DBX 160VU power supply

[beatnik]

Hi everyone,

I have acquired a vintage DBX 160 VU on evilbay
This unit was in really bad shape someone with very poor skills attempted at repairing it

I have repaired the faults and recapped the unit but I am still having one problem, it's impossible to get the power supply section putting out the correct +/- 15V DC. The voltage is not symmetric, if I trim the positive side to +15V the negative sits at about -16.5V and vice versa

I have already replaced the 723 regulator, my feeling is that the LM301 opamp or some of the transistors are out of spec

I am very tempted to just put a LM317/LM337 combo but I would prefer keeping the original power supply in case I will have to sell the unit

 

[Bo Deadly]

That PS really has no endearing qualities about it and it most certainly doesn't affect the performance of the unit in any positive way. I would replace the PS in a heartbeat. Especially if the unit is in "really bad shape". A new PS would probably reduce the noise level (although the noise of the VCAs might still dominate so it might not matter that much).

One option would be to make a PCB for two PCB mount SMPS (like MeanWell MFM-05-15) with capacitance multipliers so that you can put a fat filter cap on the output without putting the SMPS output in protection mode. That would be super quiet and very sturdy. Put that in a little extruded aluminum enclosure with an IEC socket at one end and a cable gland on the other with a 4 conductor power cable (earth, power ground, +15, -15) running into the unit maybe using another cable gland in some existing hole or in place of the IEC socket perhaps. Then do the minimum necessary to disconnect the existing supply, leaving all of those parts there in case someone want's to undo what you've done, and then insert your supply source.

But again, the noise floor of the VCAs is probably higher than a mediocre PS so making an external SMPS is probably overkill. If you have a conventional linear supply that would fit in there and work with the existing PT, that would be just fine too.

 

[jazzcrisis]

Here's a different perspective about the original power supply. I've heard it said that it doesn't have enough gas, so when a big transient comes through, the compressor sort of "ticks" or ducks down right after the leading edge, which is supposedly why the 160vu is so loved on drums. I haven't tested any of this, it's just hearsay, but my own experience with them leads me to believe it's plausible.

 

[abbey road d enfer]

Here's a different perspective about the original power supply. I've heard it said that it doesn't have enough gas, so when a big transient comes through, the compressor sort of "ticks" or ducks down right after the leading edge, which is supposedly why the 160vu is so loved on drums. I haven't tested any of this, it's just hearsay, but my own experience with them leads me to believe it's plausible.

I find it very hard to believe. The VCA and the side-chain impart much more "character" than whatever supposed PSU weakness.

 

[QUEEF BAG]

this isn't the problem in your case, but i always replace the caps in the power supply in those with double the size at least...you could even go 1000uf & 100uf

sag is nice in tube guitar amps, but....

 

[beatnik]

Think I found the problem... someone had subbed two BC361 in the power supply with BC461. I ended up replacing the LM301 as well and the power supply is now working fine.

Changing topic, how can I disable the output mute function ? I have read that it just increases noise and distortion.

 

[abbey road d enfer]

Think I found the problem... someone had subbed two BC361 in the power supply with BC461. I ended up replacing the LM301 as well and the power supply is now working fine.

Changing topic, how can I disable the output mute function ? I have read that it just increases noise and distortion.

You must disconnect the FET's (Q10-11-12-13). It's the only way.

 

[guy_4]

Think I found the problem... someone had subbed two BC361 in the power supply with BC461. I ended up replacing the LM301 as well and the power supply is now working fine.

Changing topic, how can I disable the output mute function ? I have read that it just increases noise and distortion.

You can easily do it by cutting the link between P3-2 ( output ) and the FET's.
These FET's are all sort of toubles... better forget this " Mute " function !
Any of the 160's that came thru my hands I have always cut this link.