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Post by itisonlyme on Jan 16, 2023 21:20:07 GMT 12
Grateful for any advice from anyone who understands what's going on with autoformers and bridged amps! I have speakers that are nominal 4 ohm and very low sensitivity ( 81.5 dB) If I wanted to bridge some amps to increase power to the speakers: it seems this is recommended using minimum 8ohm speakers . This seems to have something to do with bridging already lowering the resistance that the amps see. ?? SO, could i use an autoformer (like anticables sell) to increase the resistance the speakers see, and safely bridged amps? And I suppose... would i still get the benefits of bridging?? ![]()  
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Post by sadface on Jan 19, 2023 12:10:33 GMT 12
It looks technically possible to me however I'm not sure if it would give the results you hope for.
I can think of a few issues.
Sufficient power handling in the autoformer. Probably not cheap
Sufficient quality in the autoformer. Probably not cheap
I would guess that there will be a negative impact on sound quality.
What are the amp and speakers currently in use?
How much more power do you need?
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Post by michaelw on Jan 19, 2023 17:06:37 GMT 12
All the above plus yes, bridged amps usually sound worse.
Lose-lose
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Post by colinf on Jan 19, 2023 18:47:01 GMT 12
The load each amp phase sees is half when a balanced output stage is in use. The autoformer would increase the impedance the amp phases see. But the amp needs to be capable of the expected power output in order to have an increase in volume from the speaker. If the amp, assuming it’s one with zero output impedance and thus ‘perfect’ and capable of limitless power, balanced would put out 4 times the power of single-ended configuration. Unless it’s a Krell, most amps wouldn’t be capable of that.
AMR-iFi R&D
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Pundit
Post by peter0c on Jan 20, 2023 10:56:55 GMT 12
I have a circuit for bridging Quad 11 amplifiers, kindly provided by the manufacturer many many sleeps ago. I think it would be suitable for any p-p transformer coupled valve amp. PM me if you want a copy and want approximately 20 watts pc from two pairs of Quad 11s.
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Member
Post by itisonlyme on Jan 21, 2023 16:00:49 GMT 12
It looks technically possible to me however I'm not sure if it would give the results you hope for. I can think of a few issues. Sufficient power handling in the autoformer. Probably not cheap Sufficient quality in the autoformer. Probably not cheap I would guess that there will be a negative impact on sound quality. What are the amp and speakers currently in use? How much more power do you need? Thanks for your advice! Speakers are MBL 126 Amp is an int Plinius Hautonga. Drives the speakers well. No problems. Sounds great. Freakin awesome ( to my tastes) actually. I expect different amps to sound different - sorry A*dio Sc*nce R*view. So with no problems with my set-up, it's fair to say I'm just interested in exploring different set ups and synergies. But, trying to avoid the big Plinius, Krell, Emitter, Pass, Gryphon et al route. Tempting as they are, they don't suit my usage any more. Quality Class D - like Spec Corp and AGD are interesting. But dubious whether the affordable range -cough - Spec will drive my speakers. Golden Note PA series looks interesting - built in BTL mode Benchmark AHB2 ... same. Spec Corp too Bakoon, need BTL just to get 97W - and just one amp costs $$ Crayon looks interesting... not up in the 300W that MBL recommend, but, getting closer. And i think someone once told me " it's not all about the Watts" :-) Optimism bias comes in too ;p Hence why I thought, before i jump down a rabbit hole... You fullas might give me a reality check! kia ora.
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Member
Post by itisonlyme on Jan 21, 2023 16:03:27 GMT 12
All the above plus yes, bridged amps usually sound worse. Lose-lose Michael , why you always gotta be so brutally honest ?  it hurts. but is much appreciated ! 
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Member
Post by itisonlyme on Jan 21, 2023 16:10:08 GMT 12
The load each amp phase sees is half when a balanced output stage is in use. The autoformer would increase the impedance the amp phases see. But the amp needs to be capable of the expected power output in order to have an increase in volume from the speaker. If the amp, assuming it’s one with zero output impedance and thus ‘perfect’ and capable of limitless power, balanced would put out 4 times the power of single-ended configuration. Unless it’s a Krell, most amps wouldn’t be capable of that. Colin, why you always the smartest guy in the room?  Why is me wanting something for nothing so unrealistic? Your wisdom quashes my blind optimism... and I thank you for pulling my feet back onto the ground! Sincerest gratitude.
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Member
Post by itisonlyme on Jan 21, 2023 16:23:02 GMT 12
I have a circuit for bridging Quad 11 amplifiers, kindly provided by the manufacturer many many sleeps ago. I think it would be suitable for any p-p transformer coupled valve amp. PM me if you want a copy and want approximately 20 watts pc from two pairs of Quad 11s. Peter, Very kind offer thank you . I somehow screwed up a simple NCore kit build! I'll venture beyond an all in one unit, but in the world of electronics, I have learnt my place. (My Ncore amp latest 3 day and then ... nothing. No repair shop would touch it except one dodgy company, who when asked said they had experience with Class D, charged me, (twice) to fix it. Then wouldnt even return the dead amp so i could pass on the chassis i bought. ) my lesson one - don't buy 2nd hand kits off TM my lesson two - if reputable service guys say they cant fix it, don't bother with dodgy ones! maybe lesson 3 - asked advice from the kind folk on Darklantern before going down rabbit holes I don't understand enough about!
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Post by colinf on Jan 22, 2023 20:51:08 GMT 12
MBL 126, great speaker! The Hautonga puts out 280W into 4 ohms so should be ok for the recommendation from MBL of 300W. From the Plinius website: POWER 200 watts RMS per channel into 8 ohms. 280 watts RMS per channel into 4 ohms. Both channels driven from 20Hz to 20kHz at less than 0.2% total harmonic distortion Class D amps are getting better these days with GaN fet technology.
AMR-iFi R&D
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Member
Post by itisonlyme on Jan 23, 2023 14:31:26 GMT 12
MBL 126, great speaker! The Hautonga puts out 280W into 4 ohms so should be ok for the recommendation from MBL of 300W. From the Plinius website: POWER 200 watts RMS per channel into 8 ohms. 280 watts RMS per channel into 4 ohms. Both channels driven from 20Hz to 20kHz at less than 0.2% total harmonic distortion Class D amps are getting better these days with GaN fet technology.
6moons.com/audioreviews/spec3/2.htmgoody goody?
or wotever?
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