Matchless/Bad cat build thread

[norburybrook]

I need to get to the bottom of this gain issue though. i remember someone mentioning getting the gain pots backwards. I'm going to investigate that comment.

Hi Marcus,

I was going to comment on that. On the Badcat schematic, the Level control is shown this way:


Hotcat Level.png


But on the Ceriatone layout, the pot is wired "normally, like this:


Straycat Level.png


Also, it is hard to tell (and I think I can see the connection...white wire), but is that 220k on the Master connected to the Treble control?


Master.png

Dave,

I don't see a difference here. The wiper takes the feed from the 0.01uF and pin 1 takes from the 470k and pin 3 goes to ground that tallies with the schematic.

yes my 220k is going form pin 1 on the master to the wiper of the treble pot.


M

[Colossal]

Dave,

I don't see a difference here. The wiper takes the feed from the 0.01uF and pin 1 takes from the 470k and pin 3 goes to ground that tallies with the schematic.

yes my 220k is going form pin 1 on the master to the wiper of the treble pot.


M

Ah yes, my apologies. Dyslexia strikes again. I edited my post so as not to confuse the record.

Good to know about the 220k.

[norburybrook]

Ok, so I've gone over this again, checked every resistor value, every joint it all checks out.

So I took a cable with a jack on one end and nothing on the other and piped some music through it.

So If I touch the signal end of the cable to V1 inputs so that's pins 2 and 8, the clean and the gain then the amps works as I expect it to , the clean volume is fine and then when I thought the cable to the gain input there is a nice boost in volume.

Now if I plug my guitar into the amp the clean sounds fine but the gain is weak.?

So It must be something to do with the jacks? yes?

edit: looking at the schematic the tip signal goes to the 5.1m resistor first THEN on to the 100nF which goes top the 68k and 1M (voltage divider I presume). The C Tone layout doesn't seem to do that, am i correct here in my reading of this. Cliff jacks always confuse me so I could be wrong.

So IMHO the 1M resistor on the jack should be the 5.1m and then the 100nF should be on the socket before the 68k-1M voltage divider

M

[martin manning]

The 5M1 has to be on the grid pin, that stage is grid leak biased (schematic is wrong). The gain input jack should be wired same as the clean, except the lead going off to the grid has the cap in line at the jack end of the shielded cable. Note the lugs closest to the panel on both jacks are all tied together and grounded.

Are your screens connected before or after the choke? That looks wrong on the schematic too.

[norburybrook]

The 5M1 has to be on the grid pin, that stage is grid leak biased (schematic is wrong). The gain input jack should be wired same as the clean, except the lead going off to the grid has the cap in line at the jack end of the shielded cable. Note the lugs closest to the panel on both jacks are all tied together and grounded.

yes, I realise I was touching the signal after the cap so it was that that was giving me the impression of the gain.

Ah well back to square 1.


M

[martin manning]

Where are your screens connected on the power rail? Sorry I edited that in...

[norburybrook]

Screens are connected from S1 on the CTone layout, so from where the choke connects. Is that a better place than the Schematic?


It seems re doing the whole 'Gain' input stage back and forward has cured the gain problem. I shortened the screened cable at one end as well as replacing the resistors and a combination of this has led to it working as I expect....few!!


I'm done for the day now but I think we're there. The gain channel is still a bit noisy but the whole thing feels better now, it's still no where near what I'd call a high gain amp but perhaps that was a misunderstanding form my part. I'm curious to up the biasing on the power tubes to around 90% as Martin has suggested so I will follow up on that. I might just order some 300R and some 270 10w resistors and get on with it

IMG_20200709_175505.jpg

I shall report back tomorrow.

thanks again everyone.


M

[martin manning]

Screens are connected from S1 on the CTone layout, so from where the choke connects. Is that a better place than the Schematic?

Yes I think so.

If you do a test by putting some 1k across your 360Ω Rk's you can determine what value to order.

[norburybrook]

Screens are connected from S1 on the CTone layout, so from where the choke connects. Is that a better place than the Schematic?

Yes I think so.

If you do a test by putting some 1k across your 360Ω Rk's you can determine what value to order.

closest I have is 1.2K will that do? ..just checked..277ohms so yes



M

[martin manning]

Yes, and you can see what the difference in sound is.

[norburybrook]

Yes, and you can see what the difference in sound is.

I would imagine...LOUDER.... ...which as we all know is always better.

I need to start thinking about providing some clothes for this beast.... Its got to be either blonde or snakeskin that's what I have left in enough quantity to do a head.
I shall get my crayons out and do some designs.

M

[norburybrook]

Well after a 'difficult' day yesterday rewiring the gain input cured the issue and I left the studio fairly happy.

This morning I came down with fresh ears and fired up the amp. Very, very nice amp. Cleans are very clear and chimey, reminds me a bit of the express clean but it doesn't break up like an express. Its also incredibly well balanced considering there is zero tone stack, the clean literally goes form the v1a straight to the P.I. the only tonal change is the 'brilliance' control which is on the PI. It's well voiced, no flub on the bottom, chimey top, overall clear and bright is how I'd describe it.

The gain channel is great, lots of control, and will do 'hair' 'crunch' and 'OD' . The gain channel has the full tone stack along with a gain, level, Edge and Master volume along with the shared PI brilliance. Again it's very well balanced, very crisp and clear, focused, tight bottom end. The SS and tube recto is subtle but the is a difference, the tube recto is slightly softer and more forgiving slightly, but it is subtle.

I've just wired a pair of 1.2k resistors across the 360's to give 277R which will up the bias closer to the original, I think I'm still way under the 118% though. This has added some more 'girth' to the tone in a nice way, still crisp but has more bottom end and thickness, reminds me of the difference between a 50 and 100w amp I wasn't expecting this so a nice surprise. Can i leave these 1.2k 1 w resistors in place until I get new ones or will they burn up?

So my Cathodes are now 21.6v ...Martin or anyone can you tell me what % that now is? can I go lower than 270R or is this a safe place to be as it's sounding good?

Time to start thinking about an AB switcher and a cabinet.

M

[martin manning]

Great, Marcus, nice work and thanks for the report. Measure voltage on pins 3, 4, 6, and 8. I'll run the numbers. Voltages will be different in SS vs. vacuum rectifier mode, so if you have the time, get them both ways. That should be interesting in itself. Right now I'm estimating 93% based on Vk just above and the old plate voltage. The 1k2 resistors are running at V^2/R Watts, so 21.6^2/1200 = 0.39W (at idle), so yes you can leave them in.

[Colossal]

Very, very nice amp. Cleans are very clear and chimey, reminds me a bit of the express clean but it doesn't break up like an express. Its also incredibly well balanced considering there is zero tone stack, the clean literally goes form the v1a straight to the P.I. the only tonal change is the 'brilliance' control which is on the PI. It's well voiced, no flub on the bottom, chimey top, overall clear and bright is how I'd describe it.

The Brilliance control is a high cut and this channel is pretty much the same as the Spitfire (although that has paralleled triodes, but same 220k/1k5/22uF voicing). Such as great sound. I really love that simple format, like a Marshall 18W Normal channel; single gain stage (usually paralleled for bit more richness) and Volume/Tone controls, then PI. Very bare bones, but killer.

Glad to hear things got sorted out and the amp is sounding good.

[norburybrook]

@Martin @Dave thanks. Yes I'm really pleased with the amp. I'm not sure what I expected but I've already used it today in the studio on a new track which means it must be good. It really seems to suit my Gray guitars telecaster and I've been doing all the testing with the 1x12 Dumble oval backed cab sporting the Celestion BN300s a neo speaker that's supposed to sound like an EVM12.


I'll do the voltage measurements tomorrow with SS and Tube rectification. Part of me is interested in pushing the envelope and seeing what the at would be like @100% bias , however it is sounding good at 277R at the moment and it will mean tubes will have longevity.

Quick question: as the output tubes are cathode biased does this mean you can use tubes that perhaps weren't a good match for fixed bias ? reason I'm asking is a I have a box of old Mullard EL43's but they're random tubes and I remember they didn't match up well in a fixed bias amp when I tried them.

I'll post some sound clips as and when I get time.

this is a good amp, I think a relay switchable clean/gain single input would be a worthwhile modification, not sure how that would be done but it could stop the extra gain noise form the gain channel affecting he clean if it was sent to ground when using the clean channel only. I'm surprised that with the switching jacks the dirty channel isn't grounded when using the clean.


M