Hi, being enamored of my MoFos I'm tempted to try the common drain/follower configuration of post #109 (the ToFo? schematic attached) with a pair of 2SK180's, and I have some possibly foolish questions.
I would ideally like to repurpose some 19V laptop bricks for power as monoblocks. Does anyone have opinions on 19V, ~2A as an operating point for these SITs? I know this is half of the Vds chosen by Ben Mah. I don't need much power out of these, I don't drive my ~6 ohm speakers very loud at all, so I'm not concerned about underpowering them. I'm after the SIT sound here mostly.
These laptop bricks don't produce a -ve supply that I know of so I don't know where I'd get the negative bias from. There was discussion of leveraging the voltage drop across the choke as the bias? I'm not sure how that works but the chokes I want to use have a stated DCR of 0.3, so at 2A that would be -0.6V? Would I then need to connect the ground side of the choke to the bias resistor R2 to produce the negative bias? It looks like to get an operating point of 19V, 2A I'd need a bias of less than -3V, not the -0.6V that the choke drops.
Thoughts appreciated!
I would ideally like to repurpose some 19V laptop bricks for power as monoblocks. Does anyone have opinions on 19V, ~2A as an operating point for these SITs? I know this is half of the Vds chosen by Ben Mah. I don't need much power out of these, I don't drive my ~6 ohm speakers very loud at all, so I'm not concerned about underpowering them. I'm after the SIT sound here mostly.
These laptop bricks don't produce a -ve supply that I know of so I don't know where I'd get the negative bias from. There was discussion of leveraging the voltage drop across the choke as the bias? I'm not sure how that works but the chokes I want to use have a stated DCR of 0.3, so at 2A that would be -0.6V? Would I then need to connect the ground side of the choke to the bias resistor R2 to produce the negative bias? It looks like to get an operating point of 19V, 2A I'd need a bias of less than -3V, not the -0.6V that the choke drops.
Thoughts appreciated!
Attachments
The name ToFo was not created by me. I did call my amp Fokin for Follower Tokin. They are my Fokin amplifiers.
As for Vds of 19V, I would suggest trying various Iq. Perhaps 1.5A might work. The best thing to do is to try various Iq and measure the distortion, and pick the operating point that you like best.
The choke will not drop enough voltage so that you will most likely need a bias voltage supply. The amount of bias voltage will depend on your SIT, and it varies greatly from sample to sample.
By the way, here is an updated schematic, showing an 18V Zener diode at the SIT gate to protect it from overvoltage.
As for Vds of 19V, I would suggest trying various Iq. Perhaps 1.5A might work. The best thing to do is to try various Iq and measure the distortion, and pick the operating point that you like best.
The choke will not drop enough voltage so that you will most likely need a bias voltage supply. The amount of bias voltage will depend on your SIT, and it varies greatly from sample to sample.
By the way, here is an updated schematic, showing an 18V Zener diode at the SIT gate to protect it from overvoltage.
Attachments
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Ben, excuse me, I mistakenly called your followers ToFo. The correct name is Fokin. I like.
About a Fokin to drive planar magnetic headphone. This is an interesting point. The very light membrane is constrained only on outer perimeter. The central part is held in place by the magnetic field. there is no the spider. A high damping (low output impedance) amp, such a Fokin, would help the membrane stay taut. The bass would be super controlled.
What do you think?
About a Fokin to drive planar magnetic headphone. This is an interesting point. The very light membrane is constrained only on outer perimeter. The central part is held in place by the magnetic field. there is no the spider. A high damping (low output impedance) amp, such a Fokin, would help the membrane stay taut. The bass would be super controlled.
What do you think?
hello ZM,
so with singing bush lower/gain pcb
can we replace the upper pcb with a choke
will the current stable?
frankly, can't remember did I specifically investigate that - tempco of big Tokins
one thing will give you very useful info, if you have functional Singing Bush - observe and write down what is SIT drain voltage in cold vs. hot (temp equilibrium) state
My own Singng Bush is in build state, so I can't easily do that right now....... even making fast mock up on T-Bed would took time which I can't spare soon
Wasn't overly interested to pursue choke as load from several reasons ..... increased distortion (vs. Mu above) being just one of them
one thing will give you very useful info, if you have functional Singing Bush - observe and write down what is SIT drain voltage in cold vs. hot (temp equilibrium) state
My own Singng Bush is in build state, so I can't easily do that right now....... even making fast mock up on T-Bed would took time which I can't spare soon
Wasn't overly interested to pursue choke as load from several reasons ..... increased distortion (vs. Mu above) being just one of them
Hi, I have been looking for a SMPS. For my chocked 2SK182.
Candidates:
1) Meanwell UHP-200 24 volt - 200Watt. Hiccup mode start
2) meanwell HRP-200 24V - 200 volt. Constant current limit start up.
Hiccup can be heard. CC is smoother. I think.
The latter would seem a good candidate because of the possibility to creat a large reservoir - I have a chassis with 4 x 47.000 large cans already on it (as used for F5) so would like to reuse it.
My question is:
Candidates:
1) Meanwell UHP-200 24 volt - 200Watt. Hiccup mode start
2) meanwell HRP-200 24V - 200 volt. Constant current limit start up.
Hiccup can be heard. CC is smoother. I think.
The latter would seem a good candidate because of the possibility to creat a large reservoir - I have a chassis with 4 x 47.000 large cans already on it (as used for F5) so would like to reuse it.
Transformer fed is too encumbrant: my transformer gets warm also, just a little bit less than the heatsinks.. The bridge is not efficient (although I am waiting for an ideal bridge) and has quite some voltage drop at my 4 amps total.
My question is:
- which would you prefer, what is best.
- which is best for audio (for flexibility I do not want the cord-embedded power supply from the diy-store
Interesting... I'm doing something similar for my F3 build: a 15000uF Silmic cap bank for extended bass and a pair ok 500uF MKPs for fullranges on SLOBs
triode_al,
I don't have any experience using SMPS to power amplifiers but I looked at the specification sheets for the two that you mentioned plus the 35V SMPS sold by the diyAudio Store. The one thing that jumped out at me was the maximum inrush current of the diyAudio Store supply was much higher than that of the supplies that you mentioned:
diyAudio 36V (GST-160A) - 95A/115VAC 120A/230VAC
UHP-200 - 40A/115VAC 80A/230VAC
HRP-200 - 35A/115VAC 70A/230VAC
That may have a big effect on the amount of capacitance that you can put after the supply. The 4 x 47 mF capacitors that you want to use may be too much for any of the supplies.
The ripple and noise in SMPS are high frequency so the standard linear power supply filtering of large capacitance does not necessarily work. The specifications show 100 to 200+ mVp-p, depending on the voltage output, measured at 20MHz. There may be lower amounts of ripple and noise at frequencies about 20kHz. Filters designed to filter out these high frequencies are probably more important and more effective than just adding large amounts of capacitance.
PO89ZB , an inline DC filter for SMPS wall warts . Preamps, HPA, Korg NuTube, etc
You may get some good advice if you start a thread asking for information/advice on SMPS for Class A amplifiers.
I don't have any experience using SMPS to power amplifiers but I looked at the specification sheets for the two that you mentioned plus the 35V SMPS sold by the diyAudio Store. The one thing that jumped out at me was the maximum inrush current of the diyAudio Store supply was much higher than that of the supplies that you mentioned:
diyAudio 36V (GST-160A) - 95A/115VAC 120A/230VAC
UHP-200 - 40A/115VAC 80A/230VAC
HRP-200 - 35A/115VAC 70A/230VAC
That may have a big effect on the amount of capacitance that you can put after the supply. The 4 x 47 mF capacitors that you want to use may be too much for any of the supplies.
The ripple and noise in SMPS are high frequency so the standard linear power supply filtering of large capacitance does not necessarily work. The specifications show 100 to 200+ mVp-p, depending on the voltage output, measured at 20MHz. There may be lower amounts of ripple and noise at frequencies about 20kHz. Filters designed to filter out these high frequencies are probably more important and more effective than just adding large amounts of capacitance.
PO89ZB , an inline DC filter for SMPS wall warts . Preamps, HPA, Korg NuTube, etc
You may get some good advice if you start a thread asking for information/advice on SMPS for Class A amplifiers.
My Fokin build is only intended to drive the full-range unit and I'll have a sperate amp for the bass driver. Work to do on the crossover down the line but first I need to get the Fokin finished, hook up the drive unit on a temporary baffle and take some FR measurements.
If the choked 2SK182 can run on a single rail (+ Gnd), then I would recommend a separate GST-160A for each channel. These have performed well for the new crop of VFET amplifiers. They can accept a limited amount of capacitance on their output, perhaps 2200 uF to 4700 uF total. Check out the VFET builders threads for some of the results.
Maybe I wrote it too bad
I intend to use the F3 only for fullrange in SLOBS. Caps bank with 15mF will not be used on that setup (I'll place another pair of opt sockets on rear panel). I'm building a modified ACN in order to use another amp for the woofer section. 
Yup
https://www.diyaudio.com/forums/pass-labs/241729-aleph-illustrated-build-guide-689.html#post6712015
Also Mr MR described that in his L'Amp PDF.