Advent 300 Rebuild: Let the jaws hit the floor, let the jaws hit the flooooor!

[eedork]

Pat -

I don't have the schematic in front me at the moment, but are Q206 and Q207 the FETs in the muting circuit?

My recapped 300 has a thump and some hiss that I haven't been able to track down. Unfortunately I don't have enough test gear (ie oscilloscope) to adequately chase the hiss. I've replaced the muting circuit FETs and tested it - the mute circuit works fine - and I've also replaced all of the transistors in the preamp section with modern equivalents. Still no luck. My last shot in the dark might be to replace the tantalums.

-Matt

 

[patfont]

Yes those are the FET's I always pull them and check out of circuit. And yes replace the 4.7uf tants.

Pat -

I don't have the schematic in front me at the moment, but are Q206 and Q207 the FETs in the muting circuit?

My recapped 300 has a thump and some hiss that I haven't been able to track down. Unfortunately I don't have enough test gear (ie oscilloscope) to adequately chase the hiss. I've replaced the muting circuit FETs and tested it - the mute circuit works fine - and I've also replaced all of the transistors in the preamp section with modern equivalents. Still no luck. My last shot in the dark might be to replace the tantalums.

-Matt

 

[eedork]

Thanks pat! Do you just replace the tantalum caps with electrolytics?

-Matt

 

[Tinnkindling]

The thump is normal for the Advent 300. Mine does not produce a bad hiss.

 

[Ballylongford]

Alot of times Q206 and or Q207 are bad and when replaced there is an improvement. A thump at start up is normal, when rebuilt it should just be a nice soft gentle ttthhhump, not a hair raising thump.

The thump is normal for the Advent 300. Mine does not produce a bad hiss.

I agree there is a normal thump with the Advent FM300 units; I heard it in brand new units in store when they were first offered for sale.

However as Pat references above some develop a hair raising thump which is not normal....

 

[patfont]

Thanks pat! Do you just replace the tantalum caps with electrolytics?

-Matt

I used 4.7uf 50V Silmic II

 

[eedork]

Excellent. I'll have to order some and see if that helps with the hiss.

-Matt

 

[eedork]

Pat -

When replacing the tantalums with electrolytics, how to handle the polarity?

-Matt

 

[mech986]

Pat -

When replacing the tantalums with electrolytics, how to handle the polarity?

-Matt

Look very carefully before unsoldering, the polarity should be marked on the tantalum cap. If not trace one lead or trace back to either ground or a positive or negative rail. If negative goes to neg rail, then positive will go to ground. If negative goes to ground, then positive will go to positive rail.

That's how it works for a bipolar power supply.

 

[patfont]

On the Advent tants, on one side is a "white dot" so looking at the side with the white dot right is positive left is negative. if you look really hard the board is also actually labled. If you run into any problems let me know.

Pat -

When replacing the tantalums with electrolytics, how to handle the polarity?

-Matt

 

[eedork]

Thanks for the help guys!

Could these tantalums be the cause of my hiss?

Unfortunately I don't have any electrolytics on hand at the moment, so I'll have to order some. As a temporary fix I could also just replace the tantalums with some of the old electrolytics I pulled out during the recap.

-Matt

 

[patfont]

hissing one or both channels? hissing in phono, aux, tuner, does hiss increase with volume rotation or is it always the same?

Thanks for the help guys!

Could these tantalums be the cause of my hiss?

Unfortunately I don't have any electrolytics on hand at the moment, so I'll have to order some. As a temporary fix I could also just replace the tantalums with some of the old electrolytics I pulled out during the recap.

-Matt

 

[patfont]

The tuner board is recapped and dead center is Q802 which was replaced, muting button now works and stereo indicator light works and is adjusted.

 

[eedork]

thanks Pat

Hissing is the same on both channels on all inputs. It is in the preamp section somewhere .. if I remove the jumpers the hiss is gone and it is dead quiet.

I've replaced electrolytics as well as the two FETs in the muting circuit and the six transistors in the preamp (three per channel). The hiss isn't that bad through speakers, but it is quite audible with headphones.

-Matt

hissing one or both channels? hissing in phono, aux, tuner, does hiss increase with volume rotation or is it always the same?

 

[patfont]

I doubt the hissing is the tants but they should be replaced. have you checked all your work? Does yours have the updated grounding strap on the back of the board?

 

[patfont]

ok time for the main board now:

a combination of Silmic II in the signal path, Nichicon FG in the filtering locations, and Sonicap Gen II's in the importiant locations.











I will let this burn in for some time and then comment on the sonics.

 

[eedork]

Hi Pat,

Thanks! Yes, mine does have the grounding strap. It was manufactured in October of 1980, so it is near the end of the production run and looks to have most of the factory updates.

I have double checked my work. Early on I found one cap in the phone section that was installed backwards. I've fixed that, but am still having problems.

-Matt

 

[patfont]

just checking, across both emitters what is your bias set at?

 

[patfont]

I would like to thank Leestereo for some input on the F3 cut-off of some of the films I replaced. This little Advent 300 is punching well above it's weight and making it very hard to think what more could you want?

 

[rmoreau61]

This is what I love about AudioKarma! With a bit of searching, you can learn just about anything you want or need about audio. A local business has an Advent 300 and I had no idea if it's worth pursuing. Sounds like I could get some good fun with a refurb and great sound as a reward. Let's just see if I can get a steal worthy price. Just getting into the rehab hobby and am completely hooked.