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Old 8th November 2009, 05:22 PM   #41
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Again the HPS 4.0 thread prompted me to design a bare bones single ended version of the MPP. Here it is and again more information is on syn08`s thread
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File Type: pdf MPP Basic Structure single ended 1.0.TSC - TINA.pdf (56.2 KB, 427 views)
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Old 8th November 2009, 10:24 PM   #42
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This is an even more purist version i call the Malkolm Hawsksford Homage because it has some resemblance to the Essex Battery Phonostage that was made by LFD . It has no voltage feedback at all does amplification and RIIA in one stage and uses no integrated circuits.
It has an interesting gain structure : I-U, U-I, I-U. U-I
expect more distortion from that stage but it could sound good.
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Old 9th November 2009, 09:22 PM   #43
anatech is offline anatech  Canada
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Hi Joachim,
Thank you for sharing these!

I do know that the output buffer in the Malkolm Hawsksford Homage sounds excellent. It's almost exactly what I do except that I use red LEDs as the voltage reference in the CCS sections. So nothing negative to blame on that output buffer design.

Your input stages are a bit less familiar to me, so I'll have to get my head around that. Interesting designs.

-Chris
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Old 9th November 2009, 09:50 PM   #44
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Was it Giovanni Stochino who first demonstrated the complementary LTP (albeit with slightly less elegant CCS loading)?
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Old 10th November 2009, 02:27 AM   #45
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Do you mean Complimentary-Longtail-pair ?
I think James Bonjiorno and Borbely where the first.
The first folded cascode i have seen was around 1983 in L`Audiophile by a guy named Rambeyrolles. I do not know if i spell his name correctly. He certainly inspired me.
The advantage of the folded cascode is quite high gain with very little topological complication. As you see in the MPP the signal is only flowing trough two transistors and has the resistors in parallel so you could say they are not in the direct signal path.
Nevertheless distortion of that stage is quite low. I have access to an Audio Precision
SYS-2522 here in Vienna and my engineer friend was quite surprised that distortion remained under the noise floor at 1V output without voltage feedback in the input stage.
Some integrated circuits use the folded cascode gain stage albeit not balanced as i do and with bootstrapping.
The AD797 and LT1469 are examples. Their gain structure can be considered as single stage and still they belong to the lowest distortion op amps on the marked. I like both very much if i use op amps and they are recommended for the instrumentation amp stage in the MPP. Used in the correct topology they have a very neutral and true "matter of fact" sound that i like to compare my more holistic tube or discreet designs too.
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Old 10th November 2009, 07:38 PM   #46
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Default AP measurements

Here are some measurement on the AP analyser of the MPP.
Distortion is under the noise floor at 1 kHz and 1V output.
The noise shows a lot of 50Hz harmonics. We had a hum problem we could not quickly remove. Nevertheless you see that signal noise ratio is -80dB in the midrange improving to -90dB in the treble. Not bad, i am happy.
Also the transfer linearity is shown. Overload margin is ca.20dB at 1kHz for a 0.5mV input improving to ca.40dB at 20 kHz due to the way i implement the 75 usec time constant. This is no world record but the improved margin in the treble will make shure that there is no overload due to scratches and dirt on the record that are the major cause of overload in designs that have no satisfactory overload margin in the treble.
Attached Files
File Type: pdf MPP FFT.pdf (54.3 KB, 267 views)
File Type: pdf MPP Linearit_t dbv.pdf (51.0 KB, 227 views)
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Old 10th November 2009, 07:45 PM   #47
Salas is offline Salas  Greece
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Hello Mr. Gerhard

I am interested in your experience, objective and subjective, on the matter of MC cartridge correct loading value. Please expand if you feel like it at a point.
I am following your current circuit investigations and findings with much interest.
Thanks for contributing.

Regards
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Old 11th November 2009, 03:11 AM   #48
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Hello Salas !
Nice to have you around.
Tell me your cartridge and maybe i have an idea what to say.
I watched your simple riaa thread and that attracted much more attention then what i am doing hear. great that you are coming up with something that people actually need and will build. i have the parts that you suggest and could build it too but i am too occupied with what i do. sorry.
to anatech : could you post your buffer ? i would be very interested
buffers can be extremely use full for a lot of circuits and can improve the sound (i think especially dynamics ) a lot
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Old 11th November 2009, 03:28 AM   #49
Salas is offline Salas  Greece
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I have DL103R and I use 150R load. But I want to know more general things about your approach to the matter of loading also when you got time. Thanks.
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Old 11th November 2009, 03:46 AM   #50
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the cartridge and the input impedance constitute a low pass filter.
so i need the equivalent circuit as we say in germany
a passive filter can be modeled with equivalent capacitors, resistors, losses (hysteresis) and transformers. the active element is harder to grasp because noise and distortion are creeping in from the circuit, the layout and the power supply. today there is a lot of concern about electromagnetic radiation too. passive parts are not ideal and i could come up with ever so complicated "equivalent" circuits. the lumped parameters of the poor capacitor contain resistors, capacitors and inductors in spades the higher you look in frequency. it simply is not that simple. a friend of mine has a DENON DL103R and that is shurely on the agenda.
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