[David Ellis]

The pupose of this string is to address the modifications I performed for the Jolida 302b.  I believe the componets I upgraded were the most critical parts under the hood of the 302b.  Please query me in this forum with any questions you may have regarding these modifications.  

Also, if anyone has significant fear about soldering under the hood of their Jolida amplifier, I highly recommend Bill's work at Response Audio.  He has much more experience with these amplifiers than me, and has gone deeper into the amplifier.  I suspect that Bills mods should & will sound a scosh better because his mods are more pervasive.  

http://www.responseaudio.com/

My mods

http://www.ellisaudio.com/jolidamods.pdf

The Schematic

http://www.ellisaudio.com/302b.pdf

As a side-note, I think there is something very interesting happening with the Jolida 302b.  It seems to be todays version of the Dynaco ST-70.  The sound quality is extremely good, and the ability to putter with the 302b is very good.  I agree the Jolida 302b is a very good amplifier worthy of time & listening.

[pem]

Dear Dave,

what a good idea!
Many thanks for the documents and the explanations.

  regards,
  Pierre-Etienne

[pem]

Dear Dave,

I have absolutely no doubt about the result (even if you say yourself that you are not an "amplifier guy"). I am just a bit impressed and curious to know you selected the components you had to upgrade?

There is a very interesting discussion in the Response Audio circle about modifications.

  kind regards,
  Pierre-Etienne

[David Ellis]

They are direct signal path items and power supply tweaks.  

All of the signal goes right directly through the coupling capacitors, and resistors.  

The power supply diodes and bypass capacitors reduce power supply ripple.  The diodes are very fast and have a nice soft recovery.  The bypass capacitors should better filter any ripple after the rectification.  Elecrolytics have a very high ESR.  I actually performed the bypass capacitor upgrade in isolation.  I was very skeptical about this before this part of the upgrade.  I wasn't skeptical afterward.

These elements are very basic to any guy that can read a schematic.  

Dave

[shelt59]

Hi,

This is good stuff!  I've just done similar mods this week, except I also replaced all the signal path resistors with Dale Vishays, removed the balance circuit, added new interconnect wire, rca jacks, a logarithmic TKD volume pot & ELMA switch, and converted to PP Triode mode (which I like a lot).  Since I removed the balance knob, I sanded a piece of cherry trim, oiled it up, and added some heavy gold-plated knobs to finish it up!  I ended up removing the xformer cover -- it had a broken internal support and kept vibrating (60hz) due to the magnetic field in the power xformer...

Interestingly, my 302B schematic (and my unit) have several different resistor sizes from yours.  The generic SJ-502/302 schematic, http://www.drtube.com/schematics/jolida/sj-502a.gif, has at least the following differences:  R13&R16 are 1K vs 10K; Trim Pots are 30K vs 22k; R14&15 are 12K vs 20K.  There may be other diffs as well.  First I've heard of that!  

Anyway, my 2001 302b is of this seemingly older design.  It might be worth mentioning in your writeup...

From my mod experience, the most shocking difference was the addition of the HEXFRED rectifiers (I used 1200v/6A IR's).  They seemed to dramatically tighten up the bass and lower mids -- I'm not entirely sure why!  I haven't changed or added to any of the PSU caps yet.

The Auricap coupling and ground caps made the next biggest improvement, followed by the TKD pot.  Finally, the signal path resistors seemed to quiet the amp even more, and seemed to smooth the upper mids and treble.  When finished, I was amazed by the overall change.  A dramatically better amp -- all for ~$300 or so.

I did the Triode mod last.  While you lose half of your power (only 3dB at the ears...), I found the amp lost a little of its raw edge, but sounded much more engaging, smooth and warm on acoustic vocal music & instrumentals.  It may be a little less tight overall on heavier rock, but I think I'll keep it this way since I like the overall change.

Just my $0.02!

Rich

[David Ellis]

Interestingly, my 302B schematic (and my unit) have several different resistor sizes from yours.

This appears to be a 302A/502A schematic.  I didn't realize the schematics could be so similar.  Mine is a 302B schematic.  This would probably explain matters.  At first it appeared there were errors in the schematics, but at second glance these are likely some of the differences between the "A" and "B" series Jolida amplifiers.

I didn't implement the diodes in isolation in the amplifier, but did accomplish this in my CD player.  The diodes to have an impact, but I think this impact is lesser than coupling capacitors.

About 2 years ago I tried Auricaps behind my tweeters.  I liked, them.  They had a very smooth/lush midrange, but lost some detail compared to the Sonicap.  I can easily understand how folks really like the Auricap and why it has become so popular.  All-in-all, I thought the quality of the Auricap was on par with the Sonicap.  I perfer the detail of the Sonicap, but this is my opinion.

Do you have empty holes for bypass capacitors on you power supply board??  My 302b had these, but I don't know if you amp has them.   As mentioned, I accomplished this in isolation and it worked very well.

Indeed your work is more pervasive than mine.  You are very welcome to post your iteration of mods with pictures in this forum.  I am a bit curious about removing the balance control knob.  This makes very good sense, but I didn't putter with anything serious, but this mod is free.

Dave

[shelt59]

I agree the schematic is an older 302a/502a version, but up until now, I've understood the difference between the A and B models was the cosmetic faceplate.  Mine is an early B model, but matches the earlier A schematic.  I would guess they evolved the design a little over time.

I have the holes for the three extra capacitors, and I think that's a great idea to add the bypass caps there. Pretty easy mod, and I can see where you got a nice result from that.  

I actually took a number of pictures while I was doing the mods (great insurance when you screw something up:) ).  I'll try to sit down and document some of the things I did.  

My input circuit has two tiny, cheap pots (and questionable hookup wire) between the RCAs and the L&R input solder joints on the PCB board.  I decided to remove both the vol pot and bal pot/board, then replaced the RCAs, input wire and added a single, high quality 100k volume pot (tapered) whos output is connected to the PCB input at the same location as before.  The TKD is expensive at $58, but sounds great (and fits well in the tight space).  The Alps Blue Velvet is another recommended pot, and is much cheaper.  The Alps Black, and several others, are too large to fit.  I figured this out from some AA posts.   I also replaced the input wire with some 21.5 gauge Cardas silver shielded cable.  That was probably overkill, and was tough to work with.  Some nice unshielded hookup wire would probably be fine.

I've also heard that some of the 302s & 502s have better volume pots than others -- mine was definitely junk, and very scratchy/noisy!

One warning -- at first I just removed the balance circuit and used the old Vol pot.  You lose a fair bit of resistance in the input path (50K I think), so the vol pot got very touchy.  It also sounded terrible, and tended to distort at what I thought was a fairly low volume.  I couldn't figure out why it sounded worse than it did with the balance resistor in the circuit.  Anyway, I forged ahead and bought the 100k TKD.  After installing it, all was well again, and the sound was clean and smooth throughout the input range.   I also replaced the selector switch at the same time since Bill at Response felt that was a weak point in the circuit.  Very strange...

I think I'll try your bypass cap mod next...   I'll let you know how it goes!

Here's a shot of the resistor mods, the ELMA selector switch, and the TKD pot:


http://

[shelt59]

Hi Dave,

One question...   I was looking at my power supply PCB photos and I see places for C1x (x not legible - located near end of PSU board) and C12 (near center of board) which correspond to the two .47 uf sonicaps you have on the top of the psu board [EDIT: see yellow arrows on added photos below]. C12 goes from +B to ground.  C1x appears to go from +B2 to ground.  Here's the problem. I don't see a spot on either side for the third cap, which I infer goes from +B1 to ground.  Is that right, and if so, where did you attach it?  I can see where I could simply spot solder it to the +B1 connection on the PCB, but where do you attach the ground?  It seems to be a long run from my photo...

Thanks!

Rich

[David Ellis]

I don't see a spot on either side for the third cap, which I infer goes from +B1 to ground. Is that right, and if so, where did you attach it? I can see where I could simply spot solder it to the +B1 connection on the PCB, but where do you attach the ground? It seems to be a long run from my photo...

Well, these aren't in the schematic, but I had holes in my power supply PCB for the .47uf capacitors.  They appeared to bridge across the power supply to ground (filtering).  So... my amp(s) had holes present. They weren't immediately obvious.  However, on both amps the holes were present.  The 2nd time for the mods one of the hole pairs took me some time to find.  These holes should be present on your amp too - unless the accounting department eliminated the holes to save more money  .

Oh, you might have to look on both sides of the PCB for the holes.  Someimes there is excess solder from other connections that will fill the empty hole on 1 side (normally the bottom) of the board.  Generally the hole will remain visible from the top side of the board.

Dave

[pem]

Dave,

I have just ordered the parts from SonicCraft.
But, I have just realized that my amplifier has a 220V power-supply.
Since I have ordered some sonicap capacitors, I guess they are rated for 600V. Could it be a problem for my 220V amplifier?

  thanks,
  Pierre-Etienne

[David Ellis]

You will have no problems.  All amplifiers have a transformer to match the external (i.e. 220 or 110 volts) voltage to the desired voltage AFTER the transformer.   The internal voltage will be the same.  the parts you ordered will be fine.

Also, a higher voltage capacitor is never bad.  Well, there are some issues, but for 99% of applications a higher voltage rating will have no downside.

Dave

[pem]

Dear all,

I have opened my 302B (bought in February 2005) but I am not able to see the holes for the 3 extra capacitors. Do you know if the schematic has been modified recently?

In the explanations, its seems that the "after" pictures, page 3 and 5 are reversed, like in a mirror.  Is it possible or did I misunderstood something?

Since I am not expert, I may ask a stupid question: can I remove (unscrew) the PCB, or is it better to let them in place?

  thanks again for your help,
  kind regards,
  Pierre-Etienne

[David Ellis]

I am not able to see the holes for the 3 extra capacitors. Do you know if the schematic has been modified recently?

The holes do NOT appear in the schematic.  The do appear on the vertical PCB holding the power supply capacitors, diodes, and resistors.  You will find the holes in this PCB.

In the explanations, its seems that the "after" pictures, page 3 and 5 are reversed, like in a mirror. Is it possible or did I misunderstood something?

Yes, exactly.  This is so that you can see the mods from both angles.

Since I am not expert, I may ask a stupid question: can I remove (unscrew) the PCB, or is it better to let them in place?

You will have to unscrew the vertical (power supply PCB) to solder some items.  Work gently and you will be fine.

You should not have to unscrew the larger PCB.

If any of this isn't clear, please try to indicate where you need further help.  

Dave

[pem]

Dear all,

as mentioned previously, I have applied the mods. suggested by Dave.
Everything went quite smoothly, except two things:
 - the diodes were too short to fit in the holes
 - I did not find the holes for the bypass capacitors.

Here the overall picture, where you can see where I have added some holes:


This shows the problem with the diodes:


This shows how I have connected the capacitor that goes from +B to ground (the hole exists on my PCB):



This shows how I have connected the capacitors that goes from +B1 and +B2 to ground:



I have carefully verified everything before turning the amplifier on, and this works great!
This sounds to be a big improvement with respect to the stock unit, but I have to continue my listening session

  Thanks again,
  Pierre-Etienne

[David Ellis]

Yep, it looks like the newer/different versions of the 302 don't have the holes for the capacitors.  However, your insights are correct and your work looks very clean.

The diodes.  I bent both legs of my diodes outward.  Then at the very ends of the legs, they are bent straight down.  I have bent some of them extremely without breaking.  I believe the diodes leads are quite mallable.  I suppose they could be broken, but I didn't break any.

Your work looks darn good.  Please do convey your results about the sound quality improvements.

Dave

[pem]

Dear all,

Your work looks darn good.

I have to say that a friend (an electronician) helped me to perform the upgrade the amplifier.

Please do convey your results about the sound quality improvements.

Since I am quite new in this domain, I do not necessary have the correct terms to describe the impact of the modifications. I also have to mention that I am a bit skeptical about various things. But, I was curious to the see (or ear) the impact of electronic components.
To be honest, I am very surprised by the result.

The first thing that comes to mind is: precision. I do not know why, but everything become more distinct: you can more easilly discern the different musical instruments. The voice is also more distinct, like extracted from the musical background.
When you concentrate on sounds, they seem to be more defined in the sense that "they know where they want to go, and how they are going to finish". This remind me the notion of firmness. Similarly, the bass seem to be tight.
The main impact of all these phenomena is that the soundstage is larger and more precisely defined: you can more easilly ear a dialog between the instruments. This gives me the feeling that the artist is closer to me.

I do not have a big experience, but the last time I have felt this sensation was on an Accuphase E-406 (much more expansive than the Jolida).

As mentioned by Dave, this seems to be the best investment that you can do in Hifi. For $120, the Jolida 302B is transfered into a better category.

Thanks again Dave!

  Pierre-Etienne

[teiki arii]

Hello everyone,
when I came to meet pemo for buying a pair of Ellis 1801b, I could notice that he was using Jolida/EH 12AX7 and 12AT7 valves on his amplifier Jolida JD-302B. What a pity! So we changed "Jolida's tubes" for RCA 5751 -12AX7 sockets- and for Mullard CV4024 -12AT7 sockets-. I found the soundstage beautiful and wide opened, very "musical" indeed.
When, two months later, I came back to pemo's, for "recessing", improving tuning, the Jolida JD-302B was burning with "Jolida" 12AX7/ Mullard CV4024. Even if we changed the AOP in my Cayin CDT-17A, it was less magical than with RCA 5751.
If you are afraid of RCA 5751 (mu=70 vs 100 for 12AX7), please try the very cheap JJ/Tesla ECC-803S with long plates -not the E83CC-.
Kind regards, that's my two cents,
teiki.

Ps: as pemo is a pure skeptical scientist, he did not unfortunatly change the 12AX7 yet...

[David Ellis]

when I came to meet pemo for buying a pair of Ellis 1801b, I could notice that he was using Jolida/EH 12AX7 and 12AT7 valves on his amplifier Jolida JD-302B. What a pity! So we changed "Jolida's tubes" for RCA 5751 -12AX7 sockets- and for Mullard CV4024 -12AT7 sockets-. I found the soundstage beautiful and wide opened, very "musical" indeed.

I am not certain which "he" you are referring to, but don't think this was Dave Ellis.

I used Amperex Bugle Boy tubes (orange logo?) for the 12AT7 and 12AX7.  I also had some Mullard tubes for comparison, but I don't recall which these replaced.  I also had the OEM Jolida tubes.  Anyhow, I did find a modest improvement when using the Amperex tubes and did prefer them over the OEM tubes, and the Mullard.  

For the output tubes (i.e. El34s). I really enjoyed the Svetlana "C" logo models, but my Jolida 302 would "eat" 1 of these tubes about every 3-4 months.  This became frustrating and I eventually returned to using the OEM output tubes.  These didn't sound as good, but lasted very long.  I don't have an explanation for the very short life of the Svetlana "C" logo El34 tubes in my Jolida 302.

I have learned that having a slow turn-on circuit, or delay will significantly improve the lifespan of tubes.  The heaters really need to get started before the B+ voltage is applied.  Unfortunately, 99% of tube amplifiers don't have this type of circuit.  My Golden tube SE40 has an aftermarket switch to turn-on the heaters before the B+ voltage.

Dave

[JoshK]

FWIW, apparently those who have tested a LOT of EL34s are praising the virtues of the JJ EL34s, even over the Svetlana "C" wing type.

[David Ellis]

FWIW, apparently those who have tested a LOT of EL34s are praising the virtues of the JJ EL34s, even over the Svetlana "C" wing type.

Thanks Josh, and indeed I have never tested these.  

I have also learned that Groove Tube http://www.groovetubes.com/ actually has a very solid product, but they don't get much press in hifi.