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heady

Building the amp5

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Hi guys, just read through the notes last night. I think we have to change some resistors value if we are using the =/-20V transformer right?

 

and heady, what input stage gain you choose to use? for 'general use' or for use with preamp?

 

kross,

The only change I made is the value for R60 - instead of 220ohm, I jumpered it instead. This is the only change necessary due to using the 20V tranformer.

 

I used the general use values for the gain.

 

 

 

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kross,

The only change I made is the value for R60 - instead of 220ohm, I jumpered it instead. This is the only change necessary due to using the 20V tranformer.

 

I used the general use values for the gain.

 

I used the General Use values (gain=-1) as well for my AMP3, guess I'll follow suit in AMP5. What I find is that if you are not using a active pre-amp but just a volume pot for volume control, the gain is a little on the low side.

 

Regards

CK

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Finished all the miscellaneous parts to connect the transformer to mains and to the pcb, to check the 5V output. Got rubbish setting - started out at 6+ volts and slowly dropped to zero.

 

Turn out my big beautiful lighted switch is faulty. The switch lamp now comes on even in the off position but no AC output discernable to my DMM.

 

Changed the switch to some spares and then I realised the new switch is rated only 4A at 250V. So, I have changed it again to another switch, this one rated 10A 250V. Thank goodness I got spares.

 

So, please do check the ratings of the switch you are buying for the amp5. Like one of my favourite columnist (Jerry Pournelle in BYTE) used to say, "I do stupid things, so that you don't have to do them." :))

Edited by heady

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Finished all the miscellaneous parts to connect the transformer to mains and to the pcb, to check the 5V output. Got rubbish setting - started out at 6+ volts and slowly dropped to zero.

 

Turn out my big beautiful lighted switch is faulty. The switch lamp now comes on even in the off position but no AC output discernable to my DMM.

 

Changed the switch to some spares and then I realised the new switch is rated only 4A at 250V. So, I have changed it again to another switch, this one rated 10A 250V. Thank goodness I got spares.

 

So, please do check the ratings of the switch you are buying for the amp5. Like one of my favourite columnist (Jerry Pournelle in BYTE) used to say, "I do stupid things, so that you don't have to do them." :))

 

Actually you don't need such a high rating for the switch. For a 200VA transformer at max rating, it will only draw 200/230 = 0.87A @ 230VAC. On the 20-0-20 side, you get 200/40V = 5A max. Your 4A one will probably work well too. :)

 

Regards

CK

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Actually you don't need such a high rating for the switch. For a 200VA transformer at max rating, it will only draw 200/230 = 0.87A @ 230VAC. On the 20-0-20 side, you get 200/40V = 5A max. Your 4A one will probably work well too. :)

 

Thanks CK, I only thought of the secondary side will be 5A. Shows my experience! :blush: AND the strange behaviour is due to the fuse blowing. The recommended fuse for testing was 200mA, I used 250mA. Remembered vaguely now from reading somewhere that the recommended fuse for testing is much too low. Have to read up again.

 

The falling voltage due to the power caps discharging. Fuse blow because of the in-rushing of current into the power caps too.

 

 

 

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Replaced fuse with 4A slo-blo fuse. Now I am taking things real slow:

1. measure voltage supply to transformer primaries - 232V AC

2. measure voltage across the secondaries - 22V AC

3. measure output from rectifier - 59.2V DC

4. measure across C60 - 29.6V DC

5. measure across C63 - 29.7V DC

6. measure across J10 - 4.99V DC

7. measure across C154 (1000uF 10V) - 4.99V DC

 

I don't know if the above measurements 1 - 5 is ok but the measurement 6 and 7 seems to indicate the 5V part is ok.

 

BTW - I used a 4A fuse because some people in the 41Hz forum said the initial rush of current on turn on seems to blow fuses up to 2A. Don't know if what I did is correct in using a 4A fuse.

 

Any comments, CK?

 

**EDIT** Just realised this. The forum posts are from people in US, so their 4A will work out to be 2A here where our main supply is 230V. Wow, I am really very slow up there. :D

 

Edited by heady

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Ok, realised the above measurements meant my rail voltages are +/- 29.6V which means I need to put in the R60 220ohm to control the current through the relay. Took out the jumper and soldered in the resistor.

 

Tried to solder the toroids and realised they are coated with clear varnish and solder won't stick. Had to use a knife to scrap off the varnish. Quite thick too.

 

 

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Hi guys, need your help. The transformer I bought started humming. Even when the amp is not connected, just the transformer alone is connected to the mains, there is a hum, like something is loose.

 

Anyone knows what this means? Before today, I did not hear this hum. It appeared when I turned on the transformer to test the relay switch of the amp5. Also could set the DC offset of the amp.

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Hi guys, need your help. The transformer I bought started humming. Even when the amp is not connected, just the transformer alone is connected to the mains, there is a hum, like something is loose.

 

Anyone knows what this means? Before today, I did not hear this hum. It appeared when I turned on the transformer to test the relay switch of the amp5. Also could set the DC offset of the amp.

 

Not sure how to fix a humming transformer, maybe you can post the question to the 41hz forums? Your voltages above looks pretty much ok to me.

 

Regards

CK

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Update on transformer - reading up on internet on this matter led me to the topic of DC offset in AC power supply. I built a DC blocker but it did not solve the buzz. After I complained to Farnell, they are replacing it. I hope the new transformer will be ok.

 

On another note, I tried the amp and it works with my normal speakers, not sure re: the quality since the transformer buzzes so loudly.

 

Regarding the mute switch on the board, do you guys think it is of any use? The amp already have a delay relay so no speaker thump. So, what can we use the mute function for?

Edited by heady

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Update on transformer - reading up on internet on this matter led me to the topic of DC offset in AC power supply. I built a DC blocker but it did not solve the buzz. After I complained to Farnell, they are replacing it. I hope the new transformer will be ok.

 

On another note, I tried the amp and it works with my normal speakers, not sure re: the quality since the transformer buzzes so loudly.

 

Regarding the mute switch on the board, do you guys think it is of any use? The amp already have a delay relay so no speaker thump. So, what can we use the mute function for?

 

When the phone rings and you are playing some loud music.... :P

 

Or maybe can think of it as a standby kind of function, i.e. the amp is always "ON" and the components are nice and warm for your listening when you unmute.

 

Regards

CK

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When the phone rings and you are playing some loud music.... :P

 

Or maybe can think of it as a standby kind of function, i.e. the amp is always "ON" and the components are nice and warm for your listening when you unmute.

 

Ok, I thought of the first reason too but then I thought, what if I forgot the volume (I do play quite loud) and then I un-mute it when the music is at its loudest? :doh:

 

But I think your second reason is a good reason for having it. I did buy a nice toggle switch for this but wondering if it will be useful.

 

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Farnell was very nice, they informed me that they will send me a new transformer and they don't want back the noisy transformer. So, since they did not want it back, time for the DIY spirit to work here.

 

I checked and found the entire centre black portion of the transformer loose. So I pumped some silicone (green arrow in pic) into the gap between the plastic black part on all four sides and both ends. Wait for it to harden and voila, the noise is gone. :grin:

 

To warn both CK and Kross, if you are ordering this transformer, please check that the centre black part is not loose. My transformer also came with distorted mounting brackets (red arrows) so my guess is, somebody dropped it before packing because the cardboard box was fine. The transformer is really heavy for its size.

Transformer3.jpg

Edited by heady

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Been listening to the amp. The mids and bass are quite good but the treble is very brittle and artificial. Alto voices and cello were particularly good, portraying the vibrato very well. And the bass is more extended and fuller than my Meridian monoblocs. I guess the treble is where it will need running in. It is very silent, now that the transformer is not buzzing.

 

What are you guys going to do for heatsink? The transformer, Tripath chip (no heat sink) and the LM317 regulator (with clip-on heatsink) were all at about 60 degrees Celsius. (I have a infra-red thermometer).

 

I am still thinking of some way of making the LM317 heatsink bigger and also find a way to add a heatsink for the Tripath chip.

Edited by heady

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Been listening to the amp. The mids and bass are quite good but the treble is very brittle and artificial. Alto voices and cello were particularly good, portraying the vibrato very well. And the bass is more extended and fuller than my Meridian monoblocs. I guess the treble is where it will need running in. It is very silent, now that the transformer is not buzzing.

 

What are you guys going to do for heatsink? The transformer, Tripath chip (no heat sink) and the LM317 regulator (with clip-on heatsink) were all at about 60 degrees Celsius. (I have a infra-red thermometer).

 

I am still thinking of some way of making the LM317 heatsink bigger and also find a way to add a heatsink for the Tripath chip.

 

From the reviews of the AMP1 (which is basically the same thing) @ 41hz.com, it does seem to require a long running in time to sound good. This guy has roughly the same experience as you in terms of sound.

 

http://www.41hz.com/Forums/topic.asp?TOPIC_ID=218

 

For heatsinking, maybe you can consider bolting regulator and/or the Tripath to the casing? The Tripath chip should't need something too big. Maybe something smaller than this.

 

http://img342.imageshack.us/my.php?image=dscf15477xs.jpg

 

For the regular, maybe something like this.

IPB Image

available from Farnell.

 

Farnell also has some ridiculously expensive heatsinks :P

 

Regards

CK

Edited by ckng

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