That looks fantastic, very tidy. I also received my classic kit and I couldn't wait to get started, first time I have attempted a project like this.
Couldn't be happier with the product, still have a long way to go though (need a toroidal and case along with everything else to get it connected). Can't wait to get it done.
Couldn't be happier with the product, still have a long way to go though (need a toroidal and case along with everything else to get it connected). Can't wait to get it done.
How did you drill the Corian? Were you able to do it with a conventional hand drill and steel bits, or did it require diamond tipped bits and a drill press, or some other method?
I've never worked with Corian, but I once made a pair of custom speaker stands with granite bases. It took me a couple of hours using diamond bits to drill a total of eight holes.
(Awesome looking GainClone case, by the way.)
Hi Lightman
thats the beauty of Corian you can basicly use normal powertools such as routers and drill bits because its Man made from resin. you can thermo form it heat it sand it bend it drill ,cut it all with normal tools when i cut it on the table saw theres no melting what so ever my friend makes kitchen worktops from it he often glues offcuts together to form sheets and you cant see any joints.you can see here i just used a collar on the router and a guide i made using some thin ply and a hole saw to make the volume knob resess.
i only intended this as proof of layout before i find someone to CNC a piece of 10mm aluminium plate which will serve as additional heat transfer when bolted to the front .
a great tip is to use Front Panel Designer its free i made a 2d layout and you can print it out to scale stick it on the panel and you have all the drill holes exact ready for the drill press.
Thanks k00gar
thats the beauty of Corian you can basicly use normal powertools such as routers and drill bits because its Man made from resin. you can thermo form it heat it sand it bend it drill ,cut it all with normal tools when i cut it on the table saw theres no melting what so ever my friend makes kitchen worktops from it he often glues offcuts together to form sheets and you cant see any joints.you can see here i just used a collar on the router and a guide i made using some thin ply and a hole saw to make the volume knob resess.
i only intended this as proof of layout before i find someone to CNC a piece of 10mm aluminium plate which will serve as additional heat transfer when bolted to the front .
a great tip is to use Front Panel Designer its free i made a 2d layout and you can print it out to scale stick it on the panel and you have all the drill holes exact ready for the drill press.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Thanks k00gar
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Hello I've just finished my kit, I used the dual mono configuration with a 20V 150VA center tapped transformer on each channel
It's simply amazing! The kit quality and the sound! Thank you very much Peter!
And here are some photos.
Since the transformer is center tapped I'm using only one bridge per supply.
No pot was used since I'm going to use a preamp for volume control. Red plexyglass was used for front and back plate (it was the only one that I had available)
Both together over the preamp (sorry for the blur photo)
And now a question, actually two...
The first is, does anyone have a schematic showing the single bridge configuration with a center tapped transformer? I try to understand how the connections are, but I am a big newb...
And second is, does anyone have an idea about a cheap transformer cover?
It's simply amazing! The kit quality and the sound! Thank you very much Peter!
And here are some photos.
Since the transformer is center tapped I'm using only one bridge per supply.
An externally hosted image should be here but it was not working when we last tested it.
No pot was used since I'm going to use a preamp for volume control. Red plexyglass was used for front and back plate (it was the only one that I had available)
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Both together over the preamp (sorry for the blur photo)
An externally hosted image should be here but it was not working when we last tested it.
And now a question, actually two...
The first is, does anyone have a schematic showing the single bridge configuration with a center tapped transformer? I try to understand how the connections are, but I am a big newb...
And second is, does anyone have an idea about a cheap transformer cover?
Bride schematic with CT will look like this: http://www.tortran.com/drawings/dual_center_tap_rectifier.gif
I think Antek, Inc, the transformer supplier now has toroid caps.
Lets see....
Yep, here they are. Not cheap though.
Antek - Products - List View[]=3
Uriah
Lets see....
Yep, here they are. Not cheap though.
Antek - Products - List View[]=3
Uriah
Thank you very much Peter!
Again thank you for this amazing design!
Thank you very much my friend, I have already checked Antek, but as you said they are not cheap, at least for what I want to do.
I have some ideas in mind (a cd cake box cap for example, painted). I have the whole summer in front of me to decide.
I fired up my gainclone for the first time last night, for the most part I think it is working correctly but I have some questions.
The DC offset of each output is -80mv for the left, and -40mv for the right with the volume maxed (25K pot). Is that just the luck of the draw with the chips, or should they have similar DC offset?
I'm happy to say I don't have any hum after following the star ground advice at the start of this thread. I do however have a buzzing noise that seems to be amplified with volume through both channels. It's not loud enough to be heard over any music, but you can hear it if you place your ear within ~30cm of the speaker. This is with no source connected, I'm guessing this has something to do with my input wiring?
My last question (hopefully) is that when I touch my potentiometer, it makes my speakers pop slightly. If I connect my voltmeter between the pot shaft and my starground, it reads between 0 - .10mV. I'm guessing that's not normal.
If anyone can shed some light on those questions, or point me in the right direction, I would be very appreciative.
Other than that, I have to say that I am very impressed with the sound that this amp produces, I have enjoyed building it greatly.
The DC offset of each output is -80mv for the left, and -40mv for the right with the volume maxed (25K pot). Is that just the luck of the draw with the chips, or should they have similar DC offset?
I'm happy to say I don't have any hum after following the star ground advice at the start of this thread. I do however have a buzzing noise that seems to be amplified with volume through both channels. It's not loud enough to be heard over any music, but you can hear it if you place your ear within ~30cm of the speaker. This is with no source connected, I'm guessing this has something to do with my input wiring?
My last question (hopefully) is that when I touch my potentiometer, it makes my speakers pop slightly. If I connect my voltmeter between the pot shaft and my starground, it reads between 0 - .10mV. I'm guessing that's not normal.
If anyone can shed some light on those questions, or point me in the right direction, I would be very appreciative.
Other than that, I have to say that I am very impressed with the sound that this amp produces, I have enjoyed building it greatly.
the position of the volume control should not alter the output offset.
DC coupling of the input will allow variations in source resistance to change the output offset. DC coupling of the input will also allow a fault producing DC on the signal to pass right through to the amp output.
What schematic have you used?
DC coupling of the input will allow variations in source resistance to change the output offset. DC coupling of the input will also allow a fault producing DC on the signal to pass right through to the amp output.
What schematic have you used?
Hi Andrew
I'm afraid I am still very much a newbie to DIY audio, so I will try my best to answer your questions. You might need to spell things out for me if I miss the point. So you are saying that my input is DC coupled and it shouldn't be?
I used Peter's LM3875 classic kit with a 300VA 25V transformer. I followed his instructions at the beginning of this thread to connect the components.
I'll just take this time to mention that I removed the pot from the input and just joined the wires and the buzz is gone. I don't know if that points to the pot being of poor quality or if it has something to do with how I grounded the pot to the PCB (to the SG as per the instructions in this thread).
After I removed the pot, my DC offset between the posts climbed to -111mV on the left channel and -68mV on the right (roughly -30mV difference for each channel).
I'm afraid I am still very much a newbie to DIY audio, so I will try my best to answer your questions. You might need to spell things out for me if I miss the point. So you are saying that my input is DC coupled and it shouldn't be?
I used Peter's LM3875 classic kit with a 300VA 25V transformer. I followed his instructions at the beginning of this thread to connect the components.
I'll just take this time to mention that I removed the pot from the input and just joined the wires and the buzz is gone. I don't know if that points to the pot being of poor quality or if it has something to do with how I grounded the pot to the PCB (to the SG as per the instructions in this thread).
After I removed the pot, my DC offset between the posts climbed to -111mV on the left channel and -68mV on the right (roughly -30mV difference for each channel).
The DC offset will depend on particular chip and on volume setting as presented here: http://www.diyaudio.com/forums/audi...-kit-building-instructions-5.html#post1524877
When no source is connected, the amp will produce some buzzing noise which should disappear with volume turned down. With source connected, you shouldn't hear any anomalies.
This is all normal for this particular design.
The chassis should be grounded and pot housing as well, that should prevent any static discharges when you touch the pot.
When no source is connected, the amp will produce some buzzing noise which should disappear with volume turned down. With source connected, you shouldn't hear any anomalies.
This is all normal for this particular design.
The chassis should be grounded and pot housing as well, that should prevent any static discharges when you touch the pot.
Over the past couple of days I've been playing around with the Ci capacitor in place of the R1 resistor in an attempt to lower the DC offset between the posts. I must be doing something wrong as I have not experienced what others have in adding Ci to the input.
I bought 2 x 4.7uF polarised electrolytic capacitors and installed them with the positive pin on the input side. The brand escapes me atm, it was just what was available at the local electronics store. What I experienced was DC offset climbing to 111mV on one channel and 68mV on the other. This is what I experienced when I ran the amp without a pot. It is locked at those values regardless of the volume setting which is to be expected, but why has the offset value increased, rather than decreased?
I even tried swapping the capacitors for the spare 10uF ones that I had spare from the second rectifier from the LM3875 kit, made no difference to offset. I also have witnessed that if I turn off the amplifier and then turn it on 2 - 3 seconds after, I get a spike in DC offset whilst the speakers are connected to them. On the channel that normally reads 111mV, it jumps to ~300mV very quickly. I don't know if this is just my DMM playing up but it happens very quickly. As stated previously, I'm a novice to DIY audio, but it seems as if the coupling capacitors are not doing what they are meant to be.
On a slightly different topic, but possibly related, ever since I changed the R1 resistors out for coupling capacitors, my speakers pop quite noticeably when I turn off the power to the amp, but a good 2 - 3 seconds after the switch has opened. Is this normal behaviour? Whilst it still did pop slightly before I used the Ci caps, it was far quieter. I have also noticed that I have no pop if I turn off the amp before the source.
Other than that, the amplifier works very well and puts out a terrific sound in my opinion.
Can somebody please tell me what I am doing wrong? Is it due to using a polarised capacitor instead of a nonpolarised one? Should I use a 22uF cap as indicated in some other schematics I've seen? I'm not intentionally trying to be bothersome, I have been searching the forums for days trying to find closure on my problem before resorting to asking for help.
I bought 2 x 4.7uF polarised electrolytic capacitors and installed them with the positive pin on the input side. The brand escapes me atm, it was just what was available at the local electronics store. What I experienced was DC offset climbing to 111mV on one channel and 68mV on the other. This is what I experienced when I ran the amp without a pot. It is locked at those values regardless of the volume setting which is to be expected, but why has the offset value increased, rather than decreased?
I even tried swapping the capacitors for the spare 10uF ones that I had spare from the second rectifier from the LM3875 kit, made no difference to offset. I also have witnessed that if I turn off the amplifier and then turn it on 2 - 3 seconds after, I get a spike in DC offset whilst the speakers are connected to them. On the channel that normally reads 111mV, it jumps to ~300mV very quickly. I don't know if this is just my DMM playing up but it happens very quickly. As stated previously, I'm a novice to DIY audio, but it seems as if the coupling capacitors are not doing what they are meant to be.
On a slightly different topic, but possibly related, ever since I changed the R1 resistors out for coupling capacitors, my speakers pop quite noticeably when I turn off the power to the amp, but a good 2 - 3 seconds after the switch has opened. Is this normal behaviour? Whilst it still did pop slightly before I used the Ci caps, it was far quieter. I have also noticed that I have no pop if I turn off the amp before the source.
Other than that, the amplifier works very well and puts out a terrific sound in my opinion.
Can somebody please tell me what I am doing wrong? Is it due to using a polarised capacitor instead of a nonpolarised one? Should I use a 22uF cap as indicated in some other schematics I've seen? I'm not intentionally trying to be bothersome, I have been searching the forums for days trying to find closure on my problem before resorting to asking for help.
Glad to see you have a solution. With that much offset I sort of think you have a bandaid rather than a cure. I dont know whats wrong but something is not right with 111mV offset.
I think if you use caps in the signal that you should try something other than electrolytics. At the very least try a WIMA of around 2.2uf. You dont need more than 2.2uf and even down to about .68uf will be fine. Polypropylene films will sound much better than your electrolytics. If you find an improvement you may consider spending a bit more and going to something like an Obligatto capacitor of 2uf or so. Might run around 20 dollars but they are very very good input caps.
Uriah
I think if you use caps in the signal that you should try something other than electrolytics. At the very least try a WIMA of around 2.2uf. You dont need more than 2.2uf and even down to about .68uf will be fine. Polypropylene films will sound much better than your electrolytics. If you find an improvement you may consider spending a bit more and going to something like an Obligatto capacitor of 2uf or so. Might run around 20 dollars but they are very very good input caps.
Uriah
Thank you for the advice.
I think the chip that outputs 111mV is just an average example. These LM3875s can have up to 10mV input offset voltage from what I've read, that multiplied by the gain would lead to a fairly large offset between the speaker terminals, unless I've understood it completely wrong.
I have noticed what I would consider some sound degradation since fitting the input and feedback caps. I will most definitely be changing them to something nicer as per your post. Electrolytics were only chosen as they were easily obtainable for me, I will be changing them for something else soon. Running without these caps is not something I really want to risk, I like the piece of mind, especially considering this is my first amp.
Thanks again.
I think the chip that outputs 111mV is just an average example. These LM3875s can have up to 10mV input offset voltage from what I've read, that multiplied by the gain would lead to a fairly large offset between the speaker terminals, unless I've understood it completely wrong.
I have noticed what I would consider some sound degradation since fitting the input and feedback caps. I will most definitely be changing them to something nicer as per your post. Electrolytics were only chosen as they were easily obtainable for me, I will be changing them for something else soon. Running without these caps is not something I really want to risk, I like the piece of mind, especially considering this is my first amp.
Thanks again.
Its great that you have finished your first DIY amp! Congratulations!
I think that you will find most people fiddle with the input cap and spend hundreds trying different caps there. I think the WIMA is a great place to start just to have a better sound right away and the Obligatto is much better than its price. Some folks like the 'sound' of a cap. I like that this one has no 'sound' that I can hear on my chipamp. The nice thing is that these caps are so sturdy that you can use them in many many amps to come. Soldering them in and out of a board or circuit will be fine and will not damage them. 111mV is still not a good number, but your cap takes care of that.
Uriah
I think that you will find most people fiddle with the input cap and spend hundreds trying different caps there. I think the WIMA is a great place to start just to have a better sound right away and the Obligatto is much better than its price. Some folks like the 'sound' of a cap. I like that this one has no 'sound' that I can hear on my chipamp. The nice thing is that these caps are so sturdy that you can use them in many many amps to come. Soldering them in and out of a board or circuit will be fine and will not damage them. 111mV is still not a good number, but your cap takes care of that.
Uriah
Thank you, it feels very satisfying to build one of these amps for the first time. I didn't even know what a gaincard was a few weeks ago, let alone a gainclone. Being a 21 year old, full time uni student leaves me with little money to spend on high end audio as it is a luxury (not to mention that I have spent far too much money on high end computer equipment, and then water cooling it...).
I feel now that I have an amplifier that will produce a comparable if not better sound than anything similarly priced from any store. It was hugely entertaining to build, this will not be my last DIY amp for a long shot.
I feel now that I have an amplifier that will produce a comparable if not better sound than anything similarly priced from any store. It was hugely entertaining to build, this will not be my last DIY amp for a long shot.
When you want it to sound even better the boutique components will make a difference. After the input caps your best improvement in my opinion is an obscene power supply. I like the one from chipamp.com that is meant for the miniA amplifier. 9 dollars for the board and then probably 40 more to populate it. Use a decent 160VA transformer up to about 300VA. Toroid transformers are preferred and are cheap from Antek, Inc. He is super reasonable on shipping as he uses flat rate USPS and will put as many as fit in one box for only one shipping charge.
Uriah
PS so where's the pics!
Uriah
PS so where's the pics!