[Netdewt]

Hello all, new here,

I have a Jolida 202a circa Dec 2009 (from Maryland), and I've got a couple issues I'd like to work out, and possibly do some mods in the process. I found this site by doing searches on the topic, so I was hoping there would be some Jolida people here!

- volume pot is scratchy, put in an ALPS?
- noticable hum on left speaker, not affected by volume change
- would tube dampers be effective for me?
- some sound bleeds through from other inputs, new selector switch?
- how tough is it to recap, etc? I have a Weller soldering station, not a pro by any means
- walnut or ebony face plate for it, and rear plate also, where to start?
- remove the transformer covers. Is that dangerous?

I don't have a ton of money. Looking into how I can do as much by myself as possible!

Thanks.     

[Netdewt]

This are the threads I had found here about Jolida mods.

http://www.audiocircle.com/index.php?topic=17354.0
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1273085377&read&keyw&zzjolida

This is what I'd love my amp to look like:

[Netdewt]

Okay, simple question. I'll try that.

Do exposed transformers pose a shock hazard?

[BobMajor]

You can also try Audioasylum. You'll have to register to post:
http://db.audioasylum.com/cgi/search.mpl?forum=amp&searchtext=Jolida+202a
http://db.audioasylum.com/cgi/search.mpl?forum=tubes&searchtext=Jolida+202a

[Netdewt]

Thanks I'll try that.

[Bill Baker]

Hello Netdewt,
 Something to keep in mind when working on the 202. I don't know if it has changed but the 202 always used a double sided circuit board meaning the board willl have to be removed to properly replace/exchange parts on it.

The volume pot can be cleaned with some contact cleaner if it is an open style. I thought they already used an Alps Blue pot? If so, you would have to replace it.

Tube dampers won't help if your noise is a ground loop. I would do some rearranging of your system before determining the absolute cause.

Replacing the selector with a higher quality piece would help with the bleed through.

You should not have any problem with the exposed transformers but keep in mind that they may not have the bello caps on them and will not look like those in the pictures you found.

[Netdewt]

I don't know if it has changed but the 202 always used a double sided circuit board meaning the board willl have to be removed to properly replace/exchange parts on it.

The volume pot can be cleaned with some contact cleaner if it is an open style.

Tube dampers won't help if your noise is a ground loop. I would do some rearranging of your system before determining the absolute cause.

Replacing the selector with a higher quality piece would help with the bleed through.

You should not have any problem with the exposed transformers but keep in mind that they may not have the bello caps on them and will not look like those in the pictures you found.

I wish this site had a subscription page... I missed a response from Bill Baker! Thanks for the input.

What is a ground loop? I'll have to Google that. Should I look into getting something like this? Is there a way to verify that my ground is the problem? http://www.bhphotovideo.com/bnh/controller/home?is=REG&sku=365781&Q=&O=&A=details

Yes, I guess the pot is an ALPS, but it is bad. Seriously it sounds like someone blowing in a microphone every time I adjust the volume.

I got a response from Jolida as well, so this is what I will try first as far as the left channel hum and scratchy pot (the worst issues) are concerned. I'll take pictures of the underside and post up here for anyone that's interested.

First, if you have not biased the amp, that would be the place to start.  Once thing you can do is remove the sources and see if the hum is still there. IF it goes away, put the sources in one at a time and when the hum appears, if may be coming from that particular source. If it does not go away, then turn the amp off and exchange the tubes from the right side to the left side.  If the hum moves to the right side, then it is probably one of the tubes.
 
For the volume pot, turn the unit upside down and remove the bottom. Make sure the amp is off. This should expose the volume pot.  There are small slits on the side, spray in and make sure you turn the pot several times.  Make sure the pot is thoroughly dry before turning on. That should clear things up.

[doug s.]

I wish this site had a subscription page... I missed a response from Bill Baker! Thanks for the input.

it does.  click the "notify me of replies" when you post...   

doug s.

[chrisby]

This are the threads I had found here about Jolida mods.

http://www.audiocircle.com/index.php?topic=17354.0
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1273085377&read&keyw&zzjolida

This is what I'd love my amp to look like:

Those are Response Audio's very pretty mods to the  physically larger 302/502, which has much more internal space for tweaky parts, and the elbow room to comfortably work in.   

You could of course take inspiration from the list of mods described on the Response site, but be aware that as Bill Baker indicated they both use double sided PC boards, and from my own experience with an over 10yr old 302, the quality of plating leaves rather a lot to be desired, so no matter what mods / upgrades you decide on, take particular care when desoldering and removing components with folded over leads.

As for recapping, the ease and expense of that depends on how carried away you want to get - in the case of the 302/502 there are total of 7 HV caps in the power supply and 4 film or ceramics in each channel of audio circuit, and there have been mods that include additional stages of filtering or bypass.   

[randytsuch]

Tube amps contain potentially lethal voltages, make sure you know what you're doing before working on this.

I always add in bleed resistors on the high voltage caps, so after a few mins the voltage will be dissipated.

Randy

[planet10]

Yes, I guess the pot is an ALPS, but it is bad. Seriously it sounds like someone blowing in a microphone every time I adjust the volume.

I had a similar issue with a succession of pots & stepped attenuators in the Fornacodiy pre-ampi'm using... turned out lack of grid stoppers was causing 1.65 mHz oscillation (ie the pre was trying to be an AM transmitter). Grid stoppers and things are better (better sounding & a quiet volume control).

dave

[Netdewt]

Oh man, I hope the issue is not that complicated.

If I let the amp sit unplugged, after how long is it safe?

The more I think about it, the less I want to mess with the circuit in any way. I should use my energy to build some frugalhorns.

[planet10]

I should use my energy to build some frugalhorns.

dave

[Bill Baker]

Hello Netdewt
 It sounds like there is some concern about going inside the amp. My recommendation is to take it to someone locally who can fix it for you. One thing about tube amps is that they are very easy to diagnose by someone who understands them and repairs should be quite inexpensive.
 I wouldn't risk it. It's not worth risking your safety. The amp can be replaced if something goes wrong but your safety should be first and foremost.
 Build the speakers and let someone else tackle the electronics.

[JakeJ]

I'd like to thank everyone for the great responses so far.  Especially the safety related ones!

This thread caught me out as did I see it, but like so many threads in my Tube-O-Phile Circle, I felt I had no input as I have no experience with this particular unit or, more importantly, any mods to this circuit.

However, in the light of the OP considering performing the mods, then first and foremost safety must be of the utmost concern.  Please enlighten us as to your experience level in electronics and particularly with vacuum tube electronics and high voltages.

Thanks,
JakeJ

[Netdewt]

I am a relative beginner at electronics, but I'm not reckless. I just built a CMoy headphone amp and it worked with no troubleshooting, only a few mV on the outputs. On to the tweaks! Next up I'm building a mini USB DAC called a Skeleton DAC. I do all my own home wiring, and I ask questions when I don't know something. I'm very careful, and I check for voltage every time I touch something, sometimes multiple times.

I think I could do it, I just don't want to ruin my amp or waste my time.

[JakeJ]

Cool, thanks for responding.  So when you open up the amp then find the big caps and discharge them carefully with a big resistor.  Check several points for stray voltage and once you're confident it's dead then you can tear into it.  Take pictures, if not to post but to have as references for reassembly. The old "rule of thumb" would be keep your non-dominant hand in your back pocket until the amp is safe.

Good luck on your journey!