy, but the MN3005 chips seem too expensive and I want to buy the MN3205. The problem is that the MN3205 only works from 9V, which means that if the brightness of the repeats depends on the increased power (15V), then my idea does not make sense.
What is the reason for the brightness and readability of repetitions? Filtration or increased power?
9) The NE570 chip remains a mystery to me. I understand that it works in compressor / expander mode, compresses the signal to the delay section and returns it to its original state after the delay section. But I do not understand what components affect, in Datasheet I did not find the information, where can I read it?
I will be grateful to your answers.