Peranders:
Did you ever try to hear a possible difference in 'sound' in your SMD GC with or without this DC servo?
Many people claim this difference. As I always try to avoid caps in the signal path and thus use servos when I need a dc free environment, I am not sure anymore about my own 'objective' hearing.
Uli
PS: even my phono stage is completely dc coupled.
Did you ever try to hear a possible difference in 'sound' in your SMD GC with or without this DC servo?
Many people claim this difference. As I always try to avoid caps in the signal path and thus use servos when I need a dc free environment, I am not sure anymore about my own 'objective' hearing.
Uli
PS: even my phono stage is completely dc coupled.
No, I haven't tested it yet. But as you know my DC servo is in world's class using a AD8620, not like LM324 or uA741 exactly.
I'm pretty sure that many of those "bad" DC servos are made of not very high classy opamps. The servo is an integrated part in the audio chain so it must be good, at least up to 1 kHz.
I'm pretty sure that many of those "bad" DC servos are made of not very high classy opamps. The servo is an integrated part in the audio chain so it must be good, at least up to 1 kHz.
experiences
up to this point my experiences with dc servos are just good ones. the only issue is the costs of the extra parts and the design, which in fact isnt really an issue. I started like many Europeans with that famous hi end preamp from "Elektor" in the late 80ies. Soon I swapped the outputcaps as there is a servo circuit in the phonostage already. I copied this circuit to the output opamps (old PMI OP27 better than BB) and the performance gain was enormous!
Recently I designed some kind of balanced opamp with diff in and diff out. This circuit although well sounding is very difficult to control without servo. During tweaking people often loose their objective standards and exactly this is my problem. Now Im seeking for other opinions.
Uli
up to this point my experiences with dc servos are just good ones. the only issue is the costs of the extra parts and the design, which in fact isnt really an issue. I started like many Europeans with that famous hi end preamp from "Elektor" in the late 80ies. Soon I swapped the outputcaps as there is a servo circuit in the phonostage already. I copied this circuit to the output opamps (old PMI OP27 better than BB) and the performance gain was enormous!
Recently I designed some kind of balanced opamp with diff in and diff out. This circuit although well sounding is very difficult to control without servo. During tweaking people often loose their objective standards and exactly this is my problem. Now Im seeking for other opinions.
Uli
Op177 or AD8551
Youre right.
I use OP177 and MKP in the servo because I have some dozens of them although the AD8551 has better dc characteristics.
Ive seen servos with LF353 and elkos. It is very clear (at least for me) that such a circuit wont contribute anything good to the result
Uli
peranders said:
Youre right.
I use OP177 and MKP in the servo because I have some dozens of them although the AD8551 has better dc characteristics.
Ive seen servos with LF353 and elkos. It is very clear (at least for me) that such a circuit wont contribute anything good to the result
Uli
Re: LF412
there are many possibilities to implement a dc-servo. One is to simply (?!) make an integrator in the feedback loop as often seen in manufacturers applications. You can add a RC combo at the output of this integrator to achieve a steeper curve. This has some advantages. The servo itself influences the audio circuit not as 'dramatical' as the standard integrator and thus you can use a broader range of devices. The drawback is the quality of the cap used in this RC combo. It should be of reasonable quality.
Personnally I wouldn't quote the 412 as a Volvo - more like a Skoda or Fiat, hoping that this PERSONAL opinion does not lead to another flame war about car quality!
Uli
Roushon said:
there are many possibilities to implement a dc-servo. One is to simply (?!) make an integrator in the feedback loop as often seen in manufacturers applications. You can add a RC combo at the output of this integrator to achieve a steeper curve. This has some advantages. The servo itself influences the audio circuit not as 'dramatical' as the standard integrator and thus you can use a broader range of devices. The drawback is the quality of the cap used in this RC combo. It should be of reasonable quality.
Personnally I wouldn't quote the 412 as a Volvo - more like a Skoda or Fiat, hoping that this PERSONAL opinion does not lead to another flame war about car quality!
Uli
Hi Uli,
Thank you very much for your details explanation. As far as Audio electronics is concerned I am a newcomer. I am learning reading different threads, so details logical explanation helps a lot. I have one question. In the circuit design of LM3886 (or any such amplifier circuit) how is the offset voltage generated? Is it because of the chip or the choice and quality of the outside components. I mean would a better design (other than the circuit in the datasheet) around LM3886 without using any other op-amp will help to get rid of the offset voltage? I came to know T-network help to a certain extent. May be it is not a question at all, but please let me know...
With best regards.
Thank you very much for your details explanation. As far as Audio electronics is concerned I am a newcomer. I am learning reading different threads, so details logical explanation helps a lot. I have one question. In the circuit design of LM3886 (or any such amplifier circuit) how is the offset voltage generated? Is it because of the chip or the choice and quality of the outside components. I mean would a better design (other than the circuit in the datasheet) around LM3886 without using any other op-amp will help to get rid of the offset voltage? I came to know T-network help to a certain extent. May be it is not a question at all, but please let me know...
With best regards.
I have read somewhere, peraps on the Borbelay site, that the quality of the opamp in the servo is not so important, due the fact that it works in the subsonic range.
In my discrete single ended pre I use a ne5532, and I have tested also OPA2134 and M5238P, but effectively, I have not found differences.
In my discrete single ended pre I use a ne5532, and I have tested also OPA2134 and M5238P, but effectively, I have not found differences.
In signal path is output of opamp, which make floating ground for AC signal in feedback loop. If isn't opamp good, bring distortion to feedback loop. Insertion value of this distortion is given by voltage divider of serial output resistor and parallel resistor in feedback loop. Because this voltage divider is mostly 10 : 1, isn't rising of distortion, caused by servo, critical.
pro said:
IMHO it makes no sense to use an opamp which has its own offset issues (NE5532) due to lo input impedance and thus high offset current in a servo which is commonly designed with relatively high impedance parts.
Ad "signal path":
what is meant can easily be tracked by comparing different caps for example in a passive Xover. There is clear audible difference between MKP and elko in series with the tweeter. Try this with a parallel cap and you will notice that the difference is minor compared to above.
In the passive RC combo between servo amp and injection point (+ in noninverting servos RC combo before servo amp) the cap is tied to gnd if I am not completely wrong.
Uli
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