Reflowing solder joints on Eros Phono c.2011

[Henry2011]

A general question for those who have done it.  How far does one go in reflowing solder joints on an Eros Phono?  I’m up to the point of disassembling circuit board connections to access joints that are inaccessible (i.e. trying to get at them while in an assembled state would risk heat damage to proximal components).

I’m very interested in what the folk at Bottlehead Service have to say.

Background: I’ve had a low level hum (equal on both channels) that I’ve been living with on my Eros since day 1.  A lot of different techniques to reduce it have been tried (different amps, cables, power supplies, tubes, physical locations, tapping and prodding components and connections while in service, reflowing of accessible solder joints, connecting Eros and SEX grounds).

Current configuration is Grado TR cartridge through CJ Walker turntable (recent dc motor mod) to EROS Phono to SEX Amp through Sennheiser HD-600 headphones.

Thanks in advance for your responses, Henry Moore

 

[Paul Birkeland]

Before you rip apart your Eros, if you use a pair of clip leads to short the inputs of the Eros, does the noise go away?

 

[Henry2011]

Paul, thanks for the quick followup.  I’ll be back home Wednesday evening and I’ll perform that check then post the results. Henry

 

[Henry2011]

Paul, I checked my Eros Phono in the following ways with these results (essentially very little change).

Completely electrically disconnected the turntable (leads, ground and power supply).  Installed RCA cables (0.2 nanofarads each) at the Eros input jacks and shorted both pins and grounds at the other end of the leads with two alligator clips.  The volume of the hum was about the same as it was with the turntable properly connected (but a little more tone and less buzz).

Disconnected Eros and SEX power supply and plugged them directly into the same wall outlet (same circuit - they were previously plugged in to a power strip supplied by this outlet). Same configuration as above and essentially no change in results.

Reconnected the turntable and it’s ground lead with the amps still plugged directly into the wall outlet. Hum still there same as before.

I did some other checks using my Hafler DH-110.  The Hafler power plug is not polarized and does not have a ground connection).  I connected the Eros output to the EPL Return on the Hafler (this is between the phono stage (disconnected by EPL switch) and the line stage).  The hum followed the Eros.  Next I removed the Eros from the equation by connecting the Hafler phono stage to the SEX amp via the To EPL jacks (output of phono stage).  No hum on SEX (brushed the Grado to verify my connection).

General info:  The hum volume changes with the volume pot on the SEX amp.  I’ve been calling this a hum but it is not even close to a sine wave noise.  Lots of buzz or fray. I think its primary frequency is 120hz but I don’t have an oscilloscope.  I tried to simultaneously listen to the hum (headphones) and recordings of 120hz and 60hz (earbuds) (both frequencies fit but 120 sounds closer).

 

[Paul Birkeland]

Resoldering is likely in order, as is a voltage check. 

 

[Henry2011]

First, this is a long post with lots of data just to ask a few questions. For most folk this will fall into the "non-read" category.  Its about early stage troubleshooting of my Eros Phono low level buzz/hum.  My reference values are from my EROS PHONO manual, Rev. 5.19.09 (not the EROS 2).

For the following voltage readins, mains voltage was 121.2 vac and I'm using Amperex BB EF86's, Amperex 12BH7A, and Sylvania 7308 tubes (have been for a while).  I have 12 lit LEDs (4 each board).  For the voltage readings, both input RCA jacks are shorted with jumpers (signal to ground).

The questions are:
1) Are the Kreg's voltages too high?
2) Are the OA's voltages too low?
3) Tube sockets A4/B4 and C4 are all reading 620 ohms.  The references for A4/B4 are "*" and for C4 is infinity. It seems like ~620 ohms should be the correct reading coming out of the +/- 6.3vdc power supply (is that right??)
4) C3 and C8 reference is "*" but what I'm getting is a reading that repeatedly decreases from infinity to 1K ohm with an approximate 5 second period.  Seems like it ought to be 27K (same as A1/B1) - (from schematic 27K + 174)  (right??)
5) TB points 2 and 14 are 85.5K/85.4K but reference is 71K. Consistent side to side so probably OK.  (from schematic 10.5K + 75K)  - (right??)
6) TB points 4 and 12 are 75.1K/74.6K but reference is 60K. Consistent side to side so probably OK.  (from schematic 75K resistor) - (right??)

EROS Phono c.2011

Voltage readings:

T.P.                  "A"                      "B"
Kreg                1.864vdc            1.863 vdc    (reference ~1vdc)
OB                    97.0vdc            97.8vdc
bA                    0vdc                  0vdc
bReg                98.3vdc              99.2vdc
OA                  150.3vdc            151.4vdc      (reference 170vdc)
IA                    223vdc                222.9 vdc


************************************************************************************************
Resistance readings (tubes removed, all readings in ohms):

Terminal Strip points:

1) 0.2
2) 85.5K (reference 71K)
3) 0.2
4) 75.1K (reference 60K)
5) 0.2
6) 467K
7) 466K
8) 0.2
9) 46.7K (reference 39K)
10) 46.7K (reference 39K)
11) 0.2
12) 74.6K (reference 60K)
13) 0.2
14) 85.4K (reference 71K)
15) 0.2
16) no connection
17) no connection
18) no connection
19) 47.2K
20) 0.2
21) 0.2
22) 0.2
23) 0.2
24) 0.2
25) 0.2
26) 0.2
27) 46.9K
28) no connection
29) no connection
30) no connection

Left input 46.9K
Right input 46.9K

Left output 466K
Right output 466K

Tube Socket pins (tubes removed, all readings in ohms, * denotes increasing R to values >20K ohms (I did not wait for stabilization))

A1/B1 26.9K/27.0K
A2/B2 0.2/0.2
A3/B3 */*
A4/B4 620/620 (reference is "*")
A5/B5 0.2/0.2
A6/B6 75.1K/74.9K (reference is 60K)
A7/B7 0.2/0.2
A8/B8 */*
A9/B9 47.3K/47.2K

C1 46.8K (reference is 39K  (but from schematic 100 + 47K))
C2 75.3K (reference is 60K (but from schematic 220 + 75K))

C3 reference is "*" BUT I get a decreasing reading from infinity down to 1K that repeats about every 5 seconds (e.g. OL initially followed by ~3M, ~1M, etc decreasing over about a 5 second period to ~1K, then back to OL, 3M, …. (repeats about every 5 seconds like a semiconductor being biased on then off by charging capacitor ??).

C4 620 (reference is infinity - (I didn't find a schematic for the 6.3vdc routing to the tubes)
C5 0.2
C6 46.8K (reference is 39K (but from schematic 100 + 47K))
C7 75.1K (reference is 60K (but from schematic 220 + 75K))

C8 ****similar response to C3****

C9 0.2