Mpp

[Holger Barske]

No too bad, Joachim. What transistors did you use?

[Joachim Gerhard]

the original 2SB737 i bought all low noise BJ´s i could
nice to have you here Holger. you can hear it in my house at 22.12. if you dare.

[Holger Barske]

I dare . Great, I am looking forward to it.

[Joachim Gerhard]

i listened a bit to the Hiraga le pre-pre optime how i will call it and i was surprised. the sound is not bad at all. i had some terible hum problems but after substituting the RIAA stage and also grounding the RIAA stage it was gone. noise is low because the high gain alows for a very low volume setting of my preamp. i whould say it is some 3 dB worse then my MPP but that is still very good. the soundstage was somehow bigger, more up front and more difuse that i am used to but the music was intact. no spittyness, no nasties. in terms of speed and resolution it is no match to my Goldstandart and tonal palette is not as diferentiated as my MPP low Z but that did not distract from the enjoyment. i can now better understand why it is so popular with DIYers and it also reminds me on my first contact in the early 80th. it can be build in some hours and works right away. OK, i took some provision for succes in matching the transistors for Hfe. i took the better ones for the active devices and the lower grades for the current mirror and found 4 in 5 that matched, no pain at all. i trimed DC offset at the input with a resistor after i have found the right value with a trimmer. it was simply a 33kOhm on top of the resistor to the positive supply so i did not trim the current mirrors like Hirage. i have some trouble with the high gain in my system and could not advance the volume to more the 20 on my display. i usually listen at 40 so i will rebuild the Hiraga for less gain with the advantage of lower distortion and lower output impedance. i have also other interesting ideas that could help your version to sound better and better match your system. if all is ready and well i plan a small run for sales. Although not worldclass any more it is the most afordable way to high end nirvana i know.

[Joachim Gerhard]

today i cut the output impedance, the gain and distortion in half and raised the upper frequency limit to double the original value (have you seen Walk Hard ?) and now we talk business. the sound improved at lot and the gain is now in a comfortable range. it is no more diffuse and much more extended in the treble. i came up with a weighting scale to describe better what i am hearing. i came up with a scale from 50 to 100. 50 is average, 60 is good, 70 is satisfying, 80 is very good, 90 is excellent, magic, 100 is perfect, hand of god, paradise, satori, state of bliss. so the Hiraga 2.0 scored 85 after modification and advanced to 90 during the next hour of listening. to put it in perspective i would give the MPP Low Z 93 and the Goldstandart 96. it crossed the border of magic and that does not happen often at chateau Gerhard. i also came up with some additional descriptions to put everything more in perspective. PH : philosophical design, changes the way we think about circuits, PSY : psychological design, changes the way we listen, TA : technical advantage, measures sate of the art, is ether very pretty build and compact or battleship luxury, shows new circuitry with a genuine advantage like lower distortion and wider bandwidth. BC : budget champion, very good performance price ratio. so i would give the Hiraga 2.0 85-90 PH, BC and here is the circuit. i selected the active transistors to Hfe 240 and the current mirror to 210 similar in both channels.

[Joachim Gerhard]

can that circuit be improved without destroying the PH quality of extreme simplicity of the signal path ? you bet, and i will try them all. first is the Cagomat version with low pass filtering of the current mirror. Cagomat uses a 200uF capacitor that i will try but i think it´s to small for optimum suppression in the lower reaches so i will try up to 2200uF several types here. second is an improved current mirror and third is substituting the bias resistors with constant current sources of various designs. here the simple Fet solution is shown. Fet cascodes or LED bias could be used for even stiffer regulation. i have seen so many biasing arrangements in my life that i came to the conclusion that it must be a major problem for some.
of cause you can combine all or leave out what you do not like. as simple as that circuit is, it has a lot of tweeking potential.

[Salas]

Very good revision then. You sound chuffed! So to put it into final perspective, what is the best transistor part there, how many dB of gain you finally settled with the hfe you describe, and what range of Ro carts is best for the circuit you posted on#355 above?

[Allen Wright]

Joachim,
Am I correct in assuming the two jfets in the third circuit just posted would have to be VERY well matched, so as to not create DC offset at the input?

Regards, Allen

[Salas]

Or to use 500R trimmers for R3,R4 until least offset is hit? Then again Jfets are quirky with ambient, 24h/7d operation match possible?

[Joachim Gerhard]

hi salas. circuit in 355 is the one that i am using momentarily. it has 32dB of gain (still a lot but it sounds great) and i use a 5.5Ohm cartridge with 0.6mV output. i forgot to thank Christian of Music World in Brilon for the donation of the very nice sounding 1W metal film resistors.
Allen: the circuit is theoretical. to avoid thermal drift i would search for fets that need around 0.65 volts of gate voltage and produce 2mA. then i would thermocouple both. at that voltage temperature dependence of fets is near zero. i am really surprised that you come up with that kind of questions. don´t you know that i have studied with some really extraordinary people and that kind of problems are so easy to solve it is a joke ?what do you think about a servo to keep the current stable? give me any complicated circuit to analyse and i make it even more complicated. simply enjoy what i am doing here. it´s a gift to the DIY society. malkolm always said to me : "you crack every code"