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SX-1250 pre/power amp issue

B

bernie Stag

New Member
I have a unit that plays fine when the jumpers are connected to all speakers whether A, B, or C is selected, but when I remove the jumpers to connect a graphic equalizer the left channel has no sound passing through to any of the speaker whether buttons A, B or C are selected, what can the issue be?
Thanks
 
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A, B and C speakers selection is just a switch after the output of the power amp inside. If you are missing a channel with the gr eq device connected you have a bad cable or bad equalizer.
Put the jumpers back in, and try the eq in a tape monitor loop or the Adapter loop. That way you can bypass it with a switch change for testing.
 
Thanks.
Yes I did the Tape monitor bit with the jumpers back in and it plays through both channels but there is a drop in volume when I engage the tape monitor with the eq in play, but I do have sound through both speakers in all three switches at this point, and the led for sound levels work for both channels when the eq is engaged so it is supposedly working.
 
bernie Stag said:
Thanks.
Yes I did the Tape monitor bit with the jumpers back in and it plays through both channels but there is a drop in volume when I engage the tape monitor with the eq in play, but I do have sound through both speakers in all three switches at this point, and the led for sound levels work for both channels when the eq is engaged so it is supposedly working.
Click to expand...
What EQ are you plugging in to that SX1250?
 
Do you have the Stereo/Mono switch in Stereo?
Is the channel that is missing when using the Pre-Power jumpers the same one that has lower volume in the Tape Monitor?
Did you try the Adapter connection?
 
merlynski said:
Do you have the Stereo/Mono switch in Stereo?
Is the channel that is missing when using the Pre-Power jumpers the same one that has lower volume in the Tape Monitor?
Did you try the Adapter connection?
Click to expand...
Yes it is in stereo mode.
When I plug the eq into the adapter connection there is no sound when the Adapter is engaged from either channel.
When I use tape monitor and engage the tape monitor switch there is a significant drop in volume to the speakers they are 4ohm Paradigms.
I brought this used in great shape and it was listed as working, at least when running as is straight up, the sound is good.
Is it possible to run the eq through the Pre/Power instead?
 
The Pre/Power jacks are the last connection in the signal path before the input to the power amp stage. The signal there is controlled by the volume control and the other signal shaping controls upstream. Equalizers are usually used in a "Line Level" portion of the signal path, like the Tape Monitors and Adapter connection. Those "Line Level" connections are upstream of the Tone controls, High & Low filters, and Voltage Gain stages. The SX-1250 schematic shows the Line Level as 150mV RMS at the Tape Monitors and Adapter jacks. Feeding the Equalizer with the Pre outputs may overload the inputs of the Equalizer. Certainly, people have used Equalizers in that location successfully. So the real answer is 'it depends' on the equipment. Look at the User Manual for the EQ device and see where they want you to connect it.

But 'where should I use it' is a different question than 'why is it not working'. Though they may be related.

The EQ may have a Tape Monitor loop on it as well, many do. If the EQ is not set correctly it may not be passing a signal to its outputs. The Adapter connection is not quite the same as a Tape Monitor connection. You did not specify the exact model of your EQ so I could not look it up.
The Adapter Out should go the the EQ input, and the Adapter In should connect to the EQ output.
You can test your cables with an ohmmeter, or use them in place of the jumpers to see if they pass signal correctly.
Have you tried the EQ on a different Amp? It seems to me that the SX-1250 is not the problem. The EQ may not be perfectly calibrated to have no effect on the overall level when it is engaged, that is not unusual either. Sometimes there is a level adjust on the front, on the back, or internally to match level in to level out, with the EQ set flat all the way across.
Forgive me if I am repeating things you already know, just trying to be thorough. I can be pedantic at times :rolleyes: . . . but I want to help.
 
Thanks for the responses, I am of the thought that the eq is defective. I am just hoping that if it is it has not caused any damage to the receiver.I have used it on a different smaller receiver
and I have now noticed that there is some low level static in the right channel when unit is turned on and speakers engaged without the eq connected, and I also noticed now that when engaging either of the push in buttons for the filters on the unit there is a little static like clicking sound emanating form the left speaker. So much to consider now.
Thanks for taking the time to help me troubleshoot this issue.I have ordered the ART EQ-341 - Dual-Channel 15-Band 2/3 Octave Graphic Equalizer as an inexpensive replacement.
That should eliminate the questions on the eq issue altogether.
 
Noisy switches is often related to age, and Deoxit D5 applied repeatedly between repeated exercising of the switches often clears that up.
Low level 'static' is likely a symptom of aging transistors. The cure for that is replacement.
Here is a link to an AK list of problem transistors: Top Ten Worst Transistors - noisy, failure-prone, whatever... and replacements
The SX-1250 is a fine machine, well worth the effort and expense of refurbishment.
There are many threads here on AK about repairing and refurbishing your SX-1250, and lots of people willing to help. You are in the right place.
You will need to download the Service Manual, hifiengine.com has one for a free download, you do have to register, that is free and safe also.
And if it has not been said yet, Welcome to Audiokarma!
 
Thank you for all your shares and suggestions. I agree with you it is a fine piece of equipment that keeps amazing me with every piece of music I play.
Be well, stay safe.I am happy to have found and joined this forum.
 
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