two-stage NIC amp without global feedback
- Solid State
- 50 Replies
Another design I've come up when thinking further on negative impedance converter topologies:
Ignoring the input buffer, this is a 2-stage amp. Standard CFP output stage fed from a bootstrapped opamp implementing a NIC with gain of 20.
The input point at XXX has a -2k impedance, which is why the buffer is added (although it simulates fine without it, if driven from a low impedance).
The -2k is the difference between the R4 and R2, as the non-inverting input is impedance converted to -20k (reflection of R2).
The inputs to the opamp (grey line below) swing at half the output voltage, allowing the overall opamp supply range (cyan/magenta) to swing completely above and below ground:
(There is a 33V zener to define the opamp supply voltage plus decoupling cap)
Square waves are handled fairly well (a little bit of raggedness, hard to see on the 10kHz plot)
I've not tried this for real yet - I suspect it will be fussier in real life than simulated. And it will need a proper bias circuit.
R21/C8 form a snubber needed to shunt any unwanted HF feedback via the bootstrapping path leading to oscillation - the simulation needs it, I suspect this will be somewhat different in reality.
Ignoring the input buffer, this is a 2-stage amp. Standard CFP output stage fed from a bootstrapped opamp implementing a NIC with gain of 20.
The input point at XXX has a -2k impedance, which is why the buffer is added (although it simulates fine without it, if driven from a low impedance).
The -2k is the difference between the R4 and R2, as the non-inverting input is impedance converted to -20k (reflection of R2).
The inputs to the opamp (grey line below) swing at half the output voltage, allowing the overall opamp supply range (cyan/magenta) to swing completely above and below ground:
(There is a 33V zener to define the opamp supply voltage plus decoupling cap)
Square waves are handled fairly well (a little bit of raggedness, hard to see on the 10kHz plot)
I've not tried this for real yet - I suspect it will be fussier in real life than simulated. And it will need a proper bias circuit.
R21/C8 form a snubber needed to shunt any unwanted HF feedback via the bootstrapping path leading to oscillation - the simulation needs it, I suspect this will be somewhat different in reality.
Transformer Wiring for SE
Hi
I have an Tubelab SE and am finally wiring it all together.
I cannot locate a code for the transformer joints. Help please?
Wayne
I have an Tubelab SE and am finally wiring it all together.
I cannot locate a code for the transformer joints. Help please?
Wayne
Tubelab SE 300b Build Thread
Finally started my TSE build tonight and thought I would document it and ask questions here. I soldered in R1-R7.
When soldering R7, some of the solder might have flowed onto the adjacent pad for R6, but I can't really tell. It could just be some flux in there (or it could be nothing). If I read the schematic right, R6 and R7 are actually connected at this point.
Anything to worry about? Should I try to clean it out?
Here's a closeup image.
r6-r7-cropped by jeffdrouin, on Flickr
Not my cleanest work.
When soldering R7, some of the solder might have flowed onto the adjacent pad for R6, but I can't really tell. It could just be some flux in there (or it could be nothing). If I read the schematic right, R6 and R7 are actually connected at this point.
Anything to worry about? Should I try to clean it out?
Here's a closeup image.
r6-r7-cropped by jeffdrouin, on FlickrNot my cleanest work.
Non-switching complimentary output stage
- By U130421
- Solid State
- 148 Replies
Sometimes ,you need to circum navigate the planet to find out, it was just behind your shoes.
The quiescent bias current is 145ma . As you can observe on scope , the minimum current falls to 90ma at 32.8 vp on 8 ohms with 33vp input 1khz, with Dtot of 0.04% .
The quiescent bias current is 145ma . As you can observe on scope , the minimum current falls to 90ma at 32.8 vp on 8 ohms with 33vp input 1khz, with Dtot of 0.04% .
Attachments
What is the best/recommended way to wire the bias trim-poti ?
- By alujoe2
- Tubes / Valves
- 29 Replies
Attachments
A most mysterious (to me) power transformer
- By yannikab
- Power Supplies
- 44 Replies
Hello again, I 've recently acquired a power transformer in order to feed a Linkwitz-Riley crossover and/or solid state preamp. Both can work great at +-15VAC. The device works, but I can't understand how it does it, as you will soon see.
So here's my power chain:
1) LED power supply, input 240VAC, output 24VDC
2) DC Voltage regulator with which I can decrease or even increase DC voltage
3) Mysterious power transformer 24VDC input, +-15VDC output and ALSO an intermediate dual AC output (that's the mystery part)
4) L-R crossover board (or discrete solid state preamp)
Now, the power requirements of the L-R board should be very low, about 2-3VA. The manufacturer states that it works within a range of dual 14VAC to dual 19VAC. Now to number 3), the mysterious device.
The device's stated purpose is to turn 24VDC to +-15VDC. However, I got it for its intermediate output, which is marked as dual AC. Only recently after inquiring with the manufacturer I realized this must be some not very supported output, and the only reason for this intermediate dual AC conversion is to create the +-15VDC output.
However, powering the LR board (~2-3VA) with this output does work. It can also turn on my pre which has a bit higher power demands(~10VA).
I'm certain most of you have recognized the board's design, I shall now be a bit more revealing. If I feed the device with 24VDC, this is what I get with my recently acquired True RMS multimeter at the dual AC output.
Yes, the reading is correct, it's a miniscule 15mV but with frequency of a whopping 20KHz! The device works ok because the dual DC output is pretty much spot on at +-15VDC.
Can you help me figure out what this board's principles of function are? I mean roughly how it is designed and how it works. Then I can see if and how I can utilize the intermediate dual AC output for powering stuff (safely). I'm pretty sure things flow from top left to top right to bottom right to bottom left. I suspect the tiny width voltage is used to feed the two caps near the +-VDC output, but can I use it elsewhere? Thanks for any insights/help.
So here's my power chain:
1) LED power supply, input 240VAC, output 24VDC
2) DC Voltage regulator with which I can decrease or even increase DC voltage
3) Mysterious power transformer 24VDC input, +-15VDC output and ALSO an intermediate dual AC output (that's the mystery part)
4) L-R crossover board (or discrete solid state preamp)
Now, the power requirements of the L-R board should be very low, about 2-3VA. The manufacturer states that it works within a range of dual 14VAC to dual 19VAC. Now to number 3), the mysterious device.
The device's stated purpose is to turn 24VDC to +-15VDC. However, I got it for its intermediate output, which is marked as dual AC. Only recently after inquiring with the manufacturer I realized this must be some not very supported output, and the only reason for this intermediate dual AC conversion is to create the +-15VDC output.
However, powering the LR board (~2-3VA) with this output does work. It can also turn on my pre which has a bit higher power demands(~10VA).
I'm certain most of you have recognized the board's design, I shall now be a bit more revealing. If I feed the device with 24VDC, this is what I get with my recently acquired True RMS multimeter at the dual AC output.
Yes, the reading is correct, it's a miniscule 15mV but with frequency of a whopping 20KHz! The device works ok because the dual DC output is pretty much spot on at +-15VDC.
Can you help me figure out what this board's principles of function are? I mean roughly how it is designed and how it works. Then I can see if and how I can utilize the intermediate dual AC output for powering stuff (safely). I'm pretty sure things flow from top left to top right to bottom right to bottom left. I suspect the tiny width voltage is used to feed the two caps near the +-VDC output, but can I use it elsewhere? Thanks for any insights/help.
Attachments
How would be a good proportion graphic of distortion for triodes ?
- By santitrucco
- Tubes / Valves
- 26 Replies
Attachments
Revox B77 problems
- By erdebear
- Analogue Source
- 13 Replies
Revox b 77 problems
I have a Revox B77. The motor that controls the play function, runs, but when play is engaged, the pinch roller's drag on the capstan, stops the motor running. It also does so when switching from 7.5 ips to 15 ips. Anyone with any knowledge, or Revox service manual etc.
I have a Revox B77. The motor that controls the play function, runs, but when play is engaged, the pinch roller's drag on the capstan, stops the motor running. It also does so when switching from 7.5 ips to 15 ips. Anyone with any knowledge, or Revox service manual etc.
Methods to reduce crossover distortion?
- By northumber82
- Solid State
- 72 Replies
In a push-pull class AB amplifier, I want to reduce the crossover distortion of the output (called also zero crossing distortion).
I used the following solutions:
1) Use a Vbe multiplier like that:
2) Using a CFP output stage:
In a class AB analog amplifier the polarization cannot be infinite, and even if it were, it would never eliminate the crossover distortion, it would only reduce it to a certain point.
As we have seen and demonstrated several times over time, the CFP type output stage offers numerous advantages, including better thermal stability and better linearity than the other output stages.
However, I would like to experimentally try to make the circuit further linear in the crossing area, trying to reduce the odd harmonics even more.
But honestly I don't know what to do, I tried to read all the books that talk about amplifier constructions (Cordell, Self, Crowhurst, Duncan, etc) but I didn't find anything more complex to apply.
Do you have any ideas, or do you think of any particular amplifier that introduces an efficient method to reduce crossover distortion?
I used the following solutions:
1) Use a Vbe multiplier like that:
2) Using a CFP output stage:
In a class AB analog amplifier the polarization cannot be infinite, and even if it were, it would never eliminate the crossover distortion, it would only reduce it to a certain point.
As we have seen and demonstrated several times over time, the CFP type output stage offers numerous advantages, including better thermal stability and better linearity than the other output stages.
However, I would like to experimentally try to make the circuit further linear in the crossing area, trying to reduce the odd harmonics even more.
But honestly I don't know what to do, I tried to read all the books that talk about amplifier constructions (Cordell, Self, Crowhurst, Duncan, etc) but I didn't find anything more complex to apply.
Do you have any ideas, or do you think of any particular amplifier that introduces an efficient method to reduce crossover distortion?
FS: Twisted Pear Buffalo III se Complete + Amanero/Hermes/Cronus/Rhea Free Airmail
Full Set and free Airmail to Asia, Europe and USA (tracking and express available at additional charge) - USD $350 Paypal only
Buffalo III se with complete AVCC and Trident Modules x 1
IVY-III Analog Stage x 1
Placid HD x 1
Placid Bipolar x 1
Amanero Combo384 x 1
Hermes Isolator for Amanero x 1
Cronus Re-clocking Module with 45.1584/49.152MHz Rhea Pair x 1
OTTO SPDIF selector x 1 (Brand new)
Just add wiring, casing, connectors and transformers to start playing great music!!!
Buffalo III se with complete AVCC and Trident Modules x 1
IVY-III Analog Stage x 1
Placid HD x 1
Placid Bipolar x 1
Amanero Combo384 x 1
Hermes Isolator for Amanero x 1
Cronus Re-clocking Module with 45.1584/49.152MHz Rhea Pair x 1
OTTO SPDIF selector x 1 (Brand new)
Just add wiring, casing, connectors and transformers to start playing great music!!!
FS: High quality trafos & pcb with ferrite coils
Hello.
I have for sell some high quality trafos and pcb with ferrite coils.
Lot of them 😀
All items is used and was dismantled from old military equipment.
It was some radio line, made between 1964 to 1968, made in Germany (Siemens, TeKaDe, Telefunken).
I think that trafos and coils can be rewound to get high quality audio tranformators. They have high quality core.
Small trafos and medium was used as signal trafo, large was probably as power supply.
On the foto i have write diemensions.
If you interested or have any questions, please write PM.
Small Trafos
All have almost same size:
Medium Trafo:
Large Trafo:
PCB1 with ferrite coils:
PCB2 with ferrite coils:
I have for sell some high quality trafos and pcb with ferrite coils.
Lot of them 😀
All items is used and was dismantled from old military equipment.
It was some radio line, made between 1964 to 1968, made in Germany (Siemens, TeKaDe, Telefunken).
I think that trafos and coils can be rewound to get high quality audio tranformators. They have high quality core.
Small trafos and medium was used as signal trafo, large was probably as power supply.
On the foto i have write diemensions.
If you interested or have any questions, please write PM.
Small Trafos
All have almost same size:
Medium Trafo:
Large Trafo:
PCB1 with ferrite coils:
PCB2 with ferrite coils:
Easy-MOS is a simplistic, efficient and evolutive all-MOS amplifier for beginners
- By Elvee
- Solid State
- 131 Replies
This amplifier is terminally simple, cheap and forgiving, but it remains capable of amplifying in the seventies style: it would have been capable of meeting some HiFi standards of the time.
Of course, nowadays a THD of 0.5% and a full-power bandwidth of 50kHz is only tolerable in audiophile or tube amps, but even compared to a chipamp, it remains easy and accessible.
The design came to birth as a by-product (understand reject) of a request from Daniel: he asked me to design a discrete amplifier that could match a chipamp in performance, simplicity and ease of construction.
I examined a number of options, and I rejected this one because of its inverting design and its (relatively) low performances: in its best implementation, it manages 0.1% THD and 100kHz power bandwidth.
It is nevertheless a neat and effective amplifier, and importantly, it is highly evolutive: this is the plain vanilla version, but serious improvements are possible without too many complications; more on that later.
The main drawback of ultra-simple MOS-followers based amps is their output voltage swing heavily curtailed by the MOS threshold voltage, typically several volts under load.
Add the inevitable losses from the source resistors and the drivers and you are left with an output of Vrail minus 5 to 10V for each rail.
For high-power amps, the loss is relatively benign, but with 10 or 15V of total supply voltage, practically nothing is left to drive the load.
EZ-MOS solves the problem by bootstrapping for the positive rail and a "bias memory cap" for the negative one (or GND for a simple amplifier like this one).
The result is a 3-transistor + bias topology capable of swinging 28.5Vpp with a 31V supply: not bad for a simple follower-based amp.
One of the main drawback is the inverting configuration, but even renowned designers like Renardson use it.
Here are pics of my prototype:
The low-power MOSfets can be almost any low-power type like 2N7000, and the OP can be any approximate complementary vertical pair.
My prototype is wired for a ~30V supply and is capable of putting out ~12W @ 8Ω, but other voltages and load impedances are possible just by scaling R13.
You can probably notice that the board is heavily populated compared to the schematic: that's because of the evolutive aspect.
The prototype includes all the options, but here the jumpers are in the "plain vanilla" position.
More will follow
Here is the 10kHz, large signal squarewave response:
Not blindingly fast for this version obviously, but clean and sufficient for audio purposes, at least in principle.
The simulated THD is a shade over 0.5%; in the same conditions, the measured THD is a shade under 0.5%, thus very close, which is normal for "high" THD levels.
Of course, nowadays a THD of 0.5% and a full-power bandwidth of 50kHz is only tolerable in audiophile or tube amps, but even compared to a chipamp, it remains easy and accessible.
The design came to birth as a by-product (understand reject) of a request from Daniel: he asked me to design a discrete amplifier that could match a chipamp in performance, simplicity and ease of construction.
I examined a number of options, and I rejected this one because of its inverting design and its (relatively) low performances: in its best implementation, it manages 0.1% THD and 100kHz power bandwidth.
It is nevertheless a neat and effective amplifier, and importantly, it is highly evolutive: this is the plain vanilla version, but serious improvements are possible without too many complications; more on that later.
The main drawback of ultra-simple MOS-followers based amps is their output voltage swing heavily curtailed by the MOS threshold voltage, typically several volts under load.
Add the inevitable losses from the source resistors and the drivers and you are left with an output of Vrail minus 5 to 10V for each rail.
For high-power amps, the loss is relatively benign, but with 10 or 15V of total supply voltage, practically nothing is left to drive the load.
EZ-MOS solves the problem by bootstrapping for the positive rail and a "bias memory cap" for the negative one (or GND for a simple amplifier like this one).
The result is a 3-transistor + bias topology capable of swinging 28.5Vpp with a 31V supply: not bad for a simple follower-based amp.
One of the main drawback is the inverting configuration, but even renowned designers like Renardson use it.
Here are pics of my prototype:
The low-power MOSfets can be almost any low-power type like 2N7000, and the OP can be any approximate complementary vertical pair.
My prototype is wired for a ~30V supply and is capable of putting out ~12W @ 8Ω, but other voltages and load impedances are possible just by scaling R13.
You can probably notice that the board is heavily populated compared to the schematic: that's because of the evolutive aspect.
The prototype includes all the options, but here the jumpers are in the "plain vanilla" position.
More will follow
Here is the 10kHz, large signal squarewave response:
Not blindingly fast for this version obviously, but clean and sufficient for audio purposes, at least in principle.
The simulated THD is a shade over 0.5%; in the same conditions, the measured THD is a shade under 0.5%, thus very close, which is normal for "high" THD levels.
Attachments
What is the purpose of these bjt lead sleeves?
- By Fusion916
- Solid State
- 16 Replies
I'm in the process of replacing blown output transistors and this car amp uses small sleeves on all of the leads of the output transistors. Why are these necessary?
