[spaceace1014]

Here we go again... 

A few months ago I bought my first Stax setup. An SR-507 along with an SRM-1/MK2 to power it. The unit being an A series was likely somewhere around 30 years old... enough time for the electrolytic caps to have dried out.  As some of you may remember I chronicled my search for capacitors and the steps I took to replace them and perform the bias and offset to get the unit back into running order. I plan to do that again here with the SRM-717 this time. 
 
I just purchased a 717 which may be as much as 14 years old. I haven't as of yet been able to find any good pictures of the inside that would show me the voltages of the power supply caps though there appear to be 4 large ones which at a wild guess I would imagine are 220uf @ 400v. I have a mind to replace the caps with ones of the highest uf value that I can unless anyone thinks that might be a bad idea...

Does anyone know what the physical dimensions of those caps are and what their values are? 

Does anyone have any suggestions for other mods that I should attempt while im poking around in there? 

 

[spritzer]

According to the schematic the main caps are 220uf/400V but there are more electrolytic in that amp and I would change all of them. 

 

[spaceace1014]

You're absolutely right. I see at least 10 or 11 small caps beyond the 4 large ones that I mentioned. I'm planning on replacing all the electrolytics as long as I'm digging around in there. Are there any caps that I shouldn't uprate the uf values on?

 

[duncan1]

The small ones in front of the mains transformer  beside -IC -1 and IC-2  Are smoothing caps for those 2 +/- 15 V regulators in my conversion of  the 727[ which is the same as 717 in this]   I separated  those regulators cut the PCB copper strips and added  2 more regulators  so that BOTH channels had their OWN regulators thus stopping overhearing interaction between them causing a degradation of the stereo image.
                I increased the values and also added more at the sockets of both channels- It has been proved scientifically that over a few  
                 inches of track can pick up radiated or induced noise/distortion .therebye affecting the quality of the reproduced signal.
                  See my longer posts on the 717/727 elsewhere.

 

[spaceace1014]

That's very interesting Duncan. Do you have any photos and may I ask what caps you used and what their values were? 

 

[duncan1]

Thanks for your polite comment I seem to be the target for attack from some because I am a "subjective" .But they all listen subjectively but wont  admit it and yet profess subjective comments on Head-Fi- hypocrisy comes to mind.  I replaced the existing ones with quality 470UF  35V working bypassed with  0.1 polyprop film caps and the same again at the terminations of the daughter board sockets[ traced the copper track to the sockets]. You will find that each regulator feeds BOTH channels that's not good in Hi-Fi terms as has been proved Scientifically in the past by many engineers in many mags. It allows overhearing of both channels via the regulator circuit.Degrading the clarity of both channels. I don't know why some here wont accept this as I am forced to say once again -It has been proved scientifically. I am fed up writing that word . If they wont take my advice maybe someday they will read a non-subjective and believe him.as its all down in print world wide.
 I have to apologize I have not got a digital camera -high quality analogue and yes I should get one . Sorry about the rant. 

 

[spaceace1014]

It sounds like an interesting mod and I went back and read a lot of your old posts it sounds like you've tried a lot of stuff with these amps so I'm inclined to try it.  
 
What I'd like to do with this thread is create an explicit record of everything I do both so that I in my inexperience don't mess my shiny new amp up and so that in the future when someone goes looking for information on restoring their 717 they can see what I did in clear terms even if like me they don't have an extensive background in electronics. 
 
1.When I get my amp in I'll take detailed photos of it inside and out and post them.
2.I'll measure the physical size, record the marked voltage and capacitance, and mark the position of each capacitor on a photo of the amp.
3.I'll go over the regulator division and the bypassing on a photo marked to show what I believe you mean. as well as any other minor mods you, spritzer or anyone else with experience thinks would benefit the project. 
4.Once its crystal clear exactly what needs to be done to the amp; Trace cutting, drilling, adding caps, replacing caps, wiring, whatever I'll build an explicit parts list that shows who made it, what it is exactly, a link to buy it, shows what it replaces or if its new(like the bypass caps), and if the part has deviated from the original and how(such as a larger capacitor). Then I'll give people time to chime in on the brands,  the sizes, etc.... 
5.I'll go through with the mod and restore and post any difficulties I had and how I solved them along with how much it ended up costing and how long it took to physically do it. I will also post a series of post mod/restore pictures.
 
If I am making or planning on making a mistake please say so and be as clear as possible on the reason why. Nobody is going to hurt my feelings, this is not a cheap piece of kit, I'm a noob, and I don't want to leave a record for someone else to find that is useless or wrong so please speak up. This goes for everyone on this thread not just Spritzer and Duncan1.  

 

[duncan1]

That sounds just great!-.Down to earth /practical/ logical- I dont think anybody can criticise that.For the record as the caps were larger than the ones fitted I fitted them underneath the PCB it also made it very easy to fit double regulators as both the IN-Common[earth] could be soldered directly  onto the soldered terminations of the original regulators  all that needs to be done is cut  the Copper tracts and terminate the output of each regulator to each side IE- one positive/negative pair on each channel its not hard to trace the circuit to the sockets. It means you dont see any alteration from above. Remember the negative regulators are not pin for pin the same as the positive ones.But if you do as I say and terminate them straight onto the top regulators soldered connections underneath leaving the output terminals of both to be soldered to the cut copper on the PCB. you cant go wrong.

 

[Argybargy]

Spaceace,
Looking forward to seeing your work. It'll be very useful for future modders/restorers since well documented and photographed projects like these are hard to find.

 

[spaceace1014]

Quote:

Spaceace,
Looking forward to seeing your work. It'll be very useful for future modders/restorers since well documented and photographed projects like these are hard to find.

I know, I'd probably just be a permanent lurker on here were that not the case! If at any point something isn't clear to anyone reading this please say so so that we can clarify it for the record. 
 
 
In an entirely different vein are there any thoughts for or against:
1.replacing the rear panel jacks with newer high quality ones.
2.Replacing any or all of the internal wiring. 
 
If so with what and if not why not? 

 

[spaceace1014]

CAP	Voltage	UF	Hight	Diameter	Note
C31	25	10	11.5	6.5	Not much room for increased size
C32	25	10	11.5	6.5	Not much room for increased size
C33	25	10	11.5	6.5	Not much room for increased size
C34	25	10	11.5	6.5	Not much room for increased size
C35	35	47	10	5	Lots of room for hight, 1.5mm extra for diameter
C36	35	47	10	5	Lots of room for hight, 1.5mm extra for diameter
C39	35	47	10	5	Lots of room for hight, 1.5mm extra for diameter
C26	35	47	10	5	Lots of room for hight, 1.5mm extra for diameter
C27	35	47	10	5	Lots of room for hight, 1.5mm extra for diameter
C22	35	470	15	10	Not much extra diameter but lots of room for extra hight
C23	35	470	15	10	Not much extra diameter but lots of room for extra hight
C24	35	470	15	10	Not much extra diameter but lots of room for extra hight
C25	35	470	15	10	Not much extra diameter but lots of room for extra hight
C18	400	220	46	25	No room for extra diameter but caps could be 60mm high
C19	400	220	46	25	No room for extra diameter but caps could be 60mm high
C20	400	220	46	25	No room for extra diameter but caps could be 60mm high
C21	400	200	46	25	No room for extra diameter but caps could be 60mm high
C11 #1	400	10	20	10	30mmHighx16mmDiameter would be easy.
C12 #1	400	10	20	10	30mmHighx16mmDiameter would be easy.
C11 #2	400	10	20	10	30mmHighx16mmDiameter would be easy.
C12 #2	400	10	20	10	30mmHighx16mmDiameter would be easy.

 
 
 

 

 

 

 

 

 

 

 

 

 

 

 

[spaceace1014]

Is there a trick to getting the rear half of the volume knob off? The front off came off with some moderate pulling but the rear half wont budge and I'm reluctant to pull harder unless thats exactly whats needed. I will need to remove the volume pot in order to work on the capacitors that it covers.

 

[spaceace1014]

Ok, so here's what I'm thinking so far. This simply covers the basic capacitor swap at the moment.
 

[size=inherit]CAP[/size]	Voltage	UF	Hight	Diameter		New Voltage	New UF	New Hight	New Diameter	Price	Part number
C31	25	10	11.5	6.5		25	100	11.5	6.3	1.58	ELXZ250ETD101MFB5D
C32	25	10	11.5	6.5		25	100	11.5	6.3	1.58	ELXZ250ETD101MFB5D
C33	25	10	11.5	6.5		25	100	11.5	6.3	1.58	ELXZ250ETD101MFB5D
C34	25	10	11.5	6.5		25	100	11.5	6.3	1.58	ELXZ250ETD101MFB5D
C35	35	47	10	5		35	82	15	6.3	0.42	EEU-FC1V820
C36	35	47	10	5		35	82	15	6.3	0.42	EEU-FC1V820
C39	35	47	10	5		35	82	15	6.3	0.42	EEU-FC1V820
C26	35	47	10	5		35	82	15	6.3	0.42	EEU-FC1V820
C27	35	47	10	5		35	82	15	6.3	0.42	EEU-FC1V820
C22	35	470	15	10		35	560	25	10	0.41	EEU-FM1V561L
C23	35	470	15	10		35	560	25	10	0.41	EEU-FM1V561L
C24	35	470	15	10		35	560	25	10	0.41	EEU-FM1V561L
C25	35	470	15	10		35	560	25	10	0.41	EEU-FM1V561L
C18	400	220	46	25		400	570	50	25	12.17	EET-HD2G471JJ
C19	400	220	46	25		400	570	50	25	12.17	EET-HD2G471JJ
C20	400	220	46	25		400	570	50	25	12.17	EET-HD2G471JJ
C21	400	200	46	25		400	570	50	25	12.17	EET-HD2G471JJ
C11 #1	400	10	20	10		400	47	25	16	1.23	EEU-ED2G470B
C12 #1	400	10	20	10		400	47	25	16	1.23	EEU-ED2G470B
C11 #2	400	10	20	10		400	47	25	16	1.23	EEU-ED2G470B
C12 #2	400	10	20	10		400	47	25	16	1.23	EEU-ED2G470B

 
Links to each capacitor type:
 
ELXZ250ETD101MFB5D
http://www.mouser.com/ProductDetail/United-Chemi-Con/ELXZ250ETD101MFB5D/?qs=sGAEpiMZZMtZ1n0r9vR22fqp084l1X3eJEaeLzgvhAQ%3d
 
EEU-FC1V820
http://www.mouser.com/ProductDetail/Panasonic/EEU-FC1V820/?qs=1JauBbJkKR7oiTk5Vd2JzQ%3d%3d
 
EEU-FM1V561L
http://www.mouser.com/ProductDetail/Panasonic-Electronic-Components/EEU-FM1V561L/?qs=sGAEpiMZZMtZ1n0r9vR22RbNZXJIUr%252b%2fd87FZ8WfBWA%3d
 
EET-HD2G471JJ
http://www.mouser.com/ProductDetail/Panasonic-Electronic-Components/EET-HD2G471JJ/?qs=sGAEpiMZZMtZ1n0r9vR22UHAJHRtExyPaCy2J%252b%252b%252bWaA%3d
 
EEU-ED2G470B
http://www.mouser.com/ProductDetail/Panasonic-Electronic-Components/EEU-ED2G470B/?qs=sGAEpiMZZMtZ1n0r9vR22U%252bm9vN9m10LY2HVP7bTJbo%3d
 
 
1.What are your thoughts?
2.Which of these capacitors should be bypassed with a film cap?
3.Which film cap manufacturer would you recommend? 

 

[duncan1]

Good photos -Spaceace1014- Caps =C11/C12 I changed for 100UF-450V .To fit them I removed  C11/C12 and bypass caps C3/C4  and fitted the larger caps Sideways. I replaced  the bypass caps on the reverse side[soldered side.] You are right! There is a trick getting the inner volume control off  there is a small hole with internal screwing for a very small ALLAN screw you will need to get  a very small ALLAN key and make sure before you turn it it is securely fitted into the allan screw. I don't think Stax supplies that size. They don't want you doing anything to it. It "foxed" me for 5/10 minutes . Sorry have to go out to do the shopping as My wife  has been handicapped by a severe medical condition . Get back in a few hours.

 

[duncan1]

John Lindsay Hood and the designer who made the cutting edge capacitor test equipment to prove his views correct  bypassed ALL the electrolytic caps with good quality FILM caps do NOT buy metalized poly prop  .All the test equipment electrolytic caps feeding the high quality audio chips used to null the signal through the test caps he bypassed . Also watch out some poly prop caps use packing grade poly prop which sounds just as bad as polyester. I realize some people sneer at the mention of bypass caps so instead of my own words or Johns I will quote the words of professor  Paul Horowitz of Harvard university and Winfield Hill of[at that time] Sea data corp. Newton.Mass. in their book--The Art of Electronics--page 34-Bypassing-Quote-The impedance of a capacitor goes down with increasing frequency. This is the basis of another important application: bypassing-There are places in a circuit where you want to allow a DC/slowly varying voltage but don't want signals present. Placing a  capacitor across that circuit element [usually a resistor] will help to kill any signal there. You choose the capacitor value so that its IMPEDANCE at SIGNAL  frequencies is small compared to it is bypassing-end quote.So fit low value caps to bypass the electrolytics  especially at higher frequencies that electrolytic caps cant influence  both connected to a ground to send the unwanted signal to earth.Now I don't think anybody in their right mind is going to disagree with a Harvard Professor --But you never know. I will look at your suggestions and get back Although I know there are plenty of others on this website who have made it part of their life to suggest  the quality of a large variety of film caps. I can only suggest the ones I and some others use.
       Looked at them I like Panasonic the ones I would pick are the EEU-FM 1V561L and    the EEU-ED2G470B.