New Construction. Some issues solved. Some not. Need advice.

H

harv-e

New member
Decided to ressurect my turntable and record collection.  I took great care of them and they sound great (for the most part).  So then, time to upgrade my preamp, wandered across the Bottlehead site, was impressed, and here I am with my completed EROS.  No difficulty with construction, though I have some difficulty stripping wires, even though I bought a new wire stripper just for this project.  I followed the testing procedures throughout.  First problem was with ground to one of the tube sockets.  Close inspection showed that I had soldered the insulation covering the wire, actually missing the wire completely!  After final completion, all voltages/resistances checked.  Fired it up - horrendous noise in left channel only when attached to the turntable.  Switched plugs.  No effect.  Took it all apart, including circuit boards, and resoldered everything I could see.  No luck.  Somehow I moved the input wire from the phone IN jack with my finger as I was becoming frustrated........and the noise stopped.  Close inspection showed that the ground wire was broken inside the insulation from the ground lug on the jack!  UGH.

OK.  Now it's working!  Next two issues.  There is a distinct hum when I turn up the amp.  But I am reading that I need to burn things in a bit more, so I am not too concerned about it.  However, there is a definite "motorboating" sound that I cannot isolate by changing tubes or inputs, that seems to be coming from both channels.  Power supply issues?  I cannot find anything in the forum searching for "motorboating," but I don't know what else to look for. 

So any help would be appreciated!

Thanks from the newbie!

Harvey
 
First thing is to get or make some shorting plugs - RCA plugs that are internally shorted, either with wire or a low-value resistor (100 to 1000 ohms?). Cheap plugs from Rat Shak will do, and they will come in handy for years to come. Plug them into the input, thus removing the turntable and its wiring from the equation. If the hum goes away, then you've found the problem; otherwise you've at least eliminated one possibility.

Checking the connection between Eros and the preamp is more difficult, depending on what the preamp is and how it's powered (2- or 3-prong plug? Can it be reversed? Are they on the same power circuit?)
 
Does the oscillation occur with no turntable plugged in?
Does the oscillation occur with the inputs shorted?
Do all the voltages and resistances measure properly? (I'm wondering if you're not getting 0 Ohms in certain places where you should)

Also, if you have any power conditioning ahead of your preamp and/or Eros, try plugging them both straight into the wall.
 
Thanks guys for your input.  I have had to resurrect this thread as I just cannot live with this sound!

So I have completed all tasts to no avail.

I disconnected the turntable.
I shorted input plugs
I bypassed the power scrubber.
I even disconnected to output to see if the issue was behind the EROS.
I tapped the tubes to see if they make a noise (nope)
I must admit that I have not rechecked the voltages, as I checked them after unit construction and there were no issues then and this motorboating sound was immediate.  There was an early hum that I noted in my initial post......that has resolved.

The issue of motorboating still persists.

Frustrating!

H

 
Motorboating is typically due to a problem with the filter caps. It's most usually due to filter caps having been damaged or resistors between the caps having been damaged. Are the caps in the proper orientation and are the correct cap values in the correct places? FWIW I think this is the first time I have heard of one of our kits having this problem.
 
I'd be extra cautious with those little silver capacitors mounted to the front PC boards.  I put some in backwards in a BeePre prototype and they took a very, very long time to give out.

I'd be very interested in the voltages, especially those coming off the power supply board on the power transformer.

-PB
 
Harvey,

I hear the frustration in your post.  Where are you?  If you are near an experienced Bottlehead you might seek out some assistance.
 
So I went to test the voltages.  My Bottlehead Manual CD case.....was empty.  I had version 5-26-09. Can't find it!  More frustration.......Is there a link to download this....or do I have to wait for snail mail and order one?

BTW, I live in Erie, PA
 
Incomplete last post.
Voltages in the boards looking from underneath (all four LEDs are lit on all boards).

LEFT    Kreg 0.6 breg 80.1 OB 80.8 OA 124.4 bA 0 1A 200
RIGHT  Kreg 0.6 breg 80.7 OB 80.4 OA 128.6 bA 0 1A 200

Hope this helps
 
Can you double check that those silver caps across Kreg are properly oriented? 

Everything looks a little low, I suspect there may be a pair of swapped resistors, or a miswire.

-PB
 
Voltages at the Power supply board are as follows:

T4/5 = 7  T6/7 = 106.1      6.3 VDC pins measures 5.46      275VDC pins measures 234
 
The fact that both regulated voltages are low by the same percentage (16%, more or less) suggests either you meter is bad (worn battery?) or perhaps you are measuring DC with an AC voltage setting.
 
I considered that.  It could be that the battery needs to be changed.  The meter is made in China and that might be a factor too.  And I noticed that the manual states the AC mains voltage at which the figures were obtained from the circuit board duirng testing.  I didn't check my wall voltage.  But if all the figures are low by the same percentage, doesn't that mean that they're all OK?  For instance, the voltages on the Left and Right boards may be low, but they're pretty close to one another. 

I'll change the battery tonight and post again, but after all, it's a $10 meter from Harbor Freight.
 
IA and IB are regulated, as is the 6.3V supply on the power supply PC board.  When you put in a fresh battery, measure that 6.3V pad to be sure that the meter is working properly.

-PB
 
New battery installed in meter.  Voltages seem worse!

Power Supply Board
T4/5 = 6.4    T6/7 = 95.5      6.3vdc pins measures 4.9vdc      275vdc pins measure 216vdc

LEFT Board      Kreg 1.02  breg 80.2  OB 78.8  OA 122.5  bA 0  1A 187
RIGHT Board    Kreg 0.83  breg 80.2  OB 79.4  OA 126.2  bA 0  1A 187

Harvey
 
Hey Harvey,

With the amp on, put the black probe on the "-" pad on the 6.3V corner of the board, and the red probe on the "+" pad on that same corner, then see what that DC voltage is.

Though this may seem annoyingly redundant, any differences here will provide useful information.

-PB
 
When I listed the voltages on the power supply, they were all taken directly from the pads on the board.

I compared the DC voltages with the neg lead on the pad with the negative lead on the chasis and they were the same.

Harvey
 
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