ultrasimple mm/mc riaa preamp

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#63
Re: MC stage

rookster said:
I am very inexperienced in the area of electrical circuits, but why is the 10H inductor/choke needed? I thought it was a filter, but the circuit is already running of a DC supply anyway. Thankyou for the details on the inductors, but I feel the cost and logistics of ordering 2 of these from Germay to Australia, would make it quite a hassle. Can i substitue something else? Any ideas? If this is the best option, then I will implement it.
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I think you have figured out that designing electronics is like painting pictures. Many solutions are right, many are wrong :bigeyes: . I would have used a inductor as a last option. The goal is to make a very quite DC voltage because this first stage is very sensitive for noise in the voltage. One other idea is to use R+C+R+C. The advantage of a inductor is that you don't need so big capacitors effective filtering but on the other hand caps are rather cheap and available so what is best?

My suggestion is:

22 ohms + 6800 µF + 22 ohms + 6800 µF = cut frequency 1 Hz / 40 dB/decade => -80 dB at 100 Hz quite OK if the raw voltage already is stabilized.

You can increase the R and also the C, and even the amount of R-C sections.
 
#66
CAPS AND CAPS.

Hi,

6800µF may sound very slow and thick in a simple common source config. While a choke and a small cap may sound much more agile and musical.
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Peter,

I am rather at odds with your statement here.
From experience I often prefer oversized filter caps and small value coupling caps.

The bigger PSU caps provide good PSU filtering and ample current reserve , whereas the small coupling caps provide for the agility and musicality... they also tend to sound faster than their larger brethren.

Also, just from listening experience I find the higher voltage coupling caps to sound way better than the lower ones.

Does this go against your own experience?

Cheers,😉
 
#67
Frank

My remark is only for the specific case of MC input. Current pull is generally low and the 'sound' of electrolityc caps very exaggerated. I would seriously prefer to break a large cap into a smaller + choke. With a reasonable choke you get better regulation and filtration which is easy to calculate.
This deceptively simple circuit with a FET and batteries, when implemented well sounds amazingly good. I got mine powered by NiMH batteries and two 100µF BG caps close to the FETs. To my ears it plays better than my Koetsu step-up transformer in every respect but S/N.


cheers

peter
 
#68
THE TRICKBOX.

Hi,


Peter,

Thanks for the swift reply...

To my ears it plays better than my Koetsu step-up transformer in every respect but S/N.
Click to expand...

Doesn't come as a surprise to me.😉

Here's what I do in my MC stage:

I use a capacitance multiplier after a voltage reg and have that followed by a ccs sitting almost right on top of the anodes.

In order to bring noise down to inaudible levels I also need to put a few triodes in // which is indeed a necessary evil as you pointed out.

Bass shouldn't be an issue since the RIAA filtering is done in the following stages.

Cheers,
 
#71
Per: The input-compensated bootstrap idea is admirably suited for DC servos, because yotu normally want a high input impedance anyhow.

Like Jung, I find that having some sort of output buffer in place is a good idea.

The test results of the input-compensated bootstrapped configuration were fine. I don't utilize this concept at the present, but this is primarily because the DC servo circuit that I do use is inverting with bipolar inputs. OTOH, this latter type of circuit has its own unique quirks that need to be taken into account during the schematic design and board layout phases. You normally don't even receive a discount on lunch, let alone getting one for free. 🙂

Should I decide once again to make a high-impedance, non-inverting, JFET input DC servo circuit, chances are that I will revisit the input-compensated bootstrap concept and see if it is possible to advance it further.

Examples of other interesting DC servos would include the simple design that Luxman used in their A901 battery-powered preamp. The "AOC" discrete differential servo that Akihiko Kaneda has been using for his more recent designs is also worth trying, and this is fairly similar to the output buffer section of my own DC servo circuit.

In any case, it is surprising how important the DC servo design is for the overall sonics. As I mentioned in a previous post, you will need to put much more effort into designing a DC servo than you will in selecting an output coupling cap, and there is a commensurately higher risk of getting something wrong. But as far as I can tell, the concept is fine - the actual design and implementation stages are where it is likely that you will stumble.

hth, jonathan carr
 
#72
Update

Finally I have made a version more in line with Thorsten's recommendations. What can I say? It is simply wonderful! Some pics:
 

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#74
The "cheap" phono pre with expensive sound..?

Just finished a phono pre based on Thorsteins El Cheapo (MM part only). Simply great sounding......:bigeyes: 🙂 😀

Later tonight I`ll try this one...😀
 

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#77
Konnichiwa,

analog_sa said:
Lucky you! I haven't been so lucky mixing phono with opamps - even a simple Pearl or Ono offer lots more soundwise and are likely not more expensive to build.
Click to expand...

Let me guess. Op-Amp's, passive EQ between two of them, possibly attempting MC sensitivity with Op-Amp's, mains based supplies. I never had any luck that way either.

Sayonara
 
#78
Re: Ultrasimple mm/mc riaa preamp

Konnichiwa,

Elso Kwak said:
Hi,
While surfing on the net I stumbled upon this interesting site showing a very simple phonoamp:
http://home.att.net/~patslab/3fbd0fd2.gif
😎
Click to expand...

I would call this neither simple nor particulary suited to being a RIAA EQ.

An externally hosted image should be here but it was not working when we last tested it.


Even if the errors in the RIAA EQ are fixed, this circuit throws away nearly 20db overload (and slew) margin at 20KHz, compared to an active EQ and even more by selecting a poor distribution of gain around the passive EQ. You can hear the result easily with dirac pulses often called "click" & "pop".

Circuits like this, even when optimised always seem to emphasise these noises rather much, as do slwerate limited active EQ circuits (the classic Dynaco PAS phonostage comes to mind as excellent example of how not to do it).

And why on earth insist on using two Op-Amp where one suffices?

Sayonara
 
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