Use of 220uF and 330uF in bass channels.

[Mark]

I saw this on You Tube and I could help but feel this guy has got it wrong.

He is using these large caps and bypassing them with a 0.68uF cap. In my mind a 10uF Vishay MKT 1813 would sound the same and take up a lot less real estate.

http://www.youtube.com/watch?v=CWgZ62x4a0E

Any thoughts?

[Reeltarded]

He has only misused the Friedman fat cap idea a stage too early because he doesn't know math.

Common on the pre-CF stage but never up front. The small cap is waynfaster than the big one so you still get am reble boost over the low boost.

There are better ways to get lowend than to throw the farm at it first shot. A tiny resonance cap would be my first choice on an amp that already has the gain going on. Bass late, treble early you know.

Haha nothing fancy on the tone settings. Near full up everything but a total bass dump. Amp sounds pretty good until you turn it up to stage volume though. So tired of Van Halen medleys at room temperature.

[Structo]

Sounds buzzy.

[Reeltarded]

haha! Not what I'd call buzzy, just too much potential lost to poor staging.

[Mark]

just too much potential lost to poor staging.

Sorry I'm not sure I understand this new fangled Marshall jargon.

What do you mean?

[Reeltarded]

So try this on your friend's Marshall. Try it over V1B, then move the same electrolytic to V2A.

If you use it on the first stage the second stage wallows in fuzzy bass. It works at low volume, but crank the amp. You have to go nearly full bass cut. On the second stage it takes the nice distortion from stage one and adds some meat in the lows. Bass settings still in the middle, not full dump.

That amp would never work at big volume. It will turn into a swamped flub machine to be eaten alive by any drummer.

2.7k//330uF is full bypass to under 1Hz. People want the lowend but they think they want more than they really do.

Friedman uses 2.7k//.68u bright and 820r//330u next stage. That works.

[Mark]

Thanks for the info Miles.

I've read in a number of places the 220uF or 330uF is over kill. To be exact Blenecowe's Pre-amp book (1st edition) page 26 chapter one. The link has some of the info, but not all of it. (A damn good read all the same!)

http://www.valvewizard.co.uk/Common_Gain_Stage.pdf

Blencowe mentions the use of low voltage caps and high value cathode bypass caps to reduce distortion. He is also a big advocate of poly caps such as the MKT 1813.

Do you notice a difference between a 22uF cap and the 330uF cap in the V2a position?

As I've previously mentioned somewhere I don't have a lot of experience with Marshalls, vintage amps do tend to be surrounded by myth which leads me to challenge accepted practise.

[Dai H.]

I like the big cap (obviously you don't need something with such a high voltage rating as the video seems to show). I think it works since the coupling cap preceding is small (2200pF), plus smaller cathode bypass (.68uF). One supposed brown sound eyewitness spec with tied cathodes (the Bassman type circuit) and the large cap on V2a Ck doesn't make much sense due to the issues mentioned (i.e. too much low end).

As far as the small film (.68uF) paralleled together w/the big cap, if put to test, I'd guess the results would range from insignificant to very subtly different.

[Reeltarded]

Yes I notice the difference between a 25u or 50u and a 250-330u. A 10 to 50u works good there without so much furry bass.

For dialing in something nice try a .68uF bypass over V2a and add a 10u to 50u with a 25k trimmer to make that a partial. It really won't need full bypass with the big cap.

Make gain in the preamp, add bass in the NFB. 4700pF to 5600pF over a 5k to 20k resistor in series on the NFB tail at the 8ohm tap. Experiment with which tap works best too. Friedman uses 100k on 4ohm tap. That is very little feedback. Crunch for free.

[Roe]

I like the big cap with shared cathode but not with split cathode (the circuits are not the same). having said that, I do find the shared cathode circuit bassy and prefer to reduce the low bass slightly

[ChrisM]

The small cap is doing nothing when in parallel with the big electrolytics. The fact the small cap is a film cap does do a bit to the tone though.

[Mark]

Chris M: I would have thought the 0.68uF cap was placed in parallel with the 220/330uF cap to negate the ESR/inductance of larger cap.

Miles: Regarding resonance type circuits, is there an issue with flappy bass?

I noticed many years ago how the bass sounded quite loose in my modded Boogie SOB when I turned the gain up and the post PI master volume down.

All: The reasons for these cap questions is my involvement with Fender, Trainwreck and Dumble amps where 22uF caps seemed an overkill let alone a 330uF. In my limited experience with Fender amps I'm fairly sure I wouldn't hear the difference between a 22uF and a 330uF in a Blaceface pre-amp. Which is not to say I wouldn't hear a difference in a Marshall circuit.

The question in the back of my mind is why does the Marshall react to the larger caps where the Fender seems quite indifferent?

[Reeltarded]

The resonance is great with a cascaded circuit. Limiting it is a good idea on a 4 holer type amp. If you moderate the bass control and give the resonance some room to be adjusted it's a good thing. I like thump..

I use .0047 and a 1MA pot. I have used as big as a .0022uF in a fixed resonance amp over a small resistor to add just a bump in the bottom.

[Stratoblaster]

Thanks for the info Miles.

I've read in a number of places the 220uF or 330uF is over kill. To be exact Blenecowe's Pre-amp book (1st edition) page 26 chapter one. The link has some of the info, but not all of it. (A damn good read all the same!)

http://www.valvewizard.co.uk/Common_Gain_Stage.pdf

Blencowe mentions the use of low voltage caps and high value cathode bypass caps to reduce distortion. He is also a big advocate of poly caps such as the MKT 1813.

Do you notice a difference between a 22uF cap and the 330uF cap in the V2a position?

As I've previously mentioned somewhere I don't have a lot of experience with Marshalls, vintage amps do tend to be surrounded by myth which leads me to challenge accepted practise.

I always thought the same. Then one day I heard a 100 watt 69 Plexi with 470uf on the bass channel. Not stock ,the rest was though. I would have thought this completey crazy but it worked a treat. Adds 'more' with no more flub than a 220uf or 330uf. More Eric Johnson and Dumble like I thought.

Cheers Mark

[Mark]

Not stock ,the rest was though. I would have thought this completey crazy but it worked a treat. Adds 'more' with no more flub than a 220uf or 330uf.

Thanks for your reply Mark, apologies but I don't understand.