[VncentValntine]

Quote:

Originally Posted by el_matt0 /img/forum/go_quote.gif cool, thats just what i thought. cant remember if its explicitly mentioned on AMB's site, but how strong of a trafo would i want for each s22?

A 100VA trafo should be used for each psu for this kind of application.

 

[n_maher]

Quote:

Originally Posted by el_matt0 /img/forum/go_quote.gif cool, thats just what i thought. cant remember if its explicitly mentioned on AMB's site, but how strong of a trafo would i want for each s22?

More than anything you'll want to take a close look at the heatsinking for both the power supply and amp boards. If you're building a dedicated speaker amp you really should go with something other than the stock, board mounted sinks.

 

[el_matt0]

ya thats what i was thinking as well. what case companies make nice outboard sinks down the sides that could be worked with?

 

[thrice]

Quote:

Originally Posted by el_matt0 /img/forum/go_quote.gif ya thats what i was thinking as well. what case companies make nice outboard sinks down the sides that could be worked with?

ATI Reseach might have something, but shipping is going to be expensive.

You might look at DIY Enclosures... a couple of their cases feature side heatsinks.

 

[luvdunhill]

Quote:

Originally Posted by el_matt0 /img/forum/go_quote.gif ya thats what i was thinking as well. what case companies make nice outboard sinks down the sides that could be worked with?

hifi2000 does

The second largest has two heatsinks that have a Rt°C/W of 0.23. The smallest have a Rt°C/W of 0.62, just to give you an idea.

 

[cotdt]

as a speaker amp, you want to turn up the gain to around 20x or so. for most speakers lower is OK, but it should be higher than 8x. it's easiest to get higher gain by using balanced, since the stock build for the balanced is already 16x gain. for 2/3-channel higher gain would mean tighter transistor matching. I would also turn up the Class A bias a little, and use larger heatsinks. I don't hear any difference with Class AB and Class A on this amp, but if you're using very efficient speakers it's not too hard to acheive pure Class A.

also beef up the heatsinks on the S22. the math says that one is enough for 2-channel Beta22 speaker amp, and two is enough for 4-channel Beta22 speaker amp. But using more S22 spreads the load and it doesn't have to handle as much heat. You don't really need a big transformer since even the recommended Beta22 build is all about overkill and going over that is overkill of the overkill. Transformers are heavy.

the 2-channel and 3-channel Beta22 has around 20W of continuous output and the 4-channel version 3 to 4x that. but don't be too obsessed with power output, 20W is pretty loud already. most speakers that advertise 300W of output will actually melt if you give it a 10W sine wave (the tweeters will melt). Besides that, for music the peak output is more important, and the amp can deliver very high peak power.

 

[el_matt0]

thanks cotdt, very helpful post. on a different note, back to my own 4 channel b22. listening on balanced senn 650s, i can hear a very faint fuzz when my pot is in the off position and at VERY low volumes (lower than any volumes i listen at reastically so its not a huge concern for that reason). it disappears altogether giving a clean black background as i get close to my listening volume range. however, at the upper end of the pots range, i get a significantly louder intermittent humming and other weird loud buzzes, and again with that same faint fuzz as before underneath it all as before. again its not a huge issue as this is in the very upper range of the pot only, and at a level far above what i listen to. should this be something of concern for me? it doesnt affect me persay but id like to know my amp is in tip top shape anyways...! what can symptoms like this usually be attributed to?

 

[amb]

el_matt0, does your build have the output Zobel network? If not, try installing it across the outputs of both channels and see if it fixes the fuzz.

 

[el_matt0]

Quote:

Originally Posted by amb /img/forum/go_quote.gif el_matt0, does your build have the output Zobel network? If not, try installing it across the outputs of both channels and see if it fixes the fuzz.

no it doesnt, i could do it fairly easily i guess. if the hum doesn't bother me enough to do it (at this point at least), is there any potential harm in any of what ive described, or is everything "fine" to use normally?

 

[el_matt0]

Another quick question im a little confused about. if i want to additionally add in a couple of single ended 1/4" outputs for using SE cans with. can i just wire as shown but without the RCA inputs? i dont really want to have to install rca inputs as well, i have no need for them and dont wanna hafta hassle with an input selector.

if i just keep my inputs AS is, and add in the additional two 1/4 outputs as shown wired, is that all there is to it? if thats the case my pot will simply just control everything at once? (balanced headphone outs, and both SE outputs?) obviously listening on all wouldnt be that doable because of impedence etc, but theoretically doable right

 

[amb]

el_matt0, yes, you don't have to install the RCA inputs. The two unbalanced amps in each channel will each amplify the non-inverting and the inverting signals, respectively. You can listen to either one relative to ground.

-Ti

 

[gates_2]

Quick update on my attenuator woes...

there is definitely something weird going on. I have the Input ground from the amp connected to the signal ground of the attenuator board. What I don't understand is why there is a varying level of "white noise" depending on what step you are on.. with 2 steps in the middle and one at the very top being silent(black background)

I have attached a schematic

 

[amb]

gates_2, do you have a completely separate PSU powering the attenuator? If so, the attenuator board has an inductor L1 connecting its digital ground to the analog ground and it should be ok to remove it. Try and see if that makes the noise go away. The attenuator portion is comprised of only resistors being switched by relays, there is no reason the digital control section's ground has to be connected to the analog ground if the PSUs are separate.

 

[gates_2]

Quote:

Originally Posted by amb /img/forum/go_quote.gif gates_2, do you have a completely separate PSU powering the attenuator? If so, the attenuator board has an inductor L1 connecting its digital ground to the analog ground and it should be ok to remove it. Try and see if that makes the noise go away. The attenuator portion is comprised of only resistors being switched by relays, there is no reason the digital control section's ground has to be connected to the analog ground if the PSUs are separate.

Hi Ti,

I have a completely separate PS powering it(trafo + little 7805 I put together). clipping the L1 inductor just induced a large hum in to the circuit.. When I touch the leads of the severed inductor back together, the hum goes away...

Just to clarify, imagine having a 3 channel B22 build with the stock gain on the E22 backpane. Now, disconnect the L/R volume from the front... That hiss is what I'm still getting(although less so) with the attenuator in...

Oddly enough, with my source(comp. soundcard) turned up high, I can hear my music faintly through the B22...normal?

 

[amb]

Quote:

Originally Posted by gates_2 /img/forum/go_quote.gif I have a completely separate PS powering it(trafo + little 7805 I put together). clipping the L1 inductor just induced a large hum in to the circuit.. When I touch the leads of the severed inductor back together, the hum goes away...

Hmm, ok.

Quote:

Just to clarify, imagine having a 3 channel B22 build with the stock gain on the E22 backpane. Now, disconnect the L/R volume from the front... That hiss is what I'm still getting(although less so) with the attenuator in...

When you unplug the pot/attentuator from the ε22 backplane, the amp will have an open input except for 1M resistors (R2) going to ground. This is going to pick up noise, and is the hiss that you hear. When a pot is plugged in, at low volume positions the amp board's input is shunted to ground through a low resistance in the pot. Near the maximum position the input is shunted to the equivalent of "ground" (the low output impedance of the source). At middle position the input "sees" the paralleled value of the two pot sections to ground, and it also keeps the noise low.

Now, with your stepped attenuator, the situation is similar, except that it's six cascaded stages of resistor dividers switched by the relays. I don't know what state each relay is in for any given position of the control, but if there is any circumstance that the amp board's input would "see" an open circuit or high impedance, then you'll hear noise.

Quote:

Oddly enough, with my source(comp. soundcard) turned up high, I can hear my music faintly through the B22...normal?

With the attenuator set to minimum? Looking at its schematic, it would appear that there is no relay position that correspond to "fully off". In other words, its lowest volume position would still allows a little bit of signal through...