Thanks Dr. Gilmore.

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

if its just one channel, likely a noisy input that340. if its both channels, you can reduce the overall gain.

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

Is there any difference between using 2SA1486 or STN9360?  I have both, but not sure which one to use.

In the KGSSHV then, not the Dynahi?    They are functionally identical, the STN9360 is just easier to source.  

Sorry, wrong thread.  Yes, I was talking about KGSSHV.  Thanks for the answer.

In the KGSSHV then, not the Dynahi? They are functionally identical, the STN9360 is just easier to source.

Rly?

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 !

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.

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

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 !

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?

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 July 14, 201411 yr by kevin gilmore

Understood...  It makes perfect sense when you put it that way

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?

For the stepped attenuators I use 1/8W Xicon 270 Serie resistors

Edited July 20, 201411 yr by Remolon

I figured 1/4 watt would be fine

Any one is OK but I choose 1/8 because its smaller size

Dr Gilmore;

Have you calculated the exact value I need for a balanced gain around 11 ?

 

Thanks !

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

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).

5pf is 3db down at 278Khz

3pf is 3db down at 500khz

Thank you !

Time to order the last parts and finish the boards.

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