krell ksa5 klone

[jboehle]

Powered up the amp for the first time last night!  After adjusting the trimmers, without the op-amps in, I had ~55mV offset on channel 2 and ~5mV offset on channel 1.  With the op-amps in, it drops to ~1mV on channel 2 and ~0.1mV on channel 1.  I have a few questions.

 

1) Are there any other "first power on" checks I should do before hooking up a source and headphones?

 

2) The TO-3 heatsinks in the PSU got up to ~60C, and the PSU is currently uncased.  What are the max heatsink temps for the PSU & amp before bad stuff starts happening?  I am using the 2 inch heatsinks (the ones with the single hole, from Newark) in the amp.  Just wanted to know what temps are okay so I can double check once I get it cased up.

 

Now to get it cased up.  Unfortunately I still haven't figured out I want the final casing to be, but I have a 16x16x4 Par-Metal case I am going to put both the PSU & amp into for now.

 

3) How should I do the grounding when putting everything into one case?

• AC safety ground tied to enclosure
• Signal input ground tied to enclosure through ground loop breaker (0.1uF X/Y-rated cap in parallel with 10 ohm 5W resistor)?
• Input RCA jacks isolated from enclosure
• Volume pot tied to enclosure?
• Output jack isolated from enclosure
• Output ground connected only to output jack, never connected to enclosure
• Does the 0V line from the PSU just float, or is it tied to the enclosure through a ground loop breaker?  If not floating, can 0V line from PSU and input signal ground be tied to enclosure through the same ground loop breaker?
• Should output ground on the output jack be tied to the output ground on the amp board, or go directly back to the 0V line from the PSU?

[GrindingThud]

I think fishski13 had some links earlier to photos of a single chassis build he did....could see a lot of the wiring.

http://s23.photobucket.com/user/fishski13/media/012_zpsdfd46a29.jpg.html

I can't believe you're not listening to it yet with just alligator clips.

• AC safety ground tied to enclosure - yep
• Signal input ground tied to enclosure through ground loop breaker (0.1uF X/Y-rated cap in parallel with 10 ohm 5W resistor)? - I floated mine
• Input RCA jacks isolated from enclosure - yep
• Volume pot tied to enclosure? - only by the mounting shaft on my ALPS
• Output jack isolated from enclosure - yep
• Output ground connected only to output jack, never connected to enclosure - yep
• Does the 0V line from the PSU just float, or is it tied to the enclosure through a ground loop breaker? If not floating, can 0V line from PSU and input signal ground be tied to enclosure through the same ground loop breaker? - mine made noise when floated
• Should output ground on the output jack be tied to the output ground on the amp board, or go directly back to the 0V line from the PSU? - I used the amp board, I've seen the other way like in the beta22...I think fishski13 did it that way.

Edited April 13, 2014 by GrindingThud

[Remolon]

I am making some simulations of the KSA-5.

The maximum output voltage without clipping obtained is a little less than 20Vpp, that is 6W on a 8 Ohm load, and I guess that, with the two pair of mje15030/15031,the amplifier can provide enough current to move (to drive, is better) a efficient loudspeaker.

If the load is the 300Ohm of a Sennheiser headphones pair, and adjusting the bias, the output voltage can reach 22.5Vpp, providing a maximum of 210mW to each phone.

Is that correct?

Edited April 15, 2014 by Remolon

[kevin gilmore]

5 watts rms into 8 ohms is the spec.

[jboehle]

Latest status.  Getting there, slowly but surely.

 

[Remolon]

The main question is for the response to the headphones. I was considering to built a RSA-5 but, if the results of the simulation are correct, I do not see any advantage of the KSA-5 over a well constructed Dynalo, with a good PSU for each channel of +/-18VDC and a XLR-4 output with separate ground from the respective PSU, able to provide a excellent response and only a little less power

[jose]

A simulation is just this.. a simulation.

 

I don´t discuss that a "full Dynalo" exceeds to Krell but you should listen this amp.  

[nopants]

The real question is why hasn't anyone made a balanced version yet

[jose]

Good question. I only wanted clone the original... I didn't think on a balanced version

[Remolon]

@jose

It is clear from my post that I have not listen to a KSA-5 but, in any case, I guess that we are talking about different Dynalo. I think that your reference is the one you built with the PCB I gave you at the beginning, when I started the project, and mine is from one a little more evolved, with the same flat response but more powerful, a darker background, more transparent and with a better response to the transients.

There is a very simple solution: I can send my Dynalo to the Island, you listen to both, my Dynalo and your KSA-5, an later you send both to the Peninsula, I listen to both for a while and return yours KSA. In this way we can talk having a common reference.

[jose]

Hi Remolon.

 

Thanks for your offer. In this moment I´m waiting for a good box for my Krell. When I finish it, I will send you a MP.   

 

It's different EMO. You're speaking about of a highly evolved Dynalo (your current development) and the Krell is disadvantaged. Under the same conditions, SE input/output, single PSU, etc.. Does dynalo is superior?

 

My advice is If you can get one, don´t hesitate.

[kevin gilmore]

The real question is why hasn't anyone made a balanced version yet

really, is that so... balanced version more than sufficient to fry your ears on he6

[Zashoomin]

The real question is why hasn't anyone made a balanced version yet

I personally think that it is because the PCB for the amp boards are so big and a bit more expenisve than the average board to stuff.  I mean they aren't that big but the way they are, it would make for a very easy one chassis build or simple small 2 chassis build.  also a bit part i think is that the original amp only was ever single ended.  

[GrindingThud]

I'd push the rails to +/- 35 before going balanced. If a pair ever showed up at a meet we could bridge them.

[kevin gilmore]

have to use a different opamp, and probably have to adjust a few resistors.

probably can get away with +/-30 but that is it.

[jboehle]

Got everything wired up in the case, powered up, was doing some final checks with my meter.  Thought I'd check the V+/- voltage at the op-amps one last time.  Fudged my test lead and bridged pin 3 & 4 (+In, V-) on one of the op-amps.  I was using OPA227P.  Now that channel that used to be at ~0.1mV DC offset, is anywhere from 7-12mV DC offset.  So, other than the op-amp, did I ruin anything else?  Without the op-amp, the channel still measures ~5mV DC offset, which is what it measured before I did this.

[jboehle]

So, I put the op-amp from the other channel into the channel where I had shorted +In & V- last night, got the same results, 7-12mV DC offset after warming up, whereas I used to get ~0.1mV DC offset on that channel before I shorted those pins together.  So, I guess I fried something else in that channel?  What should I look at first?  Any test points I can check to give some ideas?

[DefQon]

I think you fried just the shorted opamp, I would swap the good opamp into the shorted socket and measure the offset if it is drifting between 7-12mV as you're stating with the shorted opamp.

[jboehle]

Well I guess it would help if I was using opamps rated for the voltage they are seeing.  Next time I need to read the spec sheets a little more carefully.  The OPA227P is only rated for +/-18V.  Who knows if that is causing an issue as well or not.  I have some OPA445AU but ran out of SOIC to DIP converters, so I won't be able to do anything more with this until next week....sigh.

[DefQon]

I feel your pain when you run out of parts you need for building and troubleshooting in case you damage stuff, I blew up 2 500v coupling caps accidentally shorting them with the wrong polarity in a 300B amp I was working on the other day 3 in the morning with half a litre of vodka in my system, good thing the house had a safety switch. 

[jboehle]

I feel your pain when you run out of parts you need for building and troubleshooting in case you damage stuff, I blew up 2 500v coupling caps accidentally shorting them with the wrong polarity in a 300B amp I was working on the other day 3 in the morning with half a litre of vodka in my system, good thing the house had a safety switch. 

 

Holy crap, I bet that was scary!

[DefQon]

Kind of use to it now, not the first time I've escaped near death. I remember enthusiastically looking at the hot iron wires in my toaster while it was on 10-12 years ago and thought to myself, what would happen if I poked it with a full stainless steel butter knife (the type with no insulated handle), suffice to say I got zapped, burnt the toaster and tripped the house safe switch. My toast turned out fine though. Guess the next time I do something with electronics the safety switch won't be triggered. 

Edited April 19, 2014 by DefQon

[livewire]

Darwin has a special award waiting just for you!

BTW - what's your favorite booze to use while you are shorting out amps?

[DefQon]

Darwin has a special award waiting just for you!

BTW - what's your favorite booze to use while you are shorting out amps?

 

Anything that gets me pissed except for wine. 

[jboehle]

So, got the Brown Dog adapters in today for the OPA445AU chips I have.

 

In channel 2 of the amp (the one I did not short out the opamp on), I get 57mV DC offset w/o the OPA445, and 0.3mV DC offset with the opamp installed.  Does that seem reasonable?  Does the servo usually do that well?

 

In channel 1 of the amp (the one I did short out the opamp on), I get 5.9mV DC offset w/o the OPA445.  But I get 64mV DC offset with the opamp installed.  That doesn't seem right, does it?  That the DC offset would go UP 10x with the opamp installed?  Any ideas what else I may have damaged in channel 1?  Should I replace the output transistors?  Or is this expected behavior when the channel starts with a low DC offset to begin with?

 

I feel like I'm so close to getting this working!