I only ask this Q in an abundance of caution for an apparently unique intended application.
The amp is a British late 80s 25W dual EL34 w/3 output taps: 4, 8 and 16 ohm, designed by Peter Qvortrup.
If needed scroll down to Fig. 7 for the schematic here: Amplifier Audio Innovations Series 500
The speaker load has 2 discrete sections each with separate input and xo: primary section is about 9 ohm, the reverberant field section is about 25 ohm, both with moderate minimum impedance and benign phase angles.
Please comment on this intended application:
8 ohm tap > primary 9 ohm speaker section
16 ohm tap > 25 ohm reverberant field section
Or do you prefer?
4 or 8 ohm tap > 9 + 25 ohm in parallel
Of course I can try both and see which one sounds better.
Or...?
Please 'splain your reasoning.
TX!
The amp is a British late 80s 25W dual EL34 w/3 output taps: 4, 8 and 16 ohm, designed by Peter Qvortrup.
If needed scroll down to Fig. 7 for the schematic here: Amplifier Audio Innovations Series 500
The speaker load has 2 discrete sections each with separate input and xo: primary section is about 9 ohm, the reverberant field section is about 25 ohm, both with moderate minimum impedance and benign phase angles.
Please comment on this intended application:
8 ohm tap > primary 9 ohm speaker section
16 ohm tap > 25 ohm reverberant field section
Or do you prefer?
4 or 8 ohm tap > 9 + 25 ohm in parallel
Of course I can try both and see which one sounds better.
Or...?
Please 'splain your reasoning.
TX!
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The main counterquestion is: what are those speakers and (more importantly) are they designed to be driven with sections in parallel (i.e. both sections should get equal AC voltages)?
Different transformer taps provide different output voltages - for every 1V at 4 Ohm tap you get 1.41V at 8 Ohm tap and 2V at 16 Ohm tap.
Different transformer taps provide different output voltages - for every 1V at 4 Ohm tap you get 1.41V at 8 Ohm tap and 2V at 16 Ohm tap.
Ah, very good question!
Yes, the two speaker loads are designed to be driven in parallel by one amp with suitable current capacity. It's OK to drive the reverberant field section with a second amp.
The reverberant field section has a passive volume control with (IIRC) about 9 dB of range. If a separate amp w/level control drives the RF section, the RF section's volume control would be set to maximum.
With a solid state amp driving both speaker sections in parallel, the level control on the RF section is adjusted about 2 dB below maximum (ca. 27 ohm).
The load impedance of the RF section varies by level control setting: minimum volume = about 25 ohm, maximum volume = about 40 ohm.
Driving both speaker sections with the tube amp alone is more elegant, but I have a great SS amp to drive the RF section separately.
Yes, the two speaker loads are designed to be driven in parallel by one amp with suitable current capacity. It's OK to drive the reverberant field section with a second amp.
The reverberant field section has a passive volume control with (IIRC) about 9 dB of range. If a separate amp w/level control drives the RF section, the RF section's volume control would be set to maximum.
With a solid state amp driving both speaker sections in parallel, the level control on the RF section is adjusted about 2 dB below maximum (ca. 27 ohm).
The load impedance of the RF section varies by level control setting: minimum volume = about 25 ohm, maximum volume = about 40 ohm.
Driving both speaker sections with the tube amp alone is more elegant, but I have a great SS amp to drive the RF section separately.
In that case you have two reasonable options:
a) driving the primary 9 Ohm section with 8 Ohm tap and the RF section with SS amp;
b) driving both sections in parallel (the combined impedance is about 6.7 Ohm) still with 8 Ohm tap.
Driving the 9 Ohm section with 8 Ohm tap and the 25 Ohm section with 16 Ohm tap is equivalent to driving the single 5.3 Ohm load with a 8 Ohm tap, which is a bit too far from optimal in terms of the reflected impedance.
a) driving the primary 9 Ohm section with 8 Ohm tap and the RF section with SS amp;
b) driving both sections in parallel (the combined impedance is about 6.7 Ohm) still with 8 Ohm tap.
Driving the 9 Ohm section with 8 Ohm tap and the 25 Ohm section with 16 Ohm tap is equivalent to driving the single 5.3 Ohm load with a 8 Ohm tap, which is a bit too far from optimal in terms of the reflected impedance.
after looking at the schematic i'm at a loss to see this :"reverberant field section" you mention...
Some experimental speaker systems had an aditional coil to provide feedback to the amplifier and include the cone of the driver in the servo loop.
Is that what you're working with here?
If so, one of them is not designed to be driven from an amp.
Its there to provide an error correction signal back to the front end.
Is that what you're working with here?
If so, one of them is not designed to be driven from an amp.
Its there to provide an error correction signal back to the front end.
Seems some people are looking for your speakers in the schematic. I can't imagine why.
FWIW, I agree with TG's option "b)"
FWIW, I agree with TG's option "b)"
No. Earlier I accurately described the intended amplifier source for the 2 speaker sections and the speaker loads. Both speaker sections are simple moving coil dynamic type with passive crossovers.
I have to swap the tube amp PS from 240V to 120V. As soon as that's done I'll try option B as recommended, which I agree is "reasonable."
Yes, I posted the amplifier schematic and described the speaker load relative to the Q.
2-way main satellite section: true 91 dB/1W/1M
Earlier I wrongly inverted the RF section impedance vs. SPL: minimum SPL about 40 ohm, maximum SPL mid-high 20 ohm range. My setting about 2 dB below maximum, high 20 ohm range. The relationship is inverted: the higher is SPL the lower is the impedance, and vice verse.
Yes, I posted the amplifier schematic and described the speaker load relative to the Q.
2-way main satellite section: true 91 dB/1W/1M
Earlier I wrongly inverted the RF section impedance vs. SPL: minimum SPL about 40 ohm, maximum SPL mid-high 20 ohm range. My setting about 2 dB below maximum, high 20 ohm range. The relationship is inverted: the higher is SPL the lower is the impedance, and vice verse.
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The OP’s question was confusing to me too. The reference to the amplifier schematic (you got the right one) seemed to imply that he was talking about the amplifier.
What I think is that he has a peculiar loudspeaker (not clearly explained) that he wanted to hookup to this rather ordinary amplifier.
What I think is that he has a peculiar loudspeaker (not clearly explained) that he wanted to hookup to this rather ordinary amplifier.
He clearly explained that he was considering hooking up the peculiar speakers in a peculiar manner by using two separate taps of the OPT secondaries (the title of the thread). I'm not very educated about these matters (at all) and it was also clear that he posted the amplifier schematic so people could determine whether or not it was safe to use two separate output taps to drive two drivers in the same speaker system, separately but simultaneously.
Anyway. It's sorted now.
Anyway. It's sorted now.