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Topics - AAmer75

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Phono RIAA amplifiers / DYNAVECTOR 20XL Cartidge on QSXM2 RIAA amplifier
« on: September 14, 2011, 03:56:38 PM »
HI PA,

I thank you for earlier guidance on troubleshooting the heating issue of transistors. I realy appreciaty it.

I would need to ask you for one more advice and would realy like to have your opinion on it.

As I will use the QSXM2 amplifier for my DYNAVECTOR 20XL Cartidge What load resistor and capacitor should be most adequate for my cartridge?

Should I use the following components as per original QSXM2 Scheme and only adjusting the jumpers J1-J4 for MC Cartridge?
R1 (56kΩ), R2 (1kΩ) R3 (100 Ω) and
C1(470pF),  C2 (10nF)

Should I replace them with with some other values in order to have the QSXM2 preamp "accept" my cartdifge?

I ask this as I have doubts if I should do something like one of the QSXM2 Builders did - Please see the photo available at http://postimage.org/image/2nhs8jqys/

Although on this photo it is clearly the case of the QSXM2 build for MM Cartridge, should Insert some additional capacitors/resistors on  the PREAMP Input like it is shown on the photo?

For your information The cartridge DYNAVECTOR 20XL specification (the one I will use permanently on my KUZMA Stabi1)  is as follows:
 
Type  High/Low output moving coil cartridge with flux damper and softened magnetism
Output Voltage  2.8mV / 0.3mV (at 1KHz, 5cm/sec.)
Channel Separation  25 dB (at 1KHz)
Channel balance   1.0 dB (at 1KHz)
Frequency response  20 - 20,000Hz (± 2dB)
Compliance  12 x 10-6 cm/dyn 
Tracking force  1.8 - 2.2grams
DC resistance   150 ohms / 5 ohms
Recommended load
resistance  > 1Kohms / > 30 ohms
Cantilever   6mm length, hard aluminium pipe
Stylus  Micro-Ridge
Weight  9.1 grams
 
More information available here: http://www.dynavector.com/products/cart/e_20x.html

I would appreciate your thoughts on the above mentioned.
Cheers
AAmer75

2
Phono RIAA amplifiers / QSXM2 build - TRANSISTORS ARE RED HOT!!!
« on: September 13, 2011, 11:37:22 AM »
Last weekend I have compleated the assembly work onthe QSXM2 The extreme phono (RIAA) amplifier.

I have some doubts as during my measurments I hadsome inconsistency with measured values and also some heating issues with T31,T33,T35,T32,T34,T36group of transistors.

I am talking about the LEFT Channel of course, as itis the one I started with.

Therefore I need to ask you some questions and youranswer or recommendation would be most appreciated.

I am using your QSXPS -Regulated Power Supply.

1. The instruction on your web site says that  +/-15 is used, while on the PREAMPschematic  it is +/-18 volts.  Which one is true 15V or 18V?

2. I used tranzistors  MAT02 on positions T5,T23 and MAT03 onpositions T6,T24.

The resistor  R16 and R17 were replaced with 3K3 instead of  15K because of MAT transistors. Is thisresistance 3K3 of R16 and R17 OK?

3. the „begining“ of the PREAMP LEFT CHANNEL, on position R35shows voltage 1,13V,  while it should be0,926V. This causes that H1 LED has 2,105 volts, which causes voltagedecreasement on R43,R45,R47,R42,R44,R46,R47 for – (minus) 0,515V, which makesthe tranzistor group (T31,33,35,32,34,36) to have huge disipation, close to itsruin – THESE ARE RED HOT!!!

My MAIN question to you is the related to fixing theheating problem of course.

3. Would  theincreasement of resistance  for theresistance group (R42-47) from 22R to 33R fix the problem with Transistor group(T31,33,35,32,34,36) HEATING problem?

I think that with the resistance increasementfrom 22 Ohm to 33 Ohm I should get the proper current value through thetransistor group (T31,33,35,32,34,36) and reach the required voltage  0,320 mV on the R42-R47,  thus this HEATING problem should be fixed.

 Please seethe attached images below for better  reference.

I would need your opinion on this as well as anyother recommendation or advice for fixing the heating problem.

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