across the bench [season-2] the electron strikes back

[sae-7125]

for season-1 [diy location]

audiokarma.org/forums/threads/across-the-bench-an-electronic-menagerie-of-diagnostic-oddities-plus-photos-and-design-analysis.1061536/

taking a walk on the wild side with "general audio" location.


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first noteworthy item, the entry cost of thermal camera technology in y26 of this millennium/kiloannum. using the holocene calendar we would be looking at 12026 vs 2026.

en.wikipedia.org/wiki/Holocene_calendar


youtube.com/watch?v=xAxj7dZLgR4



nice comparison of devices tested, and current pricing. something with 30hz refresh rate or higher would be a good idea.

the season-2 thread will be more of the same vs season-1, lots of photos and thermal images plus random filler. a rather large backlog of photos has accumulated and sorting what makes the grade will be a challenge (digital spring cleaning).

a few cliffhangers to resolve first on the list though. including classe, musical fidelity, primare and vincent brands.

 

[sae-7125]

picking up from the previous thread:
audiokarma.org/forums/threads/across-the-bench-an-electronic-menagerie-of-diagnostic-oddities-plus-photos-and-design-analysis.1061536/page-77#post-18168852


classe audio seventy, power amp

diyaudio.com/community/threads/questions-to-classe-audio-model-seventy-70-power-amplifier.420349/
*basic photos and schematic


checking out power cap info and physical measurements for possible upgrades


lots of axial caps that need updating/upgrading

this "potential" project is sitting on the sideline. possibly due to a recent acquisition involving a sansui ba-5000 that needs some work.

Sansui BA-5000 Amplifier Repair & Review | LiQUiD AUDiO

Happy New Year everyone and as promised, here is my article about the beautiful, incredible, unobtainable Sansui BA-5000 power amplifier.

liquidaudio.com.au

*difficult to ignore a faceplate like that, hello back brace when lifting

doesnt look like i did a thermal analysis on the classe or at least didnt take/save any images.

so, on to the next loose end which will be the a1008 integrated amp. seems to be a proprietary dead end in regards to diy repair potential.

 

[sae-7125]

https://musicalfidelity.com/uploads/manuals/English/a1008int.pdf

taking a look inside the dynamic duo, power supply and integrated amp


a lot of activity for a simple outboard power supply. this one was modified by another bench out in the world due to a power button issue on the integrated amp chassis.


nice amount of spacing between hot spots and power caps although the electrolytics near the glassware are of concern. digital daughter board on top is easy to remove, this system has an issue with digital as well.

 

[sae-7125]

the power cables between boxes seems a bit cumbersome


and the fun begins, with a 12F683 pic (Peripheral Interface Controller)

https://ww1.microchip.com/downloads/aemDocuments/documents/MCU08/ProductDocuments/DataSheets/41211D_.pdf

PIC microcontrollers - Wikipedia

en.wikipedia.org

factory/custom programmed pic in the power supply box is just the tip of the proprietary iceberg. the hardware might be easy to source and replace but the programming contained within can brick the system at any time.

 

[sae-7125]

removed the front panel to inspect the power switch


simple construction with a thick chunk of metal that should not warp over time


face plate button assembly seems straight forward. no plastic or springs nor complex sub-assembly.

resistance checks with the various switches measured ok, reflowed some solder connections just in case.

 

[sae-7125]

digital board removed


main board and what is under the digital board

 

[sae-7125]

the other custom programmed mystery box, primary controller/cpu. starting to look like the prime suspect for power button function issues. another issue being the digital board, non-functional or at least no pleasant output possible. almost as if one of the digital board flatpack chips has a clock issue or something. a few lanes of communication connect from the digital board to the primary cpu.


underside of the main board can be accessed without disrupting the output transistors, bit of a mess either way. high voltage tube power supplies in the front behind the face plate.


watching the idle numbers after warm up via the usual digital hunchback dim bulb test fixture (bulb mode off)

 

[sae-7125]

some thermals to round out the inspection


overall the filter caps are outside of the high heat zone with a few small diameter exceptions. need to do 1 hour idle with the chassis fully assembled to get a better idea as to the oven effect.

the amp section is functional and input selector (plus LEDs) seem to work. phono section works as well so the only limitations for this system are the main chassis power/standby button and the entire digital input array. probably make a decent garage/barn system since the outputs still pack a punch. slumming it with a tube flavored hifi integrated, oh the horror.

next...

 

[sae-7125]

primare 30.5 five channel amp made in sweden. pile of "spoiler alert" sitting on left side of the photo.

Primare A30.5 Five Channel Power Amplifier; A-30.5

Buy, sell, and trade thousands of pre-owned audio gear. All tested, certified, and backed by our Certified Pre-Owned Risk-Free Guarantee, with expert HiFi guides to help you at every step.

tmraudio.com

*more photos

https://www.primare.net/wp-content/uploads/2017/06/A30.5-user-manual.pdf

nice amount of ventilation which helps

https://audiocircuit.dk/downloads/primare/Primare-A30_5-pwr-sm.pdf

 

[gadget73]

thats a questionable font choice. I read that as "Blasse Audio" which is not quite a ringing endorsement of either the audio quality or their ability to spell.

"
blasé (comparative more blasé, superlative most blasé)

1. Unimpressed with something because of overfamiliarity. "

View attachment 3735685
classe audio seventy, power amp

 

[sae-7125]

thats a questionable font choice.

some days i do wonder if a marketing dept was involved and if any consultations existed prior to the initial production run. although these days "anything goes" regardless of consumer perception.

the first letter looks like an overinflated letter "P" which makes even less sense. hifi gear has nothing to do with a sierra nevada resort/campground. battery pack plus class-d integrated amp (with bluetooth aptx-hd input) and portable speakers is a tent friendly solution though.

Campground | Plasse's Resort

Visit Plasse’s Resort at Silver Lake in the Sierra Nevada Mountains. Enjoy camping, hiking, fishing, kayaking and many other activities while taking in the fresh Alpine air and the breathtaking scenery.

www.plassesresort.com

interesting to see the evolution of business names and product model font/cosmetics. probably a thread somewhere catering to brand names over the years.

The History of Fonts That Built Big Brands - Artiveko Studio

Typography has come a long way from carved letters on stone to slick, responsive fonts we use on websites, apps, and packaging today.

artiveko.com

The Evolution of Brand Typography: Trends Every Designer Should Know in 2025

Discover the evolution of brand typography and current trends every designer should know in 2025. From historical context to cutting-edge design innovations.

www.fontinlogo.com

 

[sae-7125]

chassis could have been a better design, rear panel not removable. cheap plastic rca-inputs are delicate, ended up installing chassis mount inputs. three of five toroids in the photo, other two set outside of chassis to make it possible to remove main board assembly. not an easy to service design and thats before we look at the smt/smd areas.


stock board with blue power caps, lots of under-board potential and it will be utilized.

system initially came in for a low cost inspection and assessment due to a channel or two being down. after replacing a fuse and reinstalling a toroid output wire harness removed by a previous owner things progressed into the testing stage. most of the dc offset servo's were reasonably capable but that deteriorated quickly soon after, when the amp went home and the new/current owner starting exercising some hours on it.

amp came back to the shop for a revised inspection and possible upgrade options (modz to the max, is it worth it type of thing). the upcoming photos and analysis will shine some light on what was found and the final outcome i.e. design flaws and all plus soic-8 surgery.

 

[sae-7125]

main board extracted from chassis. multiple inline cylinders wonder if its petrol or diesel, miniature version of a lake freighter propulsion system.


took a while to figure out a convenient way to test the amp outside the chassis. jumper wires needed to connect amp outputs to binding posts for easy speaker connection. amp channels 2 and 3 shown connected after doing the recap.

one glaring design flaw other than chassis headaches would be the shoulder-to-shoulder output transistors. thermally stepping on each others toes, wonder which channel outputs get cooked the most when exercising all five.

 

[gadget73]

wow thats definitely packed in there. Some things are just not built to be worked on easily.

Guessing the basic design like 5 mono amps stuck in one box, each with it's own power supply?

 

[sae-7125]

Guessing the basic design like 5 mono amps stuck in one box, each with it's own power supply?

correct. basic cookie cutter clone layout for the bulk of the design.

would be interesting to do a txf delete and piece together five 300w GaN smps modules or diy something similar.

 

[sae-7125]

back in the chassis after the cap upgrade, power caps from 10000uf now 15000uf which is limited by height and availability. a few other supply caps bumped up not to mention converting the four small electrolytics mounted near the heat sinked regulators (way too close) over to film and now under the board.


side profile before the chassis mounted inputs were installed. bit of a pain to unbolt things and the binding post connections take time.

 

[sae-7125]

removing surface mount op-amp servo chip, mc1458 and its unique specifications. one of five channels shown above, ch-2 specifically. which happens to be labeled u2, sunday comes to mind for some odd reason.

https://www.st.com/content/ccc/resource/technical/document/datasheet/af/f7/9a/48/2e/cf/43/f5/CD00000472.pdf/files/CD00000472.pdf/jcr:content/translations/en.CD00000472.pdf

https://www.digikey.com/en/products/detail/stmicroelectronics/MC1458IDT/6579062

*supply voltage (max) and operating temp for the mc1458dt is the starting point. upcoming thermals will show a design flaw, hint: 70c/158f. when shopping around, how many op-amps have a +/- 22v voltage rating? the slew rate is nothing special (0.8v/us) although chances are it doesnt need to be. further testing/experiments might shed some light either way, hello circuit sim.

the mc1458idt was selected as replacement for all five channels, for obvious reasons. there are some surface mount zener diodes that feed the +/- chip supply which reduces 53v down to 21-22v. the zeners should have been a couple volts higher so that a higher grade op-amp could be universally dropped-in or something. rail-to-rail chips do exist and can provide 18v of offset.

when the channels were slowly flaking out due to heat/ageing into retirement, the unloaded outputs were showing 5v (chip issue) or -16v (+reg issue) of offset (volts, not milli-volts). when loaded with dim bulb active the output protection relay would start to toggle on and off e.g. circuit issue detected.

root cause for ch-2 appeared to be a weak +voltage regulator, unloaded it could barely do 4v. after researching the op-amps it is no surprise that ch-4 was flaking out and the regulator was fine. these are just the tip of the iceberg points of interest regarding this amp...

 

[sae-7125]

and now, about that smoking gun of the design. a view from a different spectrum of light.


this is an unhealthy channel. it also helps that there are neighboring channels to compare.

 

[sae-7125]

this is what a healthy/functional channel looks like. balance for both hot and cold running devices (+/- rail pairs)


and now a repaired and updated 5 channel amp after some exercise with a transducer array treadmill (8r 120w, 4r 200w). the patient has a pulse and is able to climb stairs less than an hour after multiple operations.

note the line of fire near the back wall of the chassis. its always hot even at idle and nothing connected, average temp around 160f/71c. so comparing the op-amp chip environment max temp of 70c vs 71c, i wonder if operational lifespan will be affected. these repairs are not accidental, just more design flaw maintenance that will happen to all of these systems, would be my guess.

next...

 

[sae-7125]

vincent integrated amp with tube front end


vincent sv-236mk

Vincent TubeLine SV-236MK integrated amplifier Specifications | Stereophile.com

Sidebar 1: Specifications Description: Tube and solid-state, remote-controlled, two-channel integrated amplifier with six line-level inputs. Tube complement: three 12AX7. Maximum output power outputs: 150Wpc class-AB into 8 ohms (10Wpc class-A), 250Wpc class-AB into 4 ohms. Frequency response...

www.stereophile.com

Vincent TubeLine SV-236MK integrated amplifier Measurements | Stereophile.com

Sidebar 3: Measurements I used the top-of-the-line Audio Precision SYS2722 system (see the January 2008 "As We See It" and www.ap.com) to measure the Vincent SV-236MK; for some tests, I also used an Audio Precision System One Dual Domain.

www.stereophile.com