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Philips MFB speakers
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Fatmangolf View Drop Down
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Points: 8989 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jul 2021 at 6:22pm
Clipping mullimeter leads onto the top of R670 and bottom of R673 allows you to measure the dc millivolts across 1 ohm, which translates into the bias current in milliamps with no music playing. In fact I shorted the input before this. As I wrote earlier the amp should be allowed to warm up before the measurement and then R665 can be used carefully to set the bias current flowing through the output stage.
Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Fatmangolf View Drop Down
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Points: 8989 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jul 2021 at 9:08pm
Last weekend I used REW to take some readings from my RH544's using calibrated microphone. I don't want to measure the pleasure out of my old speakers like a certain science project forum. However the responses were pretty flat, the waterfall graphs showed subtle room modes not driver or cabinet resonances, and the THD plots were pretty good. And the sounds are realistic with detail, good instrument positioning and space.

Edited by Fatmangolf - 23 Jul 2021 at 9:10pm
Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Fatmangolf View Drop Down
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Points: 8989 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 25 Jul 2021 at 11:55pm
More listening to the natural sound, good stereo instrument positioning and depth. I tested the Philips drivers this morning using a Proprius amp, REW and my Majestic dac. I was surprised how low the squawker and tweeter distortion came out, about 0.25% for 90dB at 1 metre. Both are domed units. The woofer distorts more, 1 or 2% below 60 Hz, but it sounds solid and warm. And comes with 30 Hz extension thanks to the MFB design.



Edited by Fatmangolf - 26 Jul 2021 at 7:07pm
Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Fatmangolf View Drop Down
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Points: 8989 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jul 2021 at 9:46pm
I downloaded a Philips catalogue with their range of 1970's drivers and realised the tweeters in my RH544's are not the AD0160 stated in the service manual. Instead they are the AD0140 model. They are shallower and I checked their backs too. Curious but both models of driver have polycarbonate 'mylar' domes and the FR curves are close. Even so I am tempted to try a modern 25mm dome tweeter to hear the difference. It will have to be 8 ohms nominal impedance so the crossover frequency is unchanged and of similar sensitivity. Hmm...
Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Fatmangolf View Drop Down
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Points: 8989 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jul 2021 at 10:34pm
I have been going through lots of music and enjoying the sound of these old speakers. They are a real contrast with my GX300's with their clarity and presence. Today I thought the Dunedin Consort's Brandenburg Concertos were great through the RH544's, themusicians set back a bit like moving the microphones away or drawing the curtains in the recording venue.
Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Fatmangolf View Drop Down
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Points: 8989 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2021 at 10:09pm
I have temporarily fitted a pair of modern tweeters, Monacor DT-105, in place of the original AD0140's. I needed something similar in size and sensitivity, but without the dip from 5 to 10 kHz of the Philips tweeters. The extra detail is nice and overall I like the change which is easily reversible.
Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Fatmangolf View Drop Down
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Points: 8989 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 2021 at 4:58pm
I have changed the passive crossover frequency back to 4 kHz by replacing the 4u7 polester capacitors in my RH544's with polypropylene 3u3 capacitors. 3u3 was the original value and I have read the change was made to adapt to a different Philips tweeter. I used REW to measure the raw driver responses and their combined response with the crossover. Moving up has evened the midrange response and further improved the sound I am hearing.
Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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