The idea of the choke (it was a 4m7 iron core, FWIW) was to keep the inner driver active only at bass frequencies (avoiding any comb filtering) and gradually transitioning the outer driver loading from isobaric to closed box. The DA500 had the best sounding bass I've ever experienced from a loudspeaker.
OH, OK. I guess one can't really get the speaker cones close enough to avoid acoustic delays or breakup at HF. But now the gears are set in motion....
Lets take a speaker driver that has two voice coils on the same cone/magnet. (ie, zero separation cones)
We drive one with a current source amp sufficiently strong to overcome cabinet back pressure. Then a voltage amp (nominally a SET amp) drives the other voice coil to "SET" the sound pressure (a V source). Ah, but then we can just combine an I source Amp and a V source amp without problems, so we are right back to a normal speaker driver. So we can just make the cone twice as big instead.
Well, one might want to "tailor" the contribution of the I source amp to match the back effects of the cabinet. Probably a 6dB/Oct LF pass filter again.
Lets take a speaker driver that has two voice coils on the same cone/magnet. (ie, zero separation cones)
We drive one with a current source amp sufficiently strong to overcome cabinet back pressure. Then a voltage amp (nominally a SET amp) drives the other voice coil to "SET" the sound pressure (a V source). Ah, but then we can just combine an I source Amp and a V source amp without problems, so we are right back to a normal speaker driver. So we can just make the cone twice as big instead.
Well, one might want to "tailor" the contribution of the I source amp to match the back effects of the cabinet. Probably a 6dB/Oct LF pass filter again.
Last edited:
Lot's of dual VC speakers out there.
Have at it?
Interesting idea, but rather OT...
_-_-
Perhaps, but McIntosh made its reputation long before the age of even stereo!
There was little to compete with McIntosh in terms of power and quality at that time. Marantz was the other USA company that had developed a reputation for quality.
Of course there were other companies that made power amps. McIntosh patented that rather successful output stage design. That helped. There were other cathode coupled designs that predated. They're all shown in the Radiotron Designer's Handbook, if you want to look. McIntosh was commercially successful, which counts too.
Whatever subjective impressions one may have of the actual McIntosh product don't be confused, there is a difference between the commercial amplifier product(s) and what the patented output circuit can and/or will do.
_-_-
The schematic has swapped screen and control grids in the output. Wonder what other (deliberate?) gaffes exist in this schematic. I've seen essentially this topology before in an ancient copy of the audio anthologies without the cathode follower driver stage. (Not sure about the cathode feedback, whether it was present in the design I am thinking of) I can't see the values on the schematic clearly, but the basic topology looks OK.
People do wind transformers to order, none of the ones I use in my designs are off the shelf. This might be a bit trickier, but I imagine AJT could make some, and several European makers certainly can. PP transformers with cathode feedback windings are commercially available if somewhat unusual.
i make my own, so that is not an issue as far as i am concerned...
there seems to be a supplier of C cores in the states...Silicon Steel C-Cores / Goss C-Cores for 60 Hz and 50/60 Hz Frequencies
shipping to my side of the pond will be a killer...
i believe that for an added setup charge, Edcor can make one for you, although they use EI's...
btw, if your OPT has 0, 4, 8 and 16 ohm secondaries, then using to 4 ohm tap as center tap, then the 0 ohms and 16 ohm taps are available for cathode feedback...
Lundahl makes a 25% CFB OT:
LL1620CFB
http://lundahl.se/wp-content/uploads/2013/05/shortform_list1.pdf
and Plitron makes a CFB toroid, a Unity Coupled OT and Screen winding OT among others:
Tube Output - Specialist Range
LL1620CFB
http://lundahl.se/wp-content/uploads/2013/05/shortform_list1.pdf
and Plitron makes a CFB toroid, a Unity Coupled OT and Screen winding OT among others:
Tube Output - Specialist Range
Does it really improve sound? I am a little skeptical of McIntosh. They seems to be overly complicated. According to the paper of Vacuum State, they do it with simple CCS differential power tubes driving straight into OPT the conventional way.
I was looking at Plitron. How's the sound/quality compare to Lundaghl? So far I saw some high end amps use Lundaghl like Vacuum State. The Lundaghl LL1679 4.4K:4ohm seems to fit my needs for EL34 or KT88 with UL. It is $260 each. It's a C-core, so it's going to be a little losy than toroid. but It's going to take DC current more gracefully just in case any imbalance.
I think Plitron OTs are used in a number of high end amps. I haven't heard one. I did hear someone comment that they were so transparent, that one could not hear any OT effects, and the amplifier no longer sounded like a tube amp. I guess if you make it perfect, it sounds like SS like they say. They do have phenomenal bandwidth. And of course they will require a DC servo in most cases.
If I were going to make something like the Mac, I sure wouldn't use class B anyway. Getting the crossover distortion out is the 1st priority, so either some clever gm smoothing technique, massive NFdbk like they used, or class A.
A constant current tail only gives constant gm sum for bipolars. With P-P tubes, it will give a hump in the gm curve centered on zero. However, that would mean that small signals would be operating with near constant gm on the flatter center. That would seem to give a little compression with peaks, maybe not much. One of the big bonus's of low feedback setups that everyone touts is smooth saturation, so maybe it just widens that some.
If I were going to make something like the Mac, I sure wouldn't use class B anyway. Getting the crossover distortion out is the 1st priority, so either some clever gm smoothing technique, massive NFdbk like they used, or class A.
A constant current tail only gives constant gm sum for bipolars. With P-P tubes, it will give a hump in the gm curve centered on zero. However, that would mean that small signals would be operating with near constant gm on the flatter center. That would seem to give a little compression with peaks, maybe not much. One of the big bonus's of low feedback setups that everyone touts is smooth saturation, so maybe it just widens that some.
Last edited:
Unity coupled transformers will give you more HF bandwidth at the expense of significantly greater driver requirements.
Around here almost all of the industrial shaker table amps were industrial versions of the MC60 and MC75 amongst others.
McIntosh amps were used in audio testing labs because like more modern solid state amps they have somewhat lower source impedance, very good distortion performance compared to most tube amps and act somewhat more like an ideal voltage source than the typical tube amp. Several output transformer options provided a variety of impedances or voltage levels for driving specific loads.
They are actually quite good at driving things like Magneplanars and other difficult loads. The pair of MC-30 that I traded for in the early 1980s clobbered the Adcom GFA-2 I was using at the time.
Around here almost all of the industrial shaker table amps were industrial versions of the MC60 and MC75 amongst others.
McIntosh amps were used in audio testing labs because like more modern solid state amps they have somewhat lower source impedance, very good distortion performance compared to most tube amps and act somewhat more like an ideal voltage source than the typical tube amp. Several output transformer options provided a variety of impedances or voltage levels for driving specific loads.
They are actually quite good at driving things like Magneplanars and other difficult loads. The pair of MC-30 that I traded for in the early 1980s clobbered the Adcom GFA-2 I was using at the time.
So Lundahl it is. I am going to build a SS power amp also. I don't need a tube amp that sounds like SS. I just feel like tackling the tube amp first at this point.
I read the review in the article.http://www.vacuumstate.com/fileupload/dpa300B_brochure_lo_rez.pdf, They claimed it's better than SE, have to best of PP and SE. Vacuum State are very very expensive amps, if it's good enough for them, I am guessing it's good enough for me!!! It's not hard to do CCS tail. That I can actually try with or without relatively easy.
Now the question is whether I go with triode strap EL34 or UL. What is the ra of EL34 and KT88 in triode mode? How about in UL mode?
If the goal is output replicating the input, then yes. Very low distortion across the audio band, low and even output impedance. Not so much for Allen's amps.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.