Foreplay II : anticipation upgrade - check out problem

[choff]

I just dug up my C4s anticipation upgrade kit purchased 8-9 years ago and installed in my Foreplay II.  Unfortunately.  I appear to be getting some different readings that I'm concerned about on a number of the terminals and don't know really how to proceed.  I have shown what each one is supposed to be in parenthesis. 

Please advise....thank you.


Terminal    Resistance

2                28  (infinity)

10              380 (infinity)

15              0 (470K)

A1              1293 .......the (1) blinks on the meter (infinity)

A2              .625  (0-80k)

A4, A5          64 (infinity)

A6                730  (1 megohm+)

A7                1291 .......the (1) blinks on the meter (infinity)

A9                55.8  (infinity)

B1                1460 .......the (1) blinks on the meter (infinity)

B2                .441 (0-80k)

B4,B5            53 (infinity)

B6                325  (1 megohm+)

B7                1450 .......the (1) blinks on the meter (infinity)

B9                64  (68k)

 

[choff]

Well,  given there was no response to the above issues I posted,  I threw some caution to the wind and plug in the tubes and fired the Foreplay up.  Tubes glowed....all the LED's light up and there was no smoke.  Left it on for a couple of minutes before turning off. 

Any thoughts on proceeding?  Thanks.

 

[Doc B]

Well,  given there was no response to the above issues I posted,   I threw some caution to the wind and plug in the tubes and fired the Foreplay up.   Tubes glowed....all the LED's light up and there was no smoke.   Left it on for a couple of minutes before turning off. 

Any thoughts on proceeding?   Thanks.

The scale that the meter is set to will help you to determine if the numbers mean ohms, kohms, Mohms, etc. It's a little difficult to decipher your readings as posted. Does anyone know of a tutorial about reading DMMs? Might be good if we had a link to one. Since you have test fired it what I would probably do at this point is move on to the voltage checks and see if they are correct.

 

[choff]

Looking at the digital display on the meter the Kohms is showing on the right hand side.  I dug around yesterday and for the life of me I don't know where the meter manual went. 

Does this help?  Proceed with voltage checks?  thanks.

 

[Grainger49]

If you didn't get smoke voltage checks are in order.  Then, if within 15% of Doc's voltages, music.

 

[choff]

Voltage checks completed.  A few are above the 10% threshold.  The numbers in parenthesis are the ideal readings listed in the manual :

Terminal        Voltage

2                  182 (164)

7                  170 (153)

A3                2.1  (1.7)

B1                59  (47)

B3                2.1 (1.7)

B7                60 (47)

B8                64  (51)



Is there something going on the 'B' side as it seems these are where most of the high readings are?  Thanks for the help. 

 

[Grainger49]

Most of the voltages are within 15% of expected.  Since you didn't post A1 then it is probably good.  B1 should be at the same voltage as A1 if the boards are right.  Well, within a few volts.

Terminal 2 and 7 are in the power supply and might be a little high because of incoming voltage or the B tube not passing enough current.  Check and post your incoming voltage (remember AC here).

A7 and B7 should be at the same voltages as A1 and B1 respectively since on each tube pin 1 and pin 7 are hard wired together.  You measured close so that is right.

Since most of your problems are around the B side tube, swap tubes and see if the higher voltage follows the tube.

 

[choff]

Swapped tubes and the measurements did in fact follow.    Is one tube better than the other?  Should i replace one of the tubes for more balance?  Am i good to go regardless?

thanks,
Carl

 

[Doc B]

If the balance sounds OK you are good to go.

 

[Grainger49]

One tube is worn.  The one that was in the B channel to start with.  Try a new pair, or just a replacement for the worn one and see how you measure.

I'll bet even the worn tube sounds pretty good now.

 

[choff]

Up and running.  This is a wonderful new sound.  DEEEP Bass extended bass that I have never heard my system reproduce.  Nice highs.....maybe a tad bright at times but I expect they might break in. 

I'm one happy camper with the exception of one issue......microphonics.  The turntable is ultra sensitive now and when set to the cd player i noticed right away a high degree of air / hum coming from the speakers that was not their before the mod.  In fact,  things were near dead silent compared to what I'm hearing with no music playing now. 

Got to be a grounding issue but where do I start?  Frankly,  I'm kinda tired of picking at this crazy box of brains and just want to enjoy how nice this new upgrade sounds.  Fun stuff.

 

[Paul Joppa]

The upgrade should not have any effect on hum, so I'd look at the cables and their connections first. Especially the ground (outside) of the RCA plugs.

I'm assuming you mean there are noises; microphonics usually refers just to vibration of the tube internal elements, unrelated to the turntable or CD player.

If you are getting noises when you touch the turntable, it may be that the turntable ground wire is not connected properly. Or it may be that the connection in the Foreplay between chassis ground and signal ground is broken (you did do that mod, years ago, right?!)

 

[choff]

If you are getting noises when you touch the turntable, it may be that the turntable ground wire is not connected properly. Or it may be that the connection in the Foreplay between chassis ground and signal ground is broken (you did do that mod, years ago, right?!)

hmmm..........not sure what modification you are referring too here?   but what you describe is definitely one of my main problems at present.

 

[Grainger49]

I think PJ refers to the jumper between T13 and T14 that grounds the signal common.  Carl said he had done that already.

 

[choff]

Some more info on this issue in case it helps determine the cause :  When i turn the Dynaco 70 on alone i get that "air" coming thru the speakers.  This sound is then amplified when i turn on the Foreplay.  The sound neither increases or decreases when turning the pots.  Even more background noise when Seduction is selected.  Tonearm exhibits reaction sound when tapped similar to when a microphone is tapped.

Not sure what you mean by "outside" of RCA ground.  Terminal 13 and 14 are connected as Grainger mentioned. 

 

[Grainger49]

Each RCA connection, male and female, has an outer conductor which is called ground, shell or outer conductor.  This is the part of an RCA plug that you can grasp.  There is also a center conductor that is called hot or center conductor.  This is the pin that goes into the hole of the RCA jack.  Since audio signals are AC part of this is a bit of a misnomer.  The outer, shield, ground is most often grounded, but not always.  The inner is the signal which is "hot" relative to ground but in actuality it swings positive and negative around ground.

It sounds like tube rush, a noise that can sound like white noise, a sleep machine, to a low frequency rrrrrr kind of noise.  The best way to check the ST-70 is to use shorting plugs on it, or just use jumpers to short the input RCA jacks.  That tells you the minimum noise produced by the ST-70.  The same for the FP 2 and Seduction; short the input and listen.

Since each C4S board only has 3 wires you can easily re-wet each of the terminations just to assure yourself on those.

 

[Doc B]

The upgrade increases the gain slightly and therefore increases what from your description sounds like tube rush coming from upstream. The Stereo 70/Foreplay I/II combo has been pretty well documented as having a ton of gain that emphasizes the noise floor of the tubes in the source and preamp, and usually the easiest solution is a couple of in line attenuators between the FP and the ST70. Parts Express sells them. A search on the forum archive will turn up a fair amount of discussion about these attenuators.

 

[choff]

Thanks guys.  Without question there is a bunch of additional gain in the system now after this upgrade.  Probably 2 clicks worth on the sweet whispers.  Thought it odd that the noise I hear is not affected at all by the position of the pots?  It's just very consistent.  Air and a tiny buzz noise like a bee would make (or tubes i guess in this case).  Really not noticeable during playback except for very quite passages it can be annoying and when switching out music.

I'll check into the attenuators you mention.  Did I mention this is one awesome upgrade?  Feel like I just got a whole new stereo system. Thank you Doc!!  Got to love the fact that it only took me 10 years to sit down and finally get it done : )

 

[choff]

any thought on the DB reduction factor I should chose as they seem to come in 3, 6 or 12 db : http://www.parts-express.com/wizards/searchResults.cfm?srchExt=CAT&srchCat=725

also,  I would attach this to the output end of the Foreplay or the input of the Dynaco.....or does it matter?

 

[Doc B]

The noise comes into the circuit mostly from after the Sweet Whispers, so the volume control won't change the noise level. That's why an inline attenuator to cut the high gain of the Stereo 70 is the best approach. The "air" is tube rush and that might change a bit with different tubes in the FP. The buzz is ground loop noise and that could be due to the terminal 13/14 thing mentioned by Grainger, cables or cable connections that are less than perfect, ground loops between the preamp and amp, light dimmers, or a whole bunch of other less likely sources.

If you still have four or more clicks left at the high end of the attenuator range when listening at average levels I'd suggest the 12dB, which will have the strongest effect on lowering the noise. If you are listening with the attenuator higher than that try the 6dB attenuators. Put them right at the input of the amp.