Rowe AMI CD100 -- speaker thump at power on

I have the first model CD100 and have always been annoyed by its characteristic speaker thump at power on.

Does anyone know if Rowe provided an upgrade to suppress the thump?

I'm aware of numerous speaker protection circuit designs on audiophile sites, etc, that include a speaker connection delay to eliminate on-thump, but I would prefer to use a Rowe-specific solution if one exists.

Yes--there is a "Rowe provided solution"--
Do you have a Service Manual ? If so, look at the power supply wiring for a "Domestic" phono, and rewire yours as such. This will eliminate the thump, if the on/off switch on the back of the phono is used (also keeps the amp "hot" at all times ??).
Ron Rich

Yes, I do have a service manual -- somewhere. It was inside the juke when I bought it, just need to find where I have put it.

Many thanks indeed for the tip!

The mod that Rowe offers simply connects the amp directly to the incoming AC line. That means it will consume several watts off the mains even when the rest of the machine appears off. If you remove the plug, it will thump when plugged back in anyway.

The reason for the thump is that these amps (Seeburg included) have no relay that disconnects the speakers till the DC component stabilizes.

This is preferable in the longterm as the relays used in that application, even in commercial amps, often develop erratic contacts and cause annoying service calls.

For typical consumer amps where the speakers are directly connected a protection ckt w/some form of DC sniffing is important to prevent blowing out speakers when the amp finals fail.
In commercial amps where there is a blocking cap and/or a transformer, a relay is just another failure point.

Rob-NYC

Guyz,
It ain't all that simple--yes-"domestic" wired Rowe CD phonos leave the amp powered up at all times--but also everything else !
The only thing shut off/turned on by the "power switch" on the power supply is the lights ! On most of the "non-domestic" ( depending on country/and or voltage {?} ), some were wired so the amp stayed hot, others not--and a different power switch was used ( going from the schematics). Reasons--I dono--and the only guy I can think to axk, is no longer here with us Ron Rich

Ron, the older, pre-Rowe AMI continentals were wired with the mech and PSU on 24hr and only the lights switched.

The reason I was given was to avoid the loss of credit if a customer inserted a coin.

Needless to say, I changed that.

Rob

Rob,
Yes--I am aware of that--and I too, have "changed that"--many times !! I also heard the reason was so the amp stayed hot, and could be used as a PA, when the juke was off ?? Ron Rich

All this fuss over a momentary "thump"?
I'd just let it go, because it's a fraction of a second thing, and not worth bothering over.
And no, I wouldn't want the amp constantly sucking /wasting juice.

Hi Matt,
I agree--but I also agree it can be pretty annoying on Rowe's. They changed PART of the mute circuit, on the CD's. The mute relay wound up being "slower". so when powered up, the amp power supply is able to fully power up prior to the other power supply, which is what energizes the relay--you do hear a LOUD "Thrump"-- ( I swear, I once saw a large dog sleeping in front of a JB--he jumped at least six feet high, when that thing was powered up !) Ron Rich

There are thumps and there are THUMPS. Rowe is in the latter class. the combination of efficient speakers and no early muting (at that point) in the voltage amp stages really gets attention. I've had customer yell "what happened" and 'are you ok?" when I turn one on from a cold start.

....As they say..it is always "something"....

As for the old mic-paging it would be fairly easy on the AMI-Rowe because all that was needed to turn on the B+ was to open the mute-squelch relay coil ckt. The stereo phonos would require a phase flip because of the unique speaker operation.

I've never seen a mic kit on any phono here in NYC. A few of my locations have sound racks (that I installed) but they rarely use the mic in's.

Rob

Rob-NYC wrote:There are thumps and there are THUMPS. Rowe is in the latter class.

Yep, and that's why I want to suppress it at home.

Thanks for all the comments. I'm steering towards installing a time-delayed relay. Maintenance of relays is not an issue for me given it's a private domestic installation, but I'll probably use a sealed relay for good measure.

Okay, now that I've found my service manual, and familiarized myself with the CD100's innards, I figure that "de-thumping" via the existing mute function is the easiest way to go.

I'm thinking of using the service outlet to power a delay relay that mutes the amp by default until 5 seconds or so have elapsed.

This ready packaged variable delay complete with base for a few dollars seems to be ideal:

http://www.ebay.com.au/itm/262060451014 ... EBIDX%3AIT

Not sure if an AC relay might introduce hum into the system via inductive coupling with the mute line.

I can get a 24 volt DC version and power that from the 28V DC supply, too. (Omron relay coil spec allows 85% to 110% of rated supply voltage). Could put a dropping resistor in circuit to keep the coil happy.

Upon reflection--I don't think that will stop it ! Check it by removing the AC plug from the power supply --turning the phono on, then plug in the amp--I THINK you will still get the "thrump" ?? Ron Rich

Yeah, I had the same thought after sleeping on it. The mute affects the input, whereas the thump is a function of the power amp output stage.

Am thinking of using this 135 watt per channel kit which also protects speakers against DC and can optionally monitor heat sink temperature and can also suppress off thump (not a big issue with my CD100) :

http://www.altronics.com.au/p/k5167-ste ... amplifier/

Since there is no description, or schematic, I'm unsure of exactly what this board does ?
Ron Rich