2250 blowing rear fuses with Modulus pre

[Kidgreen]

Hello all,
I am hoping someone can shed some light on my issue.
I have an AI Modilus pre with a CJ 2250 totally rebuilt and modded by CJ. I took everything in my rack to rebuild it and now once put together, I am blowing the 4 amp fuses.
I am a little confused by inverting phase for the Modulus. Not sure I am doing it right.
Your thoughts are greatly appreciated.
Ken

[admin]

The MF-2250 is phase correct. So you only need to worry about correcting phase is if you have an odd number of phase inverting components in your system. If that is the case, you can just flip the Pos/Neg connector on one of end your speaker cable to correct.

As for the fuse blowing issue that can be caused by multiple things. I always go for low hanging fruit first. I would check on all 5 fuses in the unit to make sure they are of proper value and in good condition. 2nd I would do a visual inspection of the internal components to look for any clear signs of faults,.. such as cap bulging, burn marks, signs of a bad solder joint etc. After that, it gets more complicated.

Let us know what happens.

PS- CJO is undergoing some upgrades this week so the site may be down for a few days.

[Kidgreen]

I will replace all the external fuses. I was inverting both speakers, now I will do just one and cross my fingers. This setup worked beautifully before.
Will keep you posted.
Thanks

[admin]

Just to be clear, if the Modulus is inverting, you would flip both speaker cables as both channels are inverted by the modulus. Not sure if that is what you mean as the way your write it was a little unclear?

[AnotherJohnson]

I will replace all the external fuses. I was inverting both speakers, now I will do just one and cross my fingers. This setup worked beautifully before.
Will keep you posted.
Thanks

You need to wire both speakers in the same phase.
Positive amp wire to positive speaker terminal. Negative amp wire to negative speaker terminal. Or out of phase, positive amp to negative speaker terminal and negative amp to positive speaker terminal.

BOTH SPEAKERS MUST BE WIRED THE SAME TO THEIR SIDE OF THE AMP OR YOUR BASS WILL DISAPPEAR.

Usually if fuses are blowing after an amp has been changed, it is because there is a short at one end of the speaker wires (amp end or speaker end). That is the low hanging fruit.

Where are you located? Did CJ in Fairfax do the repairs? Or are you dealing with an importer in another country?

If the speaker wires are not shorted (one strand barely touching from + to - at amp or speaker is enough to short), box it up and send it back, This quirky charm and half-a$$ed service is no longer charming.

[Kidgreen]

All fuses were replaced, preamp switched out and all four blew. Called CJ and they said to send it in. I had it all modded in 2022 by them so looks like it is going back.
It is always something right?

[Kidgreen]

Initially I had both speakers inverted but upon closely reading the Modulus manual I thought it said only one speaker was necessary, which I thought strange.
I then switched out the pre with my Apt Holman and all 4 blew. Before I took my rack apart this setup worked great into ADS 910s.
More to come I am sure

[admin]

Sorry to hear it wasn't a quick fix but at least it's going to be repaired right and you won't have to worry.

As for the phase, the Modulus is phase inverting and BOTH speaker cable channels need to be flipped.

[AnotherJohnson]

I would be cautious about how much money I put into this amp. If CJ is fixing it for free, you are still probably on the hook for serious shipping. The amp would not likely bring $1000 at resale. Pre-COVID it would have brought about $750 in working condition.

This model is not super transparent, or super dynamic, or super sweet. It’s not even super euphonious.

If CJ will warrant it, maybe it’s worth the shipping. But the repairs were done two years ago, and if they warrant it, it will be out of love, not out of obligation.

I do not think that it goes without saying that it will be fixed right … I said to send it back to them because I thought it had just been serviced. Had I known the service was two years ago, my advice would have been to bin it. I have personal anecdotes dating back to the PV5 when I had to show patience with service. It was not just the incompetent handling of my LP275Ms. I can think of three other examples where I had to overlook things.

This unit is very old and it is not being chased by anyone as a bucket list amp. CJ cannot do magic. Many OEM parts are no longer available. This sort of project can turn into a series of trips back to Fairfax with significant downtime and expense.

If I were in your shoes, I’d cut my losses.

[Kidgreen]

They did email me a quote of $728 to fix my issue. No explanation and no communication other than the email. No breakdown of what is wrong. I have left several messages asking for a call back to explain this cost after a complete rebuild only 2 years old. I do really like this amp but this treatment from customer service is intolerable. I am in my own business as a manufacturer and when a customer has an issue I do my darndest to clarify and make good. This is all making me very sad.

[AnotherJohnson]

They did email me a quote of $728 to fix my issue. No explanation and no communication other than the email. No breakdown of what is wrong. I have left several messages asking for a call back to explain this cost after a complete rebuild only 2 years old. I do really like this amp but this treatment from customer service is intolerable. I am in my own business as a manufacturer and when a customer has an issue I do my darndest to clarify and make good. This is all making me very sad.

It is never a complete rebuild. There are always parts that checked out OK and weren’t replaced.

That estimate to repair is just an estimate. That’s not a lot at their labor rate and bench fees.

This unit is VERY old. It has been discontinued for a LONG time. I understand being sad … but it is expected. Stuff ages out and fails. This is the wear out failure regime, not the infant failure regime or the constant hazard rate failure regime. If you fix it, one or two years from now, you will be going through this again.

I would take this as good news. Now you know that it’s going to cost more than it’s worth to keep it going and you can start shopping for something from the last decade. There are a lot of great units out there, and they have superior sonic performance compared to vintage CJ. Enjoy the hunt.

[roberto]

Hola Kidgreen,

Only few things could cause fuse blowing. A short in the speakers connectors, a bad power supply or one channel with power transistors in short. These are the most common failures. You have to repair the unit. Fuse blowing is a big warning. A lot of current is passing through the amp. You could burn the speakers if DC passed to the speaker's binding posts. Be careful. If you checked for a non short in the speakers terminal, you must take to an electronic repair shop the amp.

The estimate from CJ is either possibility above mentioned. It is not an easy task to service a vintage SS device. You did a fresh updated components. But not all. Many components could be blown. Why this happened? It could be many reasons what happened. You can't know when an electronic component will have a failure. The reason for a bad fuse, is to keep your amp protected for a bigger problem.