Why are my tape cassette decks popping??

[Sound-Design-Live]

ATTN Cassette Tape Deck Masters

I am working with Charlie over at Sonic Zen Records on a cassette tape transferring project and I?ve hit the wall! Where are these pops coming from?
Example 1 http://tinyurl.com/3mser5k
Example 2 http://tinyurl.com/3jssf2o

Here?s what I know:

• 1. It?s not a digital clocking issue because I can turn off all other equipment and just monitor the decks through a mixing board
  2. The decks have to be running, not just on.
  3. The particular tape or it?s position doesn?t matter
  4. The popping always comes in groups, one pop per deck in a random sequence
  5. I have tried different grounding schemes without success
  6. I have tried running a single deck on an alternative power supply. Still pops.
  7. All heads have been cleaned and degaussed and decks are new

Here is a photo of the 15 decks in a temporary rack setup. http://tinyurl.com/3zt4shk They are surplus marine decks that we have modified to have line-outs and a single power supply. I could provide more detailed information if it would help.

I have run out of ideas. Any suggestions would be appreciated.

[Studiodawg]

Are you transferring from CD? Is it the source?

[RickvH]

I'm assuming you're using the cassette decks for playback. I don't really understand why you need so many decks, but that may be beside the point.

I would first focus on trying to get one deck working without pops before trying to get them all working.

Other thoughts/questions:
Is the power supply adequate and does it provide clean DC?
It looks like all the decks are being powered from that one power supply--can it handle it?
It also looks like all the power is being transferred thru that single pair of unshielded wire coming out of the PS. Are the power wires forming a daisy chain from deck to deck--that might not be so great.
There's a lot of what appears to be unshielded speaker wire in the photo. What's that for?

[Sound-Design-Live]

@Studiodwag I'm recording from cassette to Protools through various interfaces.

@RickvH
- Is the power supply adequate and does it provide clean DC?
With all of the decks running the power supply still comes in below it's amperage rating. Whether is clean I'm not sure, but I haven't seen any spikes or dips on the meter even during these pops.

-Are the power wires forming a daisy chain from deck to deck--that might not be so great.
No, the power comes from the supply to a mult (can't remember what this thing is called, but I posted a blurry photo here - http://tinyurl.com/3f75tgc

There's a lot of what appears to be unshielded speaker wire in the photo. What's that for?
Low voltage wire running from the power supply to each deck

[rhythm ranch]

It almost sounds like static electricity. I wouldn't think it would be a problem in the bay area, but are you in a particularly dry workspace? I've encountered problems with static that sounded like this, but here in NM it's not unusual to be at 20% relative humidity.

Also, is there any space between the decks, or are they touching each other. Even though they're all connecected to the same power supply, you might try physically separating them.

[RickvH]

Other random thoughts:

The wire from the PS to the mult is carrying 15 times the current that a wire from the mult to a deck is carrying. Is that wire sufficient for that job? (If that wire has too much resistance, it could contribute to interaction between decks.)

A meter is probably too slow to show any spikes present on the power supply.

Can you play the radio in a deck to see if any pops occur with that?

Maybe try adding some filter capacitors where the power enters the deck?

Have you tried grounding the chassis of the decks?

[Z-Plane]

I'm recording from cassette to Protools through various interfaces.

Now there's novelty for you. Don't explain any further unless its equally or even more insane than those pictures. Bravo!

[Snarl 12/8]

I don't know why, but I suspect the "low voltage" wire connecting the power supply to all the decks. Have you tried powering it all off a car battery to see if perfectly clean DC makes a difference? Or power those low voltage wires, if they're necessary off a battery. Just for a test.

[Gregg Juke]

Trouble-shoot, powering only one deck at a time, then two, etc., etc. ?

I can't even wrap my mind around what and why you're doing...

GJ

[Studiodawg]

Sound-Design-Live...I have heard something similar in my lifetime. I will continue to ponder any possibilities to help you...Studiodawg.

[trevord]

yeah - i kind of agree with power supply stuff -
(remember it not just a question of capacity - thinner means more resistance which causes shifting levels)

power supply cables as short as possible

thicker gauge where needed

bus bars for ground and proper grounding for bus bar (massive braid/chain to plumbing)

use single point power source for deck power supply and digital interfaces

also

TURN OF ALL THE DAMN CELL PHONES AND WIRELESS NETWORK CRAP!!!!

you'd be surprised what has a wireless network in it (printers, tvs etc)

[trevord]

After looking close at the picture
I would recommend since you went thru the trouble of building that frame

1) Run ground and +12 bus bars down the back and connect the power inputs directly to them
2) bolt the power supply some where in the middle of the frame and connect to bus bars

3) get some shielding around the frame and connect to ground
http://www.lessemf.com/fabric.html

4) put a RCA pair for each deck audio out - connect correctly to frame shield and ground

5) use RCA cables to go from deck assembly to digital interface


That way you manage your supply issues and keep everything shielded

what your have there now is a nice collection of antennas just happily picking up rfi.

I don't understand why - but once you decided to go the frame - just follow thru and complete the design properly

[Sound-Design-Live]

@rhythm ranch
I don't think our workspace is especially dry, but this area is drier than others, so it's a possibility. Also, the room is carpeted.
The decks are touching, some by the chassis, but most only by the face plate, which is plastic. I'll try separating them.

@RickvH
- Yes, I think that wire is fine for testing, but I have tried powering only one unit at a time without successfully eliminating the popping.
- Ahh, I didn't know that about the meter. Thanks.
- No, I disconnected the radio from power in all unit.
- What kind of filter capacitor would you recommend? There was a ferrite looking thing on the wiring harness with a transformer inside. I tried wiring that inline, but it didn't help.
- The chassis should be grounded through the circuit board in then the negative leg of the power connection, but I will try a direct connection for chassis to earth ground.

@Snarl 12/8
-I haven't tried a car battery, yet, but I will if other methods fail.

@Gregg Juke
- It's an archival project for hundreds of lectures recorded on cassette tape.

@trevord
Thanks for the suggestions

@trevord
Thanks for the suggestions. That shielding fabric is great!

[RickvH]

Typical filter capacitors arrangement:

-Use one large electrolytic, several thousand microfarad: 2200, 3300 or 4700uF etc.
-Make sure the cap's voltage rating exceeds the power supply voltage.
-Make sure to connect according to the polarity markings on the cap.

-Use one regular .1uF (non-polarized).

-Connect both caps in parallel, across the power rails, as close as possible to the load (deck)

[RickvH]

3) get some shielding around the frame and connect to ground
http://www.lessemf.com/fabric.html

Interesting site that sells the fabric shielding.

Some of their products seem to be targeting the "tin foil helmet" people.