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Old 12th February 2011, 06:53 AM   #3651
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Output transformers should be screwed directly to the metal chassis (should be DC coupled).

Amplifiers will suffer a lot (even if they don't "show that" – they may sound okay!) if the ultrasonic noise is not filtered properly; the amplifier negative feedback will go into overdrive to attenuate those frequencies (remember the 10-100pF capacitor in parallel with feedback resistor?), so make sure there's no ultrasonic noise at the transformer outputs - especially if the output transformer is of high output impedance.

The hum you are referring could be of broad spectrum + the amplifier could've suffered from "its own", internal broad spectrum oscillations generated by hum coming from the DAC....

100MHz CRO is a good tool to fault find issues you've been having... I’ve found that if everything looks clean and okay on the scope, your ears will like it too.

Boky
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Old 12th February 2011, 06:09 PM   #3652
Ryssen is offline Ryssen  Sweden
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Hoewer I foud that the temp rises about 10degres when Not playing musik.
Any comment on this.


When not playing it is about 60-65degres.

Last edited by Ryssen; 12th February 2011 at 06:11 PM.
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Old 12th February 2011, 07:03 PM   #3653
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That's an easy one, class A amps dissipate more power at idle than when they are providing power to spkrs.
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Old 12th February 2011, 07:53 PM   #3654
Ryssen is offline Ryssen  Sweden
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Yes,but I thought it was a bit much difference,10-15 degrees.
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Old 13th February 2011, 01:59 AM   #3655
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Wasn’t aware you had class A amp.... I also have class A amp that dissipates a lot of heat when in idle - that is normal for this class of operation. if it has mosfets in output stage then you have to check for are any oscillations... the output mosfets can oscillate A LOT without any noticeable side effect, so I think you ought to stop asking questions and start checking your sound chain with the CRO. Load your amp with a capacitor (around 2.2uF / 250 – 400V DC); if it’s stable with this load it will be stable with any speakers and speaker cables…

Boky
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Old 13th February 2011, 02:08 AM   #3656
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Just a personal opinion, but why run push-pull if you're going class A? There is so much to be gained running SE. The F5 is not my cup of tea. I tried it and it ain't even close to the organics of SE.

Because the continious power is stationary you can subrtact the power delivered to the speakers from the total power delivered through the power cord and that leaves you with the watts dissipated in the amp.

Last edited by Bill Fuss; 13th February 2011 at 02:23 AM.
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Old 13th February 2011, 06:58 PM   #3657
Ryssen is offline Ryssen  Sweden
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""Load your amp with a capacitor (around 2.2uF / 250 – 400V DC); if it’s stable with this load it will be stable with any speakers and speaker cables…""

It is from the input it oshillates.

""Just a personal opinion, but why run push-pull if you're going class A? There is so much to be gained running SE. The F5 is not my cup of tea. I tried it and it ain't even close to the organics of SE.""

I built one F5 and one F3,the F3 has a more detalied topend.
And the F5 more bottom.
I just build a new pair of speakers that´s why I am trying the F5.
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Old 13th February 2011, 10:31 PM   #3658
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Quote:
Originally Posted by Ryssen View Post

It is from the input it oshillates.
Interesting.... the oscillations must stop somehow when they hit the VAS?

Boky
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Old 14th February 2011, 01:01 PM   #3659
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OK. I am getting back to this project after a long hiatus.

I am up to date on the reading (my eyes hurt!) and had a couple questions.

1) the Lundhal LL1690s seem to be the favored transformers from several sources, some of whom have tried many flavors. What is the best place to get these babies today?

2) If I understand correctly, I could run balanced OR single ended output. Could I possibly have two sets of connectors on the back of my unit to allow both? If so how?

3) in the case of the transformers, there apparently needs to be filter caps and some resistors as well. I have seen several examples, and at least one person using it 'bare'. What is the current 'state of the art' with regards to the components to be used in conjunction with the transformers?

4) I read something regarding the use of caps rather than transformers for output (but transformers seem to be favored). Are there any advantages to this scheme over the transformers?

5) I am reasonably certain the coax input will be relocated to the rear of the unit (remote of the board). I believe I therefore need a 'proper' RCA connector- i.e. not just a plain old audio one right? What exactly do I need, and where is a good place to get it? (or will an audio one work fine?)
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Old 14th February 2011, 01:12 PM   #3660
legarem is offline legarem  Canada
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Quote:
Originally Posted by Jim Leach View Post
OK. I am getting back to this project after a long hiatus.

I am up to date on the reading (my eyes hurt!) and had a couple questions.

1) the Lundhal LL1690s seem to be the favored transformers from several sources, some of whom have tried many flavors. What is the best place to get these babies today?

As I'M now with other projects, I bought two of these pairs and have one pair for sale if you're interested.

Also if someone interested, I also have pairs of

UTC HA108 permalloy
Tamura-Yamaha GA80080
Studer 600 to 600
Panasonic Ramsa 600 to 600
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