NAD - Fender 57 Custom Deluxe with Hum

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by murky »

Have you checked that all screws, nuts, input jacks, pots etc are tight? Don’t poke around unless you know how to discharge caps etc safely.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by olegmcnoleg »

RectifiedAmps wrote: Thu Aug 26, 2021 4:21 pm There’s nothing in the circuit between the volume and tone controls and the first grid of V2, so the problem must be V2 itself or something inbetween V2a and V2b. If other 12ax7s still hum then it can’t be the tube itself, so you’re left with capacitor C7, which may be leaking DC voltage through to the grid of the phase inverter (V2b). If you have a multimeter and you’re comfortable with electricity, you could put the negative probe on pin 8 of V2 and the positive probe on pin 7 and see what the DC voltage reading is. It should be a few volts negative. If it’s zero or positive then that tells us C7 is leaking DC from the anode of V2a.
Damn, now that is Good Service.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

RobRoyMcCoy wrote: Thu Aug 26, 2021 4:08 pm
Dano_NZ wrote: Thu Aug 26, 2021 1:26 pm Thanks for the tips. Tried a few 12AX7's just the same then a 12AT7 (quieter). I'll run with that for now for home use. Anyone had luck with "low noise" preamp tubes?
A "low noise" pre-amp tube is probably not the solution if you have tried a few. The 12AT7 has lower gain so will amplify the hum less. Is often difficult to diagnose via the interwebz so taking it to a tech once lockdown is over is certainly a good option. Particularly so if you are not confident in poking around inside a high voltage device.

Hey, you may get lucky, there are lots of smart people on here and hopefully it is something simple and/or obvious.
Thanks so much, that will be my course of action. Are there any Wellington based amp techs?

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

murky wrote: Thu Aug 26, 2021 5:09 pm Have you checked that all screws, nuts, input jacks, pots etc are tight? Don’t poke around unless you know how to discharge caps etc safely.
Yes I did thanks, even tightened the bolts/nuts on the Power Transformer.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

olegmcnoleg wrote: Thu Aug 26, 2021 7:15 pm
RectifiedAmps wrote: Thu Aug 26, 2021 4:21 pm There’s nothing in the circuit between the volume and tone controls and the first grid of V2, so the problem must be V2 itself or something inbetween V2a and V2b. If other 12ax7s still hum then it can’t be the tube itself, so you’re left with capacitor C7, which may be leaking DC voltage through to the grid of the phase inverter (V2b). If you have a multimeter and you’re comfortable with electricity, you could put the negative probe on pin 8 of V2 and the positive probe on pin 7 and see what the DC voltage reading is. It should be a few volts negative. If it’s zero or positive then that tells us C7 is leaking DC from the anode of V2a.
Damn, now that is Good Service.
That is awesome service, I think I owe you a beer RectifiedAmps! I don't have a multimeter and I'm comfortable with electricity in the sense that I won't go poking around a live circuit with bare fingers (chopsticks only). I'm an avid listener to The Truth About Vintage Amps so this may just be the thing to help me understand them better.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by goldtop0 »

A really great sounding combo that one........congrats.
Haven't got any advice as to the problem but wish you well with rectifying it.
Doin' that scrapyard thing.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by rickenbackerkid »

Dano_NZ wrote: Thu Aug 26, 2021 1:26 pm Thanks for the tips. Tried a few 12AX7's just the same then a 12AT7 (quieter). I'll run with that for now for home use. Anyone had luck with "low noise" preamp tubes?
I paid extra for a spesh and highly recommended low noise 12ax7 for my Pro Junior. Made little to no difference.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Thewilltopowerrock »

goldtop0 wrote: Fri Aug 27, 2021 4:10 pm A really great sounding combo that one........congrats.
Haven't got any advice as to the problem but wish you well with rectifying it.
I see what you did there.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

Update: Wife went out to grab some groceries. Gave me a chance to dime it, bridge the inputs etc etc. Bloody hell - I think I need an attenuator now.

Sounds awesome!

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by goldtop0 »

Only thing that I thought of was a 12AY7 in V1 instead of the 12AX7......I'm pretty sure the AY was spec'd for these '57 Custom reissues anyway.
Doin' that scrapyard thing.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

goldtop0 wrote: Tue Aug 31, 2021 1:35 pm Only thing that I thought of was a 12AY7 in V1 instead of the 12AX7......I'm pretty sure the AY was spec'd for these '57 Custom reissues anyway.
Thanks I'm running a 12AY7 in the V1, the 12AX7/12At7 was V2. Cheers

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by goldtop0 »

Yours might be the only one in the country?
Did you bring it into NZ yourself or did you get it secondhand locally.
Doin' that scrapyard thing.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Wairarapajack »

Dano_NZ wrote: Sun Aug 29, 2021 2:44 pm Update: Wife went out to grab some groceries. Gave me a chance to dime it, bridge the inputs etc etc. Bloody hell - I think I need an attenuator now.

Sounds awesome!
Having owned a MPC 5E3 clone a while back (one with an annoying hiss) they're an interesting beast to mess around with. The "interactive controls" have a learning curve. You can get pretty hairy drive at low volumes if you adjust the volume knob on your unused channel - might save you buying an attenuator.

Set your total volume using a combination of Channel volume and the Tone knob (which also controls volume and drive, to an extent). The unused Channel's volume can then act like "Clean-up" control - lower gives more drive, higher gives more clean.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

goldtop0 wrote: Tue Sep 07, 2021 9:02 am Yours might be the only one in the country?
Did you bring it into NZ yourself or did you get it secondhand locally.
Special import.

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Re: NAD - Fender 57 Custom Deluxe with Hum

Post by Dano_NZ »

Wairarapajack wrote: Tue Sep 07, 2021 11:32 am
Dano_NZ wrote: Sun Aug 29, 2021 2:44 pm Update: Wife went out to grab some groceries. Gave me a chance to dime it, bridge the inputs etc etc. Bloody hell - I think I need an attenuator now.

Sounds awesome!
Having owned a MPC 5E3 clone a while back (one with an annoying hiss) they're an interesting beast to mess around with. The "interactive controls" have a learning curve. You can get pretty hairy drive at low volumes if you adjust the volume knob on your unused channel - might save you buying an attenuator.

Set your total volume using a combination of Channel volume and the Tone knob (which also controls volume and drive, to an extent). The unused Channel's volume can then act like "Clean-up" control - lower gives more drive, higher gives more clean.
Thanks I've been doing a bit of that and it does make a big difference. TBH it's not the quietest, but does sound awesome so I'm living with a bit of "idle" hum.

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