I have 93dB sensitive speakers, nominal 8ohm load, but they definitely are better driven from 4ohm taps. No impedance graph I’m afraid.
So I have 300b SE 7-8watts, it only has 8 and 16ohm available on the output transformer.
Good idea to try a 0.5 or 1 ohm resistor (10w?) in series with the speaker cable?
The speakers not hugely sensitive, so just wondering if given I only have circa 7 watts on tap if adding a resistor would be a good idea?
My 805 tube amp drives them to perfection on a 4 ohm tap (frequency response was perfect, I’m a bit thin/lacking bass foundation using 300b currently), but 300b has other benefits over 805 so trying to get it to work. Cheers
So I have 300b SE 7-8watts, it only has 8 and 16ohm available on the output transformer.
Good idea to try a 0.5 or 1 ohm resistor (10w?) in series with the speaker cable?
The speakers not hugely sensitive, so just wondering if given I only have circa 7 watts on tap if adding a resistor would be a good idea?
My 805 tube amp drives them to perfection on a 4 ohm tap (frequency response was perfect, I’m a bit thin/lacking bass foundation using 300b currently), but 300b has other benefits over 805 so trying to get it to work. Cheers
So, you are not pleased with the way the 300b amp sounds with you speakers. What are the 300b operating conditions? What output transformers are you using? Do you know what the primary impedance is presented to the 300b when you use the 8 ohm tap?
FR balance is off - I don’t know what the primary impedance presented to 300b is unfortunately. The output transformers are Audio Note though (no model number).
All I know is that 8ohm output taps is something I can experiment with…
All I know is that 8ohm output taps is something I can experiment with…
The 4 Ohm tap gives about 2 times better damping factor to the speaker than the 8 Ohm tap.
Could that be the issue?
Damping as it affects the woofer.
Flattening out the frequency response of a loudspeaker that has large variations in impedance versus frequency, versus the amplifier's damping factor (at 4 and 8 Ohm taps).
Many manufacturers '8 Ohm' speakers drop down to 5 or 6 Ohms at some frequencies.
Take your Ohmmeter make a very good connection with the leads, and read the DC resistance at the speaker enclosures input posts.
What is that resistance?
Could that be the issue?
Damping as it affects the woofer.
Flattening out the frequency response of a loudspeaker that has large variations in impedance versus frequency, versus the amplifier's damping factor (at 4 and 8 Ohm taps).
Many manufacturers '8 Ohm' speakers drop down to 5 or 6 Ohms at some frequencies.
Take your Ohmmeter make a very good connection with the leads, and read the DC resistance at the speaker enclosures input posts.
What is that resistance?
Speakers are NSMT model 100. Just tried with Ohm meter - reading 4.5ohms… would that explain the tipped up frequency response if it can only be fed from an 8ohm tap?
I had wondered at the input side of the amp as well - direct from DAC (100 ohm output impedance), however it’s unlikely to be a miss-match…
From manufacturers website:
Frequency Response: 20 Hz - 20 kHz
Sensitivity: 93 dB 1 watt/m
Rated Impedance: 8 ohms
Minimum Impedance: 4 Ohms
Recommended Power: 5 - 200 watts
I have 8R loudspeaker driver, with voice coil resistance 6.09R.
Does it mean anything but that isn't 4R device?
Does it mean anything but that isn't 4R device?
I won’t be getting double the power into 4.5ohms - however the bass is consistently thin regardless of volume level.
I’m not sure adding a resistor in series with the speaker wire to equal 8ohms will help, given that I only have some 7watt to deal with?
I’m not sure adding a resistor in series with the speaker wire to equal 8ohms will help, given that I only have some 7watt to deal with?
NSTM Model 100 on 6Moons:
https://6moons.com/audioreview_articles/nsmt/
It's very attractive speaker, but using it with "standard" 300B SE (rather 6W than 8W) at 8R output is problematic.
https://6moons.com/audioreview_articles/nsmt/
It's very attractive speaker, but using it with "standard" 300B SE (rather 6W than 8W) at 8R output is problematic.
Output transformer isn’t saturated - music sounds very detailed and resolved, just very tipped up FR.
I use -as daily amplifier- 300B SE (5k:8), but it capable even 11W (in A2 mode).
I used it for a decade with 89dB Acoustic Energy 8R speaker, but it's very "tube friendly", despite has crossover. Moderate impedance alterations, the minimum impedance is 6R. BTW I searched this "tube friendly" device for years.
I have two full range speaker too, 8R, 95 and 96dB (2.83V, from 1m), 7-8 Ohm minimum, only one resonance bump.
Each speaker produces satisfying frequency resolution, and good tone with my 300B.
I tried other (tube) amplifiers too (have quite a few), each "compatible" with these speakers, but which have not enough good damping factor produces disappointingly flat tone.
So If you have appropriate loudspeaker, selection of amplifier is relatively easy. If the speaker is a little problematic, the assortment may be very narrow.
It seems you have to choose the jacket for the button (proverb in my country).
I used it for a decade with 89dB Acoustic Energy 8R speaker, but it's very "tube friendly", despite has crossover. Moderate impedance alterations, the minimum impedance is 6R. BTW I searched this "tube friendly" device for years.
I have two full range speaker too, 8R, 95 and 96dB (2.83V, from 1m), 7-8 Ohm minimum, only one resonance bump.
Each speaker produces satisfying frequency resolution, and good tone with my 300B.
I tried other (tube) amplifiers too (have quite a few), each "compatible" with these speakers, but which have not enough good damping factor produces disappointingly flat tone.
So If you have appropriate loudspeaker, selection of amplifier is relatively easy. If the speaker is a little problematic, the assortment may be very narrow.
It seems you have to choose the jacket for the button (proverb in my country).
"I thought these speakers would work with 300b, but perhaps not"
Perhaps not with this structure.
Other designs, with other -larger- 300B tubes (for example with EML 300B XLS, KR 300BXL) can work.
Perhaps not with this structure.
Other designs, with other -larger- 300B tubes (for example with EML 300B XLS, KR 300BXL) can work.
Any further determination of the reasons for the sound of the 300B amplifier on those speakers would be more possible with:
A complete and accurate schematic, including voltages, currents, detailed output transformer characteristics, in order to be able to do a calculated analysis of the amplifier.
Or,
A complete and accurate set of test results of the amplifier; including harmonic and intermodulation distortions, damping factor, frequency response, etc.
If a 300B amplifier design is lacking in one or more details, just using a more powerful, non real 300B will not necessarily solve the problem.
Guessing makes for more postings on this thread, but does not quickly come to a solution.
"All 300B amplifiers are Equal; but some 300B amplifiers are More Equal than others" - a highly modified quote from "Animal Farm" by George Orwell.
Just saying
A complete and accurate schematic, including voltages, currents, detailed output transformer characteristics, in order to be able to do a calculated analysis of the amplifier.
Or,
A complete and accurate set of test results of the amplifier; including harmonic and intermodulation distortions, damping factor, frequency response, etc.
If a 300B amplifier design is lacking in one or more details, just using a more powerful, non real 300B will not necessarily solve the problem.
Guessing makes for more postings on this thread, but does not quickly come to a solution.
"All 300B amplifiers are Equal; but some 300B amplifiers are More Equal than others" - a highly modified quote from "Animal Farm" by George Orwell.
Just saying
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What does it mean that "non real"?
If the "real" have capacitor coupled, cathode biased 300B, 350V/70mA operating point and 3k OPT output stage .... sorry, there are also many other options.