I need more juice - Dimming lights on SX-1250

[qguy]

I have some rather low efficiency speakers, 87dB, 3 ohms minimum (not nominal) at 70 hz, I noticed on loud bass / drum notes the lights on the receiver starts dimming.

1. Would it be possible to change to a larger capacitors, say 35000 ?
3. Add more capacitors externally by tapping into the main capacitors and locating them outside the amp ?

 

[qguy]

Found this on Ebay

Will this work ?

1x 35000uF 120V Large Can Electrolytic Capacitor 105C 35000mfd DC Volts 35,000

• • Capacitance: 35,000mfd
  • Voltage: 120VDC
  • Tolerance: 20%
  • Temp: 105°C
  • Lead Type: 2 Large Screw Post Screw Terminals
  • Diameter: 3"
  • Height: 5 5/8"

 

[4-2-7]

If your not matching equipment good your in no way heading into a direction of good sound.

That said your receiver should be able to drive the speakers, it sounds like one or both need some rebuilding. Maybe start with recapping the speakers if they are keepers for you and see what that does.

You can also add a power sub into your system if you like bass heavy music.

 

[qguy]

The speakers (12 inch woofers) are are rated down to 29hz, does not really need a subwoofer, but I also have a 15 inch sub,. The speakers are new old stock (1993 models), so the capacitors should be good, unless the caps deteriorate even when not in use ?

 

[4-2-7]

but I also have a 15 inch sub,

Is this hooked up now to the 1250?
Is it a powered sub?

The speakers are new old stock (1993 models)

Being vague in "ALL" the equipment you have is not helping anyone. You should be posting names and models for everything hooked up in your system.

unless the caps deteriorate even when not in use ?

Quality and age is the factor, not if the caps haven't been used. In fact they could be better given the same age if they had been used the past 25 years. Cap life span is around 20 years.

 

[savatage1973]

Has the SX-1250 been serviced? The speakers should be OK at this point, but the caps are 25 years old and might be better replaced; however, if the receiver has not been recapped (especially the mains), that could be a problem--those are 40 years old.

Also, what kind/size of room are you trying to fill with sound and at what volume level? Perhaps your "expectations" are beyond the limits of what the SX-1250 paired with somewhat "difficult" and low efficiency speakers can provide.

Upping the total capacitance of the main PS could help, but be cautious in going too far--the transformer and rectifiers have to be up to the power-up surge and heavier continuous demand. You could end up "playing with fire"--literally.

 

[qguy]

Speaker are Alon Model IV

Rythmik F15 powered subwoofers, yes it is hooked up to the SX-1250.

SX-1250 is untouched. Not so keen on recapping the SX-1250, I did it successfully once on an SX-1050 and it is not something I can do at this point. Replacing 4 big caps should not be an issue as it should take a couple of hours to do.

Room is on the small side, something like 20 x 25 square feet.

 

[4-2-7]

Rythmik F15 powered subwoofers

You have two of them?
Use a RCA line to send the signal to the sub, if you have a speaker wire going to it, it might be putting more load on the amp. Use a RCA cable off the Tape output.


Acarian Alón IV loudspeaker Specifications





Sidebar 4: Specifications
Description: Three-way, floorstanding loudspeaker. Drive units: 1" (25mm) metal-dome tweeter, 5" (130mm) tri-laminate cone midrange, 12" (300mm) fiber-cone woofer. Crossover frequencies: 400Hz, 3.5kHz. Anechoic frequency response: 29Hz–25kHz ±3dB. Low-frequency bandwidth (anechoic): –3dB at 29Hz, –9dB at 20Hz. Sensitivity: 87dB/W/m. Impedance: 3 ohms minimum. Amplifier requirements: 100W minimum, 200W recommended.


They are pretty low impedance, so let use know if your subs are being driven with the speaker wire and if so change it, or disconnect the subs and try it.

BTW you can drive the speakers with the amp in the sub, thats a 600 watt amp that will help your speakers a lot.

 

[Silentnet]

20x25 is a large room.

The SX-1250 needs service. That said, even in top condition, it's not a good match for your speakers. They recommend a bigger amp, and based on the reviews I've looked over real quick, the more power the better.

Good news? If it's in good shape the 1250 is worth quite a bit. Sell it and get something more appropriate.

 

[markthefixer]

Check (or put in a new one ) the soft start relay, it carries all the unit's current through it's contacts, and unless the contacts are newly burnished, their resistance could be strangling the receiver, with more and more juice going through the soft start relay.
Now if a separate lamp in the same wall socket dims, then the wall socket needs to be checked.

If I were checking a unit out, I would:

USING EXTREME CARE, HOOK IT UP WITH POWER OFF!!!!!!!!!!!!!!!!!!!!!!!

put an AC voltmeter across the soft start resistor and see how much wattage is being dissipated by it. There really shouldn't be any AC voltage across it, it is a maximum of 50 milliohms - 0.05 ohms.
At 15 amps, that would be 0.75v AC across 50 milliohms.

At the soft start resistor's full 3.3 ohms it would be 50 volts AC.

 

[qguy]

Thanks for all the advice.

The subwoofer was off when the lights were dimming

I will install a bulb in the same socket to test the electrical connection

Clean/burnished the contacts

Lastly, I will test the relay, which one is the soft start relay, is it the first click or second click ?

Thanks

 

[zebulon1]

This thread isn't sounding good. Starting to worry for the 1250.

 

[restorer-john]

First click is the soft start relay.

Power unplugged first. Attach your AC V meter to these points with clips/mingrabbers. The V drop after the first click after power on should be in the mV range.

Do not poke around with a meter probe in each hand with the power attached as this part is live.