Modding old amplifier to improve sound.

Folsom · « **on:** 19 Oct 2005, 10:03 pm »

I have an old Rotel amplifier/tuner.

I have yet to crack this old bad boy open. What I do know is it puts out more then true 20wRMS, and it responds well to certain things. A healthy plug-in vs. a poor plug in alone makes an audible difference. The power cord is that of an old lamps.....

Ideas....

Replace power cord with large style like Bolder sells (but cheaper, ha, it is not worthy of a Bolder power cord).

Replace Volume knob with a new pot/switch pot. (Any one got a web address for those? I forget where I found some before, the clicking volume knob, looking for some sub $20)

Remove all Pots for bass, trebel, balance, switches for loudness, tape monitor, and function. All of which will be carefully measured for Ohm readings, and replaced with a resistor, or simply by-pass if possible. I would just get some ok resistors from www.madisound.com I suppose

Remove FM/AM tuner if possible, I have no need or want for this, if it is easily removable, I do not need it trying to passivly pick up any signal. It is unpowered when not selected as a function.

Questions.... Should I keep the Mode/Mono button..... Basically it can Mono the Stereo input, but it ends up cancaling stuff. Would I really have a value to keep this for Vinyl play back?

The AUX/Phono and taper monitor button..... I have yet to test the tape monitor input to see if it is better then AUX. I do wonder, as the tape is designed for Stereo correct? I have no need to use the Phono function if I am inputting into tape monitor/AUX correct?

What ever input I decided to keep I will probably solder in some better RCA jacks, these ones are old and show it. I will also put new posts for the wire connection if I change chassis.

By the way I plan to possibly get that Dod (spelling?) pre-amp with tubes because, hell I want tube sound. That and it has two inputs, my computer, and my vinyl machine I will have. The amplifier will not change for some time, so if I want tube sound, and better overall sound, a pre-amp sounds appealing.

Other question, who sells good chassis for amplifiers, I hate the Rotel look, I would prefer just a volume and maybe a button or two on an aluminium brazel and wood finish for the rest or some thing. I might just make my own I suppose, I dunno, I have no desire to spend much on an old amplifier.

Just for the sake of disucssion, for in the 1970's, would a two hundred some price tag be considered a lot for a reciever? I have no idea what the original audiophile stuff cost, that is coveted as valuable still.

Thanks for your thoughts.

(P.S. I am a bored college student, so this will be fun while I am still healing some on my foot)

Folsom · « **Reply #1 on:** 19 Oct 2005, 10:20 pm »

Forget getting rid of the Tape monitor input.... Good heavens it sounds like a layer of mudd was scraped off the top!

Occam · « **Reply #2 on:** 20 Oct 2005, 12:43 am »

Apt name. It might be helpful if you'd tell us the specific model # of the Rotel. Meet us half way. Possibly someone could scrounge up a schematic. Otherwise you are simply left with the option of replacing your geriatric ps capacitors, changing coupling caps; the usual. And yes, you'll get a modicum of improvement with a different powercord, the usual audio jewelry, etc...
With such minimal information, all you've presented us with is a tremendous timewaster for all involved, especially yourself.

Folsom · « **Reply #3 on:** 20 Oct 2005, 12:50 am »

Rotel RX-203.

I just wanted to make it a little bit better. I really was not about to replace every thing in it. Just figured I would remove pots and things that are useless. It will be more of an adventure then improvement

Perhaps some one here subscribes?

http://cgim.audiogon.com/cgi-bin/bb.pl?rotel&zzrx203&showmodl&zzrx203&4&&

Occam · « **Reply #4 on:** 20 Oct 2005, 01:22 am »

DoS,

The Rotel RX203 was produced 1976-1981. The electrolytic capacitors in the powersupply and any used for coupling are shot. This applies to any electrolytic over 10-15 yrs old, regardless of manufacturer. The powersupply is the heart of any audio component. It is very much in the signal path. Unless you're willing to replace them (its not expensive or difficult, they'll be clearly marked) its simply not effective to do anything else. You'd simply be polishing a turd.

JoshK · « **Reply #5 on:** 20 Oct 2005, 02:33 am »

Occam is not trying to beat you up about this but what he says is true. Capacitors in the power supply are very much a part of the sound if they aren't doing their job appropriately. Replace them shouldn't be too difficult if you know simple soldering and part identification. Just make sure the caps are discharged before you go touching them. Don't want to destroy your own smile.

Folsom · « **Reply #6 on:** 20 Oct 2005, 05:49 am »

I can do that easily. When I tear it apart I will get all of the specs on them. Depending on how much is in it, I might just forget doing any thing to it, based on cost. I have never noticed any particular problems with it as of yet.

Occam, thanks for the help. However I did not appreciate the Apt name comment, you are a bit crude.

ctviggen · « **Reply #7 on:** 20 Oct 2005, 11:39 am »

By the way, where does one get "audiophile" grade power supply capacitors? Digikey? I need two 6.8mF caps, 85C. I'm still figuring out the package type (not my forte), but they have "CE-HC85C" and 35WV" on them. Shoot. Digikey only has one cap meeting the criteria of "6.8mf" and "85C":

http://www.digikey.com/scripts/dksearch/dksus.dll?Detail?Ref=56969&Row=443341&Site=US

And this is non-stock. Madisound does have three, which vary in price from about $3 to about $140!! Yikes! I think I spent less than $600 for my integrated amp. I could spend more than the cost of the integrated just replacing the four (two 6.8 mf and two 4.7uf) caps I see! Well, I'm off to order from Madisound.

Dan Banquer · « **Reply #8 on:** 20 Oct 2005, 12:24 pm »

You might find some good ideas here:
http://www.audioholics.com/showcase/DIY/YamahaT-80p1.html

I got all of my replacement caps from Mouser Electronics.

Hope this helps;
d.b.

ctviggen · « **Reply #9 on:** 20 Oct 2005, 02:03 pm »

Thanks, Dan! I spent way too much time searching for caps this morning, once I realized that it's hard to find 6.8millifarad caps (Madisound has 6.8 microfarad, not millifarad, caps!).

JoshK · « **Reply #10 on:** 20 Oct 2005, 02:16 pm »

*snip*..... What are millifarads anyway, caps are typically specified in whole farads, micro farads, nano farads or pico farads.

The two specs that are most relevant to you are the ufs and the voltage, not the temp. The higher the temp, usually the more robust the cap is, but I don't this has much to do with subjective quality. 35WV = 35 working voltage. Some caps are spec'd that way, meaning they can handle 35V nominally and short lived transients much higher.

For example, let's say your secondaries on your transformer are 40V, after rectification that is 56V (40 * sqrt(2)), so 56V is your WV. However, the PS will sometimes have transient spikes much higher than 56V but the caps are rated to handle it if their WV is >56V. Usually you want some breathing room, maybe 5-10%. So caps of 63WV are a good choice in this example. Usually caps for PSUs come at 50V, 63V, 80V, 100V, etc. You wouldn't want to use 50V in this example but the rest are fine (higher voltage typically = higher cost).

*edited to delete stupidity*

Occam · « **Reply #11 on:** 20 Oct 2005, 02:41 pm »

Dunno Josh - 6.8mf is 6,800uf which is pretty typical for a ps capacitor. My Aksa 100 watt amp uses 2 4,700uf 63v caps per rail, per channel. With a 35v rating, I assume ctviggen's component is either a source component or a less than 20watt amp.

ctviggen - There is generally no problem with using a 105c rated capacitor to replace a 85c rated cap. The higher temperature rating will generally indicate, all things being equal, a longer life. Similarly, using a 50v rated cap to replace a 35v rated cap is not problematic. The major constraint is usually the diameter and height. Its really depressing to replace your caps and realize you can't get the frigg'n cover back on. As to which are the 'bestest' caps, I try and avoid religious debates. For larger snap in caps, UCC/Nichichemicon SMH/KMH and Panasonic THSA a good workhorse caps. Lower esr caps such as Panny FCs and FMs, and Nichicon UPWs and UHEs are preferred by many if available in the size and voltage rating. These are available at Mouser and/or Digikey. And then there are the more bespoke audio specific caps such as the Nichicon KG, KZ, FG... available from Michael Percy. I'm too cheap to even consider Black Gates for anything but the smallest values.

JoshK · « **Reply #12 on:** 20 Oct 2005, 02:47 pm »

yes you are most right Paul. when I wrote 6.8uf, I was really thinking of 6,800uf which is normal for PSU as you say. 6.8uf would be a weird value or a bypass in the PSU. so there really is a millifarad.

Occam · « **Reply #13 on:** 20 Oct 2005, 03:25 pm »

Re:Aged caps

Quote from: Destroyer of Smiles.

....I have never noticed any particular problems with it as of yet.

Occam, thanks for the help. However I did not appreciate the Apt name comment, you are a bit crude.

Like males of a certain age (you're too young to identify with this), electolytic caps loose 'performance' as they approach senesance. Its gradual, and whether by denial or acclimation, its often not obvious, but nevertheless, when a true comparison is made (heaven forfend), its cannot be denied.

Just a bit crude? See above. Accurate and comprehensive exchange of information is the currency of DiyAudio. Without knowing the model #, I wouldn't have the info to spend a half hour seaching the internet to find the age of your component and give, IMO, the best advice in upgrading your component.
My mistake, as I assumed because of your moniker and icon, you had a thicker skin than I'd supposed. Perhaps a name change to 'Sunshine' of 'Kunbaya' would elicit a kinder, gentler response.... You must realize that Audio is much like your present Academic envioronment, words tend to be harsh, because when all is said and done, so little is really at stake.

FWIW,
Occam, Moderator of the Lab Circle

ctviggen · « **Reply #14 on:** 20 Oct 2005, 03:45 pm »

Here's another place that discusses replacing capacitors:

http://www.bext.com/replace.htm

ctviggen · « **Reply #15 on:** 20 Oct 2005, 03:55 pm »

Thanks, all. I've been spending way too much time researching caps and did ignore the temperature rating. 6,800 microfarad/6.8millifarad aren't easy to find. I think for the power supply caps (I have an integrated amp), I'm going to replace the polar electrolytics with the same values and at least the same voltage and also I'll stick to polar. I think I'll also go relatively cheap for these. I'll also replace the caps in the audio signal path with nicer caps, though I might go a little more expensive (say Solen but not "gold and silver flake, you really have to be kidding about that price" capacitors) for these. While I have this thing open, I might as well do some reasonably priced upgrades. I certainly don't want to get into the realm of putting in $1,000 in capacitors for something that cost me $600 or so 10 years ago. On the other hand, if I spend a total of $200 (including the transformer and all caps) and get another 10 years out of this, it really is a nice sounding component for a second or bedroom system. Plus, it's been a while since I've been able to do anything "fun" with electronics (even if it only is replacement).

Occam · « **Reply #16 on:** 20 Oct 2005, 05:34 pm »

Quote from: ctviggen

Here's another place that discusses replacing capacitors:
http://www.bext.com/replace.htm

ctviggen,

Excellent reference, thank you!

dunno if I fully agree with all the ascessments.... micas do make excellent compensation/Miller caps. Yes, polystrenes are excellent caps, but the low cost Xicon, etc... tubular ones are quite inductive, limiting their applicability to ps decoupling, but which make fine low value coupling caps, Relcap does make spendy radial styrenes (Partsconexion) which are good at everything.

For those interested in stacked film polyester and polypropolene, very low inductance caps for ps decoupling and bypassing, Digikey carries the stacked polyester film Panasonic V Series, as well as the Epcos (formerly Seimens) B325xxx polyesters and B326xxx polypropolenes.
For those outside of North America, Maplin carries stacked film polyesters -
http://www.maplin.co.uk/search.aspx?MenuNo=1576&MenuName=Polyester&worldid=3&FromMenu=y&doy=20m10
including the (in)famous nekk'd Epcos polyesters.

For your specific 6,800uf 35v cap needs-
Digikey has the Panasonic TSUP and size permitting, the higher spec TSHA; both have radial wire leads. They also carry the Nichicon VR and VZ in radial wire mount. Mouser carries the UCC SMH/KMH in radial snap mount leads. They also carry those Nichicons, but I don't see the specific values in the catalog.

ctviggen · « **Reply #17 on:** 21 Oct 2005, 10:50 am »

Thank you! I spent way too much time at lunch and at breakfast yesterday looking for capacitors. I found all of the caps here:

http://www.percyaudio.com/

but one of the caps (the 6800 uF) is "snap in" and I think I just need leads. Could I use a snap in? However, I've not yet started to look for (or determine the size of) the caps on the audio side. Percy Audio would be nice, as they also have black hole 5 and other things I've been wanting to try (such as fast recovery diodes). Nonetheless, I may have to either find all or some of the caps elsewhere. This is a much longer process than I thought it would be! But at least I can fix my integrated amp for not that much money, which is good right now.

Occam · « **Reply #18 on:** 21 Oct 2005, 01:38 pm »

ctviggen- assuming the caps you're refering to are the Nichicon KG Gold Type II 6,800uf caps @3.95ea (not much more expensive than non bespoke caps), there made for pc board spacing of 10mm. You can get the pdf -
http://www.nichicon-us.com/english/seihin/pdfs/e-kg.pdf
'Snap in' caps are made for pc board mounting, but you'll need to check that the holes are big enough. The first page of the pdf will give you the dimensions (they're made to mount in 2mm holes, and the leads are formed so the simply snap-in, holding themselves in place for soldering. The picture is worth a thousand words.
You'll need to measure the mounting spacing on the pc board, if you've not removed a cap, its easiest to do it from the underside.
Also check that you've adequate space on your board to take their 30mm diameter by 35mm height.
If its not those nichicons, you have to dig up their specific pdf....

[EDIT - as Josh comments below, these are, IMO, very good caps. Replacing the slightly less expensive UCC KMH caps with the Nicichon KGs of same ratings, in my AKSA power amp, yielded large subjective improvements.]

JoshK · « **Reply #19 on:** 21 Oct 2005, 02:03 pm »

FWIW, Bob, Nichicon KGs are good *sanely* priced electrolytics. Thanks to Paul for pointing that out. They are also highly spoken about on diyaudio.com.