[pumpkinman]

That looks great Bill.  Is the power switch in the center of the face plate?

Yes that's the power switch

[steve k]

Very nice work! Very pumpkinny! 
steve

[pumpkinman]

Very nice work! Very pumpkinny! 
steve

Thank you Obi Wan  may the force be with you

[zapper7]

Doug
They both hiss with no input as well, and I did add a ground when I had and hiss and a hum, but the hum was fixed by the ground, the hiss remained the same.

[DougSmith]

Doug
They both hiss with no input as well, and I did add a ground when I had and hiss and a hum, but the hum was fixed by the ground, the hiss remained the same.

Ok, you got me...  Mine are very quiet, but I'm not running them in bridged mode.  How are the XLR's connected?

[zapper7]

Without the inputs connected I have hiss, when I plug in either XLR or RCA, the hiss remains exactly the same.
Nobody seems to have an answer...

[mintzar]

If the hiss is just in the tweeter (like mine is) it's probably a gain hiss. Which means you are probably running a high-sensitivity tweeter and it will be fixed by lowering the gain on the amps. I have an email into Tom and will post back when I learn something.

On a side note... this is a great little kit! I have mine running with two TXs and two power supplies. I am next working on building a larger power supply with better parts and doing some mods to the amp boards as well. Fun project!

[srb]

On a side note... this is a great little kit! I have mine running with two TXs and two power supplies.

If you are not using two separate amp boards (bridged), how do you connect the two power supplies to the single amp board?

If you are using one power supply for the positive rail and one for the negative rail, is the entire capacitance on each power supply board utilized, or just half?
 
Steve

[mintzar]

I have two amp boards and am using 4-channels since I am actively bi-amping my speakers.

Right now I have both TXs hooked up to a single IEC (the same way a dual mono setup works). Once my chassis gets here I'll be hardwiring the TXs directly to my power cable and bypassing the IEC.

Each TX goes to its own power supply. Right now I'm only using one rail of each PSU. I hadn't even thought about using both rails per amp board -- though not sure what the implications of that are. The step after that will be to put the PSU in a different chassis from the amp boards.

Everything will be hardwired, no use of binding posts or RCA jacks. One of the largest sources of distortion in a system are the connectors used. My speakers are hardwired as well.

[luckyrolls]

I too have a hiss.  It is mainly from the tweeters  - I can hear it up to about 2 feet away .  With the the woofers. I need to have my ear much closer to hear it.   

I have the 2x250 running it into Salk Songtowers (88db).   I tried them with slightly less efficient speakers (NHT Classic 3 - 86db) and the hiss is there but not as loud.  The hiss is there if I go directly from my Squeezebox or using the pre-outs of my Denon AVR.  I don't have RCA jacks on the board -  they are wired to the board and I kind of suspect them as part of the issue.

I do have a hiss if I use the Denon to drive my speakers - but much less. (85Watts).

I have tried something called a HumX from EBTech which is successful with Ground Loop problems to no avail.

I have some shielded cables from BlueJean cables on order so I will see if that helps.   I should have those today or tomorrow.

I certainly can't hear the hiss from my seated position.  Would the hiss degrade the sound if I can't  hear it from more than a couple of feet away?

I'll report back if I have any success. 

Mark

[luckyrolls]

I tried one more thing.  Without the input cables connected, the hiss is much less.  (Probably I need to have my ears less than a foot to hear the hiss).  If disconnect the RCA terminals from the board - I still have that same, lower level hiss.  So the input cables are definitely adding in noise.

[dewardh]

I tried one more thing.  Without the input cables connected, the hiss is much less.  (Probably I need to have my ears less than a foot to hear the hiss).  If disconnect the RCA terminals from the board - I still have that same, lower level hiss.

In that case you have two hiss sources . . . one is your source equipment, the other the amplifier itself.  Regarding reducing hiss from the amplifier:

Switching (Class D) amps have an inherent noise floor.  In the IR reference design for the IRS2092 driver that noise is speced variously as “200 uV” and in the “101dB “dynamic range” figure.  The latter is perhaps more useful in understanding what is going on, since what it is really saying is that hiss will be present at 101dB below rated amplifier output in reference design amps.  With the same speaker the more powerful amplifier variants will appear to have more hiss.  The tradeoff is direct . . . higher (potential) output brings higher (actual) hiss.  Using a 500 Watt amp where a 60 will do brings with it a 9dB increase in noise.

But perceived hiss must be considered relative to signal and circumstance.  Hiss that you can hear with no input and your ear against the speaker may be of no significance at the listening position, or when playing a CD with a 90dB noise floor (dither), or if there is any masking noise in the listening environment (projector fan, vent noise from the heating system, audience breathing etc.).  That said:

Sensitive speakers (especially over 90dB) will often bring amplifier hiss up to audible levels close to the speaker.

Speakers that are “hot” on the high end will make hiss more noticeable.

Speakers with 8 Ohm or higher input impedance (particularly in the tweeter range) interact with the switching amplifier output filter to produce a high frequency response rise, and will make hiss more noticeable.

Where hiss is a problem potential corrective actions include “right sizing” the amplifier, flattening high frequency response (in most circumstances a slight rolloff sounds most natural), and a zobel to lower speaker impedance at high frequency.  There are a few other more esoteric possibilities, like noise pickup from external sources on unshielded inputs or with unshielded enclosures, or noise coupling between two amplifier boards on the same power supply, or noise from the power supply itself, but there’s not much point looking there if the more obvious issues have not been addressed first.

Ps.  the thermal limits of the reference design amps are almost entirely determined by the on-board heat sink, not the amplifier power rating.  The solution to thermal shutdown is better cooling, not a nominally more powerful amp with the same heat sink.  That means good ventilation, and perhaps a small fan or a larger (finned) heat sink with good air flow well coupled (thermally) to the existing heat sink block.

[Nick77]

Makes sense as my 120 watt board has a dead quiet noise floor.

[DougSmith]

My 2x250s had only barely detectable noise with my ear at the tweeter and the noise was essentially inaudible a few feet away (by I forget how loud they were turned up). I remember thinking that they were close to, but not quite as good as, the amps in my receiver (which are dead silent).   The speakers I used for that have a compression driver and waveguide with 95 db sensitivity and 8 ohm impedance (they tail off significantly at the high end, above 10kHz, though).  The amps are connected to subs now and are (not surprisingly, given the above) dead quiet.

[mintzar]

Tom said the hiss comes from the gain being too high. He recommended that I replace the R9 and R11 resistors with 10k-ohm resistors to lower the gain. He was also happy to do that for me. I had this same problem with one of my older, high gain amplifiers.

I'll replace the resistors in a few days once the 10k SMDs arrive. I've never heard of higher power equating to more noise.

[Nick77]

O-Noooo........... I just had a buddy over and he brought his Mapletree tube pre over and now its gone      

I think need to try that Pass Buffer out. 

Thanks again Brett!

[ebag4]

O-Noooo........... I just had a buddy over and he brought his Mapletree tube pre over and now its gone      

I think need to try that Pass Buffer out. 

Nick,
Can you tell us what you thought about the sound of the Mapletree/classD combo?

Thanks,
Ed

[Nick77]

I am still using my HK avr pre outs to the ClassD. I have a SB3 hooked up to a Paradisea then the HK. When i hook up the dac straight to the ClassD i lose quite a bit of bass and volume but sonics are more refined. The Mapletree corrected that and gave me a nice smooth top end and more defined bass. It seems to be a very good match, wish i could snag the one thats for sale. 

[ebag4]

I am still using my HK avr pre outs to the ClassD. I have a SB3 hooked up to a Paradisea then the HK. When i hook up the dac straight to the ClassD i lose quite a bit of bass and volume but sonics are more refined. The Mapletree corrected that and gave me a nice smooth top end and more defined bass. It seems to be a very good match, wish i could snag the one thats for sale. 

Thanks Nick.  Very interesting, I too am using a MHDT DAC (Havana) and am running directly into the classD.  I don't have a preamp to connect to yet.  I have plans to pick up a Dodd Buffer but I still have to save my pennies for my audio bank.

Thanks,
Ed

[shadowlight]

Tom said the hiss comes from the gain being too high. He recommended that I replace the R9 and R11 resistors with 10k-ohm resistors to lower the gain. He was also happy to do that for me. I had this same problem with one of my older, high gain amplifiers.

I'll replace the resistors in a few days once the 10k SMDs arrive. I've never heard of higher power equating to more noise.

I believe the gain on the amp is set to 32db or so unless you asked for it to be lower.  I asked for it to be lowered to 26db and I really have to have my head against the tweeter for me to hear very low hiss.  Speakers in question are 91db or 92db.