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Old 1st June 2009, 02:18 AM   #751
bluegti is offline bluegti  United States
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Quote:
Originally posted by ClaveFremen

The Obbligatos sounds very good but IMHO Mundorf Zns are better, more transparent.
Are you comparing the sound of the Mundorf Zn's to the Obbligato copper case or to their Tinfoil/Film caps? I haven't read of anyone using their Tinfoil caps before. I just saw them and thought I would give them a try. From the description, it sounds like the Obbligato Tinfoil/Film caps are comparable to the Mundorf Zn's. They aren't much bigger than the Solens so I don't think size will be an issue.

I tracked down the buzzing problem to the Lightspeed Attenuator. I must admit that my soldering job was a bit rough on the perfboard I put together. And I'm not sure if I have things grounded entirely right so that will be my next project to debug on a different thread.
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Old 1st June 2009, 08:09 PM   #752
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Quote:
Originally posted by bluegti
Are you comparing the sound of the Mundorf Zn's to the Obbligato copper case or to their Tinfoil/Film caps?
...
From the description, it sounds like the Obbligato Tinfoil/Film caps are comparable to the Mundorf Zn's.
The Obbligatos that I've tried are the copper ones, they're tin foil too.

If you listen Obbligatos and Mundorfs alone the Obbligatos seems better but when you compare both caps with DC couple the Mundorfs are clearly more transparent and Obbligatos a bit coloured (the famous 'analog' sound ).
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Old 13th June 2009, 01:03 PM   #753
bhm is offline bhm  United States
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Default Yet Another Transformer Hookup questions

I want to use center tap transformers to make the my_ref amplifier. All the pictures and sketches I have found on this thread show dual secondary transformers. Some posts talk about how the transformer needs to have 4 secondary wires. But a center tap transformer will only have three wires.

To hook up the dual secondaries two of the wires are spliced together and they go to the PGND connection on the pcb, the other two go to AC1 and AC2.
For a center tap transformer would it be correct to connect the center tap to PGND and the other two wires to AC1 and AC2?

For the Peter Daniel or BrianGT chipamp designs when one chooses to use a center tap instead of a dual secondary transformer, he must remove two diodes and install two jumpers on the bridge rectifier. Is this also required for the my_ref power supply? If not, could someone explain why not?

Finally it seems like very few people actually install fuses on the secondaries although it seems like it would be safer. Why is this so unpopular? Does it adversely affect the sound?

If I've missed the answers to these questions, I apologize. I tried hard to read all I could about it but couldn't find the certainty I am hoping for.
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Old 13th June 2009, 06:11 PM   #754
AndrewT is offline AndrewT  Scotland
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Default secondary fuses

Hi,
Quote:
few people actually install fuses on the secondaries although it seems like it would be safer
what happens to the output offset if either one of the two secondary fuses are removed?

You may need to consider adding some form of DC detection and speaker isolation if the circuit does not like losing half the supply.
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Old 13th June 2009, 09:29 PM   #755
udailey is offline udailey  United States
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I had thought that fuses on secondaries was smart to. I rethought a few weeks ago and I agree with AndrewT its a really bad idea. Put the proper fusing before the transformer and you will be safe. You dont want one half of the secondaries to go out and still have half running. The amp wont like that either.
I am not sure with the other boards you mentioned here, but with the MyRefC I dont think there is any problem taking the center tap to power ground on one condition. Fire up your transformer and measure AC current from center to one secondary and then measure from center to the other secondary. If you get equal readings on each side then that means the amp will see the center as 0V and that is exactly power ground.
Remember to use your poor mans variac.
The AndrewT lightbulb tester.
If you have power supply issues or shorts in your amp or similar problems this will save your amp.
http://www.antiqueradio.org/dimbulb.htm
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Old 14th June 2009, 10:59 AM   #756
AndrewT is offline AndrewT  Scotland
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It's not the Andrew T light bulb tester.
I read about it on this Forum and adopted it.

I happen to champion it's use, particularly since I found out how useful it has become once I learned to read the information it can give the builder and the protection it affords the test circuit/equipment.
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Old 20th June 2009, 02:09 AM   #757
bhm is offline bhm  United States
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Default One Channel is not Working

Thanks for the replies.

I left out the secondary fuses although to be honest, I don't fully grasp the DC offset implications.

When I set the amp up for testing, one channel seems to be working fine, but the other one is silent.

The working channel clicks when starting. Both channels click when stopping.


Here are some pictures:

http://picasaweb.google.com/bmargot/...eat=directlink

I'll review the thread as I recall someone else had a similar problem. But if anyone notices something amiss, I thank you for your comments.

Regards,
Blair
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Old 20th June 2009, 02:34 AM   #758
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Blair and all,

Interesting that you post this problem tonight. I have been trying to get one of my "balls out" amps working for weeks, and I have not been able to find the problem. Replaced both chips and a few other parts, checked every solder joint with a magnifying glass, checked value of every component against the working amp, swapped power supplies, pulled out my hair, cursed a blue streak, sank into a blue funk, etc. I am absolutely desperate. I would PAY someone to fix this for me. I have another amp, but it sounds like crap compared to the My Ref. A $1200 amp, and I can hardly stand to listen to it after having heard this little wonder.

Good luck with your problem amp. Have you tried any troubleshooting? Examined all components for proper orientation? Checked solder joints?

Peace,
Tom E
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Old 20th June 2009, 02:45 AM   #759
bhm is offline bhm  United States
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Default one channel not working

I have done some basic checking with my dmm.

Both transformers have 122 VAC on the primary
Both transformers also measure 24.6 V AC between the center tap (green one) and the V+ and V- output wires (red ones)

Downstream of the bridge rectifier I measure 33.6 V DC between pgnd and the plus(+) and negative(-) output of the bridge.

On the working channel I measure 0.0 volts across the + and - of both PS capacitors C3 and C8

On the non-working channel I measure 33.6 V across C8, and 3.5 V across C3.

I am using a 4A 250V fuse on the power supply and it has not blown. The lightbulb in the dim bulb tester is not bright, in fact it does not even seem to be on at all.

I also checked the solder joints and redid some on the non working board. I removed C8 and verified the PCB solder pad was intact. My next step is to remove C3 and check the PCB solder pad under it.

The channel that works doesn't have any hum that I could detect.



Blair
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Old 20th June 2009, 04:12 AM   #760
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Blair and all,

I would not suspect a lifted pad unless you did something weird while soldering. The boards are well made. I'm sorry I can't help you diagnose a problem based on the voltage readings, as I have only a very rudimentary knowledge of electronics.

One thing I have noticed while testing my boards, without power, is that some measured resistance values move upward in "steps" to the correct value on the amp that works, but read the correct value immediately on the amp that doesn't work. Does that signify anything to those who know their stuff?

I know this is DIY, but I have done all that I can by myself. I need a guiding hand.

Peace,
Tom E
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