The thing to note with my circuit is the DC offset was only 33mV. Hopefully I drew is right? The part where many nodes are joined are shown by a hump crossing other lines as in pre 1970's diagrams.
gannaji
Revising the JLH class A output stage to provide AB operation with Lateral mosfets, as in post 5060, should work well. I used a very similar topology during the 1980s when designing a 30W integrated amplifier for background music duty in the family hotel.
I later upgraded it and licensed the design to Russ Andrews where it was produced as the RATA Integrated Amplifier through the early 1990s and it was very well regarded for its musical presentation. I have fond memories of listening to music with this amplifier. It was very good dynamically but I particularly remember that it was exceptionally engaging musically at low listening levels, where most amplifiers at the time struggled. This was ideal for background music in the hotel. I did notice that customers were listening to the music quite intently at times instead of chattering and many asked about the sound system.
I used the original Hitachi Laterals for the output devices and also their TO220 Laterals as output device drivers. The bootstrap circuit was replaced with a constant current load and the voltage gain stage supply was regulated via one of my early versions of the PR3 voltage regulator. Only one compensation capacitor was required (220pf) between the emitter of the PNP input transistor and the collector of the NPN second stage transistor for stability.
Revising the JLH class A output stage to provide AB operation with Lateral mosfets, as in post 5060, should work well. I used a very similar topology during the 1980s when designing a 30W integrated amplifier for background music duty in the family hotel.
I later upgraded it and licensed the design to Russ Andrews where it was produced as the RATA Integrated Amplifier through the early 1990s and it was very well regarded for its musical presentation. I have fond memories of listening to music with this amplifier. It was very good dynamically but I particularly remember that it was exceptionally engaging musically at low listening levels, where most amplifiers at the time struggled. This was ideal for background music in the hotel. I did notice that customers were listening to the music quite intently at times instead of chattering and many asked about the sound system.
I used the original Hitachi Laterals for the output devices and also their TO220 Laterals as output device drivers. The bootstrap circuit was replaced with a constant current load and the voltage gain stage supply was regulated via one of my early versions of the PR3 voltage regulator. Only one compensation capacitor was required (220pf) between the emitter of the PNP input transistor and the collector of the NPN second stage transistor for stability.
A few days back I said the performance of my very simple Wien Oscillator whilst OK might stand some improvement at 50 Hz. I had about - 63dB ( 3rd ) with a healthy output above 5 Vrms. This version nudges - 70 dB.
It is argued that the worse performance of a Lamp Wien is due to the period of the wave being long which allows some heat fluctuation. Most likely in the 5 to 100Hz range. Adding a resistor with the lamp shows how strong the AGC ( automatic gain control ) action of the lamp is. It even encourages the best use of the lamp. Current just about OK. The maths suggested this result. In fact it was a little different to the exspected. This means anyone interested may get a little more by fine tuning. By making the resistance a mix of lamp and resistor we get a slightly better result. I had used 240R so doubled it to match the 120R + Lamp. Doubtless 470R would be fine.
I mainly want to show this as it gives a picture seldom seen. As the op amp increases it's output some distortion results. Which is op amp and which is lamp? By making a unity gain inverted stage we can get rid of a little. If you look carefully we lost 6 dB second harmonic here at stage 2. The op amp distortion is mirror image. This is called pre distortion by some. In valve designs it can be a very big free lunch as it works in a similar way as negative feedback without the gain loss ( there is some output change due to cancellation, not much in this example ). Both ways cancel distortion . One by using itself returned to it's input and the other is pre-programed to be the same in mirror image. Even when other than unity it often gives a result. Obviously the unity version is the one most likely to be best, not always.
I would imagine this circuit to be - 86dB 1kHz. That's my best guess. This started as I had a mysterious TL082 on the bench that needed to be tested before assuming it junk.
My friend Roger has a RATA amp. He invented Mars Ice Cream.
Someone is bound to say JLH did a dual op amp Wien oscillator circuit which might be even better. Not much if at all when I built one. ESP Audio did a slight update of it. The arguement is the common mode differences if one op amp causes distortion. It was argued modern op amps side step this ( not sure that's 100% right, NE5532 comes to mind as best choice ). If the lamp + resistor used the JLH Wien Bridge could be the best. On paper the mythical RA53 thermistor was better. In my experiance not really. It seems the 28V 40 mA ( 62R cold typical ) suit very well a typical op amp. When I bought my little batch I had no idea others had hit on the same. I liked it as it is plentiful and cheap. If I understand used in aircraft at a typical 24V which if being charged will near 28VDC. I could imagine many older aircraft keep it alive. Not least smaller ones.
What I like about my circuit is it is very simple and visually says how it works to someone new to op amps. Negative feedback, positive feedback, AGC, non linear resitance, inverting buffer. It's a nice litle book of building blocks.
What I like about my circuit is it is very simple and visually says how it works to someone new to op amps. Negative feedback, positive feedback, AGC, non linear resitance, inverting buffer. It's a nice litle book of building blocks.
I have a JHL Class-A Update 2003, directly coupled to the loudspeaker x-over, without output capacitor. DC-level at output is a few mV. Have a output relay to protect loudspeakers.
Loudspeaker has a three-way X-over with separate filters for each driver. Tweeter and midrange has each a highpass filter (CLC) with capacitances in line with signal. Tweeter filter capacitances are 33uF/800VDc and 50uF/800VDc.
Midrange filter capacitances are 3.3uF/400VDc and 6.8uF/400VDc.
Bass x-over is a lowpass filter (LCL), no capacitance in signal line.
Q:
Can the midrange and tweeter capacitanes work/act as ”output protection” thereby skipping the relay ie take the signal to these x-overs before the amps output relay?
The bass driver would still be protected with the relay.
Loudspeaker has a three-way X-over with separate filters for each driver. Tweeter and midrange has each a highpass filter (CLC) with capacitances in line with signal. Tweeter filter capacitances are 33uF/800VDc and 50uF/800VDc.
Midrange filter capacitances are 3.3uF/400VDc and 6.8uF/400VDc.
Bass x-over is a lowpass filter (LCL), no capacitance in signal line.
Q:
Can the midrange and tweeter capacitanes work/act as ”output protection” thereby skipping the relay ie take the signal to these x-overs before the amps output relay?
The bass driver would still be protected with the relay.
Yes, in fact it makes most sense to try to incorporate such a passive crossover into the output coupling procedure. You will still have common mode currents passing through your supply.
Johnego,
The 2SK216 and 2SJ79. Unfortunately, like many older discrete semiconductors they are obsolete. I have stopped using them but have seen some available from time to time on places like e-bay. Whether they are true NOS devices would be a good question.
I think the idea of the JLH being coupled via an ideal mid or tweeter capacitor is a great idea. I did this with my Quad 303. I used 4700 uF for the 15 inch bass, 1000 uF for the full range and a small 250V polester for the tweeter. My tweeter came in at 6kHz. As the speaker was quite untidy it often prevented disaster. Surprisingly the speaker sounds OK without the tweeter. It just sounds so much nicer with it. Very odd is 78's need the tweeter. It just sounds more in the room. I never measured dispersion. I swear it was dramatically better. Theory would say no. I kept everything in positive phase and 1st order. I brought in some piezo tweeters very high up. They very soon made me dislike them. By maths they were ideal and I have liked them in the past. Behind a friends Tannoy Lancasters they are good. I'm 62 so don't exspect to notice these things. I only really hear to 13 kHz measured now.
Wien at 47 Hz is better when warmed up. Not dramatic.
Wien at 47 Hz is better when warmed up. Not dramatic.
R3 is to arrive at a mid voltage( +33 mV if using +/- supply ). JLH did a similar thing once. It is not a good idea really. It wasn't done by maths. Just trial and error.
I made a super low THD wienbridge.. < 120dB.. the key is to use a large bulb with a very long time constant. I used a 5W 220V bulb, packed in toilet paper 😀
Do you remeber what feedback resistor you used? I like the toilet paper!! I saw a guy in the USA say similar things. He used a Christmas light. He got about - 120 dB also.
The regret I have is a didn't buy some RA54 50K termistors. They were very cheap as they never seemed to be using in popular circuits. I now realise they would have suited better than RA53. RA53 when used with 680R gave about 1 Vrms using LF351N. That's no better than a lamp as the op amp is working hard. 2040 ohms I guess is OK, It implies a larger RC load than typical to reduce common mode effects. If so about 1K total.
The regret I have is a didn't buy some RA54 50K termistors. They were very cheap as they never seemed to be using in popular circuits. I now realise they would have suited better than RA53. RA53 when used with 680R gave about 1 Vrms using LF351N. That's no better than a lamp as the op amp is working hard. 2040 ohms I guess is OK, It implies a larger RC load than typical to reduce common mode effects. If so about 1K total.
This is my idea done better. I still think at 50Hz you might get worse. I just tried toilet paper and /or tin foil. 2dB? I will try harder.
LT1007/LT1037 Ultrapure 1kHz Sine Wave Generator Circuit Collection | Analog Devices
LT1007/LT1037 Ultrapure 1kHz Sine Wave Generator Circuit Collection | Analog Devices
IIRC the opamp was a LT1027 . The circuit was a textbook standard wienbridge. Lowish resistor values IIRC
Thanks AllenB and Nigel pearson for your valuable responces:
So to be clear before I test it:
The midrange driver and tweeter will be absolutely protected from poweramp (JLH 2003) DC-faults/excessive DC by the capacitanes in the x-overs highpass section? There is no risk for these drivers - can not buy new since they are not produced any more and love the sound of them.
Therefore relay protection is not needed for these drivers?
Does that mean the relay is only protecting the bass driver?
So to be clear before I test it:
The midrange driver and tweeter will be absolutely protected from poweramp (JLH 2003) DC-faults/excessive DC by the capacitanes in the x-overs highpass section? There is no risk for these drivers - can not buy new since they are not produced any more and love the sound of them.
Therefore relay protection is not needed for these drivers?
Does that mean the relay is only protecting the bass driver?
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If they were my speakers I’d open the box and look at Xover to make sure those caps are there!
Their direct current path is broken by the capacitors in series with one lead.
All currents, including speaker currents will pass through the capacitors in the end of your power supply which maintain your virtual ground point. These capacitors can discharge through your speaker in the case of a fault. You need the protection of the relay or capacitor coupling.
I hope you persist. Thank you also.
Talking of persisting. I suspect the aluminium foil and toilet paper to cover the Wien bridge lamps has a small advantge.
One daft thing came about. I replaced the 480R ( 240+240 ) upper feedback arm with 510R. It clipped badly at 5.6Vrms, 5.3Vrms OK. It was exactly at clipping with 480R, hence more second harmonic I feel. 470R gives 5.05V rms. This was with +/- 12V. Below +/- 9V.
Now a really odd thing. The TL082 uses resistor limiting as current limiting, 5532 is more sophisticated. 5.05 Vrms suits fine at 7.4 mA. Strangely the NE5532 at this point is not vastly different. Nor is the distortion. This proves it is mostly peak voltage and lamp distortion. More strangely the phase reversed buffer ( 10K 10 K ) works best for TL082. However NE5532 is best of all if using the NE5534 version. Very small difference and neither is - 80dB at 47 Hz.
Here is something like the old JLH Wien. Same lamp. I will build a 47Hz version as I feel is will have similar performance to the one op amp version. JLH felt the common mode distortion would be lower here. 10 kHz suits Wien types very well. To be frank it suits testing also. The 50 Hz to 3 kHz is less critical. If I remember JLH uses - input to 0V. As the op amp is mostly symetrical I doubt it matters as long as both are + or -.
Talking of persisting. I suspect the aluminium foil and toilet paper to cover the Wien bridge lamps has a small advantge.
One daft thing came about. I replaced the 480R ( 240+240 ) upper feedback arm with 510R. It clipped badly at 5.6Vrms, 5.3Vrms OK. It was exactly at clipping with 480R, hence more second harmonic I feel. 470R gives 5.05V rms. This was with +/- 12V. Below +/- 9V.
Now a really odd thing. The TL082 uses resistor limiting as current limiting, 5532 is more sophisticated. 5.05 Vrms suits fine at 7.4 mA. Strangely the NE5532 at this point is not vastly different. Nor is the distortion. This proves it is mostly peak voltage and lamp distortion. More strangely the phase reversed buffer ( 10K 10 K ) works best for TL082. However NE5532 is best of all if using the NE5534 version. Very small difference and neither is - 80dB at 47 Hz.
Here is something like the old JLH Wien. Same lamp. I will build a 47Hz version as I feel is will have similar performance to the one op amp version. JLH felt the common mode distortion would be lower here. 10 kHz suits Wien types very well. To be frank it suits testing also. The 50 Hz to 3 kHz is less critical. If I remember JLH uses - input to 0V. As the op amp is mostly symetrical I doubt it matters as long as both are + or -.