[Bill Baker]

Perhaps I thought that Bill would address this, but... I certainly am able.

 Sorry guys. This one got past me. I try to keep up with most threads here regarding Jolida pieces but since I don't receive email notifications, I loose a few.

 Anyway, I don't have a schematic for the 1000A but can tell you that the circuitry is identical to the 302 with the exception of the additional output tubes.

 With the newer LED bias, things are a bit different in the bias stage.

[Noam S]

It should be noted for others to benefit as well is the combination of tubes i used for the Jolida sj502a,  the power tubes can be maximized by using a variation of the 6550 tubes,   namely the center being the v4 and v8, and the ends if you will being the v3 and v7 .   I use a for the v4 and v8 the 6550 eh  electroharmonix, and for the v3 and v7 use the svetlana 6550c.  The result is that the amp delivers lets say the remaining possible best output by using this combination.  I found this by accident and was pleasantly surprised. 

With this combination you seem to get the best of both worlds say.

Norm

I am about ready to try some new 6550's in my Jolida.  I had liked the (well used)  6550's that came with the Joli.  I replaced them with some EH KT88's that aren't as detailed and bodied in the highs -though otherwise very nice. How would you describe the sound you got from the different tubes - and what the combination is doing for you ?

thanks, Noam

[EProvenzano]

Hi guys.
What are your preferences between 6550 and KT88?
Currently I'm running my JD801A with Svetlana KT88 output tubes.  I've never tried 6550's.  What should I expect if I were to try a set?

Thanks.

[Noam S]

I found that the old oem 6550's (I don't even know what brand) that came with the amp when I got it - had more detail and body in the upper mids and highs.  Ride cymbals for instance, resonated in a very lifelike manor that was not as good with the EH KT88's. I didn't notice much difference in other aspects on my rig.
I had the Vandersteen 2ci's when the 6550's where in.  For the moment I have a modded pair of Spica TC50's in.   I am getting some very holographic imaging with this set up (with the KT88's) but do want to try some 6550's again with these speakers - to see what happens.  I may also experiment with some of Norm's mix n match suggestons.  Some day soon I will just listen to music again - I did for a while there anyway. 

-Noam

[David Ellis]

Succinctly,  I found I got more rich and detailed sound , as I mentioned by separating the power tubes.  The svetlana's  6550 on the ends and then the eh 6550 , both, in the middle.  Incredible lush sound.   I have not tried the kt 88's. However, I suspect if one were to alternate them like the 6550's , your output would be for sure richer on octave or two.

Given the push/pull nature of the amplifier, the positive and negative swings of the amplifier have a different character due to the different tubes being used.   It could also be true that the phase connection has shifted slightly when using different tubes for the positive and negative swings.  So, while you may appreciate the sound, it could be rooted in distortion.

Dave

[David Ellis]

There are still a few folks performing the mods on their 302B/502 amplifiers per my instructions.  I wish to offer a some commentary about things that I have learned and some specific feedback about the impact of the diodes.

First, Bill Baker really knows these amplifiers and mentioned a while ago that there are subtle circuit board differences, and installing power supply bypass capacitors isn't readily possible in some amps.  This is because there aren't any holes in the vertical power supply circuit board for these bypass capacitors.

Second, a few folks (not many) have used my general recipe to modify other Jolida amplifiers.  One gentlemen recently worked through his 502.  After installing the coupling capacitors he offered the following comments regarding the impact of upgrading the power supply diodes:

Dave, just wanted to let you know the stealth diodes make a huge difference. I don't measure my gear so it could be the placebo effect. I don't care what it is, the sound is much more engaging and less fatiguing even on the dreaded CD's. Thank you for the help you brought my amp up to a very high end sound at a low price. I can't wait to do the phono stage. Parts are on the way.
Just so you and your readers know, the latest version of the 502brc has seven diodes. Thats right I found two more sneaky little ones hiding when I took the power supply psb out. It goes like this(I think), two 5408's coming in from transformer, one 1n4007 going to the bias, and four 1n4007's leading to and from a plug with two wires leading to the amp section. I was two diodes short so I guessed at which ones were the least important and changed the rest. I think I guessed right because the sound is great. I have to order the other two today.

I have also accomplished diode swapping as an isolated modification to one of my pieces of source gear (I don't remember which piece).  I don't think I found a HUGE impact, but certainly an impact that was obvious.  Yes, replacing diodes does matter.  There are differences in rise time and recovery character.  Oh, and there is also a problematic issue about transient ringing that is on the fringe of my knowledge.  There is a difference between a .02c diode found in most source gear an a good Harris/Fairchild Gen 2/3 unit.  Jeff at www.soniccraft.com has the latest iteration (Gen 3) flavor of these diodes.  They are in a TO 220 format and are therefore slightly tedious to install, but easily worth the $15-$20 cost for a set of diodes to upgrade an amp/preamp/CD player.  A set of these diodes has easily more positive impact than a $800 set of speaker wires - IMO.

I know there are certainly some folks who convey that diodes shouldn't matter.  And I suppose that with enough power supply filtering and a clean waveform from the power company (yeah right  ) that a better diode might not have the same impact.  However, in varying degrees, better rectification via diode performance will have a positive impact in source gear. 

While I am primarily a speaker guy, I cannot ignore the profound impact source gear has on the signal.  Upgraded components in source gear are critical for anyone striving for better sound in their living room.

Dave

[prasen_b]

Hi,
   Firstly this post may not be very relevant to the thread. I have a Jolida 1501 RC and had recently replaced the stock 12AX7 tubes with mullard. There was a significant improvement. This together with what I have read makes me believe that analogous mods such as done by you will help. The problem is I am from India and its not feasible for me to get it modded by a reliable third party (mostly in US) so I intend to do it myself. For that I need the schematic for 1501RC (for which I had sent a mail to Jolida but got no reply) or some advise/suggestion on mods on this particular model. I would be grateful if someone can help me on this.

[David Ellis]

Prasen,

First, it has been my experience that swapping/upgrading coupling capacitors has far more impact than swapping tubes.  Other mechanical mods have less impact, but they remain very significant. 

Second, I have absolutely no idea what is lurking under the hood of your amplifier.  I have never puttered with a Jolida Hybrid.  Further, you might have problems that are deeper than what "should" be present.  Bill Baker has been the Jolida mod expert for many years, and I fully trust his commentary regarding Jolida amplifiers.  Following Bill's remarks on this webpage  http://www.responseaudio.com/AboutResponse.htm my believe is that your amplifier may not follow the schematic valid for folks in the USA and perhaps there isn't a trustworthy schematic simply because the components in your amp were chosen somewhat randomly - with VERY poor attention to quality control.  This was certainly the case for many Golden Tube amplifiers. 

So, I am really not sure that your amplifier is a candidate for mods in the same fashion that Bill or I approached the mods for the Jolida 302.     I am sorry, but I don't have a solution or direction for you.

Dave

[prasen_b]

Thanks for the reply Dave.

Following Bill's remarks on this webpage  http://www.responseaudio.com/AboutResponse.htm my believe is that your amplifier may not follow the schematic valid for folks in the USA and perhaps there isn't a trustworthy schematic simply because the components in your amp were chosen somewhat randomly - with VERY poor attention to quality control.  This was certainly the case for many Golden Tube amplifiers.

From this I suppose u r talking abt the commentory made on the chinese made Jolida products. I am not sure where it was made but the product was bought from an authorized Jolida dealer (Cadence - Pune Maharashtra). I will ask the dealer about it or check the unit itself. Also I have compared this unit with Cyrus 6VS2 as well as NAD pre/power combo both of which are costlier and it has performed better overall. Irrespective of this scenarios if I could get a schematic I could get some idea about which are the coupling capacitors (my target was just replacing/adding the coupling/bypass capacitors ) in my unit atleast. As I have mentioned I had sent a request for a schematic to jolida with no response. And ur comment that the swapping/upgrading coupling capacitors bringing a significant improvement makes whatever risk involved much more worthwile. So my main aim is to get the schematic and then work out the implementation feasibility.
 

[David Ellis]

I will ask the dealer about it or check the unit itself.

Hmm, I suggest asking the dealer to obtain a schematic. They will likely have better success.

Dave

[prasen_b]

I asked the distributer about the schematic he said he cannot share it. But he is ready to talk to jolida and see what mods could be possibly done and may also do it for me. Keeping my fingers crossed.
 I also opened up the amp and looked through, most of the electorlytic capacitors in the power supply as well as the output stage were rubycon USR series. Did the 302 amp had the same manufacturer's caps? The firm seems to have a good reputation.

[Bill Baker]

Hello prasen,
 We did not do much with the Jolida hybrid amplifiers other than completely redesign the circuitry in conjunction with another designer. I believe [one] of the reasons Jolida would not want to provide a schedule is to keep it from hitting the internet such as some of their other products did.

 Another situation is that amplifiers designed for North America are different from those for the rest of the world so I cannoteven say what potential yours may have.

 In general, some of the more significant upgrades would be as follows: (in no particular order) 1) Change out the stock silicon diodes in the power supply for a good quality 'Ultra Fast - Soft Recovery' type. 2) Change main coupling capacitors on the analog board. I won't even recommend a capacitor as it is far to subjective and personal. 3) Critical resistors on the analog board. 4) Add bypass capacitors to the main filter capacitors in the power supply. 4) Internal signal wire from RCA inputs to controls and then to circuit boards.

 Keep in mind that these are just general guidelines to upgrading this unit. Your choice of components will determine the final outcome but don't think that just because these areas use upgraded parts that it will be a guaranteed improvement. Sometimes a lot of trial and error is required to get the desired results.

[David Ellis]

I received a query regarding further mods for this unit.  My response follows:

There are three more 302b possibilities for improvement that I am aware of.

1.  Bypass the 4 circuit board coupling capacitors (.22uf) with a .022 Sonicap Platinum capacitor.  These are the capacitors circled in blue.  http://www.soniccraft.com/sonicap_platinum.htm .  

2.  Bypass the 2 circuit board coupling capacitors (.47uf) with a .047 Sonicap Platinum capacitor.  These are the capacitors circled in red.  http://www.soniccraft.com/sonicap_platinum.htm .

3.  You may already have very good tubes, and if they are surviving - GREAT !  The 302b was difficult on tube longevity.  However, you might be able to obtain slightly better tubes from Andy http://vintagetubeservices.com/contact.htm .  This guy is wonderful and profoundly knowledgeable.  I highly encourage you to purchase his used & tested tubes.  They will be fairly inexpensive, and perform perfectly.  Andy will want to know about your amplifier and the tubes you currently use.   You will need to contact any via telephone.

Please report your results herein.

Dave

[Wire Nut]

Dave, if I were to do just one set- the .47 or the .22 to begin with; which would make the most difference?
Thanks!

[Bill Baker]

Hi Wire Nut,
 The .22uF are the actual coupling capacitors. the .47 are signal ground. You will definitely want to start with the .22uF.

[David Ellis]

The .22uF are the actual coupling capacitors. the .47 are signal ground. You will definitely want to start with the .22uF.

You da' man  . Thanks Bill !!

[Wire Nut]

I have ordered the upgraded caps in the .22 value. I will let everyone know how they sound.
Thanks for the great advice! 

[David Ellis]

I....

...Actually recommended purchasing and using a .022uf bypass around the .22uf primary capacitor, BUT if you can afford the $$, using a .22uf Sonicap Platinum would probably be better.  I haven't performed this experiment and cannot comment.

Dave

[Wire Nut]

Dave,
I was just going to replace the white SoniCaps with the Platinum. Will that work? I had purchased some Mundorf but read that the SoniCap do not mix well- so your suggestion for the Platinum sounded like a great idea:
http://www.humblehomemadehifi.com/Cap.html
Thanks

[David Ellis]

I was just going to replace the white SoniCaps with the Platinum. Will that work?

Definitely!  It will probably work better.  I didn't recommend this initially because most gents prefer an easy fix and prefer a less expensive solution. 

Also, while I have never a/b tested the difference between a single Sonicap Platinum and  bypassed configuration (i.e. primary Sonicap Gen I and bypass Sonicap Platinum), when Jeff modified my Golden Tube SE40SE, he used a single Sonicap Platinum in at least 1 location for a coupling capacitor.  So, my hunch is that using a single Sonicap Platinum should work better. 

I can also convey that in 1 coupling location my amplifier I removed the @4uf Sonicap Gen 1, and replaced it with Mundorf Silver/Oil.  In another Location in my CD player, I replaced the Sonicap Gen 1 with a Mundorf Gold capacitors.  Both of these capacitors were bypassed with a Sonicap Platinum before and after the primary capacitor swap.  In retrospect, I don't recommend this.  The Mundorf Silver/Oil and Mundorf gold capacitors were quite expensive (@$300), and I am not sure if they sounded better.  There were some tonal changes, but I couldn't convey clear superiority.