Kenwood Basic C1 Preamplifier Restoration/Upgrade

Hello,

A quick update to where I'm at with this C1 upgrade.

I've got all the components, I've taken the C1 apart and was about to get started when I discovered my soldering iron is not regulating properly, It's either stone cold or sizzling hot. Being a cheapo type and a good few years old, I shouldn't be suprised. I've ordered a soldering station, while not professional or expensive it is definitely an improvement over the previous one and it can be calibrated.

(rjsalvi) I'd be happy to just be able to solder anything at the moment, blobs and cold joints included.

I'm finding those wire coiled pins/binding posts troublesome, how should I deal with them, desolder the post or uncoil the wires? The wires do not want to come off with long nose pliers.

AGhewwn.jpg



Cheers,
Rob.
 
...I'm finding those wire coiled pins/binding posts troublesome, how should I deal with them, desolder the post or uncoil the wires? The wires do not want to come off with long nose pliers.

AGhewwn.jpg



Cheers,
Rob.
There is no need to undo the wire wraps or to desolder the posts to access to the solder side. If you undo the wire wraps, the connections will subsequently have to be soldered.
 
I haven't desoldered any of the pin/coiled wire arrangement and have been ok soldering 'as is', it just looked a bit awkward turning the boards over with wires attached.

The new soldering station arrived and it's better that the old iron, I've completed the power supply section except for

D3 is a W06B type; general purpose diode, 100V, 0.75A
D8 is a 12.5V zener diode, 500mA

Which might be suspect, I cannot find these diodes at Mouser (or anywhere).

I'll have to reuse them, but test them first out of circuit, I'm a bit concerned about heat damage (I have my iron at 350c thereabouts), how often can these components be soldered/resoldered?

I've got tomorrow off work and should get most of it done.

Cheers,
Rob
 
...D3 is a W06B type; general purpose diode, 100V, 0.75A
D8 is a 12.5V zener diode, 500mA
Which might be suspect, I cannot find these diodes at Mouser (or anywhere)...

D3 can be replaced with 1N4002 or UF4002; D8 can be replaced with a 13V zener, e.g., BZX55B13.
 
Hello all, I've been a bit busy with things away from the this C1 project, but I've done all the soldering except for D3,D8 and Q1 which I took a out and tested and I wasn't happy with Q1 and also D8 was borderline.

I didn't bother putting them back in, so now it's still in bits waiting for these 3 new components to go back in.

I didn't want to order these components off Ebay, I want to be sure everything that goes in is genuine high quality and so I'm about to include these 3 components into a Mouser order that will be a big upgrade for my Quad 405-2.

Once this new order comes back I'll complete the C1 upgrade 1st.

Rob
 
Hello Leestereo,

I've 99% completed this upgrade except for a few components that look different to your C1.

In the Phono stage/EQ amp, the two little brown ceramic capacitors (100pf) C1 and C2 are not present in my preamp, the holes are there along with their names and on the copper side they've been filled with solder, it looks stock/factory (they've never been in). Do I go ahead and put the new COG capicitors in?

Again in the Phono stage/EQ amp (in your "finished" photo), there are two little blue COG caps close to the red C11/C12 (3.3uf) caps, these were not listed or mentioned in your right up, should I replace these? If so, what specs?

I've made some errors, in the Power supply section C45/C46/C47 (470uf) should all be 25V but I've put in 35V instead? Also C48/C49 (47uf), should be 16v but I've put in 25V, C50 (33uf) should be 16v but I've put in 35v and C51 (100uf) should be 16v but I've put in 25v. All these capacitor are the Panasonic FR Low ESR series, will these extra volts cause a problem (particularly C50)? I don't know how I've done it, It's quite a lack of concentration for this section, the rest I've got right.

There's an electrolytic polar capcitor 1uf connecting by the phono rca's to the chassis, can I swap for a Wima 1uf (PET) bi-polar?

I'll do a full write up of this after the weekend when finished.

Thanks for you patience,
Rob.
 
@C1bob: According to the schematic, C1/C2 in the phono stage are not present in some versions of the preamp, no need to install the C0Gs here (you are probably also missing R31/R32, which means that C1/C2 would not be connected to the circuit anyways). The capacitors near C11/C12 are C3/C4 and are 1200pF; should be replaced with C0G types. The capacitors with increased voltage ratings that you have used are not problematic at all (see my earlier response in post # 140), similarly, replacing the 1µF on the phono stage RCA with a stacked film type is fine.
 
I've ordered those Philips polypropylene caps, I did some research they are 10mm x 4mm approx, they will have to stand off away from the circuit board, the board lead spacing is about 3.5mm and so the leads will form a V shape. It will look a bit strange but should be do-able.

Thanks for finding them.
 
It's done! At last!

I've really struggled to find the time to do this little project, the longest time I've put in is two hours in any session, but it's done now.

The original:

fwkyNVP.jpg


Disassembly & Soldering:

kClZ5op.jpg


It was problematic not being able to disconnect those wires from their binding posts and having to turn both boards over and reposition the transformer simultaneously to move from component to copper side. It's easy to see what component you want to desolder when you're looking at component side, but at the start I wasn't too confident and had to check and re-check I was taking the right component out. I became tired of this juggling act and snipped the wires to the transformer in a temper, this speeded things up.

Once I was moving quickly between both sides I began to develop an 'eye' for where the component was on the copper side and my technique with the soldering iron was also improving. There was a large puddle of glue on the copper side and no amount of improvement with the soldering iron helped me with this, it was an absolute nightmare to scrape/peel off, I ended up with a yellow/grey gooey mess consisting of old solder and glue that took a long time to carefully remove.

R66 was out of spec and had to be replaced and also R61 was close to being out of spec and I also replaced it. I came close to wanting to test/replace all stand off resistors but It would have been too time consuming.


The Home Straight:
The Wima was the last component to go in and after being careful all the way, with a momentary loss of concentration, I managed to melt the rca housing.

xcjXxGK.jpg


I also lost the screws for securing the rca's to the backplate, but cannibalised one the kids toys for screws, It's Christmas he'll gets some new ones in weeks time.
60O8BXA.jpg



All Done:

akFWECs.jpg


eT95ZgR.jpg



What does it sound like?

Compared to the C1 before upgrade, based on memory there's an obvious difference, the old C1 would I think sound muffled next to this new one, treble, mids and bass are clear, present and well separated.

The first track I listened to was James Brown, Solid Gold - 'It's a man's world' and it jumped out the speakers at me (as it should!), excellent separation between singer and backing band/instruments, everything crystal clear, it was an enjoyable listen.

This listen was without any run in/burn in period, I have about 5 hours usage now and it is starting to settle down, the treble and bass were a little too pronounced at first.

Listening to 'Sara' by Bob Dylan from the Live 1975: The Rolling Thunder Revue LP I've become aware he has a backing singer starts accompanying him half way through the track, I've listened to this track countless times and never heard it before?

'Oh Sister' from the same LP has a crystal clear separation between him and his backing singers, I'm able to pick out small changes in tone in their voices.

There's now plenty of nuances and details coming through I wasn't hearing before.

Moving on to Bruce Springsteen 'Trapped' live The Essential LP, there's crescendos in this track that my previous set up tended lose focus a little bit with, I can hear the separation clearly through with the C1.

The C1 has now replaced my Caiman SEG pre/dac, it wasn't really a fair fight, the C1 won by KO early on.

I actually bought the C1 because I read this thread fist and I'm pleased I did this upgrade.

I'd like to thank yourself and rjsalvi for all the help, I'd have struggled otherwise.
 
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Hi, I recently picked up a C1/M1 pair and am planning a restore/recap of both. In reading through the list of mods, I am curious about the capacitor selection for the phono stage. For the phono stage hi-pass coupling caps (C11, C12) would it make sense to try a boutique polypropylene capacitor like this Soniccap or the cheaper Dayton? This seems to be a popular option in other phono stages that I've read about and there is plenty of extra space on the board to mount such a large cap. This is a great thread, one of the best I've come across on AK so far.
 
Does anyone know if they can use tantalum capacitors in the Kenwood C1 restoration?
If so, where would it be best? Thank you
 
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