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Curious_George

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Everything posted by Curious_George

  1. Another forum member PM'd me and asked if I would help them build the high pass filter circuit for the LaScala mod. I put together a BOM from Jameco so the parts could be sourced easily from one location. Of course there are many places to get the parts from, but Jameco has good prices and has everything in stock. I have no affiliation with Jameco. 18dB High Pass Filter EQ_LaScala Part BOM_102121.pdf
  2. Yes, still experimenting with different tweeters & crossovers.
  3. When I first bought my used LaScala's, I thought they sounded great. I had read many threads here on the forum about the K400 (metal) horn not being the best, but I could not hear the "harshness" that was discussed. After many hours of listening, especially at high(er) listening levels, I began to hear the harshness. Now even at lower levels, I can clearly detect the sound of the K400 (metal) horn. It's not totally unlistenable, but it does have a forward character to it. My LaScala's were DJ speakers and fairly beat up, but the original drivers were in good shape. When I get around to refurbishing the cabinets, I am going to change the K400 and tweeter out. If you want to experiment, I would go with a different horn, not driver. If you go with a different driver you will more than likely have to change or modify the crossover.
  4. Here is a quick & dirty REW curve. I can't find the other measurement from many moons ago. I say quick & dirty because my basement has yet to be straightened out and set-up after moving. To clarify - Blue line is with port mod, purple line is with port mod & EQ.
  5. They do look pretty. I’d buy some if they were $10 each. That’s about what they are worth.
  6. I stocked up on 6SN7, 12SN7, 7F7 and 14F7 long ago anticipating inflation. Now the only issue is is finding a good Loctal type socket. Those cheap ceramic Chinese ones suck.
  7. I have measured it. Let me find the file or remeasure with REW again. If I remember correctly, with the EQ and room gain, it will extend the low end down to 35Hz.
  8. Unfortunately, it looks like the Exodus 6.5" woofer is no longer available or hard to find at best. Here are the TS specs if you want to substitute another woofer for the project.
  9. That looks like a great sub project, no doubt. I've not heard one yet.
  10. I'm not sure. I'd have to do some research. The problem with a regular EQ is the bandwidth or Q of the circuit. It would probably be too wide and affect to many frequencies on either side of the 40Hz boost region. In addition, the high pass filter EQ has a built-in "infrasonic" slope to attenuate the lower frequencies from unloading the woofer at 1/2 the port tuning frequency.
  11. The below circuit is an example of what you would need to realize the high pass EQ filter electronically. This is only the high pass EQ filter circuit, no power supply is shown. This circuit could be inserted into your preamp's tape loop function (in/out). On some preamps, there is a specific "EQ" loop for external processors, such as this high pass filter. If you need a power supply circuit let me know.
  12. It is hard to refute facts, data and experience, but I don't recall doing any of those three. I made an observation that a lot of opinions on this forum are "half-baked" to use your descriptive words. NOW THAT is up for debate.
  13. 6SN's and 12SN's are the same except for filament voltage. Again, there may be sonic differences, but I can't hear them.
  14. The coin base is not as attractive or Art Deco as a "GT", but they should "behave" the same. I use the word "behave" because of the way some people describe the way they sound. I don't believe that a vacuum or slightly different metal choices (cathode, filament, plate) can change the sound of a tube, but I don't want to take anything away from someone's music.
  15. Everything in life is a compromise. Did we really have to debate an audio topic in order for me to make that statement for you to realize?
  16. Exactly. Thank you. This is all I was alluding to. Claude, you need to make up your mind. One minute you state the above, which I agree with, other times, you say the opposite like "half-baked". It can't be both in reality. If you want to flounder, then that is your prerogative.
  17. I know some of the newer tubes may look better (compared to USA NOS), like the Psvane shoulder 6SN7, but the shoulder or look of the tube has nothing to do with the sonics. This particular tube on Amazon says the shoulder version is made for HiFi and is warm (and fuzzy, just kidding, but is does say warmer because of the shoulder design). The metallurgy and design of the USA NOS is (or was) better than the new Chinese tubes in my opinion.
  18. I have not tried them, but the price is crazy. The best 6SN7/GT made in my opinion is a USA NOS (any brand). I have a few Chinese (generic) and Russian (Sovtek) 6SN7GT's and they are OK, nothing special. I have compared (listened & measured) NOS RCA 6SN7GT's that are used with many hours on them to the Chinese and Sovtek tube mentioned previously. The used RCA tubes have a lot of hours on them, probably close to 6k or 7k hours. The tubes have so many hours on them, there are chrome looking spots above the cathode filament "tubes" on the top glass. Compared to the Chinese and Sovtek's, the RCA's sounds just as good, maybe better.
  19. The LaScala bass modification is not half-baked, although a lot of opinions on this forum are. Yes, this is my opinion as well. Most people here give good advice, but in some cases, designs or topologies are not their favorite and instead of giving an objective view, they give a biased view, which does not steer a person who has limited knowledge in the right direction if they are asking about such. To get the full benefit from the LaScala bass modification, Dennis indicated that the high pass filter EQ was needed (and it is). I suspect most people who do modify their LaScala's do not use the EQ and this is where the "disappointment" may come in. Almost every speaker could benefit from a subwoofer, even some "subwoofers", if that makes any sense... I like a full music spectrum, but not everyone wants or needs much below 30Hz.
  20. The SRPP is a reconfiguration of the original circuit. The OE circuit was a paralleled 6N2. The main reason for elevating the heater supply was to keep the heater to cathode voltage within the specified design parameters. Noise rejection was of secondary importance, but it worked out to do both. In addition, the SRPP is a bit more versatile with tube swapping than the original circuit. For example, if you wanted to use the amp without a preamp, you could use a 5751 in place of the 12AV7, with no circuit changes.
  21. Here is an affordable single-ended stereo amp project that can use various inexpensive tetrode or pentode output tubes. The design is not an original, but inspired by a Meng Yue Mini EL34B amp that I picked up in Hong Kong on a business trip years ago. The performance of the stock Mini EL34B was not great; noisy (hiss and hum) and high distortion at low volumes. The input tube was a 6N2 capacitively coupled to the EL34B. Surprisingly, the output transformers must have been wound with some care and consideration because the frequency response of the modified amp is out to 80kHz, -3dB @ 1 Watt/8 Ohm. The low end goes down to 25Hz, -3dB @ 1 Watt. This is quite extraordinary for an inexpensive Chi-Fi amp. The main modifications to the stock Mini EL34B are the power supply, input tube circuitry and various grounding issues. The power supply was a CRC design with marginal capacitance which was the reason the hum was audible on my Klipsch LaScala's. I changed the design to a CLC with more capacitance to reduce/eliminate the hum. With my head inside the mouth of the LaScala horn, nothing is audible now. Since I always use a preamp to drive my amps, I did not need high gain in the Mini EL34B input circuitry. 0.5VRMS will drive the amp to 1 Watt/8 Ohms and a little over 1VRMS will give you full power. The input tube is now a 12AV7, which is inexpensive and sounds great. The original power transformer is 240VAC since I bought it in Hong Kong. The power transformer shown on the schematic is the closet one I could find that you can easily source in the US. Hammond, etc may have one closer than the Edcor unit. The original secondary voltage for the Mini EL34B is 155VAC. If you will notice the Edcor is 180VAC, which is why you will need a 10 ~ 15 Watt, 775 Ohm power resistor to drop some of the voltage. The actually power resistor may vary from my calculated value of 775 Ohms. If you can find a power transformer with a secondary of 150VAC to 160VAC, you can omit the power resistor. The real beauty of this amp is that you can use multiple types of output tubes in the amp depending on what you like or can afford. All tube prices are going up, but if you shop around, there are still great bargains to be had on USA NOS or tubes from current manufacturers. Depending on the output transformer used, you may have to experiment with the 22uF bypass cap on the 12AV7 cathode. Too large of a cap here will cause some peaking in the low frequency response. The 330uF bypass cap on the output tube may also need to be adjusted for the same reason. Edit - The power resistor labeled 775 Ohm should be 390 Ohm. I miscalculated and only used 1 channel of current draw through the resistor for the initial calculation. In addition, the power rating of the resistor is now doubled. If you use the 390 Ohm resistor, it should have a power rating of at least 20 watts.
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