Replacing IC's with Opamp to Modify Ramsa console pre's

Hey Group, I am a serious newbie to all things electronic, but after replacing a couple of MOSFETS in my car amplifier I feel I am ready to take on the World.. I have been reading alot of the threads here and am on my way to doing a couple of DYI preamps.. Amazing group of folks here by the way!!!! Any who enough with the introduction, Heres my deal....

We (Burle and I) have an old Ramsa 16CH Console that is pretty cool neat analog board. I want to modify the pre-amp section to get a cleaner sound. It uses a 4560DX IC in several places on each channel. I wish I had a schematic, but have not found one yet (Panasonic is looking). There are no input or output transformers on this console so it has a fairly uncolored sound. It's just a little noisey trimmed out at high levels, and theres not a lot of head room.

Would replacing the IC's with some sort of other opamp design improve the noise and headroom on this console?

Anyone have any ideas? Or is this a worthwile idea?

Open to any and All suggestions.

[quote author="Viitalahde"]Solder the sockets in first as the Butt-man said and stuff[/quote]

LOL

someone is rethinking his screenname right about now...

Shut up Beavis!

FIRE! FIRE!

dave

[quote author="buttachunk"]

get rid of any ceramics in the power supply and replace with good polys

[/quote]

What's wrong with good X7R ceramics in the PS?

[quote author="buttachunk"]
decouple the opamps with the poly caps as close to the opamp pins as possible
[/quote]

Thought film has much higher inductivity, so not a good deal for decoupling?
Samuel

LM833 could be a good option.

where exactly do you want to replace the IC's? that could possibly help determine what IC's you would want to use and where.

preamp? EQ? Insert or direct i/o? summing?


we also need to know if the console uses JUST the 4560DX or does it use other stuff elsewhere?

like my console uses 2n4403x2 as buffers to a signetics 5532 in the pres, tl084s in the eqs, some lm833 scattered for various things and 5532s for summing and all insert, direct i/o and aux.

Hey thanks for all the ideas!!! I'm going out to get sockets and and such today..

The Power Supply is an external unit that weighs about 30Lbs. Would it still be advisable to look at the caps in the PS?

The noise isn't as much of a big deal as the lack of headroom.

Thanks again for the suggestions, you guys ROCK!!!

noise could be a culprit too for lack of headroom in my opinion. If you have a high noise floor, your audio will have to be "hotter", at a higher level to sound more pronounced in the mix, thus decreasing headroom in the long run. you might as well start with a solid foundation and work from the bottom up in order to get the best possible. plus you need to plan out what ICs you want to use just in case your PS can't handle the extra load. remember that one IC may just have a few more mA of power required but 100 of them may need an amp or more! some PS get noisy when pushed harder so watch out.

let us know what your plans are and we'll help you work through it!

:guinness:

OOps. Forgot a few things. :grin:

First off to answer Svart's question. Yes amazingly it only uses one IC.
Would it be better to use different Opamps for different functions?

Second what brand (ie.. TI, Fairchild,NJR etc...) would you use for the various IC's.

What spec should I look at to determine the current draw of the original 4560's so that I don't have PS issues?

As of now my plans are to take out one channel and put sockets in the place of the IC's so that I can swap Ic's and do some tests.

Thanks again...

Most seem to agree that the Phillips (signetics) are the best, then TI when talking ne5532s.

looking at the trusty 5532 and the 4560,

they have the same bandwidth however, the 5532 has a slew rate of 9 V/us as the 4560 has a slew of 4 V/us...
output voltage swing of the 5532 is better also..

but to answer one of your questions directly:
Icc of the 5532 (per datasheet) shows 16mA
Icc of the 4560 (per datasheet) shows 5.7mA
thats almost 3 times the current draw...

i think you will need to make sure your power supply can handle driving different ICs.

I also think that most people would agree that the first place to start changing ICs is in the summing areas, this is where quiet operation is paramount. until the PS issue is sorted i would look to upgrade capacitors and the like first since having a bunch of crappy caps all over your signal chain can't be overcome by just putting better ICs in place. there are plenty of threads concerning bypassing electrolytics with polypros and shunting caps in the signal chain to clean it up, so do some searches. if that causes more questions :green: then PM me and I'll tell you about what i did to my console so far.

cheers and good luck!

:thumb:

true Butta. I just didn't include that stuff in the interest of time. I think it was a given that the 5532 are just plain better in that area.

we'll get this guy straight yet!

Let me try to sneak this op amp replacement question in under the radar.

I would like to replace the LM709 in the RIAA module of my Neumann lathe. I think everyone would agree the LM709 is a dog.

Unfortunately my scanner is not scanning so I can't post a schem.

The major problem as I see it is that there is only a +35v supply. It looks like there is a voltage divider to bring the voltage down. My math isn't good and I haven't measured it.

What op amp would be a good candidate for a single supply? I don't think there needs to be much drive capability because there is a BC107B as a voltage follower at the output. The high frequency boost is done in the feedback path of the op amp. The low frequency cut is done passively before the op amp.

Almost any op-amp can be run from a single supply...what is tricky though is getting rail-to-rail (or rail to 0) performance, and you'll need a specialized op-amp if you want that.

Cheers,

Kris

I think I'm gonna go with the OP275. It very closley matches the current draw of the the 4560 (5mA), so I don't think the PS issues will be as comprehensive, only drawback is the 22v cieling on the OP275 may an issue. High slew, and very low noise. Looks like a Weiner, just costs a little more..

Is there anything anyone knows as to why this would not be a suitable replacement?

Thanks again all....

Murt

which version is it ? is it the round can, or the 8 pin or 14 pin version ?

Click to expand...

It's the 8 pin can.

I think I may seek professional help with this. Any HF oscillation could fry my cutterhead. That absolutely can't happen. I have a spare RIAA module to try it on. There is buffering between the RIAA module and the drive/feedback amplifiers so I think testing it with the dummy head would be a good test.

a 5534 would improve that circuit, and it can handle +40v. it is a class ab output instead of class b-- which means it will probably sound a bit more musical. it should be drastically quieter and will have lower distortion as well.

Click to expand...

It's the distortion I'm after. There is another LM709 in the feedback monitor. I picked off the signal before it and listened through a Melcor line amp. It was quite an improvement. The distortion was much lower especially when the level was pushed.

or you could go with an OPA604 which will handle +48v-- and it has a softer and "silkier" sound if that's what you're looking for.

Click to expand...

I think the amplifier rack is "silky" enough. I have 5532's laying around anyway

also, make sure you look at the power supply. see the posts above :wink:

Click to expand...

The PSU can deliver way more current than needed.

How did you find your way here, Gold? (Good to see you back!)

> I think everyone would agree the LM709 is a dog.

No. It is a stunningly effective can of gain when used right. And in those days, you had to know what you were doing.

Its major flaw is that it will die instantly if the output is shorted.

> The high frequency boost is done in the feedback path of the op amp.

That's an exceptionally good reason to stick with the 709. Part of the headache of 709 design is taming the excess high-frequency gain so it will be stable. The 101 made things a lot simpler, and the 741 simpler yet, by simply removing most or all the excess HF gain at the die.

> another LM709 in the feedback monitor.

Doesn't necessarily have the same sound. The inverse-RIAA amp is pretty unique, how it interacts with amplifier bandwidth. Also the 709 does need biasing and buffering to take the curse off its Class-B output stage. This can be very load-sensitive. (If buffered to infinite impedance, the Class-B may not matter.)

> Any HF oscillation could fry my cutterhead.

Another reason to leave it alone.

What I would do: go see what Neumann did in later lathes.

Post the schematic. Those $69 scanners work fine.

> What op amp would be a good candidate for a single supply?

Any op-amp can run single-supply, same as your 709 does now.

There are op-amps intended for single-supply duty, where the ins or outs can swing to one or both rails. But in audio, that's not necessary.

Butta:

The 5534/5532 may be rated for up to 40V, but I wouldn't recommend it. 36V is about the most I would use unless I was prepared to heatsink the chips.

PRR,

Good scanners are even cheaper than that now. I have a $49 Canon which works great--best $49 I ever spent, or at least spent on something legal :green:

Hey Guys check this out..

http://www.lcaudio.dk/com/ad8065.htm

Is this ic really as good as it looks on paper? Anyone have any experience with the AD8065?

I hear they are pretty good but maybe someone can offer more experience? Looking good on paper is really just that until someone can actually hear it work. I would bet that it needs some serious bypassing though..

IIRC the 709 was used in a well respected hifi preamp in the 70's. I think the preamp used the resistor from the output to - to operate the output in class a mode.

Here's one guys opinion on various opamps.

http://tangentsoft.net/audio/opamps.html

Some interesting reading. Some potentially useful info..