#2158 R2=47kohm is approximately the input impedance. If the output impedance from the preamplifier is higher than 4.7 kohm, one may increase R2 to for instance 100 kohm.
Tks knutn, very nice explanation.
Is there any matter if I use a much lower preamp output impedance, like 80 ohm?
Im planning to use the attached Lampizator's circuit, getting the signal from the headphone amp's buffer, after c4.
Also, that 400uF cap is enough to avoid DC to the Le Monstre input?
Tks again
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Hi all, I'm a SET tube junkie and decided to build one of these to dip my toe into the world of class A SS to see if this was something I'd like. I wanted to share my thoughts on this amp vs SET 2a3 on Altec 605a's in altec 620 cabinets.
My le monstre has the following:
MJL2119 outputs
Boards and other transistors came from this kit: https://www.ebay.com/itm/112777820644
Single toroid transfomer +/- 14V, lm 317 regulated power supply, 74k uF per channel
Speaker protection circuit
As an amplifier, this is generally fantastic. I've used it on headphone duty as well as with the Altecs mentioned above. Great detail, nice stereo separation, imaging extends beyond the speakers, and speakers tend to disappear.
Vs the 2a3 SET (equipped with EML mesh plates, i also sometimes swap in RCA bi-plate NOS, single driver stage D3a CCS loaded, cap coupled, E-P iron)
Positives: this amp has more controlled bass than the SET (likely due to higher damping factor). Detail retrieval might also be a tad better.
Negatives: voices and instruments are not as natural, in the room sounding. Maybe this is SS glare? There's just some grain there that isn't there with the 2a3. I wonder if the le monstre detail retrieval is just better and more true to the recording, vs some magic that the tubes do to make everything feel more natural. The illusion that the music is being played in the room with me is just stronger. Soundstage is noticeably taller with 2a3, and also just a bit wider. I still feel chills with the le monstre, but the 2a3 takes the smiles to just another level for me.
I could live with the Le Monstre alone. I just happen to have an amp that gives me the type of sound I clearly prefer. Perhaps the Le Monstre would sound better to someone else. No matter, this amp is good enough to give great SET sound a run for its money. And, the le monstre is a good deal cheaper (200-300 bucks vs the 800-1000 I have invested in my SET amp).
FWIW my thoughts. If there's anyone else out there contemplating SET vs an amp like this, I hope this provides some perspective. Of course, we all have different ears and could have come to different conclusions.
My le monstre has the following:
MJL2119 outputs
Boards and other transistors came from this kit: https://www.ebay.com/itm/112777820644
Single toroid transfomer +/- 14V, lm 317 regulated power supply, 74k uF per channel
Speaker protection circuit
As an amplifier, this is generally fantastic. I've used it on headphone duty as well as with the Altecs mentioned above. Great detail, nice stereo separation, imaging extends beyond the speakers, and speakers tend to disappear.
Vs the 2a3 SET (equipped with EML mesh plates, i also sometimes swap in RCA bi-plate NOS, single driver stage D3a CCS loaded, cap coupled, E-P iron)
Positives: this amp has more controlled bass than the SET (likely due to higher damping factor). Detail retrieval might also be a tad better.
Negatives: voices and instruments are not as natural, in the room sounding. Maybe this is SS glare? There's just some grain there that isn't there with the 2a3. I wonder if the le monstre detail retrieval is just better and more true to the recording, vs some magic that the tubes do to make everything feel more natural. The illusion that the music is being played in the room with me is just stronger. Soundstage is noticeably taller with 2a3, and also just a bit wider. I still feel chills with the le monstre, but the 2a3 takes the smiles to just another level for me.
I could live with the Le Monstre alone. I just happen to have an amp that gives me the type of sound I clearly prefer. Perhaps the Le Monstre would sound better to someone else. No matter, this amp is good enough to give great SET sound a run for its money. And, the le monstre is a good deal cheaper (200-300 bucks vs the 800-1000 I have invested in my SET amp).
FWIW my thoughts. If there's anyone else out there contemplating SET vs an amp like this, I hope this provides some perspective. Of course, we all have different ears and could have come to different conclusions.
Attachments
Hello Grunf, its really nice to read, that you are successful with reulators and LeMonstre, may be, if you don't like to share the results in publik, you share it by PM? I am not only currious but I like this little amplifier quite a lot but with the original supply is a lot too bulky . So good hints to a suitable regulator will be verry welcome.
br,
helmut
br,
helmut
Don't worry, when everything is ready I will open a new thread and post all about these regulators. It will be able to be used with most amplifiers in class A with supply voltage up to +/-35-40V and current up to 3-4A. I hope we will find someone interested in making a PCB for group buy. It is also better for each channel to have its own regulators due to better performance at lower currents.
Igor
Hello Igor,
many thanks, thats sounds really good to me. I use this little amp for about 30 years now, not all the time but I came back to it many times. so finding something like a final solution is very apealing. May be I can ask a friend with the PCB. I am still using the Monster with 0.6 A, complette classical transistors, all are still available . I am looking formwards to your new thread
Helmut
many thanks, thats sounds really good to me. I use this little amp for about 30 years now, not all the time but I came back to it many times. so finding something like a final solution is very apealing. May be I can ask a friend with the PCB. I am still using the Monster with 0.6 A, complette classical transistors, all are still available . I am looking formwards to your new thread
Helmut
Last night first time testing.
setting about 30Minut to 2 hours
DCO 0,02v dc hard
Driver D756/B716 •@ 8,xx Volt
SB754 @ 0,560
SD844 @ 0,630
trying adjust trimpot 1K hard to get balanced
Small Heatsink @70 degrees after 1 Hours
Xformer 12Ct 50 degrees temp and drop to @10volt.
PSU Cap Multiplayer TR C5200/A1943
•sound notyet test.
•using original schematic and input Tr Gr version.
it is normal with heatsink hot 🥵 70 degrees? … or I have doing wrong setting
pls advice me thanks 🙏
sory newbie’s 🙏
Best regards
RG
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Hello, depends how large your heatsink is. Mine are not that large and keep cool under 50°C. But I have around 13 V +/- and 0.6 A idle current. How large is your transformer? You should use something with 150 VA upwards, I use for each channel 500 VA, only because I have them. My trainies have 2x15V AC.
Thanks for your replay 🙏
my xformer CT 12V 200watt
my setting is correct or wrong ?
with Bias 0.560 / 0.630
DC out 0.02
amplifier chassis attachment
About 宽度162x高度60x深度246 mm
：1.74kg
🙏
Attachments
At first glance I would say, sufficient heat sink.
200VA is nice, 12 VAC and a PSU Cap multiplier may be not compatible, I never used such a device but I guess you need some additional Volts. You may take that from my configuration, 15 VAC at the trainy and 13 at the amplifier. I use 6 ohm resitors to smooth down the current.
Remains the question about the heat. The bias is the voltage you take over the 1 ohm resistors? If so, its not realy high, near to optimum. Sometimes this little amplifier tends to oszillate, that may be curred with a small C across the feedback resistor (220 ohm), I guess around 47 nF, not critical.
200VA is nice, 12 VAC and a PSU Cap multiplier may be not compatible, I never used such a device but I guess you need some additional Volts. You may take that from my configuration, 15 VAC at the trainy and 13 at the amplifier. I use 6 ohm resitors to smooth down the current.
Remains the question about the heat. The bias is the voltage you take over the 1 ohm resistors? If so, its not realy high, near to optimum. Sometimes this little amplifier tends to oszillate, that may be curred with a small C across the feedback resistor (220 ohm), I guess around 47 nF, not critical.
•Bias measures from base transistor-+
•power drops to 10v does hiraga not match with psu cm.
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Sorry I don't get the point, the bias is verry easy to measure with voltage drop over R12 and R11
Last night test Monstre 8w
•R2/R3 VR1K in pararel 470ohm about 300ohm SD844/SB754 output Basis -+0.62Volt. Temp down about 45-50 degrees. 3 hours test and play music.
•DO out = with VR100 easy to get Zero.
•R11/R12 =12v
is there something wrong 12Volt a cross 1 ohm ! 😥
do i have to change VR100 or R 1K to get 1A input transistor GR version?….
My transistor below
j47/s170 GR
SA872/SC1775
SB716/SD756
SD844/SB754 Green
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VR100 is only to balance out the offset.
R3 / R4 need to be changed to alter bias. Higher value means higher bias. Take a higher value for the potentiometer across R3/R4.
J1 and J2 should be selected for same IDSS, Original Monster has FETs grade y with IDSS of about 2.4 mA (9 V), but nobody has seen grade since 40 years. I use grade GR around 3.6 mA and R3/R4 around 750 ohm for bias 0.6 A, that means about 900 ohm for 1 A bias (only roughly estimated values)
R3 / R4 need to be changed to alter bias. Higher value means higher bias. Take a higher value for the potentiometer across R3/R4.
J1 and J2 should be selected for same IDSS, Original Monster has FETs grade y with IDSS of about 2.4 mA (9 V), but nobody has seen grade since 40 years. I use grade GR around 3.6 mA and R3/R4 around 750 ohm for bias 0.6 A, that means about 900 ohm for 1 A bias (only roughly estimated values)
Thanks for your share and advice
Last night burning 🔥 test
Pararel VR 1K with 3K3 = 767 ohm
Current increase to 1.8A 🔥🥵
•now I’m understand
Tonight I will test with 470ohm and 680ohm in pararel with vr1K to get under 1A my planing is 0.6-0.8A adjust my small heatsink
Best regards
RG 🙏
Finally done my Hiraga 8W
Been testing listening to hiraga's amps for the past week and have to say, they perform very well. Better than anything I've experienced in the past (including high powered pure class A units). Sound is exceptionally clear and precise. Imaging is very solid and resolution is extreme.
Special Thanks to @HelmutHolz @prasi @triode_al and all mamber 😍
Been testing listening to hiraga's amps for the past week and have to say, they perform very well. Better than anything I've experienced in the past (including high powered pure class A units). Sound is exceptionally clear and precise. Imaging is very solid and resolution is extreme.
Special Thanks to @HelmutHolz @prasi @triode_al and all mamber 😍
