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Transformer covers

beta24

Re: Transformer covers

Postby Kabal{MSU} » February 3rd, 2020, 6:46 am

Pieterh wrote:I am still wondering whether dc offset on the 230V mains could explain some of that humming.


Yes, it could. DC filter on mains makes humming toroidal transformer at least quieter (it was the case with my previous amp with Talema transformers), if not deadly silent. The toroidy transformer (400VA) in my build (over 100mF of capacitors, soft-start circuitry) is deadly quiet after 1 second after being directly connected to mains.
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Re: Transformer covers

Postby Hasren » February 3rd, 2020, 7:06 am

PS: On my built, I also got rid of the SSR and connected directly to the MJN2CE (K1 on the schematic) relay. This has eliminated all the hum. Only once (and I guess it was at a certain time of the day) did I pick up some faint distance hum by putting my ear closer to the RKD, but besides that, it is dead quiet. My next step was going to be an implementation of the DC offset circuitry, but it became unnecessary.
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Re: Transformer covers

Postby amb » February 3rd, 2020, 10:01 am

I think I should point out that the original poster was referring to hum induced by the transformer’s magnetic field, and heard in the speakers (correct me if I’m wrong). This hum is reduced or eliminated by increasing the distance between the transformer and the amp boards, as what he did when he relocated the transformer outside the case.

That is a different matter to a mechanical hum or buzzing noise from the transformer itself, which has entirely different causes. Some of you are bringing up this type of issues.

Just trying to bring some clarity to it all, for those readers of this thread who might be confused.
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Re: Transformer covers

Postby mpa2 » February 3rd, 2020, 11:42 am

Hasren wrote:PS: On my built, I also got rid of the SSR and connected directly to the MJN2CE (K1 on the schematic) relay.


I wouldn't feel comfortable switching mains and a secondary circuit with a single relay...
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Re: Transformer covers

Postby Hasren » February 4th, 2020, 2:34 am

Ti has clarified this matter. Indeed that solution (SSR) is for fixing mechanical hum and not exactly what the original post intended. However, those solutions were offered because there were suggestions of changing the trafos...
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Re: Transformer covers

Postby trampo » February 6th, 2020, 12:27 pm

I have ordered the Toroidy transformer, which was far cheaper than expected. It actually worked out only a few pounds more than the unshielded ones I bought originally.
On a different note, if the amplifier sounds better with a balanced input, is it worthwhile to install a unbalanced to balanced converter on the input?
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Re: Transformer covers

Postby amb » February 6th, 2020, 12:56 pm

trampo wrote:On a different note, if the amplifier sounds better with a balanced input, is it worthwhile to install a unbalanced to balanced converter on the input?

That's not necessary. The β24 serves as a great unbalanced-to-balanced converter itself. Just short the - input to G.
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Re: Transformer covers

Postby trampo » March 6th, 2020, 10:16 am

Just got the new transformer and have connected it up. I am getting a fair bit of mechanical buzzing from it. There isn't a diagram so I may have connected the centre taps up incorrectly. It has markings for the + but I am not sure if it matters which + and - I connect together and if this would cause the buzzing?
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Re: Transformer covers

Postby amb » March 6th, 2020, 10:32 am

Post photos of the wires and markings and let's try to figure it out.
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Re: Transformer covers

Postby trampo » March 6th, 2020, 11:00 am

The 2 pictures connect to the regulator boards. I couldn't get a clear picture of the others. They are wired with blue and pink to the bridge rectifier (the pink has the marking) and the orange and red (orange with the marking) to the other rectifier.
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