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BPA300 Round 2
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Old 14th September 2011, 10:44 PM   #1141
regiregi22 is offline regiregi22  Europe
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But sorry for not answering properly; the BPA300 will be used with a preamp I diy-ed. It is a OPA627 with a BUF634 on its feedback loop, that way I can use it with almost any headphone too. I placed 50ohm in series with the line out, to mitigate capacitante effects of long cabling.
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Old 14th September 2011, 10:49 PM   #1142
regiregi22 is offline regiregi22  Europe
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Jeff Rowland? Wasn't Bridge-Parallel configuration of LM3886s standard practice of the manufacturer's white papers?
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Old 15th September 2011, 01:04 AM   #1143
tryonziess is offline tryonziess  United States
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The LM3886 is a fabulous invention. It has been used in many applications where it probably should not have been used and succeeded flawlessly. We must at first consider that this is a monolithic device on a rather limited footprint. There are a plethora of circuits in this small device ie, preamp, output section and staibizing circuits all which must be cooled by the external dimensions.
If this chip is properly implemented it will surpass many a discrete design. We must not try to incorporate it into amp layout where it was not ment to go.
DIY types like us will always be pushing the envelope to achieve more performance from an item than the design engineers ever expected.

I like the Jeff Rowland clone layout and with adequate heatsinks and frugal expectations this BPA 300 amp will surpass many properly designed discrete amps.

Using a well designed an robust power supply with limited DC voltage into a sane load any DIY can have a world class amp at very affordable monetary outlay of currency.

I must again applaud Alexw for his gift to this community. Without the many hours of study and trial and error we would not be building this nice amp.

Now if we want a truly superior amp driving difficult and insane loads the Marshall Leach amp can not be beaten.

I would couple the BPA to a nice high treble speaker system and bi-amp with a discrete unit in the middle and lower end.

Tad
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Old 15th September 2011, 05:48 AM   #1144
Munga is offline Munga  Australia
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I don't suppose anyone has 4 of these boards they would be interested in selling me do they?
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Old 15th September 2011, 10:42 AM   #1145
bcmbob is offline bcmbob  United States
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Hey Tad,

Here' s an outline of my project that is similar to your suggestions. The first photo is a set-up rig to test and compare the BPA150 to the MyRef.

Click the image to open in full size.

This is the proposed layout of the two amp types combined on one level. All the transformers will be encased below, either by themselves or with the BPA power boards also on that level. I'm taking this approach to simplify outboard cabling between amps and Xover - keeping amp/s ins and outs on one level..

Click the image to open in full size.

The sandwich is completed with a dbx 234 crossover on the bottom (to allow BPA/MyRef heat sink ventilation) on the lowest level. The active crossover has a "Low Sum" mode that can be used to drive a single Hefler DH-120/Sub for a full three way configuration.

Click the image to open in full size.

Initially, this whole system is attended to be used in a rack mount (the layout board is the standard 17" W for racks) home studio setting and not for a "living room" audiophile approach - but who knows - I'll see what sounds best after testing and comparisons.

Suggestions Welcomed!
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Last edited by bcmbob; 15th September 2011 at 10:48 AM.
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Old 15th September 2011, 04:25 PM   #1146
tryonziess is offline tryonziess  United States
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Munga, Let me scrounge around in my parts box. I think there are some of these boards in there. I know for sure that I have 4 of them stuffed already I would be willing to part with. I initially bought 10 of the boards.

Tad
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Old 15th September 2011, 06:52 PM   #1147
bcmbob is offline bcmbob  United States
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BPA-150 test rig wired and ready to audition.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.


Click the image to open in full size.

Will report back on results and comparisons this evening or in the morning. Sorry for the super el-cheapo posts - better stuff on order.

Regards,
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Old 15th September 2011, 10:14 PM   #1148
tryonziess is offline tryonziess  United States
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bcmbob, Where did you get the power supply pcb's. They make for a nice clean professional layout. Are you going to keep the heatsinks inside the cabinet or have the fins exposed to the outside? I think a small fan would be very beneficial here.

Have any of you gone to the diy forum site BPA300 built and measured by Alex. He also has a website with a plethora of good stuff. I think it is shine7.com or something close. He has done a great deal of work with this board including the transformer splitting input signal and some other really cool stuff.
The original Jeff Rowland Consort10 or whatever got really good press with this setup. The interior of the amp is awesome to say the least. I think the pcb's are 3d. At least they look that way from the photos. One real class act. Alex has some good shots on his website.
There are also some good builds utilizing the LME frontend chips which gives you the choice of monolithic frontend and discrete output section. These also have fabulous specs. You can use the same power supply and experiment.
For me now I am going retro with tubes and all. I want to see what all of the hoopala is all about. I love working with 850 volt circuits. Kind of like parachuting but never leaving the ground.

Remember what your friends see is the chassis and cabinet. Spare no expense or time making it looooook GOOOOOd.

Tad
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Old 15th September 2011, 10:40 PM   #1149
bcmbob is offline bcmbob  United States
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Default I should have known!!

Early but clear verdict.

I set up the BPA-150 rig on the big three-way Sunflowers with my modded PS1 as a source playing through the Lightspeed attenuator. The sound again was clear, extremely well defined and balanced.

On Spyro Gyra "Road Scholars" track 2, I thought I had a problem when I heard a muffled static, and was about to pull the plug when I realized it was the background singers clapping. I've played that CD forever and never heard that (or noticed it) in over six years.

Next I played Nancy Wilson's "If I Had My Way". This CD is very tricky - meaning if a system has any tenancy to produce syllabance (that super sssse distortion) this album will bring it out in spades. The BPA was as clean and free of this type of distortion as anything I have owned. I'm getting excited now!

The third piece was the Vienna Philharmonic playing "The Ride of the Wolkure" on a London Digital Disk. Everything was balanced from top to bottom and again, the stage presentation reminded me a lot of what one hears with headphones. Very precise and deep with no hint of horizontal pitch-dependent shift
.
At this point it dawned on me that with three LM3886s working (six actually), I wasn't getting a higher SPL. I have always twirled the LDR attenuators close to max so it was time to introduce some gain. I replaced the Lightspeed with a Carver C-1, using Aux 1 input and all tone control switched out of circuit. Got all the volume I could ask for and still almost as clean as the LDR attenuator. The slope of the volume knob on the Carver is, by design, gradual up to about 12:00 and thereafter much more active. Set at 2:00 gave me just under "loud" - what I interpret as an "in the band" experience. I was listening to a very accurate, balanced and well defined system.

To do the first MyRef comparison, I just turned everything off without touching any knobs and switched in the V1.3 amp. Wanna guess??

The piece was "Rob McConnell & the Boss Brass".

The MyRef-C “BLEW ME AWAY” I was instantly transported into the recording studio – No Bull !!
Not too much of an exaggeration, but the sound of the stick on the cymbal was there but I could also see what color shirt the drummer was wearing. That description is really quite accurate. I heard the difference between listening to an excellent system compared to having the impression of being in the room with the musicians. I am continually and absolutely amazed at what the MyRef-C is capable of. So the comparison results are – there is no comparison. The MyRef ,IMHO, is in a league far above the majority of amps I’ve heard – both DIY and many “Audio Boutique” offerings.

I still intend to complete the bi-amp/tri-amp studio build but that is a completely different animal. The BPA-150 will be a good fit for the mid frequencies in that system.
Be sure to understand that I feel anyone who sticks with the BPA approach will be more than pleased with the results. For a bedroom or small home studio, the BPA is an excellent choice. This is - after all - the BPA thread and I have no regrets, and learned one heck of a lot building these amps. The ability to push a variety of loads is a real plus for the multiple LM3886 design and I would not hesitate to use in again. I'll post when the studio build is complete.

Regards,
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Last edited by bcmbob; 15th September 2011 at 10:57 PM.
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Old 16th September 2011, 12:13 AM   #1150
bcmbob is offline bcmbob  United States
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Hey Tad,

Both the boards came from the same place on eBay. Check back at post 1130 in this thread for direct links.

For the heat sinks, I bought two 10"x3"x1.25" pieces from Heatsinks USA and cut one down to fit the test build. The single aluminum plate in the earlier pictures took all six LM3886 chips and never went above 110F/38C, so my first design was over built. The final case will have openings below and above the heat sinks. You probably didn't notice but there is a quarter inch gap between the bottom of the heat sink and the mounting plate that will help with air flow. I might mount them external if there is a heat problem.

I also read all the stuff at Shine 7 and that's how I got interested in the BPA design. That is indeed a good site. I originally expected much more immediate power with the 150 rating but learned subsequently that the higher number has more to do with driving different loads and not so much raw power. Still an excellent amp design.
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