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Dr Know's Audio Clinic
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Dr.
Know is our
resident Technical guru, responsible for the free Reference
Library, Technical Info, Data Sheets and the Audio Clinic. Contact the
Audio Clinic by clicking here dr.know@gbaudio.co.uk |
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| This site has gained an award from the Stagelink
Online Directory resource. They awarded a "Recommended"
status for Dr. Know's "excellent Reference Library" from
2004 - 2012. |
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Your Questions and topics covered:
1. Humming cam-corder mic
2. Identifying antique microphones
3. Seck mixer support
4. Multi-room home audio
5. How to use a compressor / limiter
6. Spare drivers for Yamaha NS10MS monitors
7. Where can I get a new turntable drive belt?
8. Where can I get user manuals?
9. How to clean clogged microphone grilles
10. Choosing a suitable turntable cartridge
11. Vibration/hum on Pioneer turntable
12. My turntable is running at the wrong speed
13. Why is my turntable humming when I turn up the amplifier
volume?
14. My Revox B77 record levels fluctuate
Q1 I recently purchased a ATR97 Microphone for use with a Sony 80X Mini cam. The microphone works fine but I am getting a constant humming noise that detracts from the noise I wish to record. Because I have to record from several locations there is a 50m length of cable from the microphone to the cam corder. Most of this is usually wound up around a cable reel. I have tried earthing the microphone cable both at the microphone and the cam corder ends but it only makes the humming worse. I cannot use the built in microphone of the cam corder because the nearby road traffic noise is distracting. As I record for hours at a time I use a mains power connection for the cam corder. Any suggestions? Many thanks in anticipation. G.D.
Dr Know' reply: You are almost certainly picking up hum due to the extension cable being used. What type of cable are you using for the microphone? For a 50M extension you MUST use screened cable and preferably balanced (two core + screen). In order to get the advantage of balanced cable you will need a small transformer at each end. These will convert the ATR97's unbalanced mini jack to balanced XLR and at the other end, back down to unbalanced for the camcorder mini jack. These in-line transformers will cost £18.17 + VAT each with the appropriate plugs fitted. If your extension is not screened or not balanced, then you will need to replace it. A basic balanced mic cable (50M) will cost £36.31 + VAT. A high quality balanced mic cable (50M) will cost £55.81 + VAT. topQ2 I like your web site, which I've visited a couple of times now. I do a bit of amateur recording as a hobby but I've never seen a microphone like the one Jack McIvor uses in "Stiff". Can you tell me what type it is and is it an antique? Yours faithfully, M. Duffy (Scotland)
Dr
Know's reply: Thank
you for your comments and we're glad you like our site. The big old mic in
the photo is actually a theatrical prop which has a cunning space inside
to hold a slim condenser such as AKG C451, C460, SE300, Audio-Technica
PRO37R, ATM33a, etc giving quality performance with retro looks.
However for
"Stiff" we only used it as a prop since all the cast were
wearing ATM73 head mics. A pre-programmed digital echo and band pass
filter was added to give the effect of an old "tannoy" system.
[added Jan 2008, see
our expanding range of original classic and vintage
microphones for hire or sale.]
top
Q3 We are a company located in Austria, specialising in repairing professional audio devices. Recently we got a Seck mixing console - unfortunately without any schematics. It would be great, if you have some drawings - or information where to get them. I'd like to thank you for your efforts, with best regards. M.M.
Dr. Know's reply: As
you probably know, Seck were taken over many years ago by Soundcraft and
much of the Seck design went into the Spirit series consoles.
Unfortunately, Soundcraft don't support Seck products and we are not aware
of any specialist Seck support companies.
We have limited tech info and
compatible parts available. We have two types of new replacement power supplies
available from stock. We often have secondhand stripped down parts
available. More detailed information and prices can be found on our data sheet
www.gbaudio.co.uk/data/seck.htm
I have now added some schematic and circuit drawing links on this data
sheet for all the people who keep asking about Seck mixers. I hope this helps
you. Let us know how you get on.
top
Q4 I read your web site with interest and wondered if you could help me with a query I have regarding my home audio set-up? I would like to install pairs of speakers in four different rooms and am looking for a simple (and cheap!) way of controlling volume in each room independently. Do I need to buy a separate amplifier for each room or is there a product on the market which will do this for me? Any help or guidance would be much appreciated! Many thanks, S. J.
Dr. Know's reply: You are obviously someone who either loves his music or can't be without the radio. There are simple switching devices around £20.00 that can switch between four pairs of speakers from one amplifier but these do not vary the volume and you will need to be careful about the total load impedance presented to the amplifier. You will need to check the impedance of each set of speakers (will they all be the same or will they be different pairs?) and work out how to combine them safely. As a rule of thumb, most (but not all) domestic speakers are 8 Ohms impedance each. Most modern amplifiers will be fine driving a total load of 4 Ohms ie two pairs wired in parallel. If you want to control some of the volumes separately and/or run all four rooms simultaneously, you will need either a four channel power amplifier (eg Yamaha XM4220) or an extra stereo amplifier (eg Denon PMA250SE), fed from the pre-amp output of your main amp. This will allow you to run two pairs of speakers from each amp so you will be able to vary the volume in two stereo zones. If you really want to vary the volume in each of the four rooms separately, you will need a separate amplifier for each room ie four stereo amplifiers or a six channel power amplifier plus your existing amp (eg Yamaha XM6150). top
Q5 Please can you help me I have a Drawmer DL221 compressor and it is my first time to use a compressor and I cannot get a good vocal sound out of it could you give me some information on settings because I have not got a clue. yours R.
Dr. Know's reply: Try
this out first with a music source such as CD or MD or sampler.
Set the threshold and gain to zero. Set
the other three controls to the left. Set
the meter switch to VU and the function switch to bypass. Sound
should be passing through, unaffected.
Now switch the bypass to Norm.
If everything is wired up
right you should hear things about the same.
Threshold determines
the level at which the compressor starts to affect the sound. So
the higher you set this, the less effect. the lower you set this, the more
effect.
Ratio sets the
proportion of sound compressed. 1:1 is no compression, 3:1 or 4:1 is usually
a good vocal setting although light, breathy vocals will need a higher
level. Infinity:1 is a maximum "brick wall" limiter.
The Attack and Release
determine how quickly the compressor acts and de-activates on the sound,
so you can experiment with these to balance leading edge dynamics and
decays with compression or limiting control. These controls can give you
some artistic control of the sound, making the compression sound more or
less natural/seamless.
The Gain control is just a
way of compensating for any loss of signal level caused by the
compression or limiting. It operates after the compressor circuit.
Using the Bypass switch
will allow you to compare levels against the dry sound.
The LED meter shows the amount of
gain reduction (GR) or you can switch it to VU to see the
actual level passing through.
If you use compression over a
stereo source, switch the Stereo link. This makes both channels
trigger simultaneously.
top
Q6 Hello,
Dr. Know's reply:
No
problem. Even though Yamaha, in their infinite wisdom, have discontinued
the ubiquitous NS10MS, we have spare bass drivers, tweeters and crossover
networks available @ £** each by mail / email / telephone order. Check out the full specs on
our
NS10MS
data sheet.
Dr. Know's reply: We have a large range of
replacement drive belts available @ £** each by mail /
email / telephone order. See the chart and measurement guide on
our
Drive
Belt Data Sheet
Q8 What
would be the cost' Canadian ' for the operational manual for the Yamaha
EMX 150 mixer , I just purchased one at a used item sale. J.W.
Use the link from our Technical Reference Library:
www.gbaudio.co.uk/info.htm#Manual
(Here you will find free links for most manufacturers' user manuals)
Q9 Question is, do you have any sprays / fluids or services for cleaning clogged up microphone heads of the round mesh variety? Or can you point us in the right direction? Yours sincerely S.B.
Dr. Know's reply: Remove the grille from the microphone and wash with hot water and detergent, using an old toothbrush or nail brush. If the grille is very clogged up, leave it to soak a while in the soapy water. If it is rusted, scrub all the rust off with a small wire brush and then seal the bare metal with a coating of enamel paint or plastic sealant spray. Take care not to get the spray on the foam inside the head. If they are really bad, it will probably be easiest and safest to just replace them. top
Q10 I have a Pioneer PL12D deck, which I am recussitating so that I can digitise my old LPs. I reckon the cartridge and stylus are probably knackered - which one of the cartridges you sell would you recommend for use with this deck? Also do you sell the rubber band that drives it - the one I have still works, but feels a bit crunchy! looking forward to your reply. regards, M.
Dr. Know's reply: Yes we sell a replacement drive belt for the PL12D for £** The AT95E, AT110E and AT120E/T are all suitable for the PL12D, depending what your budget will allow. The principle difference between them is the output efficiency. The higher output improves the signal-to-noise ratio as you go up the range. That results in a cleaner, quieter sound. top
Q11 I have replaced the drive belt of a Pioneer PL-512 turntable but now there is vibration through the tone arm when the turntable is set in motion which causes a hum when playing records. I had thought it might be that the drive belt is too tight but I've tried two slightly different belts and it hasn't made any difference. Could it be a problem with motor bearings? Thanks, D.N.
Dr. Know's reply: Hum and vibration are two distinctly different issues. Hum is electrically generated noise, either picked up by the player or noise induced on to the connecting leads and then amplified by the amplifier. Vibration or resonance is a mechanical issue which can manifest itself as a sort of buzzing or humming noise. To clarify the exact nature of your problem, we suggest you check all the following points:
1. Is the hum present even before you turn
on the turntable motor? If "yes", check that the tonearm earth wire is connected
to the amplifier earth post.
2. If there is still hum, check that the cartridge wiring to the headshell is
colour-correct and all wires are well connected.
3. How is the turntable supported? It must be level and without wobble. Then
there are two schools of thought about the support structure. Briefly, it should
be either a firm, lightweight, low mass shelf (eg 12mm plywood) or a high
density, heavy, high mass base (eg marble slab).
4. Check the tonearm bearings. The arm should move smoothly horizontally and
vertically with no play on the bearings. If the arm is sticky or wobbly, the
bearings may be damaged or worn and will probably need replacing as they are
usually not user-serviceable.
For the next check points you will need to remove the rubber mat and platter.
5. Does the deck vibrate when you switch
the motor on? If "yes", go to point 8.
6. Does the motor pulley turn easily between finger and thumb, when switched
off? If "no", the motor may need lubricating with a high viscosity, heavy duty
motor oil intended for high speed shaft application. It should be
non-evaporative, non-foaming and with good temperature stability.
7. Does the centre spindle turn easily and smoothly between thumb and finger? If
"no", the spindle may need lubricating with light oil designed for low friction
areas. It should be a non-evaporative, non-gumming type.
8. What condition are the motor rubber mounting bushes? If they are hard,
cracked or perished they need replacing to isolate the motor from the plinth -
and stop motor vibration transmitting to the tone arm.
top
Q12. I have replaced the drive belt on my old turntable and it is still running slow. What am I doing wrong?
Dr. Know's reply: We’re sorry to hear that your turntable is not running well with the belt we supplied. Before you return the belt it would be worth checking the following points:
1.
Is the
drive belt tension correct? If it is slack or slipping, that would account for
the speed running slow and the solution is to select a shorter, tighter drive
belt. See our guide to calculating the correct drive belt length at
www.gbaudio.co.uk/data/belts.htm
2. If the tension is correct, then you should
check that the belt is correctly lined up – running on the centre (widest part)
of the barrel-shaped motor pulley and not fouling on the mechanical speed-change
arm.
3. The motor may be seized up; with the platter removed, check that the motor
pulley turns easily between finger and thumb, when switched off? If "no", the
motor may need lubricating with a high viscosity, heavy duty motor oil intended
for high speed shaft application. It should be non-evaporative, non-foaming and
with good temperature stability.
4. The centre spindle bearing may be seized up; with the platter removed, check
that the centre spindle turns easily and smoothly between thumb and finger? If
"no", the spindle may need lubricating with light oil designed for low friction
areas. It should be a non-evaporative, non-gumming type.
5. Certain turntables have an electronically controlled DC motor, rather than a
mechanical shifter to change the speed. These models may have a “fine tune”
speed adjustment under the platter which is normally accessed with a preset
adjuster tool (or a mini screwdriver).
top
Q13. there is some buzzing interference which increases in loudness as the amplifier (Quad) volume is turned up. Any ideas? N.C.
Dr. Know's reply: Your buzz is quite possibly an earthing issue, meaning that the signal cable is not properly screened against interference. Alternatively it could be picking up mains interference by induction from a strong electro-magnetic field (EMF). Here are the main points to check:
Earthing:
1. Check that the four cartridge wires are
correctly orientated according to colour.
2. Using a continuity meter, check that the earth wire (beside the phono lead)
is well connected to the tonearm tube.
3. Make sure that this earth wire is well connected to the special turntable
earth point on the amplifier.
4. Make sure that the amplifier is properly earthed to its mains plug.
5. Check that the earth/screen is well connected on each of the phono connector
plugs.
Induction:
1. Check that the
phono lead is not routed next to any mains cables or power supplies.
2. Check
that there are no mains leads or power supplies sitting close to the rear of the
amplifier.
top
Q14. I managed
to get fixed up with a Revox B77 for a very reasonable price. It also
included the nab reels and 18 x 10.5 inch reels with tape (2 unopened).
Dr. Know's reply: Whilst it’s hard to diagnose 100% without seeing the actual machine, but assuming all heads are clean and demagnetised properly – as you say – and that it does actually record and playback.
When the recording is replayed and the levels are a bit low but stable, the likely causes are:
When the recording is replayed and the levels fluctuate the likely causes are:
All of these procedures should only be carried out by a suitably qualified service engineer with appropriate test equipment.
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Unsolicited Customer
Quotes:
"Thanks for this info, I had tried
cleaning fluid unsuccessfully; but your comment made me try again. I made a
really determined effort to get into the switch and SUCCESS! Thanks again,
all working like new again. Regards, C Kennedy (08/12/12)
"To thank you for the excellent
turnaround on the item I purchased on Tuesday January 3rd. - an item
which I ordered on your advice. "Dr Know, Thank you for your time and for your wise advices". Gauthier (15/11/2011) "That's brilliant! Thank you so much for the excent and speedy service. Best wishes," Lance. (03/09/2011) "Dr. Know, I wanted to send you a note to compliment you and also say thanks for your extremely concise and helpful website information regarding production wireless equipment issues. It's quite obvious that you're "TOP SHELF" ! Was just surfing the web as I'm doing some planning for The Royal Wedding and came across your site... well done. If I may ever be of assistance to you for production wireless queries within the United States please feel free to give me call as I'm most happy to return the gestures you've extended to the professional wireless user community. Thanks Again ! KP" (Senior RF Engineer, National Broadcasting Company, News Field Operations, New York, USA 07/03/2011) "Hello my name is J.K. I have found your website http://www.gbaudio.co.uk/info.htm to be a valuable resource for wireless headphones and audio products in general. Therefore I would like to place a link on our website http://www.amphony.com so that our customers can use your website http://www.gbaudio.co.uk/info.htm as a resource"."Dear Dr Know, Many thanks for your prompt and reassuring reply. Best wishes, B Bensley" (05/02/2010) "I would just like to say that when I did a uk google search (drive belt), your site was the easiest to use and understand, with good, clear insructions. I especially liked the link to Pi, it made me smile". Best wishes, Ben UK (26/03/2009) "hi, just bumped into your web site (through a search on some microphone specs i think) and its really nice. if more people actually put up some useful information on their sites then the web would be a better place..." a.f. brussels |
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