krell ksa5 klone

[MLA]

Yes, across any of the 2 ohm resistors, that's correct.

[Pars]

^ An important distinction; across the 2 ohm resistors, not from one end to ground.

[jack]

Thank you. I understand across as measuring voltage between 2 leads of the same R.
I have a problem though one channel is significantly louder.... any idea where to start investigation?

[wink]

Swap the inputs around.

That will tell you whether it is the signal in or the amp/speakees.

If still the same, swap the speakers over. If still the same, it's in the amp.

[Algar_emi]

On 6/6/2013 at 11:01 PM, Inu said:

Hi. Anyone knows where I can find the information about the supply PCB showns on thread, page 4.

It is used by spritzer into his KSA5. I want to use it for my own KSA50.Thanks

SB

 

[kevin gilmore]

that's AMB's power supply

 

[Helium]

Hi Kevin, is KA5 fully-differential amp? I guess it's not, want to make sure.

If it's not, then for balanced operation 2 boards are needed, and one board amplifies any 2 signals from L+ L- R+ R-. Is it correct?

[kevin gilmore]

not a balanced amp. you need 2 for balanced output, then an unbalanced to balanced converter or a balanced drive signal

[Helium]

Thanks.

[Algar_emi]

Hi. Just completed my own set of PCB for this amp, see pictures. I also took detailed measurements.

Here some measurements:

Sensitivity: 1.25Vin max, for 6.9Vac Out Max. into 8 ohms
Power: 5.95W into 8 ohms max.
BW (Ref 1Khz, 1V): 0.3Hz to 145Khz
Noise (gnd input): 0.08mV (Lab. power supply), 2.2mv (Standard Supply), see graph
THD (1V, see load): 0.042% (8 ohms), 0.007% (16 ohms), 0.008% (no load), see graph
IMD (1V, 1 & 2Khz): 0.007% (16 ohms)

In normal use, max volume, gnd inputs, no noise can be hear...

 

You can see the complete files at http://www.diyaudio.com/forums/headphone-systems/109618-krell-ksa5-9.html

[jack]

Hi

I tried to test the amplifier in class AB, but the lowest voltage i get is 89 mv (hot). did anyone mange to get it to work at lower voltage?

[philcrack]

Hi,
i am currently testing with a reduced voltage on the power supply and a little bit more bias. That´s really good. Thanks Kevin!

this is my test table:

 

 

[muskyhuntr]

I am curious about the board between the amp and power supply.  Dual volume controls?

Me

 

[philcrack]

this is a customizable bass mid and high level control with optional pre-amp with jumper up to +4 db at the signal way with the Motorola 33079.
A very good preamp. All Sound change components are removed in the signal away everything runs through. I use a very good epcos for the bass adjustment and a very fine old ERO for the tips.

here the circuit board.

 

[jack]

Hi

Did any of you try to play with the opamps? I am tempted to do an upgrade of the opa445. Please let me know your thoughts.

Thanks

[Pars]

Why would you want to do this? What do you hope to achieve with your “upgrade”? What voltages are you running your PSU at?


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[jack]

Pars. PSU is running @ 23.2 V DC. Transformer is 27.5 V AC.

I no not mean opamps in the PSU. as i already know that they either work or or not work. I think you told me that previously ;-) so i changed the op27 to the cheaper op07 and the psu seems fine.

I have heard Operational amplifier have their own sound charecteristics or signature, therefore looking if changing OPAMPS in the amplifier will "improve" or change anything. I have testes the op27 and OPA 445 i find the forst one less precise with to much lows.

[Pars]

If they are DC servos, then no, they will not change the sound signature if the servo is implemented correctly. But as long as the opamps you are trying can handle the voltage requirements, who knows? The opamp in question is probably implemented with dual supplies. Most opamps seem to be rated for +/- 18V. The OP27 is higher (don’t recall what exactly) and the OPA445 higher yet (quite a bit). If the offset is low and stable, you could try it without the opamp(s) in place. I don’t have a copy of the Krell schematic though, so can’t say for sure.


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[kevin gilmore]

on the ksa5 the servo's are in the negative feedback loop. So they can influence the sound a little bit.

[jack]

I am still testing. Yesterday my burson v5i s opamp arrived, they still need to run for a dozen of hours for the final test, however as of now I can tell that they bring much more improvement in my DAC (DIY based on ESS9028) than in my preamp (that is the the KSA5).
The idea of "upgrading" the opamps in the KSA5 came after i received counterfeit OP27 from ebay: the sound was terrible with lots of noise. Once i replaced them with Analog Devices original OP27G from Mouser, the KSA5 started to sound great, and then with BurrBrown's OPA445 even better IMHO, as i find it sounding natural.

I also think about replacing my nichcons KA with KG, not sure what it will change, or if it will change anything though.

Building, replacing, testing is an activity i really enjoy, that relaxes me a lot after a hard day at work. I should have chosen electronics instead of economics for my studies ;-) my lack of knowledge is a serious limiter for me, but you gentlemen and a great support and help. thank you!

[Pars]

Why do bodily parts start puckering up every time I hear the word “bursun”? Almost as bad as when I hear “bybee ”


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[mypasswordis]

What, you don't believe The Angry Realization of The Whole Truth? http://www.partsconnexion.com/burson/opamp.html

[kevin gilmore]

i'm not sure that the burson like things are going to be good for servo opamps. from what I have seen all of these things are bipolar input and have significant input offset current. Plus they drift with temperature. A low offset jfet input slow opamp is what you want for a servo

[luvdunhill]

Cryo’ing should slow it down a bit.

[Pars]

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