Driver chips for BPA300 amplifier

[alexcd]

I wanted to start this over in a new thread

I think I've decided to use the OPA1632 to drive the BPA300. Maybe some others want to get in on a group buy of the boards. I'll do the layout.

that mean you are going to design a useable driver with this chip. make the boards as good as alex88 and i want some. have you noticed the neat bridges jrdg uses to transfer the output power in there amps. nice thick elevated copper covered in epoxy. nice!! if you can machine out about 75 pounds of solid aluminum for the case we could have some amps like that. otherwise 8000 dollars u.s. i am going to build my own thanks to alex boards. have fun

The spec of OPA1632 is very good. Just use a good standard opamp to drive it.

Haha, I am absolutely not planning on using that much aluminum in my amp. I'm doing 2 channels + seperate dual power supply using 1/4" aluminum. I have some access to a machine shop but let's not talk crazy now.

I planned on following the OPA1632 datasheet exactly. If you want in, it would be cheaper for me to order more. Any extra ideas are welcome. I will start another thread if interest continues.

"Differential input sources must have well-balanced or low-source impedance." - OPA1632 datasheet p6

This isn't a problem for me but I can see why it would be nice to have additional buffering. Two opamp then, right?

1 opamp if you want to use it with single-ended input only.

2 opamps if you want to use it with balanced input as well as single ended input. I think this option has more flexibility.

I have thought of IF I would built it (ok, I won't), I will build a 3-section board that can be cut into 3 pieces and be able to use them seperately.
The 3 sections are : voltage regulation, dual opamps buffer, differential opamp line driver.

This way I can reuse these 3 modules for different applications, e.g. preamp, DAC, etc. Also this saves PCB setup cost.

haha, Thanks for the idea. That is a good one. I was thinking the same thing. I was planning on a separate +/-15V regulator board but why bother if I'm using it for here only. BTW, I was going to use my mains 25VAC and regulate down to the +/-15V with a separate diode bridge. It should be no more than a small heatsink's worth of heat for just this circuit, right?

Regulate 25VAC down to 15VAC should be ok, that's what I am doing in my amp. There is not much heat since the current is small.

 

[BWRX]

It looks like your questions were answered. What then is the point of this thread?

 

[alexcd]

The point is that OPA1632 may or may not be the right choice here. I would also like to find out if anyone else has a need for a line driver or other use for this circuit and wants to give input. I would like to make PCB's but obviously the more people the merrier.

 

[alexcd]

http://www.thatcorp.com/datashts/1600data.pdf

Anyone ever heard of this brand?

 

[tryonziess]

is the opa chip better in this application than the ths from ti. you will need to provide a balanced line in from 2 op to the ths/opa1692 i guess. now is this far superior to a standard drv134 setup. the only really good point is the cmrr of the new ths is as good as a transformer. when you get the board built let me know i will need a few. still have not ruled out the lundahl transformer. there is also a good schematic at ti about this chip and the transformer in combination. with .000? thd on this amp i really do not want to garbage it up. so any help is appreciated. if you have access to a milling machine melt down a couple thousand beer cans and mill out a jrdg billet case. would be nice.

 

[alexcd]

Good questions. I was hoping for someone to ask them. Personally, I think that a OPA2227/OPA1632 would be a mean combination with no worse than 1% resistors. I am more worried about the effects of the resistors than the chips.

That case idea sounds good but only if Sam Adams starts putting beer in cans. I wouldnt want cheap beer getting in my project.

 

[alexw88]

THS4131 and OPA1632 are pin compatible if you keep pin 7 open. You can use the same pcb and try both chips.

For resistors, I agree 1% or even 0.1% should be used. You could hand match the 1% to get better accuracy.

What voltage regulator will you use? Ever thought of the new low noise LT1763?

 

[alexcd]

I never give regulators much thought... usually the cheapest

 

[tryonziess]

more and more projects are requiring 0.1 or better resistors. has anyone found a place to buy bulk precision resistors in varying values at a reasonable price. i never thought the cost of resistors would enter the equation, but now its has. you can buy a fairchild op amp for less than a 0.1 vishay/dale resistor. any of you ever heard a leach amp playing music. i have been thinking about building a discrete amp after the chipamp projects. it looks like leach spent quite a lot of time debugging the original design and it should be quite reliable with present day components.
you could always melt the sam adams bottles and machine with diamond tooling. that would be one nice case. back light with leds. there are no limits imposed on diy projects just time. good choice in your brew.

 

[tryonziess]

that driver

i just read the datasheet on the that line driver. it looks to be a dropin driver with all the advatages of the ths/opa and all in on little dip8 chip. price is about 3.00 dollars. you could mount it right on the main board. they also have some other neat stuff and mouser sells their products. i might give this little unit a go.

 

[alexcd]

DRV134 I assume you mean? I can't find them anywhere! There seems to be a major lead time issue.

 

[banana]

I'm using the OPA1632 in my new preamp.

I choosed the DGN package with thermal pad underneath, and have followed the powerpad layout suggestion.

This chip consumes quite large quiescent current of 14mA. The extra heat should be taken care of, if running with +/-12~15V supply.

 

[tryonziess]

since the ths 4131 requires a low impedance input just what would the schematic look like if you include the buffer. what is a good buffer choice. i looked again and the that chip has poor specs not quite as good as the drv134. thanks

 

[alexw88]

highly recommend you read Banana's preamp thread here : http://av-forums.net/plus/viewthread.php?tid=27503&extra=page=1&page=1

subscribe to the forum to see the pics. he has designed an excellent preamp with excellent measurement results. (THD+N at 0.0003%, noise floor at -130db )

Banana, please share more here about opamps

 

[alexcd]

Alex, that forum isn't coming up in English. What language is that?

 

[alexcd]

I have some OPA2227's laying around that I was going to use. The TI dual opamp package is compatible with most other dual opamps so deciding now may not be required for layout at least. A little help with selection would be nice though. What are people's thoughts on a 8-DIP socket? Your choice of course but I'm going to use one if I want to swap out later. This knocks out SMD options for the buffer if I go this route.

 

[Panelhead]

Looks Japanese

Alex, that forum isn't coming up in English. What language is that?

Babelfish might decipher enough to make it readable.

George

 

[tryonziess]

the ths4131 and linear techs ltc1992 only come in 8soic package which is hard to work with. is there a pin socket for this configuration. and thanks alex i am going to read doc

 

[AndrewT]

Hi,
keep in mind that source impedance matching is just as (or more) important as around the differential impedance matching.

I have found that 1% and even 5% reistors can easily be matched to <=0.2% and with a bit more effort <=0.05%. That is total spread, not +-%

Electronic differential amps demand good matching at all usable frequencies to return the good numbers that they have initially been chosen for. Don't throw the baby out with the .....

 

[alexcd]

Desoldering SOIC's is tough if not impossible for most people. That part will have to be fixed.

So the source impedance, i.e. preamp, is just as important as in this stage. How much can this affect the output?