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Hovland HP200 Preamplifier upgrade

 

Despite a generally good design and very good parts selection, some items were overlooked. (XLR board for example felt like as an afterthought)

 

  • Added a bypass on the power supply

  • Added regulation to the balanced board

  • Changed coupling capacitors

  • Added damping to the chassis

  • deleted transistor buffer on RCA output 

 

Krell showcase amplifier (3 rebuilds, picture combined from all units)

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Full recap done (using heavy duty parts and mostly 105 degree Celsius long life caps)

 

  • Power supply section went from 80,000uF to 120,000uF (50% improvement)

  • Preamp section bypass capacitor changed from 33uf to 82uf (250% improvement)

  • Amp section 33uf capacitors replaced with 220uf (660% improvement)

  • Feedback capacitor changed from polarized electrolytic to audiophile quality "Nichicon muse" non-polar (the green one in the pics)

  • Input capacitor removed for direct coupling connection. (Krell products have coupling caps input still bugs me. A sonic bottleneck!)

  • Power supply mods to remove heat stress issue and improve long term reliability (In stock form, driver board runs 24/7 causing much of the issues associated with long term reliability) After modifications, the amp now draws ~10watts from the wall outlet versus ~75watts.

Krell 300CX

 

  • Switchable 240VAC, using 240V feed. 

  • Full recap done (127 or so capacitors replaced) - see bulged stock Panasonic capacitor on picture 2)

  • New high end resistor in signal path added

  • Internal fan added for capacitor longevity. The inside temperature actually dropped slightly more than 20°C or 68°F.

  • New high performance discrete rectifier installed. (extra soft recovery)

  • Speaker wire changed to 99.999% (5N) solid core silver wire 

  • New Hubbell power plug (stock was hardwired 240v in)

  • New custom length power cord added

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Despite having multiple amplifiers throughout the years, this remains as my ultimate reference! ( now sold)

Musical Fidelity Phono Stage

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  • New outboard fully regulated linear power supply added

  • Full recapped. Replaced the stock Jamecons to Nichicon KA’s

  • Upgraded op-amp

Benchmark Media DAC2 HGC

 

  • Onboard power supply (SMPS) replaced by an outboard fully regulated linear power supply, with a new connector in place of the 120V IEC inlet.

  • Elna Silmic II local bypass added inside the DAC in addition to some Panasonic FM’s.

  • Damping added

  • A few local bypasses here and here.

  • DC coupled (stock is not)

 

Whilst the stock unit was good, after my modifications…it became outstanding!

Kef LS50

 

A worthy speaker, and a great candidate for the following upgrades:

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  • New speaker wire (99.999% silver on the tweeter)

  • A new crossover design for both the tweeter and woofer

  • Mundorf Supreme silver+oil capacitor on the tweeter and foil inductor (2nd order LR crossover)

  • Foil inductor and Jentzen capacitor on the woofer (2nd order LR + compensation added)

  • Internal damping changed as well

 

The soundstage became much wider than the original design and more open with better detail.

 

The controversial Hifiman HE-6

 

Historically hard to drive headphones, never use with sub-par amplification which makes your ears bleed.

 

  • Stock cable replaced with braided cooper to a 99.999% solid core silver wire.

  • Rear dampening and dust protection fabric removed.

  • Internal dampening added and fine tuned by ear.

 

Now these are more open, with lifelike bass and midrange. Treble is much more airier. 

Overall…success!

Krell TAS Amplifier

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  • Now working on 240VAC (switch inside)

  • Complete board recap with Nichicon HE capacitors

  • Main power supply caps replaced with 380LX caps (much higher uF’s)

  • Input buffer redesigned from balanced line receiver (3 generic quality op amps classic design) to single chip. Top of line 1200 series balanced line receiver.

  • 5N silver wiring for the input.

  • No more input capacitor (stock version used sub-par Wima MKS4)

MiniDSP 4X10HD 

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  • Stock generic caps replaced with the excellent Panasonic FM’s.

  • Removed both the input and output DC blocking capacitors (DC offset remains below 9mVdc)

  • Added an over sized external power supply (7 Ampere double regulated and 80VA toroid with significant uF reserve bank)

  • Dampening added everywhere

  • Power switch added on the DSP (for convenience)

  • Opamp upgrade to AD8599 (changed one on top, the one underneath left stock as I had not enough room to change them)

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- Last 2 pictures from a fellow DIYer that I've corresponded with. He used shielding and went crazy on main PSU bypass with Mundorf caps. He claimed great result with those 2 extra steps. (he copied most mods I has already done and kept wanting to improve the SQ)

Dynavector P75

 

  • New chassis

  • New linear power supply replacing the stock SMPS

  • More bypass all around

  • AD797 op amp upgrade (on dual socket)

Behringer NU3000

 

Class D amplifier

Inexpensive and very poor sounding per stock form.

 

  • Removed input filters and mono switch.

  • Upgraded the op amp.

  • Upgraded the power supply (input section).

  • Replaced the speakon connector with traditional 5 way terminal.

  • Installed an RCA input socket

  • Bypassed the volume control

  • Changed the stock fan to a much more quiet one.

  • Added heat sink on the SMPS (new fan has less air flow)

 

Whilst the amp remains lower in the quality scale, the sound significantly improved.

 

Parasound A21 Power Amplifier

 

  • Added fully regulated power supply for the input and driver stages

  • New nichicon gold tune power supply capacitance (KG)

  • EMI filtering added

  • Added a high-performance double rectifier (discrete style)

  • Significant bypasses added

  • Signal purity achieved by removing input gain, resistors and relays. Mono switch and input buffer and added silver input wire. 

  • Critical dampening of the chassis

  • New output speaker wire (instead of a long PCB trace)

  • Ceramic fusing

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This resulted in a much better amplifier than stock version. Good controls on bass and midrange. 

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Krell KAV-400xi

 

  • Full recapping using audiophile grade Mundorf and Nichicon KA&ES

  • Installed soft recovery rectifiers

  • Chassis dampening added.

  • EMI filtration added

  • Silver wiring on the output

Roskan XPS1 Power Supply

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The original unit had a decent sinewave generator but poor output module to drive motor.

  • Replaced original output module with a gainclone module

  • Lm3886 gives an output impedance of 0.2 ohms (limited by protection resistor) and has drive to spare.

  • Fully adjustable (0.5Vac-25Vac output capacity)

  • Set at 16.5Vac as per Roskan specs

Yulong D100 DAC

 

  • New sockets installed to allow operational amplifier swap

  • Currently using the Analog Device AD8599 (all 4 opamps)

  • Power supply capacitors changed to Elna Cerafine (nos)

  • Bypass power supply scattered around.

Audio Research SP8

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  • Complete Mundorf capacitor upgrade

  • Local bypass added (Mundorf on the high voltage)

  • New CRC heater supply with better regulator

  • Wiring upgraded

  • Augmented linestage feedback to reduce gain. As a result, the output impedance dropped.  (customer request lower gain)

Analog Acoustics – Asian entry level tube amplifier

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  • The stock unit ran incredibly hot (12.5watts per output tube that are rated at 12watts. Poor design choice. I dropped dissipation to 10watts for long term reliability and almost no audio power loss)

  • Changed all cathode caps to Nichicon KA’s

  • Changed coupling caps to NOS Auricap

  • Added 330uf on the power supply (100% improvement)

Denon POA Monoblock - refurbished

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Done on a budget and retained as much stock component as possible.

  • ​Installed a high quality Holton Precision 500w/4ohm module

Bryston BP1 

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  • Modified the power supply caps (more than doubled the amount of microfarads)

  • Added a new feedback capacitor

  • Now DC Coupled!

 

Symphonic Line Preamplifier (previously updated the matching power amp but forgot to take pictures.)

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  • Upgraded the power supply caps (>2 x the micro farads and tripled it in some areas, using mostly Elna Silmic capacitors.)

  • Added a new feedback capacitor

  • Removed the transistor buffer stage (not needed)

  • New top of line AD797 opamp used

  • Equalized the power supply draw

  • Added main line filtering

 

Melodious Audio MX-U8

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USB to SPDIF ASE/EBU bridge. Highly recommended. 

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  • Upgraded power supply caps (roughly doubled the amount of micro farads and removed the stock "fake" capacitors)

  • New bypass capacitors

  • Dropped LED display intensity (much too bright)

  • Lots of internal dampening added (crystal oscillator and transformer)

  • Upgraded the rectifier bridge and added EMI filtering.

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Note: The unit is very receptive to "feet" tweak. I used DIY bamboo feet, but depending of your rack and overall system, it may not be your best option. 

 

Krell HTS 7.1 Preamplifier (internet photo)

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  • Complete recap of power supply board and analog boards with 7000hrs Panasonic FR’s  on the analog boards

  • CDE caps for the analog power supply.

  • Added over-sized power supply capacitor

 

Parasound D3 Player

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  • Partial recap of SMPS with Panasonic FM and FR capacitors

  • Bypassed audio output capacitor (removed and replaced with wire, which provides more signal purity and less coloration)

  • Upgraded most capacitors on main audio board with Panasonic FM/FR’s.

  • Chassis dampening added.

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Since the stock audio OPA2134 opamp is high quality, I chose to leave in, as changing would yield minimal benefits at best.

 

Classe CAM-200 Mono Amplifier

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  • Complete recap with LowZ capacitors

  • New soft recovery rectifier installed

  • Added bypass caps on output board (none in the stock unit, which was a mystery to me)

  • Input buffer deleted (Burr Brown OPA2134 opamp based)

 

Classe CDP-1 CD Player (Vintage)

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This unit arrived “dead” and had obviously been been repaired a few times before I got it. I quickly discovered the LM7805 regulator was blown. 

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  • Complete recap required

  • Clock upgrade

  • Output stage completely overhauled and a new Class A opamp replacing the transistor based output buffer.

 

Classe CDP-10 CD Player

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Customer requested a complete overhaul

 

  • Complete recap with much beefier low impedance capacitors all around.

  • Upgrade of opamp (and new socket added)

  • Rectifier upgrade to Soft recovery

  • Regulator upgrade

  • Clock upgrade

  • Chassis dampening

  • A few signal resistors were upgraded

  • Class A output stage

 

Classe Ct-10 Tuner

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  • Complete recap with Elna Silmic II

  • Upgrade of opamp (and new socket added)

  • Regulators upgrade

  • Chassis dampening

  • Few signal resistors were upgraded

  • Class A output stage (RCA socket only. XLR out is class AB)

  • Removal of RCA BJT output stage with signal being sourced from the XLR output

 

Mies P1000 phono stage

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  • Sparko op amp installed (at client request)

  • Bypass of output capacitors

  • feedback capacitor upgraded

 

Mid-fi unit, restrained from spending much on improvement but those 3 trick should already improve the unit significantly.

Original operationnal aplifier, the OPA2134 output stages aren't the most dynamics

Brinkmann Edison phono stage

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  • Tube change (they need to be matched)

 

No upgrade were performed, I just replaced the worn tubes in the unit and sent it back to the owner.

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