Sansui 8080 restoration

[maxhifi]

Well usually I try to stick to the original design when tweaking amplifiers. However in the same way I gladly exchange indascendent against LED's where a correct(or at least acceptable) colour can be achieved I gladly exchange components to lower the noise floor or distortion.(for example I change all 2SC458 I find with new 2SC2240 even though it is in some way a change of design). As long as it's not a change in design so its another amplifier or another sound.

Sadly I'm not aware of any newer-production BA312 and the only equivalent I know is NTE1433, however I'm a little skeptic against NTE's performance.

Then I don't know, if it was that easy to replace a BA312 with 3 transistors and 4 resistors. Why did Sansui choose the BA312 in the beginning?

Because after all it's a consumer product built to a cost, and it's one part instead of seven, and must have been cheaper - look at lots of phono amps from the era which are built with 2 or 3 transistors instead. I bet you could even find an example from Sansui by studying some slightly earlier schematics.

Is the noise equally bad in both channels? Are you entirely sure it's the BA312 and not something else?

 

[Cicaro]

Is the noise equally bad in both channels? Are you entirely sure it's the BA312 and not something else?

Its nearly equally bad in both channels and I traced the noise to come from the BA312s, and to be honest it's not that bad. Most people would probably live with it as it is and not recognize it. It's just that the noise floor is markable higher then in my AU-555 even though its not as bad as when the AU-555 got the 2sc458 in it. Its totally possible to enjoy the sound from the phono stage even as it is now the only time you will notice the noise without measuring is at a direct comparision between the AU-555 and 8080.

I'll guess that I have to build one of the equivalent circuits with low noise transistors and good metal film resistors and desolder one of the BA312 and do a test

 

[maxhifi]

Its nearly equally bad in both channels and I traced the noise to come from the BA312s, and to be honest it's not that bad. Most people would probably live with it as it is and not recognize it. It's just that the noise floor is markable higher then in my AU-555 even though its not as bad as when the AU-555 got the 2sc458 in it. Its totally possible to enjoy the sound from the phono stage even as it is now the only time you will notice the noise without measuring is at a direct comparision between the AU-555 and 8080.

I'll guess that I have to build one of the equivalent circuits with low noise transistors and good metal film resistors and desolder one of the BA312 and do a test

Good idea - I get similarly obsessed with squeezing the last drop of performance when I work on vintage gear - especially when it comes to elminating hum from tube stuff. Just as a reality check, compare the remaining hiss level with the quietest surface noise on a record, to double check how relevant beating the spec is.

 

[TubeRelic]

BA312 Replacement

Cicaro, did you ever replace those BA312's ? My 9090 uses 5 of them and I just ordered NTE1433's to replace them. Specs for 1433 are available free at several sites including MCM from whom I ordered. The 1433's are touted to be super quiet If you did a replacement, what did you use? Thanks for your pictures. Very impressive veneer work, I would think you could almost do 2 units w/ a square meter of material.
Är du i ett nytt hus? Och förhoppningsvis med några nya barn?

 

[Cicaro]

Cicaro, did you ever replace those BA312's ? My 9090 uses 5 of them and I just ordered NTE1433's to replace them. Specs for 1433 are available free at several sites including MCM from whom I ordered. The 1433's are touted to be super quiet If you did a replacement, what did you use? Thanks for your pictures. Very impressive veneer work, I would think you could almost do 2 units w/ a square meter of material.
Är du i ett nytt hus? Och förhoppningsvis med några nya barn?

No I never got that far, the 8080 was connected as my main amp in the living room and never went back on the working bench. If you can hear any improvements with the NTE please tell my since this it may make me use them for once. (I'm as I said earlier very sceptic against NTE, mainly due to one component said being equivalent to so many different that i seems impossible without going from being equivalent to "it's more or less functioning")

As an answer to your two last questions: Jo vi har precis flyttat in i villan och lämnat lägenheten men inga skrikande småkottar ännu. Däremot har jag renoverat en AU-9900 också om det var såna barn du åsyftade vilket finns en renoveringstråd på faktiskt om.

 

[kdooley]

Very nice job. I'm getting ready to replace the cheap plastic veneer on mine with real walnut.

 

[macman007]

Cool thread, if a few years old. If the poster asking about changing phono stage IC's still hasn't. I would go one of several routes. If you are capable, make up something discrete using high quality modern components to replace the BA312s' in the phono stage or various other places. It seems like the 9090 relies more on them in different places than the 8080 (which I own). Make the replacement on a breadboard and wire it to test it in circuit. You can mix and match appropriate components to improve the sound.

Another alternative is to print the specs for the BA-312 and search for the best available substitutes made from the 70's till now. Beware Chinese or other knockoffs, there are many imposters being sold today, as well as bad relabeled pulls from old scrapped boards. I'm not generally overzealous when it comes to using NTE semiconductors, specifically transistors or other switching components, beyond diodes or rectifiers. If you can, find GENUINE later model NOS substitutes, something with minimum specs better than the stock BA-312. I'm betting it was chosen more for it's price point than being the best component choice for the phono stage. Beware the Beancounters.

You could design an op-amp based replacement phono stage. I am considering is replacing the entire stage, building a modified CNC phono stage to install semi permanently. using the OEM power supply feeding the stock section.. I am leaning more to installing low capacitance cable directly to the input selector @ the phono stage audio connectors to the Phono In jacks on rear. Leave it line level, allowing you to use an external phono stage of your choice, without sacrificing a line input position to do so. There are some nice phono stages out there to buy or build yourself. I have a Muffsy DIY I built and am very happy with. I have several old receivers here with great sound, but marginal phono sections, this is becoming to be the easiest and least invasive way to go. You could build a Muffsy, CNC or similar stage of choice and install it using the receiver's own power supply modified if needed to 15vac @ 500ma to power the unit. Affix it internally, replace the covers and nobody's the wiser. Only connections on the phono in jacks and phono stage to input selector are disconnected then bypassed, making it simple to reinstall the factory stage if ever desired.

 

[AlTinkster92]

Looks great and fantastic job! My 8080DB is getting attention soon.

 

[Strongbad]

Hi so I manage to get my hands on a Sansui 8080 but it seems to have a few problems. The big ones so far are that the bias for the phono channels is going crazy. The Play NR calibration yells at you if you try to turn it (lots of snaps and pops) and quite a few backlights are out. Also, the radio dial is no longer aligned with the actual channels is there anyone out there who knows how to fix these and can walk me through it that would be great.

 

[Hipocrates]

Also, the radio dial is no longer aligned with the actual channels is there anyone out there who knows how to fix these and can walk me through it that would be great.

Welcome to audio karma, you should create a new thread and maybe we can help you... looks a lot of stuff going on. Are you experienced with electronics?