[teiki arii]

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

No, "he" refers to pemo...Sorry not to have been more clear...

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 have tried dozen and dozen of 12AX7/5751, 12AT7/5965, 12AU7/5963 and 6922/E88CC tubes. Amperex 12AX7 are good for guitar amplifier but not as preamp tubes at all, IMO. I like very much 5751 in stead of 12AX7, especially RCA Black Plates triple or double mica or Sylvania 5751 GB...For a very good pair of 12AX7, JJ/Tesla ECC803S long plates is a an excellent Quality/Price choice...
That's my two cents.

Best regards.

[David Ellis]

Thanks very much for this input.  I must admit NOT being a tube expert.

Dave

[natemil]

Hi Dave,

Here's my version of 302a.  Link shows B1 & B2 top and bottom view.

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=850

Doug

[David Ellis]

Hmmmm,

You are missing some holes in your board.  Bill (Response Audio) and I have corresponded about this, and a few other changes over the lifeline of the Jolida amplifiers.

You have 2 choices.

1.  Omit the bypass capacitors.

2.  Solder the leads of the bypass capacitors directly to the terminals of the big capacitors on the bottom side.

I think the latter would be fine, but if you ship the amplifier UPS, they might get ruptured loose.   You could use .1uf capacitors (instead of .47) for bypassing.  These will be physically lighter and less likely to break loose in shipping.  

Dave

[David Ellis]

A Retraction.

The holes are visible in 1 photo, but not the other.  They are "buried" under the power supply electrolytics.  Yes, you can put the bypass capacitor across these vacant holes.

Dave

[Noam S]

Hi Dave,

I just picked up a used 502a a week ago and have been floored by this inexpensive purchase ever since.  Replacing the 10yr old original pre-amp / driver tubes brought a great improvement and I'm waiting for my KT88's for the power tubes.

Your Jolida mods web page with the before and after pic.s inspired me to look 'under the hood' of this amp and conclude that I could indeed handle replacing a few caps,some of the resistors and the volume pot myself.  I am an electrician (not an electronic tech.) but I do solder my own cables and have replaced selectors and such in pre-amps. I know what a restor, capacitor and transformer do - but I don't yet have a complete concept of how an amp circuit works (I'm reading up on it though).

My thought is to put premium caps where they will do the most good (sonicap platinum?)
and regular sonicaps in the other positions. When looking at your site and reading the response audio upgrade info I got confused trying to figure out which are the coupling capacitors and which are the signal ground caps- and which ones I should spend the premium bucks on.

You show the .47uf caps as well as the .22uf caps as both being coupling capacitors.
the Response site lists these components as upgrades:
 .22uF VH Audio V-Cap Teflon capacitors installed in the coupling  locations.
 .47uF VH Audio V-Cap Teflon capacitors installed in the signal ground locations.

Could you clarify that, and add your opinion as to wether the platinum's are worth the premium and where they would do the most good? You can reference the red and blue
circles on your web page .

Thanks so much for sharing this information with us - and for your web page.

-Noam

[David Ellis]

Since I have ordered some sonicap capacitors, I guess they are rated for 600V. Could it be a problem for my 220V amplifier?

This is no problem.

The difference between your 220v amp and the USA 110V amp is the initial power transformer.

The internal voltages should be identical.  The Sonicaps will be fine in this regard.

The only "hook" would be capacitors before the initial power transformer.  In my recommended tweaks, there is nothing changed before the initial power transformer.  Also, I am not sure if the Joilda has any capacitors before the initial power transformer.

Dave

[David Ellis]

First, I have not compared the V-Cap and the Platinum.  Hence, I really cannot be of any specific help in this regard.  I believe both are good capacitors, but this is only via the rumor-mill.

Could you clarify that, and add your opinion as to wether the platinum's are worth the premium and where they would do the most good?

Well, I sold my Jolida primarily because it would toast a Svetlana C logo tube every @4 months. I also found the VanAlstine Ultimate 70 sounded slightly better than my Modified 302b.  However, the modified Jolida tube amplifiers are very very good amplifiers, and certainly a product that could occupy a very good hifi system for 10+ years.  Soooo, if you amp is reliable and you plan to keep it forever - sure, spend the extra $$ on some very good coupling capacitors.  This makes good sense.

I think the standard Sonicap is an extremely good capacitor that doesn't cost much $$.  In this regard, I think it's the smartest move for 99% of folks. 

In the coupling locations in my source gear I currently have Mundorf Gold / Silver-Oil capacitors bypassed with .1uf Sonicap Platinums.  Alternately, there are a few locations where I have Sonicap Platinums with no bypass (in smaller value locations).   While this stuff does sound better, it's extremely expensive.  I have @ $400 of these boutique capacitors in my system.  This is not a value-oriented purchase.  Sure, they are smoooooth, and clean, but the Sonicap is a very solid product.

I will also add that my source gear is essentially maxed out.  It's filled with Black Gate capacitors, Superfast diodes, and some great tubes from Andy at http://vintagetubeservices.com/.  The only possible tweak remaining is adding @$100 of op amps in my CD player.  I think 2111 is the designator, but I'd have to check my notes.

I haven't tweaked a Jolida 502, but believe the layout is very similar to the 302.  As such, the locations where better capacitors would be most beneficial are the locations where the metalized poly capacitors currently exist.  These are either round black (Solen) capacitor or square red/blue Wima capacitors. There should be 6 of them on your circuit board visible when removing the bottom plate.  Check the values on the current capacitors and replace them with the same (or slightly larger if necessary) value Sonicaps.  These are the RED and BLUE circles in the mod PDF.

I do NOT recommend using Platinums or VH caps for bypassing in the power supply.  This would be totally wasteful.

Dave

[David Ellis]

Please let me know if I missed anything.

[dado5]

If anyone is thinking of a more radical mod, I came across this one that brings the 302 (a version) to class A triode no feedback operation.

http://users.podolsk.ru/boga/a_pre_drv1.html

Aggressive to be sure but it may take the amp to the next level.  I'm watching the 'bay for Jolida 302/502's now - beware my wife is a master sniper

[Bill Baker]

Hello Dave,
 I hope you don't mind but I have to point out a correction in your mods as listed on the pdf list you provided.

 You mention: "GREEN - Replace 4 OEM 10k ohm resistors with Mills MRA5 10k ohm resistors"

 I have notice you also did this on your personal amp a while back. These resistors are the grid stop resistors and should be 1k ohm (up to 2.2k ohm at most) rather than 10k ohm. Using such a high value in this position would have an adverse effect on the frequency extensions and also not necessary to do it's intended job.

[Noam S]

That about covers it Dave,  Thanks again. I will probably go with the regular sonicap gen II's all around for starters and see what I get.  That and the volume & selector switch. Gotta leave some kind of upgrade path for the future anyway - what else would we have to obsess about? This amp is already a killer improvement over the various SS stuff I've had running my Vandy's anyway.  (This rig has me listening to opera fer goodness sakes - I never listen to opera)

re. RA's (Bill's?) post
" I have notice you also did this on your personal amp a while back. These resistors are the grid stop resistors and should be 1k ohm (up to 2.2k ohm at most) rather than 10k ohm"

I haven't 'read' resistor values yet but I do have a band reference color chart.  These are the resistors that come of the tube socket bases, correct ?  RA I take your word seriously as you mod these things for a living.

Noam

[Bill Baker]

I haven't 'read' resistor values yet but I do have a band reference color chart.  These are the resistors that come of the tube socket bases, correct ?  RA I take your word seriously as you mod these things for a living.

 Yes, these are the resistors that go from the power tube socket to the circuit board. The schematic value is 1K ohm. I do like the Mills but prefer a good Carbon unit such as the Riken Ohm for grid stops. You can use anything from 1/2 watt up in this position.

[David Ellis]

There are normally several Jolida amps for sale at www.audiogon.com .  I have purchased several pieces of gear from audiogon with great success.

Dave

[David Ellis]

I have notice you also did this on your personal amp a while back. These resistors are the grid stop resistors and should be 1k ohm (up to 2.2k ohm at most) rather than 10k ohm. Using such a high value in this position would have an adverse effect on the frequency extensions and also not necessary to do it's intended job.

I didn't change any typology or values when swapping compoents in my 302.  I simply upgraded resistors from the elcheapo OEM units.   I think it's very possible that factory amplifiers were shipped with a few different configurations.  I have been told by folks in-the-know this is a very frequent occurence.

I also think that Bill knows these amplifiers, and his comments are safe.  I also know that amplifiers will vary across production lines.  I have seen this before. 

Dave

[Bill Baker]

 I too have been working on redesigning the Jolida 302/502 amplifier circuitry. I want to do away with using the 12AX7 input tube. This amount of gain is not necessary and I have found other tubes (with the proper circuitry) can sound amazingly good. There may be a new version of the Bella EXtreme 3205 sometime in the first quarter 2007!

I haven't tweaked a Jolida 502, but believe the layout is very similar to the 302.

Identical other than bias resistors.

CAPACITORS:
 Well, I have played with a countless number of coupling capacitors in these amps. Here is my break-down:

1) Sound on the warmer side - AuriCap or SoniCap Gen II (they pretty much sound the same)
2) More precise but without the same level of warmth - SoniCap Gen I or Theta AudioCap
3) Seductive presentation - Jensen or Audio Note PIO
4) The best in refinement and overall most musical presentation - SoniCap Platinum or V-Cap.

 Any one of these capacitors will bring forth noticable enhancements in these amps.  I prefer to take them "all the way" but this requires completely gutting the amp and building up from the bare chassis. The prototyping of the new circuit is proving to be exceptional and I hope this will become our next 3205 Statement product. Time will tell.

 Have fun with your Jolida and enjoy the ride.

[David Ellis]

1) Sound on the warmer side - AuriCap or SoniCap Gen II (they pretty much sound the same)
2) More precise but without the same level of warmth - SoniCap Gen I or Theta AudioCap
3) Seductive presentation - Jensen or Audio Note PIO
4) The best in refinement and overall most musical presentation - SoniCap Platinum or V-Cap.

I agree with all of these comments, but have not auditioned the V-Cap.  My preference is the Sonicap Gen I for most things.

Hello Dave,
 I hope you don't mind but I have to point out a correction in your mods as listed on the pdf list you provided.

 You mention: "GREEN - Replace 4 OEM 10k ohm resistors with Mills MRA5 10k ohm resistors"

 I have notice you also did this on your personal amp a while back. These resistors are the grid stop resistors and should be 1k ohm (up to 2.2k ohm at most) rather than 10k ohm. Using such a high value in this position would have an adverse effect on the frequency extensions and also not necessary to do it's intended job.

??  Uh, er  ??

I posted my schematic here: [http://www.ellisaudio.com/302b.pdf, and the value listed is 10k ohms for R13 and R16.  My amplifier was had the same values installed, and I replaced them with the same values. 

I am not an EE, and generally make very safe decisions.  Presumably you have experimented with this and found a smaller value superior?  Please confirm. 

[Bill Baker]

I didn't change any typology or values when swapping compoents in my 302.  I simply upgraded resistors from the sand-cast OEM units.   I think it's very possible that factory amplifiers were shipped with a few different configurations.  Also... I don't think the value of these resistors was listed on my schematic.  I thought they were the emitter cushion resistors, but I could be incorrect.

 

 The emitter/cusion resistors (off the cathode of the power tubes) are 1 ohm units located on the center of the power supply board. You will find a black wire going from one end of the resitor to the cathode of the tube. This is where the bias reading is taken from. These have always been 1 ohm units except for the first 200 pieces of 302/502 ampliers ever built in 1994 which used 6922 input tubes. The value for the emitter resistors on these units was 10 ohms. (different input circuit and transformers as well) If the value of the "emitter/cushion" is changed, the whole opperation of the output tube changes.


 The Green circles you have on your diagram are the grid stop resistors. These are located between the coupling capacitor and grid of the output tube. These resistors are to stabalize the circuit to control oscilation. Using a higher value will not hurt anything but they should be no higher than 2.2K for performance.
 

I also think that Bill knows these amplifiers, and his comments are safe.

 Thank you for that Dave. Please don't take offense to my comments but I am very familiar with these products and have custom built over 700 of them over the past 9 years.

 

[David Ellis]

Sorry Bill, I had to check my work.  I think we are overlapping at the keyboard while posting.  Yep, the green ones were the grid-stop units.

These resistors are to stabalize the circuit to control oscilation. Using a higher value will not hurt anything but they should be no higher than 2.2K for performance.

Ahhhh, okay.  This makes good sense.  The factory installed 10k ohms when only 2.2k ohms is necessary.

Dave

[Bill Baker]

Yes Dave, we did end up with some overlapping.

Ahhhh, okay.  This makes good sense.  The factory installed 10k ohms when only 2.2k ohms is necessary

.

 I have never seen this happen but it is obviously very possible. Someone may have reached into the 10K bin of resistors instead of the 1k bin when assembling the amp. The schematic calls for 1K units. I have installed 8k-10k pieces just to see what the circuit does. Not realy pretty.

 By the way Dave. From what I understand, this amp once belonged to you. It was sent in for further upgrades including turning it into a straight power amp and going with the Silver face.