Download Jolida 302b Upgrade

Jolida 302b Upgrade
by
Dave Ellis
The “Before” photo listed below is a picture of Randy Romenesko’s Jolida 502b. The layout the same as the Jolida 302b, but a few
component values are be different. The “After” pictures illustrate the simple modifications I performed in the more critical areas of
this amplifier. The purpose of these illustrations is to indicate how simple the modifications to the Jolida amplifiers are to execute.
My modifications to the Jolida amplifiers completely preserve the typology and values of the OEM components. They simply
upgrade the quality of the OEM components. I performed the 302b amplifier modifications on my personal amplifier and for Kevin
Keefe. I was extremely pleased with the results and Kevin Shared this sentiment. Several folks have followed in this regard.
If you have any trepidation approaching these modifications, please post your fears and need for help in the Audio Circle string in my
forum titled Jolida Mods. This document and instructions are “living”. Changes can and will be made over time to the original
document (i.e. this one) for clarification purposes as needed.
*** Warning***
Before getting your hands inside this amplifier, ensure ALL the electrolytic capacitors are discharged by
momentarily jumping their terminals. Getting zapped with this voltage will hurt considerably, and may
be deadly to anyone using a pacemaker.
***Warning***
The general steps for performing these modifications is very simple. Unsolder the old parts, and insert the new parts. I generally
work very slowly through this process and spend about 3 hours to complete these modifications. For ease of understanding, I colorcoded the parts I recommend replacing. These same parts for the Jolida 502 are certainly present in the 302, but the values for
some/all of these may be different. I only listed the values for the Jolida 302b.
** Note: The only tricky part about these modifications is getting the diodes oriented correctly. Diodes are one-way electricity valves.
They will have an infinite resistance in 1 direction and about .5 ohms in the other direction. You must ensure the new diodes are
installed using the same orientation as the old diodes. The direction to of flow for the new diodes needs to be the same. The new
diodes are a stand-up diode and they will physically look different, but work the same. Simply check the orientation of flow with a
multimeter and install the new diodes accordingly.
** Note: You will have to clip a few plastic wire wraps when performing these modifications. This is perfectly fine and will cause no
harm.
Before
After
Key:
Red – Replace 2 OEM .47uf coupling capacitors with 2 .47uf Gen I Sonicaps.
Add 3 .47uf bypass capacitors to empty holes emitted by Jolida Accounting Department
**note – Pierre in France mentioned that his circuit board did not have holes for these capacitors. I recommend
not using them if this situation is present.
Blue – Replace 4 OEM .22uf coupling capacitors with 4 .22uf Gen I Sonicaps
Green – Replace 4 OEM 10k ohm resistors with 4 Mills MRA5 10k ohm resistors.
**note – Bill Baker of Response Audio commented that he commonly uses 1k ohm ½ watt resistors in this location, but was not 100%
certain of this application in all 302b amplifiers. Bill and I believe it is likely that many amplifiers have a 1k ohm resistor in this
location from the factory. If this is true, we suggest replacing it with the same value. Specifically, use the ½ watt PRP 1k ohm
resistor from Sonicraft. These are the grid stop resistors and their purpose controlling oscillation. The 10k ohm value is very safe, and
follows the schematic I received from Jolida for my 302b amplifier. It is likely there are variations across amplifier production runs.
** note - Bill further commented, “I think having DIY'ers check the value prior to upgrading these resistors is a good idea. The
problem with high value grid resistor is a reduction in bandwidth but sometime it is better to sacrifice a bit of bandwidth to maintain
stability within the circuit. I will continue to bench test units before and after rebuilds and apply the best value that provides the best
balance. To date, I have never had to use anything higher than 5k ohms. The goal is to apply the least amount of resistance that
stabilizes the circuit.”
Yellow – Replace 4 OEM 1ohm emitter cushion resistors with 4 Mills MRA5 1ohm resistors
White – Replace 4 OEM diodes with 4 Fairchild (Harris) Gen 3 Superfast Diodes.
The parts/price list for upgrading the JOLIDA 302B as follows. I recommend ordering all of these parts from
Jeff at www.soniccraft.com .
b Upgrade List
Description
.47uf Sonicap Gen I
.22uf Sonicap Gen I
PRP Film 1k ohm
Mills MRA5 1 ohm
Fairchild Diodes
Spool Chemwick
Strand of Cardas Solder
Approxomate shipping
Cost/ea
Cost total
$
7.60 $ 38.00
$
6.60
$26.40
$
3.85 $ 15.40
$
2.15 $
8.60
$
1.95 $
7.80
$
3.00
$3
$
7.50
$8
$8
Total Cost
$ 114.70
As a hifi enthusiast, I am confident this $114.70 will be the very best value investment you can make in hifi.
The hierarchy of value gleaned is most prevalent with the coupling capacitors and least prevalent with the
resistors, but it all matters.
Additionally, I feel compelled to provide a very positive recommendation for Andy a Vintage Tube Services
(http://vintagetubeservices.com/). The inventory on Andy’s page is not very current, but his products,
knowledge, methods, and customer service are sublime. Andy has a plethora of old tubes that are extremely
well tested. Andy also intimately understands the construction of these tubes, the materials used in these tubes,
and who produced them under various labels. His old stock (used & thoroughly tested) tubes are an extremely
good value, and his New Old Stock (NOS) tubes (also thoroughly tested) cost considerably less than I have
found at other online sources. When purchasing tubes from Andy I recommend conveying the intended
amplifier, AND also convey that the Jolida 302b does NOT have a slow turn-on circuit for the tubes, and that a
more rugged El34 tube is preferable.
Sincerely,
Dave