MF X-10D replica problem - diyAudio
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Old 25th January 2010, 02:02 PM   #1
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Default MF X-10D replica problem

Hello!
I've just purchased a brand new replica of the MF X-10D buffer via eBay.
There is a mismatch between L and R channels.The left channel sounds much louder than the right channel. Interconnects, amp, source, music program checked and OK! ECC88 tubes crossed no difference. I also tried a spare JJ ECC88 (new) in both positions, no change. I use a ''wall mart type'' psu 12V AC 10VA. Any ideas?

Thank you for your time.
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Old 25th January 2010, 03:12 PM   #2
sycorax is offline sycorax  Netherlands
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The MF X series are using a 24V AC transformer with a center tap. Sometimes they use a bridge rectifier and the center tap to get + and - 12 volts for example in their X-DAC. Or they use the 24 volts AC with a voltage doubler to get a high enough voltage for the B+ of the ECC88.

Do jou have a schematic of the replica?
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Old 25th January 2010, 04:13 PM   #3
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by t106 View Post
Hello!
I've just purchased a brand new replica of the MF X-10D buffer via eBay.
There is a mismatch between L and R channels.The left channel sounds much louder than the right channel. Interconnects, amp, source, music program checked and OK! ECC88 tubes crossed no difference. I also tried a spare JJ ECC88 (new) in both positions, no change. I use a ''wall mart type'' psu 12V AC 10VA. Any ideas?

Thank you for your time.

Your "Wall Wart" power supply sounds grossly under-rated for the application in terms of both voltage and current. I'm sure the original used a much bigger wall wart, but have no idea what its rating is.

Unless I am very mistaken your "replica" most likely is an unauthorized and unlicensed copy made by some fly-by-night outfit somewhere. That it has quality issues should come as no big surprise since it was basically built on the (unpaid) work of others. Should your wall wart not turn out to be the culprit it is quite likely that there is a defective cheap passive component somewhere on that pcb or an assembly error.
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Last edited by kevinkr; 25th January 2010 at 04:32 PM.
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Old 25th January 2010, 04:23 PM   #4
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The original Knob is rated at 12V 500mA. Or so it says on the label!
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Old 25th January 2010, 06:05 PM   #5
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seller's info: ''class A tube buffer assembled kit. Circuit design refer to Musical Fidelity tube buffer amp.
-This nice and good sound tube buffer amp can be placed between CD Player & Preamplifier.
-You cam use either 6DJ8, 6922 , 6N11 or 6H23, The assembled kit come with two 6H23.
-Using 1% metal film resistor.
-board size: L 200mm W 60mm

Features & Benefits:
  • High input impedance - Does not offer any loading to the source CD player and as a result it gives its best performance.
  • Low output impedance - it can drives any kind amplifier and ensures virtually perfect linearity.
  • Low noise, low distortion, huge overload margin and wide bandwidth - Extremely clean sound with huge dynamic range.
Audiophile grade components are used :
1.USSR militarily grade 6H23N

2.Elna 105 audio cap for filtering.
3.Fairchild’s highly reliable KSP42, KSP92 high voltage transistors are used in voltage doubling circuit.
4.Wima audio grade capacitors are used in the input stage coupling.
5.Wima audio grade capacitors are used in the output stage coupling.

In technically, the circuit use the tube in class A triode mode. The distortion has reached below <0.01% ( 1KHz), and frequency response from 10Hz to 100KHz,
and output impedance down to 200ohm.

The kit is fully assembled. It only need a AC input of 12V, 500mA. It is a assembled stereo buffer. Power supply requirement
Power supply needed: no less than AC12V/500mA
, transformer is not include''


I suppose that isn't exactly a cheap piece. The PCB is of fine quality and the welding beads too. However hardware failure is possible. I am just asking for known problems in that kind of equipment, based on the expertise of the forum members.
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Old 26th January 2010, 12:50 AM   #6
kevinkr is offline kevinkr  United States
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Did you pay via paypal? If so I would contact the seller and ask them to make it right, if they're not nice about it, then request assistance from paypal.

Before doing anything measure the voltage from your wall wart and make sure it is 12V AC minimum under load..

Good luck.
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Old 26th January 2010, 09:47 AM   #7
sycorax is offline sycorax  Netherlands
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My wall wart is 24V CT 500mA.
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