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  • 1 month later...
Posted

Hello

 

I can hear a little "ufffffff" without music on a channel (Balanced and SE output). I read that normally this type of noise is associated with the input transistors. In this case, Is it possible to be produced by the THAT340?

 

Regards

Posted

Thanks Dr. Gilmore. It´s only on a channel and I can hear it if I use a headphone sensitive.

 

I get lucky because I bought some THAT340 (around 20 units). I've been changing one by one until I found one that does not make noise but I discarded 10 for this reason   ???  ???

 

I believed that the THAT340 had a better quality ???

  • 2 months later...
Posted

What would you recommand as the most versatile balanced gain ? 10x or 14x balanced ?

What components to swap for that (especially the capacitor, to ensure proper frequency response) ?

 

Thanks !

  • 1 month later...
Posted

I'll be using a 10K balanced volume control. Balanced gain will be 10 by changing R52, R56 to 50K and C1, C3 to 5 pf.

 

Can somebody help me by confirming this ?

 

I'm populating my boards right now, and still don't know if this way to obtain a balanced gain of 11 ( (50k/10k)+1 <-> 5+5+1) is OK, especially for the compensation capacitor.

Unfortunately I don't have no scope and not much skills to guess this...

 

More generally, is a balanced gain of 11x more friendly to run headphones between say 30-300 Ohm ?

 

Best regards.

Posted

that is close to right, because of the way supersymmetry works. i will when i have

time get you the exact values. using this amp with 300 ohm headphones is probably

pretty goofy, as the voltage swing will easily fry both the headphones and your

ears. put mainly your ears.

really designed for low impedance low efficiency phones.

he6, that kind of thing.

new supersymmetry dynalo is much better for high efficiency high impedance headphones

Posted

Thank you Dr. Gilmore.

I'm trying orthos for now (LCD-2 = 50 Ohm / 91dB), so I think they'll take benefit from the Dynahi with lowered gain. I'll probably try HE-6 and / or K-1000 in the future, so this upcoming balanced Dynahi will be on duty.

 

When I switch to dynamic headphones (or higher efficiency stuff), I'll build a dynalo (or dynamid) for sure, thanks for the tip !

Posted

that is close to right, because of the way supersymmetry works. i will when i have

time get you the exact values. using this amp with 300 ohm headphones is probably

pretty goofy, as the voltage swing will easily fry both the headphones and your

ears. put mainly your ears.

really designed for low impedance low efficiency phones.

he6, that kind of thing.

new supersymmetry dynalo is much better for high efficiency high impedance headphones

Yikes, so I shouldn't use my HD650's or 250 Ohm Darth Beyers?

Posted (edited)

using an amplifier that can do 100 volts peak to peak on high efficiency

headphones that at most need 2 volts peak to peak is a fair bit of

overkill.

 

Its not that you can't do it, but any accident can fry the headphones

or blow out your ears.

Edited by kevin gilmore
Posted

I've decided to assemble a stepped attenuator for my Dynahi.  Can I use 1/4 watt PRP resistors for this if my boards are populated with 1/2 watt?

Posted

10k input resistor, 55k feedback resistor should work fine.

4 volt peak to peak balanced input results in 22 volts peak to peak balanced output.

110k feedback resistor results in 44 volts peak to peak balanced output

Posted

That's pretty clear given the formula.

My problem is the compensation cap value, without a scope I can't be sure of the frequency response, unless somebody helps me.

I read 5pf is OK for a balanced gain of 11 (10k - 55k).

  • 3 weeks later...
Posted

Hello all,

 

Managed to source balanced dynahi and PSU boards from Lil Knight and am in the process of orderings components for the boards. Long journey ahead.

 

Just wanted to confirm: Are 2 x 2sa970's a direct replacement for 1 x 2sa1349 on the amp PCB? 

 

I'm quite sure it is based on the datasheet, reading through this forum and googling, but just wanted to quadruple check :) And matching isn't a necessity with this amp is it? I'll be getting BL versions from bdent.com, think I saw a comment from spritzer saying something to the effect of 'its ok'...

 

Thanks for your help :)

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