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MG Head Bass Response (Coupling caps?)

post #1 of 17
Thread Starter 
This is my biggest quip with the MG Head DT amp. It isn't surprising, but the bass is very lean. I also realize that my Senns are going to be on the lean side too, but I'm not getting much below 70Hz or so right now (by my ears), so I know it isn't all Sennheiser's fault.

Question: I'm going to replace my coupling caps ASAP. For those who have done this, what kind of results can I expect? Right now I'm leaning towards some 1.5 uF Hovland MusiCaps. Axial leads will be a slight annoyance, but I've heard they sound great.

Any input would be great.

Thanks.

Brian.
post #2 of 17
Now you're worrying me.

Does this mean that if I listen to something like Madonna's Erotica...the bass is going to be cut off....or worse yet Sloppy?

The only Tube amp I've heard at Length was by Cary at huge price tags and the sound was amazing.

However, I have seen a lot of people mention that inexpensive Tube gear suffers with full range speakers(even if very sensitive like my Wharfedales at 95db).

I want to get into tubes but I don't want one that I'll have to re-build just to get the full frequency range.
post #3 of 17
Thread Starter 
Well, the bass response is lacking. There is no question. Maybe 70Hz wasn't the right point, but I'd bet it starts rolling off there. However, from 70Hz up, I'd consider this near bliss. So, it isn't the whole frequency range, by any means, that needs modification - just the bass. Now, of course, me being me will have to make several mods once I crack the thing open and start yanking caps. I can't limit this to just the coupling caps, you know!! But, you could. And that'd me a minor mod which would be relatively simple to make, IMO.

Brian.
post #4 of 17
Thread Starter 
I should add....

The bass, however, is not sloppy. No. What bass there is I'd characterize as tight and controlled. It is just a general lack of body in extreme bass extension that is lacking.

Brian.
post #5 of 17
what cd's do you notice this mostly on?
post #6 of 17
Thread Starter 
I listen to a wide range of music, but I can't think of how the specific CD should matter. Everything from classical to Peter Gabriel, Phil Collins, to Rammstein is lacking bass. It just isn't there. Senns 600s should be a bit leaner already than, say, Grado RS-1s, but not like this.

I've got what I consider *the* reference tubes in the MG Head right now, too. I could try swapping the Sylvania GB 5751 for a Bugle Boy 12AX7 and then again for a GE black plate 5751 (both of which are considered among the best of 'breed') and report back. But I wouldn't keep your hopes up. I suspect the real answer is coupling cap replacement.

And, I don't know if it is my imagination or not, but things seem more lean today that they did right out of the box a week ago.......

Brian.
post #7 of 17
The only time I want more bass out of my Head is on DJ, rap, electronica. Cleans up the bottom end on rock cds. .... and Yo Yo Ma is sounding just right.
However, I am interested in this mod, as long as it doesnt alter the other frequencies.
post #8 of 17
Thread Starter 
Well, this is interesting. Swapping from the Sylvania to the Bugle Boy has effected the bass in a positive way. It is indeed fuller. However the tonal accuracy and detail throughout the midrange isn't quite there now. *sigh* I'd definately choose the Sylvania over the Bugle Boy now, but am still left with lean bass. On to the GE black plate....

Brian.
post #9 of 17
Sorry to be late to the party.

I tested a stock MG Head for frequency response. I don't think it was a fantastic testing procedure, but I'm comfy with it to +/- two decibles.

Here's what I got for the bass decade:

200 hz -1.5 db.
160 hz -1.5 db
125 hz -0.5 db
100 hz +1 db
80 hz -0.5 db
63 hz -1.5 db
50 hz -2.5 db
40 hz -3.5db
31.5 hz -7 db
25 hz -9 db
20 hz -13.5 db


Not bad at all.

But you don't want to see the nasty treble peak from 3.15 khz to 6.3 khz. It gets as high as +10 db.

FWIW, this was with Senn 580s. Things were a little flatter on the low end with SR60s, but a LOT worse on the treble hump (got as high as +16db!).

Changing the coupling cap didn't alter these results much. But, it sure tightened things up (or maybe that was the power supply cleanup I did at the same time). Putting a constant current source on the plate load of the signal tube might help. Some day, I'll get around to finding out.
post #10 of 17

OKAY??

Videoshielded:

Please explain a little here. What effect do the +/- have on the sound. Does +10db add a 10db volume peak on those frequencies (3Khz to 6Khz) compared to say 1kHZ.

Does this mean that these upper frequencies are more forward?
post #11 of 17
Thread Starter 
What it really means is that the stock tubes aren't great. Get some, like the ones I've suggested before, with a linear frequency response and these spikes will diminish...

Brian.
post #12 of 17
The + means how many decibles of volume louder than the base line was produced at that particular frequency.

The - means how many decibles of volume quieter than the base line was produced at that particular frequency.

Base line in this case was 90 db at 1 khz.

The data was taken using a GE black plate triple mica 5751, and a matched pair of Amperex EL84s. I got pretty similar results using a Telefunken 12ax7 and Sylvania EL84's.

I measured similar treble peaks with a number of amps and CD players. I think it's the cans.
post #13 of 17
Thread Starter 
Wow.

That's very interesting in light of the additional info... When you said "stock MG Head" I figured that meant stock tubes. But GE black plate 5751s should have an extremely flat response curve and the EL84s you use (if they're D Getter Bugle Boys ;-) ) are probably the best ever made.

I'm using Senn HD600s, and I don't hear that kind of a treble spike. That would be glaringly apparent. There's no way its there for me. Hmmm... I may have to get the db meter out... Maybe all those concerts have finally started to take a toll on my hearing....

Brian.:
post #14 of 17
Hey, did you ever get your meter out? I'm dying to know.

I use the standard Rat Shack SPL meter, and correct the results for it's well-known deviations.

I don't think there's a problem with your hearing. I get similar treble spikes on many different amps, with several different headphones. I also get similar spikes with many different stereos. Maybe I have a bad meter, or a bad test disc (Stereophile Test CD).

If you get a chance to run some tests, I'd love to hear about it.
post #15 of 17
Thread Starter 
It's in my deep queue of things to do, but still buried fairly deep. I've got a couple Hovland caps sitting here dying to get into my MG Head amp though, and that's much higher priority.

BTW, I would just be using the same Rat Shack SPL meter too, and probably the same Stereophile test CD!

Brian.


Quote:
Originally posted by Videoshielded
Hey, did you ever get your meter out? I'm dying to know.

I use the standard Rat Shack SPL meter, and correct the results for it's well-known deviations.

I don't think there's a problem with your hearing. I get similar treble spikes on many different amps, with several different headphones. I also get similar spikes with many different stereos. Maybe I have a bad meter, or a bad test disc (Stereophile Test CD).

If you get a chance to run some tests, I'd love to hear about it.
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