A semi idiot updates his dream amp; KA-8100

neevo

Super Member
I’ve upgraded myself from an idiot after my KA-7100 and PL-518 threads, I’m now half an idiot and therefore 50% likely to balls this up.

I have a mate that was round my house a few weeks back and he was so floored by my modest stereo that he’s become obsessed with having music in his own home and has tasked me with helping source it all. I’m building him a PL-514X at the moment but that’s not getting a thread because it’s very similar to my PL-518X one.

We have been looking at amps though and in Australia anything over 40wpc is mega bucks ($600 at least). All this looking at amps has whet my appetite and I’ve been wondering if my KEF LS50’s could do with more than the 60wpc that they get from my KA-7100. Then my friend suggested maybe he buy my 7100 and I find something else?

With that I managed to find a showroom condition KA-8100 in Belgium, it was probably the finest example you’d ever see, but with shipping it was right up there in price. I declined, but then thinking about it over the weekend I didn’t want to let it go.

With a last ditch effort I posted a note on an Australian HIFI page on FB and sought to see if I could find one locally.

I was floored when a chap reached out and mentioned he had one in storage! Not one to let the deal slip through my fingers I picked it up the same day.

It needs work but he’s the original owner, it’s not had any work done, has been stored and has a suspect mark on the front (either a scratch or a stubborn greasy mark).

This is my dream amp, I actually think the 7100 is ever so slightly prettier but the 8100 looks like it means business and I couldn’t upgrade any further as I dislike the 9100’s looks and none of the Supreme series will fit in my cabinet.

So I’m 90% sure this is here to stay. So with that I want to give it the best treatment. I’m thinking a full recap, replacing any risk items, new relays and bourns trimmers etc like I did with my 7100. I want it ready for another 40 years.

I’m also thinking of replacing the speaker terminals with decent connectors that will take banana plugs. Is that a big no no?

I’m also keen to hear thoughts on some quality caps for the power supply (last time I used PK’s I think) and some really good ones for the audio path.

Obligatory pics:

1E3D60AA-8C37-4E51-9841-49666F9C91C4.jpeg D312C15A-BEB8-4110-BD19-B01875A7608C.jpeg D380C8CC-5F30-4745-A58E-FEF95E7D0A89.jpeg

It’s filthy and needs a good clean. But that’s easy I think. It was also a price I couldn’t pass up, mainly because it needed a new face plate because of a scratch under the volume knob, but on further inspection I think it’s glue residue as it’s sticky. If that’s the case I think I’ve dodged a bullet there because getting a mint condition face plate would have been a challenge:

45071ADB-22E0-428D-9E2D-382790165508.jpeg

I’ll be cleaning all the knobs and face plate in the next day or so. Also will try and clean the inside before getting it biased etc properly before I get stuck in to the renovation proper. Mouser order in ASAP hopefully. Any tips to get the front in perfect condition other than cleaning with washing up liquid. How do some of them look so shiny and glossy?
 
Last edited:
I'm very excited, plus I love a good project (and my friends TT is almost finished) so another recap will be fun. Lots of questions but first 2 are:

1. How do people get amp front and knobs looking so shiny and clean? This amp has a bit of age crust on it and I want to get it tip top condition. Is it safe to use Acetone on the knobs? What about the face plate? Or is it a scrub with a sponge in the kitchen sink? How do you cut through the grease and grime without any risk of damage? Lastly how do you get that amazing shine after? Read a post from Echowars (I think) about car polish, is that the secret for the face plate? What about the knobs (I have an ultra sonic cleaner, so they'll get a run through that at least)?
2. Starting to create my recap list. I will replace all the electrolytic caps with PW's in the power supply and some other option in the audio path (might pay a bit for those as I want quality). Any other parts that should be replaced whilst I am in there? I had a load of help with my 7100 on key items to replace.
 
Not knowing what cleaning products are available to you....

Knobs amd toggle covers - I fill a container with water and add a squirt of liquid dish soap and let them soak for a couple days - they always come out very clean

Faceplate - On an 8100 (or 9100) I remove all of the toggle switch bezels so I have a nice flat surface to clean. If you have strong thumbs you can push them out from the back side - the glue holding them in doesn't dry hard and no need to remove it first. With those removed I spray it with a mix of Simple Green mixed 50/50 with water and let it sit for about 30 seconds than wipe it off.This gets most of the grunge off. Then I wax it with Meguairs Liquid Cleaner wax for cars, buffing with the grain. I peel the glue off the back side and clean all of the little bits out of the bezel slots and the bezels, then just snap them in place. I don't glue them back in - they arent going anywhere.

I recently did an 8150 (same amp) and gleaned most of my info from the various 8100 info I found here. My cap choices were dictated more by what I had on hand, but I did make sure to use good quality caps and Silmic IIs for the few signal path caps and Wima film caps where they would fit. .http://www.audiokarma.org/forums/index.php?threads/ka-8150-overhaul.790406/
 
Thanks @gort69. I have a load of 8100 threads open on my phone but had missed that one... go figure (need to search 8150 too)!

We have Simple Green here in Australia, I'll go and grab a bottle tonight and get the faceplate cleaned up. Good tip re the knobs too, I have them all off now, so I'll get them soaking for a few days and finish off in the Ultrasonic cleaner.

I'll dig in to that thread too tonight.
 
Last edited:
I'm going to have a go at creating my parts list myself too this time. Think I'll stick with UPW's for the power section and will try and use UKZ for the signal paths with options to use FG's and Elna Silmic II if I struggle with values.

Any guidance on other parts to change is appreciated but I'll run through all the rebuild threads and check the parts they've replaced as precautions.
 
UKZs are pretty big - I don't remember if they would fit or not. Cheap enough to have a backup plan before you find out they don't. As I recall the entire amp only has 4 signal path electrolytics.

There is a ground wire that connects the front control board to the chassis grounding bar that is very likely to break while working there. Be sure and make a note of where it connects in case it does.

There is some info out there - I think on a youtube video - that recommends drilling or melting a hole in the clear plastic enclosures on the loudness switches in order to get cleaner in there. Don't do it. You'll notice that the axle for the pot is "D" shaped where it enters a round hole - perfect spot to get cleaner in.
 
UKZs are pretty big - I don't remember if they would fit or not. Cheap enough to have a backup plan before you find out they don't. As I recall the entire amp only has 4 signal path electrolytics.

There is a ground wire that connects the front control board to the chassis grounding bar that is very likely to break while working there. Be sure and make a note of where it connects in case it does.

There is some info out there - I think on a youtube video - that recommends drilling or melting a hole in the clear plastic enclosures on the loudness switches in order to get cleaner in there. Don't do it. You'll notice that the axle for the pot is "D" shaped where it enters a round hole - perfect spot to get cleaner in.

Hmmmm, yeah OK, I might rethink that then. There are only 4 signal path caps on the power supply board? Do you know which ones?

Tip noted re the earth wire. I broke it on my 7100 so I am pretty aware of those things now.

I melted my pots on my 7100, good to know I can tackle that in a different way.

I'll do some Mouser work tonight and check some of the cap dimensions against what's in there now.

What is the reco for replacing parts?

1. Replace all Electrolytic caps?
2. Replace all Zener diodes?
3. All Elec Caps under 1uF can be replaced with films?
4. Option to replace all the other general parts (trimmers, relay)?
 
Last edited:
Got stuck in to cleaning mode this evening. First up I pulled all the hardware from the front panel:

3DED3E20-7CC7-4D62-BC37-3A3FAEBEAF27.jpeg

As recommended I popped all the hardware in to a soapy bath where it will sit for a day or two:

A707CF3B-EA4B-4963-A0F5-DEC328CF43CA.jpeg

I put the front panel in the sink and gave it a warm bath, then sprayed it with straight simple green, let it sit for a few seconds before scrubbing it off with a dish sponge. Good news is that the mark under the volume knob has gone but there are a couple if minor ones on the face, but nothing you’d overtly notice when it’s back in the cabinet. Didn’t think it was clean really until I looked at the first pic, now I realise it’s scrubbed up nicely :)

83B6EE13-EB2C-4843-9CFA-B1EBEB3C13EE.jpeg

Put a coat of wax on it too and have it on the bench ready for install:

52EEC784-9F8A-4FA7-AAE2-45F17099DE31.jpeg

Next up I cleaned the insides. Blasted it wil compressed air to get rid of the dust, then coated it liberally with IPA and brushed gentle with a soft paint brush whilst blasting with air from a distance too:

78B3C07F-4089-4838-B5D6-74EBFB76205D.jpeg

Bottom got IPA and a toothbrush:

C9CFB5F0-9574-4BBB-9D62-B0161A959173.jpeg

The amp really is in exceptional condition. The only issues I see are some peeling paint on 1 transformer (not sure if I should attempt to fix that):

A1E97077-5FA4-4881-B6E1-BD29A56A2463.jpeg

And I’m pleased to say that one of the speaker posts is stripped :), pleased because I now have an excuse to replace them all with proper binding posts that take banana plugs:

08DEB18C-52B6-42F5-9F42-5A409724D8AD.jpeg

Now I’m going to sit down at the laptop and sort my caps and parts list for Mouser. Help is welcomed :)
 
I’ve found some caps from my 7100 build. A lot of PW’s and 1 lot each of various KW’s, KL’s Elma Silmic II’s and a diode.

image.jpg

Back in to my spreadsheet.
 
OK, parts list is in stage 1. Anyone care to run their eyes over it? @gort69 I found a few of your posts and tried to ensure I captured your notes around transistors, diodes etc.

Section Part Category Part Number Original Specs QTY Details Mouser Part Number Part Specs Notes
Power Amp Capacitor Ce5, Ce6 10uf, 50v 2 PW 647-UPW1H100MDD1TA 10uf, 50v Nichicon
Power Amp Capacitor Ce11, Ce12 10uf, 50v 2 PW 647-UPW1H100MDD1TA 10uf, 50v Nichicon
Power Amp Capacitor Ce23, Ce24, Ce25, Ce26 47uf, 10v 4 PW 647-UPW1A470MDD 47uf, 10v Nichicon
Power Amp Capacitor Ce29, Ce30 220uf, 10v 2 PW 647-UPW1A221MED 220uf, 10v Nichicon
Power Amp Capacitor Ce31 100uf, 16v 1 PW 647-UPW1C101MED1TD 100uf, 16v Nichicon
Power Amp Capacitor Ce32 10uf, 63v 1 PW 647-UPW1J100MDD1TD 10uf, 63v Nichicon
Power Amp Capacitor Ce33, Ce35, Ce36, Ce34 10,000uf 56v 4 KMH 661-EKMH630N153MA63T 15,000uf, 63v UCC
Power Amp Diode De1, De2 EQA01-24R 2 ON 512-1N5252B 24v
Power Amp Diode De3, De4 EQA01-30R 2 ON 512-1N5256B 30v
Power Amp Diode De16, De17 W06B 2 ON 625-1N4007GPE-E3/91 1A, 1000v
Power Amp Diode De18 - De25 8 ON 511-STTH5L06RL 5A
Power Amp Transistor Qe31 2SC1735D or E 1 ON 512-KSC2690AYS
Power Amp Transistor Qe29 1 ON 512-KSC1845FTA
Power Amp Transistor Qe30 1 ON 512-KSC1845FTA
Power Amp Trimmer VRe1, VRe2 100 ohm 2 Bourns 652-3296Y-1-101LF 100 ohm 0.5W Multiturns
Power Amp Trimmer VRe3, VRe4 1k ohm 2 Bourns 652-3296W-1-102LF 1K ohm 0.5W Multiturns
Power Amp Relay RLe1 S51-4030-05 1 Omron
653-MY4-02DC24
MY4-02 DC24
Preamp Unit Capacitor Cd3, Cd4 100uf, 6.3v 2 FG 647-UFG1A101MEM 100uf, 10v Nichicon
Preamp Unit Capacitor Cd15, Cd16 100uf, 6.3v 2 FG 647-UFG1A101MEM 100uf, 10v Nichicon
Preamp Unit Capacitor Cd17, Cd18 10uf, 50v 2 FG 647-UFG1H100MDM 10uf, 50v Nichicon
Preamp Unit Capacitor Cd19, Cd20 220uf, 25v 2 FG 647-UFG1E221MPM 220uf, 25v Nichicon
Control Amp Unit Capacitor Ci5, Ci6 100uf, 10v 2 FG 647-UFG1A101MEM 100uf, 10v Nichicon
Control Amp Unit Capacitor Ci7, Ci8 330uf, 10v 2 FG 647-UFG1A331MPM 330uf, 10v Nichicon
Control Amp Unit Capacitor Ci9, Ci10, Ci11, Ci12 10uf, 25v 4 FG 647-UFG1H100MDM 10uf, 50v Nichicon
Control Amp Unit Capacitor Ci13, Ci14 1uf, 50v 1 WIMA Film 505-MKS4B041002CJF00 1uf, 50v WIMA
Control Amp Unit Capacitor Ci15, Ci16 10uf, 25v 2 FG 647-UFG1H100MDM 10uf, 50v Nichicon
Control Amp Unit Capacitor Ci17, Ci18 100uf, 10v 2 FG 647-UFG1A101MEM 100uf, 10v Nichicon
Control Amp Unit Capacitor Ci19, Ci20 1uf, 50v 2 WIMA Film 505-MKS4B041002CJF00 1uf, 50v WIMA
Control Amp Unit Capacitor Ci21, Ci22 10uf, 25v 2 FG 647-UFG1H100MDM 10uf, 50v Nichicon
Control Amp Unit Capacitor Ci23, Ci24 100uf, 10v 2 FG 647-UFG1A101MEM 100uf, 10v Nichicon
Control Amp Unit Capacitor Ci45, Ci46 1uf, 50v 2 WIMA Film 505-MKS4B041002CJF00 1uf, 50v WIMA
Control Amp Unit Capacitor Ci47, Ci48 10uf, 25v 2 FG 647-UFG1H100MDM 10uf, 50v Nichicon
Control Amp Unit Capacitor Ci51, Ci52, Ci53 100uf, 25v 3 FG 647-UFG1E101MPM 100uf, 25v Nichicon
Control Amp Unit Capacitor Ci54 220uf, 25v 1 FG 647-UFG1E221MPM 220uf, 25v Nichicon
Control Amp Unit Capacitor Ci55, Ci56 330uf, 35v 2 FG 647-UFG1V331MHM 330uf, 35v Nichicon

I tried to use all FG series in the amp, mostly exactly the right specs however a couple are a little larger on the voltage as that option wasn't available (parts different to the original specs are highlighted red). Power amp section I used PW (and UCC for the filter caps) but I know there are 4 caps in the audio path there so I'd like to know which ones they are and replace them with FG too. Read lots of threads about what other parts to replace and only found a few that mentioned additional parts, those are included with the recommendation from gort69 too.
 
Last edited:
The original orange jacketed caps are low leakage type. If you want to follow the designers' thinking a little more closely, use Nichicon UKL caps for those in the service manual that have a part number with the suffix "MEL" Credit to hopjohn for that bit of detective work.

The signal-caps I identified are two on the pre-amp board Cd17,18 (10uf/50V) and two on the control-amp board Ci9,10 (10uf/25V). These also have the MEL suffix - I use audio grade caps here not because I have any great wisdom (I don't - I always though a recap was a tire) but because people here way smarter than me often do. Hopefully someone else will weigh in on that.

The 1uf/50V Wimas you list "might" be too large to fit - these definitely fit https://www.mouser.com/ProductDetail/WIMA/MKS2B041001C00KSSD/?qs=sGAEpiMZZMv1cc3ydrPrFwgzP98AO9idwFKwdAiDxsI=
 
Thanks @gort69! Your threads and comments have been invaluable, so thanks for that.

MEL caps found and changed to UKL's are (seems like a lot):

Ce31
Cd17, Cd18 (left as FG)
Ci9 - Ci12 (excluding Ci9, Ci10 which I've left as FG)
Ci15, Ci16
Ci21, Ci22
Ci47, Ci48

All the 1uf, 50v are "MEL" suffix too but I assume the Films are fine for those. I've also changed the WIMA Films to the one you suggested.

Is there anything else that might need attention whilst I'm in there? I hadn't planned on touching the mica or paste, should I?

Also are there any tantalums or bipolar caps I need to be aware of (couldn't find any)?

I'm also only replacing caps in the preamp and tone control board. Should I look to replace anything in there (diodes) preventatively?

Also are my use of multi turn trimmers ok in this application? I used them in my 7100 and found them brilliant.
 
Last edited:
I would remove the outputs and use new insulators with fresh compound - they're cheap https://www.mouser.com/ProductDetail/Keystone-Electronics/4636/?qs=/ha2pyFaduhESlPYY97LsoNav5I3otDJK1g5OEZd3tk=

I replaced the regulators on the control board, Qi13,14 - one of which is a 2sc1419 - a known trouble-maker.

2sc1419 > https://www.mouser.com/productdetail/on-semiconductor/mje15032g?qs=sGAEpiMZZMshyDBzk1/Wi/PUgtclNldlIbxeXkBE6a0=
2sa755 > https://www.mouser.com/productdetail/on-semiconductor/mje15033g?qs=sGAEpiMZZMshyDBzk1/Wi/PUgtclNldlWYDF5lWmMkM=
Insulator https://www.mouser.com/productdetail/aavid-thermalloy/56-77-11g?qs=sGAEpiMZZMtEZf%2bBk5/8xw2M97FUtgS6
insulated washer https://www.mouser.com/ProductDetail/Keystone-Electronics/3049/?qs=sGAEpiMZZMsQtlBhqKq43Waz4wKA0Uwv

One of the regulators must be insulated from the heatsink since the metal tabs on both are also the collector.

Yeah - the Bourns multiturns are great. If the pcb has the holes in a triangular pattern this one will probably fit better for your 1k pot. https://www.mouser.com/productdetail/bourns/3296y-1-102lf?qs=sGAEpiMZZMvygUB3GLcD7gTIXvDhNlCgPtpN7VzbB%2bU= 3296Y is triangular, 3296W is in-line
 
Last edited:
Can you explain the Qi3, Qi14 parts a little more (should I also replace Qi4 as it appears to be the same as Qi3)? eg what parts replace the ones below, which ones should I replace and which ones will need an insulator and or insulated washer?

2SC1419 is actually Qi13 on the schematic.

Qi3, 4 - 2SA640(E) or (F)
Qi13 - 2SC1419(B) or (E)
Qi14 - 2SA755(B) or (C)

All trimmers are 3 hole (triangular) so I'll check to make sure the ones I'm ordering are triangular. One of them needs a leg extending but I'm fine with that.
 
Actually is that a typo above? Is it Qi13 and Qi14 and each have a insulator and washer?

Also good pickup on the 1k Bourns, I meant to use the Y version.

Does Mouser sell the thermal paste too? Found solder paste but not thermal.
 
Back
Top Bottom