Rhodes Chroma Polaris

I was checking out Youtube videos of the Polaris today and I came across this gem:

http://www.youtube.com/watch?v=TlXI0QBOAZw

Text in the video reveals that the owner replaced the last LM348 quad op amp (Z3 on the output board) with a TL048cn. The end result is supposedly a punchier sound and more defined low end. I did some more research and came across someone else saying to use a Burr Brown OPA2604 -- which is a dual op amp.

Anyone here attempted this mod or something like it?

I'm contemplating using the 2604 since the TL048 appears to be obsolete and difficult to find. If I were to use two 2604's then is it possible to tie the 12V supply for each chip together? (effectively making a quad op amp)

try synthparts.com http://www.synthparts.com/ or synthtronics.us

Sincerely,
J. Michael Criado
Cusco Energy Resources, LLC

Fairmont, WV 26554

--- On Mon, 10/11/10, rob_ocelot <rob.ocelot@...> wrote:

From: rob_ocelot <rob.ocelot@...>
Subject: [chromapolaris] Interesting mod...
To: chromapolaris@yahoogroups.com
Date: Monday, October 11, 2010, 12:34 AM

I was checking out Youtube videos of the Polaris today and I came across this gem:

http://www.youtube.com/watch?v=TlXI0QBOAZw

Text in the video reveals that the owner replaced the last LM348 quad op amp (Z3 on the output board) with a TL048cn. The end result is supposedly a punchier sound and more defined low end. I did some more research and came across someone else saying to use a Burr Brown OPA2604 -- which is a dual op amp.

Anyone here attempted this mod or something like it?

I'm contemplating using the 2604 since the TL048 appears to be obsolete and difficult to find. If I were to use two 2604's then is it possible to tie the 12V supply for each chip together? (effectively making a quad op amp)

> From: rob_ocelot
>
> I was checking out Youtube videos of the Polaris today and I
> came across this gem:
>
> http://www.youtube.com/watch?v=TlXI0QBOAZw
>
> Text in the video reveals that the owner replaced the last
> LM348 quad op amp (Z3 on the output board) with a TL048cn.
> The end result is supposedly a punchier sound and more
> defined low end. I did some more research and came across
> someone else saying to use a Burr Brown OPA2604 -- which is a
> dual op amp.
>
> Anyone here attempted this mod or something like it?
>
> I'm contemplating using the 2604 since the TL048 appears to
> be obsolete and difficult to find. If I were to use two
> 2604's then is it possible to tie the 12V supply for each
> chip together? (effectively making a quad op amp)

TL048 must be a mistake. I expect they mean TL084, which is a quad FET-input
op-amp that's still widely available, including from DigiKey. It would be a
good choice, as would the TL074, its low-noise version (or selection). These
have a higher slew rate than the LM348, which could reduce distortion a
little at high volumes. But the Polaris still has tons of distortion and
noise from other sources, so don't expect a night-and-day difference.

That said, a friend of mine is working on a replacement for the output board
that gets rid of most of the nasty distortion and digital noise that plagues
the Polaris. I'll keep the list posted.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

I purchased two TL084CN Quad JFET-Input Opamps from DigiKey almost a few years ago after seeing this video on youtube. (Two in case one didn't work for some reason.) I've still not installed it...but if this is the correct IC, it appears to be readily available and very cheap. The opamp in my Polaris is actually soldered onto the output board, and since I have no experience removing soldered ICs, I'll have to take it to a certified tech. If any of you know about these opamps and whether I can--or should--replace the existing one, definitely let me know. Paul; your advice would most greatly be appreciated!

Thanks,
Ryan

To: chromapolaris@yahoogroups.com
From: pderocco@...
Date: Mon, 11 Oct 2010 10:21:05 -0700
Subject: RE: [chromapolaris] Interesting mod...

> From: Ryan Freer
>
> I purchased two TL084CN Quad JFET-Input Opamps from DigiKey
> almost a few years ago after seeing this video on youtube.
> (Two in case one didn't work for some reason.) I've still not
> installed it...but if this is the correct IC, it appears to
> be readily available and very cheap. The opamp in my Polaris
> is actually soldered onto the output board, and since I have
> no experience removing soldered ICs, I'll have to take it to
> a certified tech. If any of you know about these opamps and
> whether I can--or should--replace the existing one,
> definitely let me know. Paul; your advice would most greatly
> be appreciated!

Removing a DIP from a board can be done with solder wick or with a solder
sucker. But there is an alternative trick that can be used in a pinch, which
is simply to cut the leads on the old chip right next to the package, and
then solder the new chip to the old leads. The new chip will be sticking up
higher, but for an audio op-amp that's irrelevant. Personally, I'd use the
correct tools because I've got them, but if the choice is between doing an
ugly but probably reliable hack job for free, or paying a pro to do a neat
job, I'd choose the former.

But I'll reiterate, I doubt you'll hear much of a difference.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...

--- In chromapolaris@yahoogroups.com, "Paul D. DeRocco" <pderocco@...> wrote:

> But I'll reiterate, I doubt you'll hear much of a difference.

I put a TL074 in today with a socket so I can easily swap between it and the LM348 (or other 4xOPAs).

My initial thoughts are that the 074 does seem to audibly improve things. For whatever reason my Polaris seemed to have a noisier than averge headphone output and the 074 seems to have quieted that a bit. Take my analysis with a grain of salt as these sorts of things are quite subjective (as evidenced by the frequent heated back-and-forth discussions comparing the 074 and the 084 on audiophile forums). Placebo effect and big egos reign supreme in those place

I'm sure Paul could cite about 10 other sources of noise in the Polaris that would completely mask any benefits of swapping out the op amps. :-)

I'll try to make same recordings this weekend to see if I'm actually hearing what I think it is I'm hearing.

The TL074/084 in that position is not a great idea. First, the LM348 is a Bipolar op amp, while the TL074/84 are JFETS. Not necessairly a problem, but in my Polaris the TL chip sounded harsh. It's not a great chip either anyway. I finally put in two OPA2211 on a quad adapter (Brown Dog), which sounds great.
The OPA2134 is a FET chip, too, and while better than the TLs not as good as the more recent chips from TI, AD and National.

Since I had the S/H polyprop cap problem (tuning broken) I decided to do a proper recap while at it, and replaced every electrolytic (with low ESR HQ ones), all the polyprop caps and also most of the polyesters (never heard of those going bad anywhere else, but in the Polaris film caps obviously got bad) - using polyropylene and polystyrene caps. I also replaced the multilayer ceramic at the output with a high quality polyprop film cap.

Well worth it, as after recalibration my Polaris now sounds killer. The re-cap not only resulted in better timing but better sound as well. And it will remain stable and working for a long time, too.

So if you've got a soldering iron and desoldering station, I can highly recommend it. Just be carefull with static electricity and the membrane panel.

--- In chromapolaris@yahoogroups.com, "rob_ocelot" <rob.ocelot@...> wrote:
>
> I was checking out Youtube videos of the Polaris today and I came across this gem:
>
> http://www.youtube.com/watch?v=TlXI0QBOAZw
>
> Text in the video reveals that the owner replaced the last LM348 quad op amp (Z3 on the output board) with a TL048cn. The end result is supposedly a punchier sound and more defined low end. I did some more research and came across someone else saying to use a Burr Brown OPA2604 -- which is a dual op amp.
>
> Anyone here attempted this mod or something like it?
>
> I'm contemplating using the 2604 since the TL048 appears to be obsolete and difficult to find. If I were to use two 2604's then is it possible to tie the 12V supply for each chip together? (effectively making a quad op amp)
>

BTW, the 2604 should be an improvement, but there are better ones out there as well.

--- In chromapolaris@yahoogroups.com, "picardjeanluc69" <picardjeanluc69@...> wrote:
>
> The TL074/084 in that position is not a great idea. First, the LM348 is a Bipolar op amp, while the TL074/84 are JFETS. Not necessairly a problem, but in my Polaris the TL chip sounded harsh. It's not a great chip either anyway. I finally put in two OPA2211 on a quad adapter (Brown Dog), which sounds great.
> The OPA2134 is a FET chip, too, and while better than the TLs not as good as the more recent chips from TI, AD and National.
>
> Since I had the S/H polyprop cap problem (tuning broken) I decided to do a proper recap while at it, and replaced every electrolytic (with low ESR HQ ones), all the polyprop caps and also most of the polyesters (never heard of those going bad anywhere else, but in the Polaris film caps obviously got bad) - using polyropylene and polystyrene caps. I also replaced the multilayer ceramic at the output with a high quality polyprop film cap.
>
> Well worth it, as after recalibration my Polaris now sounds killer. The re-cap not only resulted in better timing but better sound as well. And it will remain stable and working for a long time, too.
>
> So if you've got a soldering iron and desoldering station, I can highly recommend it. Just be carefull with static electricity and the membrane panel.
>
> --- In chromapolaris@yahoogroups.com, "rob_ocelot" <rob.ocelot@> wrote:
> >
> > I was checking out Youtube videos of the Polaris today and I came across this gem:
> >
> > http://www.youtube.com/watch?v=TlXI0QBOAZw
> >
> > Text in the video reveals that the owner replaced the last LM348 quad op amp (Z3 on the output board) with a TL048cn. The end result is supposedly a punchier sound and more defined low end. I did some more research and came across someone else saying to use a Burr Brown OPA2604 -- which is a dual op amp.
> >
> > Anyone here attempted this mod or something like it?
> >
> > I'm contemplating using the 2604 since the TL048 appears to be obsolete and difficult to find. If I were to use two 2604's then is it possible to tie the 12V supply for each chip together? (effectively making a quad op amp)
> >
>

is there a way to get the Polaris to use all six voices in unison? -Jeff

Not as far as I know. Would be fun, wouldn't it?

--- In chromapolaris@yahoogroups.com, jeff richardson <jehf2005@...> wrote:
>
>
> is there a way to get the Polaris to use all six voices in unison? -Jeff
>

> ... is there a way to get the Polaris
> to use all six voices in unison? -Jeff

A brute force approach would be to have the same sequence sent to the
Chroma (via MIDI) on six different MIDI channels (e.g., to actually
command 6 mono voices with the same instructions).

Hey Jeff,

I was just going to recommend the 6-channel midi approach when I noticed someone else already mentioned it...but I'll elaborate. An easy method is to create 6 separate midi tracks in your sequencer, each assigned to their own channel, and then set tracks 2-6 to echo track 1. In real-time use, this should cause the Polaris to layer all six of it's voices in one note. This way you can actually perform monophonically with it, as well as playback the monophonic sequence. However, I'm not sure whether all six of the tracks can also reference the same program/patch number on six different midi channels simultaneously. You may need to experiment. This is the only way I can think of off hand, which does require a few extras steps.

~Ryan

To: chromapolaris@yahoogroups.com
From: ac151@...
Date: Sat, 30 Oct 2010 15:53:14 -0400
Subject: Re: [chromapolaris] Mono Mode?