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Old 3rd October 2012, 08:06 PM   #1
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Default Reverseengineering an HK_Ottala

Power amps are something very close to my music heart.

I have quite a lot of them around here, Zen in different versions, Accuphase, own designs etc, and my favourite for the latest few years, an ML11, the last power amp Tom Collangelo designed, a magical little amp that can drive anything and equiped with quite a lot of power despite its modest sepcs.

As all Mark Levinson amps it has a certain sonic signature, leaning towards the darker kind of voice, never bright but with brutal transientresponse and attack when delivered such.

A while ago, rather long while actually, i traded a pair of JBL HF drivers and horns for an interesting amp, as i if i needed more of these.

Click the image to open in full size.


Utterly sophisticated design, B&O has something to learn here,.
But to the reason i wanted it. This amp is designed by Matti Ottala during his time as chief engineer at Harman Kardon.

The information ive got says it was designed as a prototype for the Citation XX project and the same story/rumour says 3 or 5 of this amp was built at HK workshop.

The amp is among the best ive ever heard with an extreme lightness combined with unbelievable power and transientresponse , a "sharp" voice but still not bright, drives anything ive loaded it with the same ease.

One major flaw, as an extremely wide bandwith amp it is very prone to amplify and distribute to speakers any wire or airborne signals in the vicinity.

Fabulous buildquality.

Click the image to open in full size.

So, i will dismante this amp, primarily for replacing wiring and also check/replace caps and find the right place to insert lp filtering to
avoid interference.

If there is interest in recreating this fantastic amp, it actually is just that, among the best ive ever listened to, ill start a thread reengineering the amp and se what we can end up with.
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Old 6th October 2012, 05:19 AM   #2
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I have been a fan of the Otala designed KH amps since I bought a HK 750 integrated in the late '70s early 80s. It was a wonderful sounding amp.

I for one would love to see you put the circuit for this up for the consideration of the diy fraternity.
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Old 6th October 2012, 10:55 AM   #3
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Quote:
Originally Posted by ingvar ahlberg View Post
Power amps are something very close to my music heart.

I have quite a lot of them around here, Zen in different versions, Accuphase, own designs etc, and my favourite for the latest few years, an ML11, the last power amp Tom Collangelo designed, a magical little amp that can drive anything and equiped with quite a lot of power despite its modest sepcs.

As all Mark Levinson amps it has a certain sonic signature, leaning towards the darker kind of voice, never bright but with brutal transientresponse and attack when delivered such.

A while ago, rather long while actually, i traded a pair of JBL HF drivers and horns for an interesting amp, as i if i needed more of these.

Click the image to open in full size.


Utterly sophisticated design, B&O has something to learn here,.
But to the reason i wanted it. This amp is designed by Matti Ottala during his time as chief engineer at Harman Kardon.

The information ive got says it was designed as a prototype for the Citation XX project and the same story/rumour says 3 or 5 of this amp was built at HK workshop.

The amp is among the best ive ever heard with an extreme lightness combined with unbelievable power and transientresponse , a "sharp" voice but still not bright, drives anything ive loaded it with the same ease.

One major flaw, as an extremely wide bandwith amp it is very prone to amplify and distribute to speakers any wire or airborne signals in the vicinity.

Fabulous buildquality.

Click the image to open in full size.

So, i will dismante this amp, primarily for replacing wiring and also check/replace caps and find the right place to insert lp filtering to
avoid interference.

If there is interest in recreating this fantastic amp, it actually is just that, among the best ive ever listened to, ill start a thread reengineering the amp and se what we can end up with.
Would be great if you would reverse engineer, do go ahead. If this amp is related to the xx I might be able to help as I have some parts of schematics for it. The design is indeed very interesting, many claim this was and will still hold as one of the best audio amps ever, as scarce as hen teeth. I lack the outputstage circuit and maybe some minor details regarding the inputstage.
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Old 6th October 2012, 11:13 AM   #4
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More pics please, lots more - there definitely will be some wiring layout tricks which make-up the design and amp's sound/performance.

Please
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Last edited by s3tup; 6th October 2012 at 11:16 AM.
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Old 6th October 2012, 09:22 PM   #5
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[QUOTE][ do go ahead/QUOTE]

Will do that then.
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Old 7th October 2012, 12:00 AM   #6
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Quote:
Originally Posted by ingvar ahlberg View Post
Power amps are something very close to my music heart.

Fabulous buildquality.

Hi Ingvar,

The physical construction of your amp is very similar to several Krell and Nelson Pass Threshold designs that include:

1) Separate PCB attached to heatsink for the high heat output transistors and Re resistors.
2) Separate PCB on heat-isolating riser posts attached to the output PCB. Heat kills! Avoid putting input devices close to Hot Outputs. Some riser posts can serve as electrical connections. e.g. a mechanical star ground path.
2b) Using ThermalTrak outputs with integrated temperature sensing diodes reduces the chance of oscilation with a separate driver PCB over a transistor Vbe multiplier. The Leach Amp document discusses this.
2c) Output stages seldom change. Using a separate input stage PCB simplifies testing new driver circuit ideas.
2d) Dr. Keith Johnson (Go Stanford Cardinals) of Spectral favors putting the driver PCB at 90 degrees from the output power PCB to minimize the coupling of magnetic fields from the high current outputs from crossing into the low noise inputs. Just sketch the magnetic field lines from the high current outpu bus traces and keep the input circuits at a safe distance. Spectral uses a metal can over the JFET intput circuits for further mag shield and temperature stabilaztion.
3) Output power supply capacitors directly next to output terminals in order to optimize common star ground and feedback with speaker R-L-C complex impedance load.

4) The Magtech construction(jpeg) uses very large PCBs and wastes some heatsink length for a clean physical construction plus a simple case construction. Power Capacitors are under the PCB attached to output terminals. I think 4-ounce copper PCBs or soldering copper bus bars to the PCB would be necessary to carry the high currents.

Hope the pictures add to your thread discussion.

:-) It is not nasty to build a 3-way amplifier into one case :-) Bass+mid+tweet
Attached Images
File Type: jpg Krell1.jpg (60.5 KB, 161 views)
File Type: jpg Krell2.jpg (50.1 KB, 106 views)
File Type: jpg Threshold.jpg (67.0 KB, 107 views)
File Type: gif Magtech_inside.gif (64.9 KB, 100 views)

Last edited by LineSource; 7th October 2012 at 12:16 AM.
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Old 8th October 2012, 04:52 PM   #7
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The Magtech amplifier look very beautiful. It's very powerful, BW = DC ~ 100KHz, SR = 500V/uS, 500W/8R... do you have schematic/service manual?

Last edited by Walkalone; 8th October 2012 at 04:57 PM.
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Old 8th October 2012, 06:02 PM   #8
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Quote:
Hope the pictures add to your thread discussion.
Everything, allmost, adds to my threads.
The orderly look of these fine amps are nice and thats one reason im dismantling it, to tidy up and wire it with, at least, some concern over interference issues, also replace caps as it getting on in years.

The interior actually looks just like my workshop, a bit like if i did the latest tidy up with a handgrenade.
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