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Old 19th February 2013, 04:43 PM   #81
blu_glo is offline blu_glo  England
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The LM1036 a good all-in-one chip for 'my first tone control project' however it's signal handing is poor, for example, it's max input of 1.6V rms is easily exceeded by a typical modern CD player output (CDs normally give 2Vrms max). also distortion and noise figures are poor even at it's rated level by modern standards. It is in fact a 1970's chip designed to go with partnering Toshiba remote control ICs (no longer available IIRC) that gave the required analogue control outputs...
.... I wouldn't recommed it myself for new and/or quality designs, but don't let me stop you if you want to give it a try.

BTW, Philips do a similar chip - a TDA1524 which has much better signal handling esp. if you apply feedback network mentioned on P.4 of the datasheet...
http://www.google.co.uk/url?sa=t&rct...,d.d2k&cad=rja

Last edited by blu_glo; 19th February 2013 at 04:55 PM.
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Old 9th April 2013, 02:01 AM   #82
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Sorry to leave this thread hanging for so long. I had an online class that took up a good bit of my time the last month. Finally, after a couple frustrating mishaps and some replacement parts, I have both channels of the amp together and everything appears to be working properly. It sounds quite nice so far. I'm looking for an enclosure for it now.

I actually think I've decided to leave out the tone section... at least for now. I breadboarded the tone section and I wasn't really happy with how it sounded. I need to play with it a little more, but it just wasn't sounding right. I'll leave a little space in the enclosure in case I get it working properly and want to add it later. I found a software equalizer that's giving me much better control and sound than the tone control in the amp would give me anyway. So I'm thinking I'm going to keep the amp simple, and use the software EQ. Or maybe I'll build an external tone control instead later if needed.

I'll post final pictures once I get it in a case and clean up the grounding/wiring and all.

Thanks again to Mooly and blu_glo and others for all the help!
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Old 9th April 2013, 06:34 AM   #83
Mooly is online now Mooly  United Kingdom
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Pleased to see you have it all working... its looking good
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Old 10th April 2013, 05:58 AM   #84
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Thats a nice beefy supply board and love the star earthing point!

Curious to hear you couldn't get the tone control to sound right, was to too bright or dull or...?
Maybe it needs a more stable base than breadboard; there's a lot to go wrong in the tone section!

I was going to make a copy the tone/buffer design for myself with the op-amps you suggested but being a natural "bottlehead" decided I'd rather do it with some mini valves (tubes) as I have 6112 dual triodes kicking around, need 1 triode from each to substitute for each op-amp. Heater supply can be derived from the main transformer windings and need only 80-90V dc HT which can come from a voltage "quadrupler" to the same windings. I'll see if I can post some outcome soon. Recently got my LM3875 Sperry gainclone boards working a treat, to go with this preamp.

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Old 16th April 2013, 01:37 AM   #85
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Originally Posted by blu_glo View Post
Thats a nice beefy supply board and love the star earthing point!

Curious to hear you couldn't get the tone control to sound right, was to too bright or dull or...?
Maybe it needs a more stable base than breadboard; there's a lot to go wrong in the tone section!

I was going to make a copy the tone/buffer design for myself with the op-amps you suggested but being a natural "bottlehead" decided I'd rather do it with some mini valves (tubes) as I have 6112 dual triodes kicking around, need 1 triode from each to substitute for each op-amp. Heater supply can be derived from the main transformer windings and need only 80-90V dc HT which can come from a voltage "quadrupler" to the same windings. I'll see if I can post some outcome soon. Recently got my LM3875 Sperry gainclone boards working a treat, to go with this preamp.
Well, I think you might be right about it needing to be more stable than the breadboard. It was finicky on the breadboard. But I think it overall just didn't sound very nice. It significantly colored the signal.

The main problem seemed to be that I couldn't find a middle/neutral point that sounded anything like the straight signal. Putting the pots (linear) in the middle position didn't sound neutral at all. Moving them around, I still couldn't find a spot that felt right. It did sound kind of dull on the highs, but when I turned the treble up, it got harsh, not clear. Maybe something sounded strange with the mids too. The low certainly could add a BIG bass boost, which wasn't bad. I think it was mainly the highs and mids that just did not sound right. Muddy and weird might be the best way to describe it...

Sorry I know that description probably isn't real helpful, but I know I don't want to put it in my amp, at least yet. I think I'm going to build it on a board anyway since I have all the parts and see how it goes. Maybe it will sound better then. I'm leaving room in my enclosure if I want to add it later, or maybe I'll just make an external tone control so I can use it with other projects too.

Attached is the enclosure I ordered. Will probably take a couple weeks to come from china. Really anxious to get it finished... so close.
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Old 25th April 2013, 06:51 PM   #86
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Pleased to see you have it all working... its looking good
Got the case and put the amp together (without volume or tone for now). I'm really happy with the case. I'll post some other pictures later.

I've got one issue that's confusing me. When I hook up a MP3 player as the source, it works perfectly. No DC offset or pops, and only gets warm. But when I hook it up to my DAC/Computer as the source, the DC offset jumps to ~46mv and when I power it on, it pushes the speakers out some for a second before settling back. It also give some noise at turn off and gets much much hotter. Obviously something isn't right when hooked up to a source plugged into the wall as well.

At first I didn't include the 100ohm resistor between 0v and earth. When I add the resistor, the offset drops to ~4mv. If I remove any connection between 0v and earth, offset drops back to 0mv. So I'm guessing there's some sort of grounding issue.

Maybe I'm not making the earth connection from the right place? Right now it's connecting from between the rectifier diodes. Should I be connecting it from the power star ground? Even though the 100ohm resistor dropped the offset to ~4mv, I'm thinking that the source should not be changing the offset at all. So I'm wondering if there's an issue elsewhere in the grounding.

Thoughts? Hopefully I explained that right. Thanks for the help.
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Old 25th April 2013, 07:08 PM   #87
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Maybe I'm not making the earth connection from the right place? Right now it's connecting from between the rectifier diodes. Should I be connecting it from the power star ground? Even though the 100ohm resistor dropped the offset to ~4mv, I'm thinking that the source should not be changing the offset at all. So I'm wondering if there's an issue elsewhere in the grounding.

Thoughts? Hopefully I explained that right. Thanks for the help.[/QUOTE]

Hi,

Looking at your picture, can you clarify:
Is your star earth connected to the chassis?
Is the chassis earthed?
It is a grounding issue and I cannot quite see whats going on from the photo. Good work though!

Si.

Last edited by blu_glo; 25th April 2013 at 07:11 PM.
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Old 25th April 2013, 07:10 PM   #88
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Oh also, Make sure the bolt through the transformer CANNOT touch the lid because if it does, it in conjunction with your case becomes a shorted turn resulting in hot and/or prematurely expired transformer!!

Si.
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Old 25th April 2013, 07:13 PM   #89
Mooly is online now Mooly  United Kingdom
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That looks a really neat job

Problems like you describe can be hard to track down. Are the input sockets electrically isolated from the case ? They should be.

Without being too specific the case should be connected to mains safety earth. That goes without saying for safety. The amp grounds (and by that the star ground) can connect to the case via a low value resistor. (I don't want to give you wrong info because every amp build is different in the way it has been wired).

If the problem occurs because the source equipment is grounded then I would look at something like I've mentioned above to break the loop. Yet I see you have a low value resistor and the problem improves when its disconnected.

Other possibilities (not very likely having reread your post) are that the DAC/PC is noisy (as in assymetrical HF noise) and that is causing the issue without it having anything to do with grounding. You would really need to scope the DAC output and see what it look like.

Did I ever post a link to this.
3 stage LIN topology - NFB tappings?

It might give you some insight into what goes on with grounding.
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Old 25th April 2013, 07:20 PM   #90
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Originally Posted by blu_glo View Post
Oh also, Make sure the bolt through the transformer CANNOT touch the lid because if it does, it in conjunction with your case becomes a shorted turn resulting in hot and/or prematurely expired transformer!!

Si.
Interesting, didn't know this. The bolt does touch the top of the case. I'll cut it down. Thanks!
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