[Mo-Ro]

Hi. In advance, I have to get apologize for my bad english. This is my first post here, so if it were to end up in the wrong place, can one of the moderators be kind and place it in the right place. This is my attempt to make a pcb for a cmoy. The amplifier is intended to be table top amp. So size is not an issue. I've played with the eagle-cad for many years, but has not really made any finished pcb before and want to get other's opinion on the final pcb before I send an order to the board house. So if there is someone who has an opinion about it, welcome to comment. The design is a straightforward cmoy, with tle rail-splitter, which is powered by a rechargeable 9v battery. El-cap in the supply is Nichicon kw cap. Someone who has experience with them? If the project become what I want, I'm going to write and post more pictures here. Thank you in advance.

 

[fordgtlover]

I'm no expert on these matters, but I would offer the feedback that you might want to consider putting additional holes in for the C1 & C2 capacitors to allow the use of caps with different lead spacings (eg. 5mm, 10mm, 15mm)

 

[Mo-Ro]

You mean like this? I have thought of it myself, but made the pcb to the components I already had. Measurements may not be right yet, but with a little adjustment, I think it will be good. Thank you.

 

[fordgtlover]

Yes. Like that.

 

[sandbasser]

Very nice.

Just a question ... Why did you choose to tombstone the resistors when you have all that space available???

Please don't consider this as an attack... I'm thinking about doing some design on my own and I'm just curious about design alternatives.

Thanks,

 

[cobaltmute]

Add decoupling caps for the op-amp power supply pins. 0.1uF to ground for both V+ and V- as close to the pins as you can get them. This will help with stability.

 

[Spacehead]

Quote:

Originally Posted by cobaltmute /img/forum/go_quote.gif Add decoupling caps for the op-amp power supply pins. 0.1uF to ground for both V+ and V- as close to the pins as you can get them. This will help with stability.

And bypass those with 2.2 uF caps? I have noticed that sometimes 0.1 uF isn't enough.

 

[the_equalizer]

Quote:

Originally Posted by sandbasser /img/forum/go_quote.gif Very nice. Just a question ... Why did you choose to tombstone the resistors when you have all that space available??? Please don't consider this as an attack... I'm thinking about doing some design on my own and I'm just curious about design alternatives. Thanks,

I was wondering about that too.

cheers!

 

[cobaltmute]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif And bypass those with 2.2 uF caps? I have noticed that sometimes 0.1 uF isn't enough.

At a minimum you would want to decouple with what the datasheet says. I have read about people using 100uF electrolytics right on the pins with nothing else. You can also put a small cap (10nF to 100nF) across from V+ to V-.

I've never played with all these tweaks, but many diagrams omit the de-coupling caps as it is assumed that you will put them in.

 

[cobaltmute]

Quote:

Originally Posted by sandbasser /img/forum/go_quote.gif Very nice. Just a question ... Why did you choose to tombstone the resistors when you have all that space available??? Please don't consider this as an attack... I'm thinking about doing some design on my own and I'm just curious about design alternatives. Thanks,

Ideally, for a high speed op-amp, you shouldn't tombstone. The extra length of the lead back to the board adds length to the feedback look, which can cause stability issues.

 

[FraGGleR]

You guys are smart. Just thought I'd confirm that for you guys.

 

[Nemo de Monet]

I infer that you designed this to keep signal traces as short as possible, which is admirable, and I don't know how you plan to wire the input/output jacks, but it looks to me like you're going to have wires going every which way to and from both jacks, which is not necessarily a great idea.

You may also want to read this paper, which may help improve your layout somewhat.

 

[Mo-Ro]

Hi. There was a lot of feedback in a short time, and I will try to answer as best I can. In the case of resistors, I used cut and paste from another design I have been working on. It was intended to be as small as possible, and I thought it looked ok. I have not thought that there could be any sonically disadvantage with tombstone-style, but want to change it if necessary. This Cmoy is intended to be a gift for a colleague who retire this summer, so I want to make it as good as possible. When it comes to power supply, I'll see if I can add some decoupling caps. I'm not quite sure how the final amp is going to be eventually, but some wires are there, I'll just try to keep them as short and few as possible.

Now it's bedtime for me, and hope to wake up with fresh eyes in the morning for some SMD soldering tomorrow. Received two AMP32 kit from 41hz.com today. Looking forward to the job. Thanks for all the answers, let there be more