Kegworth Show Information

The information for this year's show is now live at or by clicking on the show banner below.

NON EXHIBITOR ROOMS NOW OPEN - Special Offer....Stay Saturday, join in all the build up excitement on Sat night and then gain FREE access to the show on Sunday



Super Wammer Plus
  • Content Count

  • Joined

  • Last visited

Community Reputation

52 Excellent

About robbie010

  • Rank
  • Birthday Private

Personal Info

  • Location
  • Real Name

Wigwam Info

  • Turn Table
    Audio Linear TD 4001
  • Tone Arm & Cartridge
    SME 3009 / M97xE
  • SUT / Phono Stage
    MoFi StudioPhono
  • Digital Source 1
    Cambridge Audio CXC
  • Digital Source 2
    PC / iPhone
  • DAC
    Chord Mojo
  • Integrated Amp
    Yamaha RX-A820
  • Power Amp/s
    Yamaha RX-A820
  • My Speakers
    Infinity Kappa 600
  • Headphones
    Sennheiser HD600 & Grado SR80e
  • Trade Status
    I am not in the Hi-Fi trade

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. robbie010

    DC Offset different on both channels

    Evening all, I finally powered on my project amplifier this afternoon, nothing blew up....... so thats good! I left the power on for 5 minutes, the heatsinks got nice and toasty and I noted a slight buzz from the transformers, which I assume is normal? I measured the DC offset at the speaker posts and got 04.7mV on the right channel and 29.7mV on the left channel. As I understand it, both these measurements would be considered ok but I have two questions: 1. Does the inbalance suggest that one channel has a faulty component? 2. Would such an inbalance have any audible effect? Thanks
  2. robbie010

    Is a passive preamp right for me?

    Thanks all. I have been doing some light reading on the subject and one number that keeps cropping up with regards to input and output impedance is at least 10x i.e. the input impedance of an amplifier should be at least 10x higher that the output impedance of the previous amplification stage but the higher the better. I have been looking at a B1 Buffer, which is another Nelson Pass design. Apparently, it has an input impedance corresponding with the value of the volume pot used, which makes it fairly easy to adjust I assume. The output impedance is 1kohm and the A40 power amp has an input impedance of 40kohms, so no problems there. The Chord Mojo has an output impedence of 0.075ohms which should be no problem but the mofi phonostage seems to be a sticking point. My phonostage has various adjustable impedance load settings for MC carts but only has one 47000ohm setting for MM. Is the impedance load the same as output impedance?
  3. robbie010

    Is a passive preamp right for me?

    I touched on this briefly in a previous post but am looking for a solid answer before considering a purchase. I am interested in understanding the limitations of a passive preamp and wondering whether it would be right for me. I have a basic set-up of two sources, turntable and CD. If you view my profile you will see I run a turntable through a mobile fidelity sound labs phono stage and I run a CD transport through a Chord Mojo. I am currently using a basic Yamaha receiver to drive my setup, but I am just about finishing a project to overhaul and upgrade a power amplifier, a Nelson Pass A40, and I really like the idea of keeping a system simple, less components colouring the sound signature and so on. So, that said, I was wondering whether I could get away with using a decent quality two input passive preamp with the power amp with my setup. Would there be any pitfalls, possible low power signals going straight to a power amplifier without pre amplification? Any thoughts on the practicalities of this would be appreciated and anyone with experience of such a set-up. Thanks.
  4. robbie010

    Lower voltage replacement capacitor??

    I’m just working through the circuit boards on my project amp and have managed to lay my hands on the original schematic and parts list. One of the capacitors is listed as a 40pf 500v silver mica cap, the circuit boards currently have a 39pf polystyrene cap in its place, for which I have bought a direct replacement rated at 39pf 160v. My question is whether the voltage requirement of the original part (500v) is of concern?? The two main caps in each board are 470pf 25v so there can’t be that much voltage running through it.
  5. robbie010

    Distortion and crackling sound from CD Source

    Excellent!! Just switch it on in the normal mode with the volume quite low and cranked up the volume on the amplifier and it sounds great, no distortion or cracking!! Thanks!
  6. robbie010

    Distortion and crackling sound from CD Source

    Whenever I turn the mojo on I use it in line level mode by pressing the two volume buttons and the power button at the same time. As I understand it, this is the correct way to use the mojo when connecting to an amp. According what I have read this sends a fixed output signal of 3v.
  7. robbie010

    Distortion and crackling sound from CD Source

    The Mojo and CDT are fairly new. I didn't use the Mojo with the iphone, I used airplay from the iphone direct to the amp and then used the CDT connected to the Mojo and then to the amp. Distortion and crackling was heard when using the CDT and Mojo but not the iphone and airplay!
  8. I am hearing distortion and a crackling sound coming from my speakers. I have just done a brief experiment by listening to the same track from two different sources and at similar volume. First via apple airplay from an iphone, no discernable distortion. Second from a CD via my Cambridge Audio CXC transport / Chord Mojo DAC and here there was obvious crackling and distortion wherever the music intensified and got louder. Would this suggest a potential issue with cabling or possibly with the amplifier, which is a Yamaha RX-A820?
  9. robbie010

    Amplifier Schematic Review

    Ah, I see. The primary side has a Red live, Black negative, yellow/green Earth (which is what you are refering to) and its also has a spare for 120v supply which osn't shown on the schematic drawing.
  10. robbie010

    Amplifier Schematic Review

    When I powered the amp up from the mains and tested the transformers output voltage I got the following results: Secondary 1 to Centre Tap - 28v Secondary 2 to Centre Tap - 28v Secondary 1 to Secondary 2 - 55v I assume this means that it is connected to the winding?
  11. robbie010

    Amplifier Schematic Review

    The prinary side earth wire of both transformers is grounded to the chassis. For some reason LTspice does not have the symbols for this.
  12. robbie010

    Amplifier Schematic Review

    Evening all, Following my earlier posts regarding my project amplifier, I have now worked out that it is a DIY Nelson Pass A40 power amplifier. Having thoroughly reviewed the amp and compared it to the published schematic there are a number of deviations from the published info and I am not skilled enough to review the schematic and discern any obvious design issues. The main deviation appears to be the use of two seperate centre tapped transformers and a triac transister in the power stage. I have attached a schematic drawing of the amp that I produced using LTspice. Unfortunately, I am not skilled enough to actually run a simulation in spice but if anyone is capable of reviewing the schematic and providing any feedback it would be much appreciated. Thanks. A40 Schematic.pdf
  13. robbie010

    Are there any prefered Output Transistors?

    Thank you.
  14. While I’m overhauling my project amplifier I am tempted to replace the output transistors as they are unmarked and of unknown quality. There are 4 per channel, two NPN and two PNP, are there any prefered transistors for audio applictions that anyone could recommend? The original schematic calls for : 2 x PMD16K100 Lambda 2 x PMD17K100 Lambda According to the spec sheet these are Bipolar Darlington transistors. Thanks
  15. robbie010

    Identifying unmarked Transistor & circuit type......

    I think I have found it!!! I accidentally stumbled upon the attached PDF online, the circuit layout and the parts list look very, very similar........ If correct, the amp is a DIY Nelson Pass A40!! Nelson Pass Art A40.pdf