Jim Lambton

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  • in reply to: How to test universal preamp #15213
    Jim Lambton
    Keymaster

    Just to confirm I understand:
    1. When you connect your preamp to the Willsenton R8 Pre IN, you get substantial hum.
    2. And when you connect to the R8 CD IN, it is silent.

    The only difference between inputs on the R8 is that the Pre IN bypasses the volume control – ALL tubes are in circuit – even the preamp tubes.

    So most likely you either have a ground loop issue on the Pre IN or you have a circuit issue on the Pre IN, the reason for this diagnosis is simple, if the Preamp was generating hum/noise you would easily hear it on the CD IN.

    One simple test is to hook the Preamp up to the CD IN, and slowly bring the volume to max – if that volume level only produces a very low level hiss/noise then you know for sure the problem is in the R8 Pre. Why, because the CD IN and Pre IN will share the same ground return, so it must be a circuit problem in the R8.

    I would just use the CD IN and call it good.
    Truly,
    Jim

    in reply to: How to test universal preamp #15178
    Jim Lambton
    Keymaster

    A couple of more thoughts – i’m presuming your preamp is making noise with no inputs connected (open RCA’s), if it only produces hum when an external source is connected then the grounds of the two devices are interacting and often just connecting a quality source will fix this problem.
    Also all of our Kits come with quality components – but when it comes to filter capacitors we use the best high quality capacitors we can source – which means Nichicon or other Japanese Manufacturers. Yes they’re expensive – but they’re worth every dollar. Same goes for coupling capacitors – Solen makes excellent quality coupling caps – that are reasonably priced.

    in reply to: How to test universal preamp #15177
    Jim Lambton
    Keymaster

    Hey Gilbert! No worries i’ll lend a hand, but unfortunately I can’t provide full support for everyone who just builds from the free schematics. Ok so first problem, you don’t say how loud the 60hz hum is? Is it loud at zero volume or do you need to come up to 1/2 volume to hear it.
    Ground topology is critical to a low noise pre or amp. Here are the basics.
    Mains safety ground (green wire) from IEC – bolt directly to metal chassis ground point – nothing else.
    Power supply ground returns to a star ground point separate from safety ground but close by. I like to take this return from the largest filter capacitor point. Important only one return from each power supply circuit – one.
    All RCA, Preamp, Potentiometer ground returns to a star ground point as far away from power supply as practical. Important you must use isolated RCA jacks.
    If you watch the build series, you’ll see all of this in practice on the Kit Build.
    Now other common sources of hum can be the system grounds interacting – so all audio equipment should be plugged into ONE quality power bar – this will keep all system grounds at the same potential.
    I’m presuming you don’t have a scope or I would give some general test procedures to help you isolate the problem.
    Never give up, ground loops and related noise are very common in all beginner builds – which is one good reason to start with a Kit – it helps you get oriented to good layout topology, build methods and of course they work perfectly on start up – most of the time!
    Good luck!
    Cheers,
    Jim

    in reply to: How to test universal preamp #15151
    Jim Lambton
    Keymaster

    Start up testing is covered in the Mellow Tone Kits YouTube Build Series. You mention checking some of the basics which is good. But the most important is to plug the tubes in and check your B+ voltage, make sure it’s close to spec and most importantly stable. If you have a scope and signal generator you can pass a signal through the Pre and check for a clean signal out, otherwise plug the pre into the R8 (Pre IN), turn the Pre volume to zero and turn on the R8. If the R8 is quiet with no volume then turn the Pre volume up to half – still quiet, go full volume – still dead quiet, then congratulations you built to the design and layout of the original Universal 6/12sn7 Kit Preamp. If noise or sound issues go back and see where your build deviates from our design. Hint: ground topology is critical for a quiet design.
    Please let everyone know how it went, including pics.
    Cheers
    Jim

    in reply to: Stock Willsenton R8 6SN7 vs Tung-Sol #15044
    Jim Lambton
    Keymaster

    Well it all depends on if your Tungs are true vintage or just reissues. The easy answer is for the stock R8 6SN7’s they are either not very good Russian (probably – mine were) or worse Chinese – so they aren’t good anywhere but in the bin. Now if your Tungs are reissues they aren’t much better than those stock R8 tubes, on the other hand if they’re vintage Tungs, then they’re among the best sounding 6SN7’s ever made and i’d put them in the Pre for sure. Now you might think i’m being hard on modern tubes – but remember the tubes ARE the Amp and i’ve listened to pretty much every common 6SN7 (and many rare ones), and quality vintage tubes beat the modern tubes hands down. Yes this is a very general statement and you will occasionally find a good sounding and reliable modern tube.

    in reply to: Stock Willsenton R8 6SN7 vs Tung-Sol #15030
    Jim Lambton
    Keymaster

    I’m not sure I understand your question. But maybe this will help. The R8 has a Pre IN option, allowing you to install a preamp ahead of the R8 (which is an integrated amp). The only change in the R8 when in Pre IN mode is the volume control is bypassed. The R8 preamp tube is v7&v8 which is a pair of 6SL7GT’s. In the R8 the 6SN7’s (v6&v9) are in the power stage and work as driver/phase inverter tubes.

    in reply to: E80CC Build unsuccessful need troubleshooting #13965
    Jim Lambton
    Keymaster

    Welcome back Jesse!
    Q. When you tested your B+ did you follow my instructions and disconnect the B+ from each power supply board to the Preamp boards?

    If your transformer is wired correctly, you shouldn’t need to rewire it. Go over the wiring and make sure the connections are correct. If in doubt send some high res pictures of the connections and i’ll verify for you.

    in reply to: E80CC Build unsuccessful need troubleshooting #13898
    Jim Lambton
    Keymaster

    So to confirm the basic operation of the power supply, disconnect the B+ from the preamp boards.
    Now check the power supply board junction out voltage, your B+ should be ~315vdc and steady on both power supplies.
    If that checks out, next will be to remove both tubes.
    connect ONE B+ to preamp board and see if the voltage stays steady at ~315vdc.
    If yes, connect up the other preamp board and check voltage.
    If all good (probably), plug only one tube in and check for B+ ~240vdc, should be steady – after a wee bit.
    unplug that tube and move it over and check the other channel.
    By now you should see the logical approach to isolating the problem(s).
    Let us know how this portion of the troubleshooting went.
    Cheers,
    Jim

    in reply to: E80CC Build unsuccessful need troubleshooting #13890
    Jim Lambton
    Keymaster

    Yes the whole design is modular, so repairing it is a simple task.
    Troubleshooting a build is normal, the more experience you have as a builder the fewer times you’ll need to go back and find the problem.
    In this case you know you have a proven working design.
    Just take your time, make notes on the schematics so you don’t need to repeat any voltage tests.
    If you find something you aren’t sure about, put a note and a picture in the Forum.
    It’ll help future builders.
    Cheers,
    Jim
    PS get into a regular habit of following the same safety precautions, that will increase your comfort and safety.

    in reply to: E80CC Build unsuccessful need troubleshooting #13887
    Jim Lambton
    Keymaster

    No worries, you’ve probably made a wee mistake.
    It happens, the important thing, as you mentioned, is to logically go through the circuits and figure out what’s wrong.
    So, if no sound, other than hiss, on both channels, then we know we have a wiring and or component error.
    It will probably only take a wee bit of troubleshooting to figure it out, then glorious sound shall commence!

    CAUTION! HIGH VOLTAGE PRESENT, ALWAYS CLIP ON WITH THE AMP OFF AND THE POWER CORD DISCONNECTED, EXCERCISE EXTREME CAUTION! NOTE: YOU SHOULD DISCHARGE THE CAPACITORS BEFORE YOU WORK INSIDE YOUR UNPLUGGED AMP.

    1. Get out the schematics, flip the amp over (on a soft cotton dish towel), clip your voltmeter ground to the middle star ground.

    2. Start at the beginning and check all voltages, compare them to the schematics as you go, mark the actual voltage reading beside my readings.
    a) J2 B+ Tubes loaded s/b (should be) 230-250vdc take all measurement with no Signal IN – No RCA’s connected (so basically the pre is in idle)
    b) P6 s/b ~134vdc
    c) P8 s/b ~2.7vdc
    d) P3 s/b ~136vdc
    e) P7 s/b 0vdc
    f) P4 across P5 ~12vdc

    3. Now if any of the voltages are out significantly, then go backward through that circuit and look for your error.

    4. Resistors can be checked in circuit, just disconnect the power cord, discharge the capacitors and set the volt/ohmmeter into the ohm function, probe each end of the resistor and check the value against the schematic – check it off as you go.

    5. Capacitors can’t be checked in circuit, so just check your polarity and value.

    6. If you’ve gotten this far and all the voltages are within spec, then it is time to have a good look at the signal path. Unplug, discharge capacitors. Plug a quality RCA cord into one IN jack, turn your volume to max, set your volt ohmmeter into the ohm function, clip one lead onto the center post at the end of the RCA cord (make sure it isn’t touching the outer ground connection). Now check the path from the RCA IN center post (s/b very low resistance), next volume IN/OUT, next P7 (v.low), next any star ground s/b ~470K, you are reading through R1. Do the same thing from the RCA OUT using a RCA cord go back to P3. Last check the ground of the RCA cord to any start ground (s/b v.low). Basically you are looking for either a dead short from the signal to ground = 0 signal in or out, or a signal or ground connection that is poor or compromised. This is harder to explain than to do in reality – just take your time and look for a section of the signal circuit that’s compromised in some way – then figure out why.

    7. Note with very high efficiency speakers +95db you will normally here a very low level hiss at your tweeters – this is normal for Pure Class A amps. I test the noise floor of my Kits both electrically and with my ears. With ~93db efficient speakers, I set my preamp for normal listening volume (2 o’clock), then without touching anything else bring my ear close to the tweeter – at about 3-6″ I can start to hear hiss at a low volume – this is acceptable. With the R8 because you are essentially adding a preamp gain to a preamp gain, you will automatically double the noise floor, so at your listening position with very high efficiency speakers you will hear a very low level of hiss, this is normal.

    That’s a good first pass, if you have any questions let me know, but first dive in, within a short while you’ll start to understand what you are up to.

    And NO Worries – the Pre will start to sing soon and if all attempts to locate the problem fail, i can always take care of it on my bench.

    Focus & Luck!
    Jim

    Jim Lambton
    Keymaster

    That’s perfectly fine, in fact I would do more shared connections like that in the Kit Build, but it just gets too complicated.

    Jim Lambton
    Keymaster

    That’s good confirmation that this is a good method to avoid the problem of flux and/or solder flowing downhill! It wasn’t until your post just now that I figured out what the heck Brian was saying. So to clarify – you mount the top plate in the plinth and put the whole thing on its side – and solder the RCA jacks in, with them in the horizontal position. This is exactly why we have Test Builders, to work out what parts you’re finding difficult to assemble.
    Carry on with your excellent work!
    Cheers,
    Jim

    Jim Lambton
    Keymaster

    Brian can you clarify what you mean when you say “soldered horizontally” is this the incoming wire position or the soldering iron?
    A picture of your finished work would be awesome!

    Cheers,
    Jim

    in reply to: 22 gauge bare connection wire #13765
    Jim Lambton
    Keymaster

    Shipped Small Packet US AIRMAIL
    12″ – 22ga. tinned buss wire
    7-8 business days
    Sorry for the shortage – with the help of Test Builders we’ll be able to correct the pick list, until it’s bang on!
    My goal is to have a wee bit more of everything so you never come close to running out, including extras of the tiny things that are easy to drop on the floor – never to be seen again!
    Keep up the good work!
    Cheers,
    Jim

    in reply to: Welcome To The ValvesNMore & Mellow Tone Kits Forums! #13673
    Jim Lambton
    Keymaster

    Thanks for setting this up Charles.
    Cheers
    Jim

Viewing 15 posts - 1 through 15 (of 15 total)