How to find out if a vintage amp has a zero DC output.

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Asraam0
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How to find out if a vintage amp has a zero DC output.

Post by Asraam0 »

I have acquired a Tundra 2.0 and the documentation has the warning ' As Tundra is DC-coupled, you can only use
preamplifiers that have zero DC voltages on its output.' How do I find out if my vintage Nexus SP1 is suitable to use with the Tundra ?

The only details I can find are:-
Specifications
Specifications Ion Systems Nexus SP1 preamplifier:
- Inputs sensitivities / Impedances:
- Phono MM: 2mV/47k
- Phono MC: 100uV/22 ohms
- Aux/CD/Aux 2/Tuner/Tape 1 & 2: 100mV/150k
- Tape outputs: 100mV
- Main output level/impedance: 0.7V/300 ohms
- S/N ratios:
- Phono MM (MC): -75dB (-68dB)
- Aux/CD/Tuner/Tape: -90dB
- Residual: -100dB
- Distortion at Rated levels: <0.005%
- Size (W x H x D): 20 x7.5 x 26 cm
- Weight: 2 kg

Specifications Ion Systems Nexus X-Pak 2 power supply:
- Size (W x H x D): 20 x7.5 x 26 cm
- Weight: 6 kg

Thanks to any advice on this as I do not want to do any damage .
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Re: How to find out if a vintage amp has a zero DC output.

Post by lejonklou »

Hi Asraam!

I remember the Ion Nexus, we sold it at The Sound Company in Uppsala in the early 90's. I also met with the designer when he visited Sweden. Very, very old school transistor designs.

None of the data you have posted relates to DC voltage out. There are also virtually no preamps that intentionally have DC on their outputs, the problem can rather arise when an amplifier gets really old and components age, break or dry out.

What happens is that any DC (a static voltage, like a battery) will be amplified by the Tundra, which will push out, or if the static voltage is negative, pull in the bass units of the loudspeakers. Constantly. And this constant pulling will generate heat in the amplifier and in the voice coils of the bass units. Not good.

The best way to find out whether the preamp has DC on its output is to measure it with a multimeter, set to the lowest setting in DCV (or maybe it's marked V=). Just switch the preamp on, attach a pair of interconnects to its outputs and in the other end of the interconnect, measure between the pin and the barrel on left channel, then on the right. The value should be in the millivolt (mV) range. 0.01 Volts for instance. That's 10 mV and not a problem.

A simpler way to do it is to connect the preamp to the Tundra, and Tundra to your speakers. With the preamp on, switch Tundra on while you look at the bass units of your speakers. It should take about a second for the two power supplies to start switching and the amplifier to light up its two blue lights. And you should hear a faint "tk" or maybe nothing at all. Did the bass units pop out and stay there? Did they pop in and stay there? If so, just switch off the Tundra immediately. It's very unlikely any harm will be done - even if your Ion Nexus is in terrible shape.

If nothing happened to the bass units, you're fine. Play some music and tell us what you think of it!
Asraam0
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Re: How to find out if a vintage amp has a zero DC output.

Post by Asraam0 »

Thanks for the advice.I will ask an engineer at work to check it out in a week as you advised. In the meantime I will set it up with my Quad 99 pre amp which is not as vintage as the Nexus. I will keep you posted.
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Re: How to find out if a vintage amp has a zero DC output.

Post by Asraam0 »

Success !!!!
I tested the Nexus with a multimeter as suggested. The results were good and surprisingly well less than your safety levels. All done by my electronically qualified younger brother. I have spent most of this morning disconnecting and cleaning the old setup and then connecting with the Nexus pre and the Tundra. The Quad 99 pre and 909 being prepared for sale, forgot how heavy the 909 was !
The afternoon was spent listening to the new setup .
The old favourites were given a spin :-

Tom Waits Blue Valentine
Sufjan Stevens :- Carrie & Lowell
Carly Simon :- No Secrets
Supertramp :- Crime of the Century

The listening was very pleasurable .The vocals were noticeable more detailed and the bass was tighter and there was a feeling of greater separation between the instruments. Tom Waits grumbling voice and the fantastic baseline at the begining of your so vein were highlights .
I understand that I have changed two parts of the system at once which is not ideal. However I am sure the majority of the change is due to the Tundra , I intend to upgrade from the Nexus SP1 soon/when funds allow then the system will definitely reach its full potential.

I am looking forward to further listening in the next few days.

Thanks again for the technical advice.
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Re: How to find out if a vintage amp has a zero DC output.

Post by lejonklou »

Great to hear that everything works as it should and that it sounds good, Asraam!

As already mentioned, the risk of any problems were likely minimal. But I appreciate you being thorough and actually reading what the manual says. And regardless, it's good to know about DC voltages. You can't hear them, but they can easily be measured and could potentially cause problems in several parts of a system. For instance when transformers, old equipment or lots of amplification is involved.
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Re: How to find out if a vintage amp has a zero DC output.

Post by Asraam0 »

Just to inform you that I am now the custodian of a Sagatun Tarandus to go with the Tundra 2.so the target has now been achieved and the Ion Nexus has been stored again maybe to pass on I am enjoying the experience of a lejonklou phono & Pre an power amp setup.
Thanks to Chris @ Hidden systems for helping me in this quest.
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