Hi, I bought someones completed amp that needs proper transformers to replace the ones that are causing hum.
I happen to have a new, old stock Toroid #767.302 on hand. Will this one work for me?
I don't know much about amp building but I think I have the nerve to remove the guts from this one and build a nice, new, larger case for this.
Any help with the transformer choice will be very greatly appreciated!
Brian
I happen to have a new, old stock Toroid #767.302 on hand. Will this one work for me?
I don't know much about amp building but I think I have the nerve to remove the guts from this one and build a nice, new, larger case for this.
Any help with the transformer choice will be very greatly appreciated!
Brian
Maybe it does not need a new tranny but maybe a thorough going through the grounding and filter cap scheme....maybe a few pictures and history of amp.
Regards.E
Regards.E
Here are a few photos. If you need any more of anything specific let me know.
I know little of the history other than the claimed use of high quality parts.
Brian
I know little of the history other than the claimed use of high quality parts.
Brian
Toroid #767.302 may not be ideal for this amp because of its 2x30v secondaries. Penultimate Zen has an onboard regulator (Q5 and associated circuitry in the original article) that provides 42 volts to the amp. The normal input to the regulator is 50 volts, but with 30v secondary you can only get 44-45 volts.
The regulator employs an IRFP044, which has the gate threshold voltage of 2-4 volts, depending on the specimen of the transistor. That is, under normal conditions the voltage at the gate of Q5 cannot be lower than 44-46 volts. In your case, it is 46 volts as provided by Z1-Z5 zeners. Add to this the 2-3 volts minimum drop on R17, and you get 50 volts as per the original design.
This amp dissipates about 100W per channel, so you would need a transformer rated at at least twice the total dissipation (400W for two channels) and with a 36 volts secondary.
If you want to use a transformer with 30 volts secondaries, you may try to replace one of Z1-Z5 with a lower voltage zener (e.g. 1N4732). This will reduce the output voltage of the regulator but will keep it regulating even with lower input voltage. It looks like the amplifier itself will not require massive adjustment if it is fed with 37 volts instead of 42.
The regulator provides the amp with some immunity to the poor filtering of unregulated supply, so I would not suspect the filtering, unless there is an obvious problem like a disconnected cap. However, the input wires and volume controls placed close to the E-I core transformers (and, I presume, rectifiers - I don't see them on the photo) may indeed be a source of hum.
The regulator employs an IRFP044, which has the gate threshold voltage of 2-4 volts, depending on the specimen of the transistor. That is, under normal conditions the voltage at the gate of Q5 cannot be lower than 44-46 volts. In your case, it is 46 volts as provided by Z1-Z5 zeners. Add to this the 2-3 volts minimum drop on R17, and you get 50 volts as per the original design.
This amp dissipates about 100W per channel, so you would need a transformer rated at at least twice the total dissipation (400W for two channels) and with a 36 volts secondary.
If you want to use a transformer with 30 volts secondaries, you may try to replace one of Z1-Z5 with a lower voltage zener (e.g. 1N4732). This will reduce the output voltage of the regulator but will keep it regulating even with lower input voltage. It looks like the amplifier itself will not require massive adjustment if it is fed with 37 volts instead of 42.
The regulator provides the amp with some immunity to the poor filtering of unregulated supply, so I would not suspect the filtering, unless there is an obvious problem like a disconnected cap. However, the input wires and volume controls placed close to the E-I core transformers (and, I presume, rectifiers - I don't see them on the photo) may indeed be a source of hum.
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...I should mention the transformers used were deemed poor quality and thought to be the source of the 60Hz hum.
If I'm reading it correctly, 117033201 has 50VAC secondaries. That's too high.
Perhaps 117018201 (35VAC secondaries)?
Perhaps 117018201 (35VAC secondaries)?
1kW, 10A transformer is an overkill, and 50v secondaries would increase dissipation from 100W to 140W per channel. If you have a choice, a Plitron 757035201 or 087035201 would be better.
...just to verify, Plitron 087053201
500VA, Output V = 175 + 175, 1.43A.
Is this correct? I just want to be sure before placing an order.
500VA, Output V = 175 + 175, 1.43A.
Is this correct? I just want to be sure before placing an order.
...or this one...
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=122-670
Which one will work best for me?
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=122-670
Which one will work best for me?
According to the article you need two 300VA transformers (ie one per channel) with two pairs of 18V secondaries.
Nelson recommends two of these: Plitron 077014201
Nelson recommends two of these: Plitron 077014201
You might get by with two of these Avel Y236651 250VA 18V+18V Toroidal Transformer | Parts-Express.com but they are only 250VA.
I would look a bit harder and find what Nelson has suggested, as stated above.
I would look a bit harder and find what Nelson has suggested, as stated above.
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Since you are from Canada, buy from this guy SumR - Richard Sumner Technology
He makes very nice transformers.
So you want 2 transformers with two pairs of 18V secondaries and at least a 300VA rating.
I would also ask him, what the price difference is between 300VA and 500VA. If it is affordable I would be tempted to get two 500VA transformer with two pairs of 18V secondaries.
The good thing about this, is once you get these transformers you will also be able to build all of the firstwatt amps as well.
He makes very nice transformers.
So you want 2 transformers with two pairs of 18V secondaries and at least a 300VA rating.
I would also ask him, what the price difference is between 300VA and 500VA. If it is affordable I would be tempted to get two 500VA transformer with two pairs of 18V secondaries.
The good thing about this, is once you get these transformers you will also be able to build all of the firstwatt amps as well.
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