jtfoo

Jason, if using electrolytic as input cap, does the polarity matter? In other words, does it matter which way you place the cap? I have used Oscons as input caps and they don't sound so bad.

For line level input, it should be alright since the voltages are so low. However, to be safe you can convert your elco cap to bipolar by connecting two similar caps in series. Connect them as such,

+  - -  +
|C1|--|C2|

   or
-  +  +   -
|C1|--|C2|

Take note your cap value is halved. e.g if connect two 10uF in series, the resultant value is 5uF.

If a few mV then it's normal ripple after the rectifier & cap.. Anyway been busy on other non-headamp project so had to spend time on other forums for a while.

I am not very sure too myself. I tried to use my osciloscope but I can't remember how does a half-bridge waveform look like.    2ms per division.

Nice scope pic, what's the veritcal scale? (volt/div)..

This is before or after the regualtor?

digi01

How much for the casing?

Zen and Grados are very good match

It's a good tool for IEC hole..

Forgot to ask, what chip you're using??

Cute, is the power supply on another casing? How do you manage the heat?

most of my other DIY amps do not hav the output resistor, at gain of 6 it still sounds ok with lower impedance cans, but if increase gain to 8 or higher, can hear noise, sound like radio or static

Those output resistors I mentioned are not for the same purpose as cmoy which is to lower noise when gain setting is too high. These output resistors I mentioned are used when you parallel two or more opamps to stabilse it. Without output resistors, the opamps will fight each other and possibly burnt out. Which explain why some opamps get too hotin your circuit.

The Ro1 and Ro2 on firefox circuit is the type of output resistor I'm referring, not cmoy type..

To minimise voltage drop after the output resistors, you can experiment with 0.3ohms first. I saw this on a application notes from national.

Maybe some output resistors might help? Paralleling opamps without output resistors is not a good idea. It's akin to stacking opamps.

How about taking it further by changing those RCA socket to BNC?

The built quailty of the rotel CD players are excellent and value for money. When I tried to mod my RCD1070, I was surprise to see a huge number of high end black gates , panny FC caps all over. So nothing much left to change on the cap side, except the output ac coupling cap, which I changes to from Panny electrolytic to solen polypropylene cap.

Thanks firefox. I notice the RTX is cheaper than the dremel.

Yup, got it. You guys are right. It's about using the good name of RA-1, where Grado spent some money in marketing it. But using the exact brand and values of caps & resistor shouldn't breach any copyright issues too right?

Sometimes I wonder what legal ground does Grado has? The circuit they used is nothing more than a text book non-inverting opamp configuration. Can someone copyright a text-book circuit just becoz he has selected a few components?

I don't like to put input caps on my gain clone amp, I might even add a zobel using only solen caps carbon resistors. Can I patent these just becoz I chose those components using existing circuit?

Does the RTX accepts the same bits as the Dremel? As most of the tools biuts I see in DIY HOmefix are for Dremel.

Looks chim.. What's the voltage regulator for ?

What model number is the Klotz? The red color gives a 'tok kong' look

For home theatre need power mah..

drv134?? Thinking of using that too for bridging..

Good work Bram.. This is going to save us some money, instead of getting the browndog.

I don't think identical opamps(unity config) in series will give higher current output. You have to parallel them to double the current rating.

Well, for me, I want to enjoy music, and to charge and discharge batteries for PPA is just too inconvenience to me

But in the spirit of the PPA, the designers themselve designed them to be portable, one of the 'P' stands for in PPA. Else it'll be a 'PA' amp, without the 1st P confusing?

The AD8620 can work close to it's spec max of 13 V. I've tried +-13.xx V with an overcharged SLA battery before.. Maybe it's oscillating? You can add some fast bypass caps to gnd near the V+ & V- pins of your opamps.

Ok.. have some spare 0.47uF stacked films around... .. just wondering if 0.47uF is enough.

 

Is the Cerafine alright? Though being an electrolytic it should be faster than normal electrolytics. Have some spare 10uF Cerafines lying around too...

For more effectiveness, or kiasu, to stabilise you opamp, you can use your 10uF cerafine connect as close to the V+ and V- pin of the opamps, and bypass the cerafines with another fast polypropylene, say 0.1uF.