I have just purchased an OA21. Original (E) version. Must date back to the mid 1980's.

I know that the OA21 was later revised with the OA21S. Among the changes included a different style SOAP connector, for the revised SOAP (SOAP 2).

Now, the original SOAP (SOAP 1) is very, very rare. The SOAP 2 (for the OA21S) comes up for sale now and again. My questions is: Is it possible to use my OA21E with the later SOAP 2 PSU? I know the connector is diferent, but what else would get in my way to ensure compatiblity.

Any help would be great here. Any one selling a SOAP 1? That would sort it out!

Both Soaps were very basic. They consist of a transformer, bridge rectifier and a pair of caps - no regulation, unlike the Hicap for example.
The Soap simply piggy backs onto the 21 supply and there is no pre/power split.

IIRC the voltage rails on all versions of the 21 are the same and therefore, connector aside, any Soap will work.

Only pay eBay prices if you must have a visual match with the 21. You can build a SOAP for about £80 with new parts and remember that the caps in a SOAP will be well shagged by now.

Rob, the soap has 24v and 32v out puts. What ones would I use?

My OA21 has a rectangular plastic connector with 4 wires coming from it going to the region where the 4x4700 micro Farad smoothing capacitors are situated.

The SOAP 2's I have seen have a 6 pin arrangement forming a circle.

How would I connect the SOAP 2 to my OA21E and what voltage would I use?

I noted your posts concerning the hardness of the OA21 when used with CD. I have listened to it with my Planet Mk1, and the sound is very dynamic. Taught, powerful bass, clean mids and a trebble that is not that harsh (for solid state anyway). perhaps it was all that digital hash that so many 1980's/early 1990's players had?

I owned a similar OA21 to your and I didn't find it not being harsh with a Meridian 507 CD. It is also very dynamic with plenty of drive, even when drivign a pair of inefficient ATC SCM12.

I now own a much newer OA21s, although it is more detailed and tighter, I prefer the older OA21 in many areas, especially the smoothness of the older amp.

In my opinion, the older Onix amps are superb value for money and they have small form factor, making them quite discrete.

Yes, it is a cracker. The sound that comes out is superb. Crisp and full bodied, with excellent timing. How a 25 year old design can better so many modern designs seems crazy... have we made any progress?

hifienthusiast: did you ever listen to your OA21 with the SOAP?

Anyway, the power supply. I am sure I could build one pretty easily. However, I am sure there is a filter network on the SOAP. This could make things a little more intresting.

Rob, the soap has 24v and 32v out puts. What ones would I use?

My OA21 has a rectangular plastic connector with 4 wires coming from it going to the region where the 4x4700 micro Farad smoothing capacitors are situated.

The SOAP 2's I have seen have a 6 pin arrangement forming a circle.

How would I connect the SOAP 2 to my OA21E and what voltage would I use?

I noted your posts concerning the hardness of the OA21 when used with CD. I have listened to it with my Planet Mk1, and the sound is very dynamic. Taught, powerful bass, clean mids and a trebble that is not that harsh (for solid state anyway). perhaps it was all that digital hash that so many 1980's/early 1990's players had?

Brad, take my comments on the 21s line level inputs with a pich of salt.
I owned a 21/SOAP2 way back in the falt earth days with an LP12 and ES14s and it still sticks in my mind as one of the most coherent and musical systems I've heard or owned.

I didn't feel the sound was as good via CD into the line inputs but that may well be a reaction to the CD players used. When I recently revisited a 21 I found the same differences and preference for it using the phono stage but it sounded great when I used a Revox open reel into the CD input. I'd say the Onix is a little fussy over the partnering CD player.

The 32v output on the SOAP will be for the 21 while the 24v was for the matching tuner. As you have discovered, the socket on the back of your 21 simply runs to the raw DC at the PSU caps and you simply match them with output of the SOAP.

have we made any progress?

hifienthusiast: did you ever listen to your OA21 with the SOAP?


If you listen to more modern amps, their presentation can be different from the Onix, but it all depends on your own taste to decide if any progress has been made. I also had a nearly new Cyrus 7 int amp briefly and I prefered the Onix in my system. Among all the older transistor amps I have tried in the last few years, I like the Sugden A48B and Stemfoort SF60 for their lovely midrange and plenty of bass. I didn't like the Myst TMA3 which is highly praised by many people. I found it veiled and the imaging is not as good as the Sugden. The Myst's case is made of thin steel so it is not half as solidly built as the Onix.

None of these amps have been serviced, so my opinion may not be true if they have been serviced.

I have never tried the OA21 or OA21s with a Soap since I don't own a Soap. I have a mini Soap with a Onix BWD1 FM tuner. This tuner is a real gem. See http://www.pinkfishmedia.net/forum/showpost.php?p=285157&postcount=37 for photos. I would rate it as one of the best sounding and most airy tuners among those I have owned including Quad FM4, Naim NAT03 and NAT05, Arcam T61. The only tuner which I own and may be better than the BWD1 is a Troughline valve one, but mine required the tuner head to be aligned and since it is mono, it needs a stereo decoder. I don't have the equipment to do the alignment.

......Stemfoort SF60......

I was soooo skint when my local dealer let me have one on home dem for a few days. If I had a wife at the time I would have sold her into slavery. Fantastic amp....and a passive pre amp section to boot IIRC. Was there not some assosiation 'tween Stemfoort and Sugden?

Stemfoort was a series of electronics made by Sugden in mid 90s. The SF60 is rated at 60W per side and Sugden also made a more powerful version called SF100. After the Stemfoort series was finished, I think Sugden introduced the Optima and Audition series. Some photos of a SF60 which I always regret selling.

http://homepage.ntlworld.com/hon.lau/StemfoortSF60.jpg

http://homepage.ntlworld.com/hon.lau/StemfoortSF60inside.jpg

Neat, and what tiny power caps in there!

I remember it being the only amp that ever made the Infinity Kappa's I had at the time sound decent.

The SF60 drove a pair of power hungry ATC SCM20 with ease, even the seller admitted that when he brought the ATC to my house. The smoothing caps are probably 63V 10000uF Rubycon or Nichicon ones, enough for what they are designed for.

Brad :) :)

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=280010826306&ssPageName=STRK:MEWA:IT&ih=018

If you are going for it, might be best to post something in case any other fish are following it and you can warn them off ;)

Yes, that is the one I am looking at.

Yes, that is the one I am looking at.

It's been a while since I fiddled inside one but sorting connectors and working out the connection won't be difficult. PM me when you get the SOAP and I'll gladly help figure it out with you.

Where are you based?

I am in Birmingham Rob. The SOAP will obviously increase the size of the capacitor bank (15,000 X 2 in SOAP, and 4,700 X 4 in OA21), total of 48,800 mico Farad, and obviously there will be another transformer (around 200 VA I would say). It must give out some serious current with the SOAP!

How does the sound improve? (it already sounds great, driving my Ruark Talisman 2's with ease).

I am in Birmingham Rob. The SOAP will obviously increase the size of the capacitor bank (15,000 X 2 in SOAP, and 4,700 X 4 in OA21), total of 48,800 mico Farad, and obviously there will be another transformer (around 200 VA I would say). It must give out some serious current with the SOAP!

How does the sound improve? (it already sounds great, driving my Ruark Talisman 2's with ease).

TBO, not a lot IMO. It has more grunt into very low loads but, unlike adding a Hicap or APX for example, the supply isn't actually any cleaner.
The toroid in the SOAP is a large beast - 400va or so IIRC.
An interesting experiment might be to mod the SOAP so that it provides a regulated supply to the OA21, perhaps leaving the internal supply to drive the phono stage via Andy's SRs. That could be a killer amp. Perhaps the regulator boards Les at Avondale uses might be suitable.

Rob, I can see where you are coming from. There is no pre amp in the OA21, just a 10K pot and a source selector.

The power supply is purely for the power amp and the phono board.

The sound of an external regulated PSU for the power amp sounds excellent. I think if I was to go down this route I would be best starting from scratch and building one.

I would have to divert the intenal power supply in order to power the MM phono board on it's own.

Out of interest, did you ever directly compare the OA21 to the early Naits and smaller Naim Pre/Powers? Where do you think it lies?

Rob, I can see where you are coming from. There is no pre amp in the OA21, just a 10K pot and a source selector.

The power supply is purely for the power amp and the phono board.

The sound of an external regulated PSU for the power amp sounds excellent. I think if I was to go down this route I would be best starting from scratch and building one.

I would have to divert the intenal power supply in order to power the MM phono board on it's own.

Out of interest, did you ever directly compare the OA21 to the early Naits and smaller Naim Pre/Powers? Where do you think it lies?

Yes I did make the comparison.

My system was LP12/Ittok/Troika/OA21/Epos ES14.

From there I added the SOAP - marginal benefit with 14s but the two Onix boxes looked nice together so they stayed for a few years.

Then I went to Naim NAC72/Hicap/140 - better but only really on A/B dem.

I've never directly comapared the OA21 to a Nait2 but have used the latter and I'd say the Onix is the better amp.

Rob, does the Onix OA21 have any special requirement for speaker cable type/length like Naim amps (and others, i.e. old Exposure, NVA).

Are in my humble opinion an extremly underared amp I have the seteup and they work wonderfully. The mm phono stage is absolutly brilliant, the best i have heard at twice the price.

Stemfoort was a series of electronics made by Sugden in mid 90s.

I don't think it was actually made by Sugden? Patrick Miller told me that it was made in the Netherlands and marketed in the UK by Sugden. :confused:

As far as I know, the Stemfoort SF60 integrated amp circuit board layout is nearly the same as the Sugden Optima 80 integrated amp. I have photos of the inside of both amps.