Coronet bass issues

BobM · « **on:** 1 Aug 2007, 05:24 pm »

OK - Jim is on vacation for the next 2 weeks, so I'm looking to the members to help me figure out where to look until he returns.

My Coronet is decidedly bass shy. I always thought it was the silver cable from the tonearm, but in a direct comparison against another phono stage I found it is not the cable, it's my Coronet. I know different tubes made the sound noticeably leaner, and thought I found a combination that added some weight, but not nearly enough. The Coronet always had a reputation of having good bass, so I'm assuming I have something out of whack inside (resistor, cap, etc.).

Anyone have a place to start my search? A key resistor or cap value that I should check, rather than checking everything? Or perhaps some voltage readings that make the most sense to see what may be the root cause?

Thanks, just looking for a place to start.
Bob

Bill Epstein · « **Reply #1 on:** 3 Aug 2007, 12:58 am »

My experience tells me the Cornet should have bass equal to or better than:
Aqvox C2I
Musical Surroundings Nova Phenomena
CAT SL-1 MKII phono section

With a Benz Micro Ace to Arc LS-1 to Simple 45 or Red Rocks Renaissance or KR Kronzilla SXI or Accuphase E-450. 2 to 220 watts, Solid state, single-ended and push -pull.

In other woids, it ain't the Cornet. Unless you have modded from stock?

Could the Cornet be less "boomy"? Are you missing the thump in the chest?

Give us some more details to work with including components and room.

amandarae · « **Reply #2 on:** 3 Aug 2007, 04:39 am »

Hello Bob,

Bill's observation is spot on for me. I have never thought of the Cornet as "bass shy".

Did you check the voltages at the test points on the board according to the manual? What is the heater voltage and B+ voltage? If the those voltages are fine, can you double check the resistor values on the RIAA section to make sure that the right value goes to the right locations? It is the circuit with R204, R205, R208 and R207 plus the values of caps C202 and C203. Remember that the RIAA circuit works like a pre-emphasis/de-emphasis function.

What voltage can you measure after R219, and after C208 with respect to ground?What about the heater voltage at R215?

We are talking, I am assuming, about the Cornet 2 right?

Goodluck!

regards,

Abe

WGH · « **Reply #3 on:** 6 Aug 2007, 04:23 pm »

Hi Bob - The Cornets are not bass shy. If my Cornet2 had any more bass I would be stuffing socks in my speaker ports.

If your resistor values are correct, check the solder joints. I had a joint that visually looked perfect but only made an intermittent connection.
I may be delusional, but the closer I got the heater voltage (H+) to 6.3 V the more bass and fullness I got.
I don't know if this makes any difference, but I am using a nice fat shielded Volex power cord.
The tubes I currently use are a 5V4GA RCA NOS/NIB, branded CBS, a 12AU7A GE branded CBS, and two Sovtek 12AX7LPS all from Jim McShane.

Wayne

BobM · « **Reply #4 on:** 7 Aug 2007, 12:24 am »

Sorry it took so long to measure my unit, but here are the (obviously LOW) voltages:

126V AC coming into the unit

Schematic value / Measured Value / Position

365V DC / 345V DC / Y-B wire
155V DC / 117V DC / R219
150V DC / 117V DC / R212
150V DC / 130V DC / R204
300V DC / 279V DC / R211
330V DC / 300V DC / R211 (other side)
6.3V DC / 5.8V DC / R215 and R223 (heater voltage)

I'm using the 370BX transformer and an RCA 5Y3GT.

So, I'm obviously getting a low reading out of the 370BX Y/B line where it should read 365V, but would that cause the other values to be so obviously low? Which resistor(s) need to be (changed or) checked first before I delve into the whole schematic?

Thanks,
Bob

amandarae · « **Reply #5 on:** 7 Aug 2007, 12:52 am »

Hello Bob,

Let me take a shot at this. Obviously, the B+ is low, thus affecting all the other measurements. So, let me ask you one quick question. What is the voltage (AC) when you measure from Red to Red on the transformer secondary? If you cannot get close to 550Vac, I believe that is the reason why your B+ (365) is low taking into account that R100, C101, R101, and R102 are correct values . If it is close, I would check the rectifier.

I hope that helps.

regards,

Abe

regards,
Abe

samplesj · « **Reply #6 on:** 7 Aug 2007, 03:11 am »

Quote from: BobM on 7 Aug 2007, 12:24 am

I'm using the 370BX transformer and an RCA 5Y3GT.

Isn't the 5Y3 that JH used for design the Sovtek, which is really more like a 5AR4 (slow ramp and lower drop) than a real old production 5Y3? Maybe you are just getting more voltage drop out of that 5Y3 than he got out of the Sovtek.

Try a 5AR4 and see what you get. Sovtek and JJ aren't that expensive for testing purposes.

WGH · « **Reply #7 on:** 7 Aug 2007, 04:04 am »

Compared to my Cornet2, your voltages don't look that bad except for R219, R212 and the heater voltage. Is the voltage for both L & R channel resistors the same? Measure the voltage at tube socket pins 1 & 6 and re-solder if needed the pins and the resistors connected to those pins.

Yours / Mine / Position

354V DC / 346V DC / B+
117V DC / 144.8-R & 150.1-L V DC / R219
117V DC / 130.5-R & 135.8-L V DC / R212
130V DC / 132.8-R & 130-L V DC / R204
300V DC / 313-R & 313-L V DC / R211

5.8V DC / 6.3V DC / center of tube sockets and low side of R223, high side is 7.06V DC. R223 has been changed/adjusted to less than 1 ohm. Directions are here: http://www.audiocircle.com/index.php?topic=41430.0

Voltages will be lower with the 5Y3GT, it is also directly heated, I bet your light turns green almost immediately. An indirectly heated tube like the Sovtek, 5AR4 or 5V4GA will give you higher voltages and may make your tubes last longer, red to green will then take 5-15 seconds.

I have a RCA 5Y3GT and tried it for a while, I prefer the 5V4GA for now. My speakers go down to 25 Hz and the 5V4GA gives a nice oomph to the bottom end.

Bill Epstein · « **Reply #8 on:** 7 Aug 2007, 10:27 am »

Great discussion.

I checked my voltages with NOS Sylvania 5Y3 and I got 5.94.

Added another 5 ohm and, Bingo, 6.35.

Thanks, guys. Sure hope it still sounds great.

BobM · « **Reply #9 on:** 7 Aug 2007, 02:31 pm »

Thanks everyone. There's lots of good info in this thread. I figured, since my voltages are low across the board I might as well replace my NOS 5Y3GT with the 5V4GA rectifier tube (I just bought a new RCA 5V4GA from www.muchstuff.com for a very good price to try it out) and see what effect it has overall. If the heater voltages are still low I will then try parallelling R223 to bring it up to snuff.

Thanks again,
Bob

WGH · « **Reply #10 on:** 7 Aug 2007, 03:18 pm »

Quote from: Bill Epstein on 7 Aug 2007, 10:27 am

Great discussion.

I checked my voltages with NOS Sylvania 5Y3 and I got 5.94.

Added another 5 ohm and, Bingo, 6.35.

Thanks, guys. Sure hope it still sounds great.

Did you notice a difference?

Bill Epstein · « **Reply #11 on:** 9 Aug 2007, 01:45 am »

It's maybe a touch brighter and the soundstage a tiny bit more forward. I won't really know until I do some extended listening and then remove the extra resistor. Can't do that now 'cause I'm up against a deadline on another phono stage I'm reviewing.

Right now I'm forcing myself to listen to a Grado Green. I need a better MM!

AudioSoul · « **Reply #12 on:** 9 Aug 2007, 03:57 am »

Bingo! That may be the reason you are not getting better bass. Is the Grado Green an older one with dried out suspension? Just a thought.......DK

Bill Epstein · « **Reply #13 on:** 9 Aug 2007, 07:08 am »

It's BobM that has the bass issues. None here. See my reviews of the XLH 1812 and Simple 45 at www.dagogo.com, "70 Miles From Nowhere". Check back in a few months and I'll have a full review of the Cornet II and Piccolo.

I was listening with the Grado just to hear the 40 dB gain and 47k loading of a Nova Phenomena phono stage I have for review. All my other listening is with the Benz Micro-Ace L cart.

WGH · « **Reply #14 on:** 9 Aug 2007, 08:12 pm »

Quote from: Bill Epstein on 9 Aug 2007, 07:08 am

Check back in a few months and I'll have a full review of the Cornet II and Piccolo.

Looking forward to your review. I was wondering what the Tantalum and Kiwame resistors bring to the party. I already have Sonicap and Mundorf caps installed and in a couple of months I'll be ready to tear into the Cornet2 again. I am getting really good at replacing parts.

Bill Epstein · « **Reply #15 on:** 10 Aug 2007, 01:36 am »

As I did the copper lining, damping, Tants and Kiwames all at once it's difficult to say what the last 2 do for the sound. The Cornet is now equally quiet as the SS battery powered stage except for a hint of tube rush. Some of that has to go to the Kiwames which I have often used as stoppers and have always been quieter than metal films. There is also a more defined and slightly more forward image which may be the Tants. I believe the damping has a lot to do with that, tho'.

Vibration control doesn't get the pub but it's sooo important, especially with millivolts.

WGH · « **Reply #16 on:** 10 Aug 2007, 02:03 am »

Quote from: Bill Epstein on 10 Aug 2007, 01:36 am

Vibration control doesn't get the pub but it's sooo important, especially with millivolts.

When I get some spare coin I may try out a trio of Herbie's dampers. All my electronics are in an adjoining room so they don't get any direct sound waves, though the bass waves travel up and around all the wood floors. When I first set everything up I would get terrific feedback through the turntable/cartridge, a really cool howl that got louder and louder, just like a lead guitarist solo in a psychedelic rock band.

BobM · « **Reply #17 on:** 11 Aug 2007, 11:44 am »

Well I received the 5Y3GT replacement, it is an NOS RCA 5V4GA. The voltage measurements are all a bit higher with this tube, as expected, but R223 is still low, at about 5.9. Better but low. So I parallelled a 4 ohm 5W that I had lying around and the heater voltage is now 6.36. A tad on the high side. If I put the 5Y3GT back in the measurement goes down to 6.24.

I do notice that the bass is fuller now, especially with the 5V4GA in place. I think I will keep it this way for a while. Is there any concern that the heater voltage is 6.36? What is the effect of having this a tad high - anything to be concerned about?

Thanks,
Bob

GRD · « **Reply #18 on:** 11 Aug 2007, 05:36 pm »

I think heater specs in general are +/- 5% and you are within 1%, which is a bullseye. Some people target 6.2V as this may extend tube life a bit without compromising performance. However, house voltage can change within a few percent during the day, so it can be tough to target heater voltage with a lot of precision. 6.3V is spec and you are there.

WGH · « **Reply #19 on:** 11 Aug 2007, 10:17 pm »

Good to hear you have a bit more bass. 1% of spec seems like it will be OK. My voltage also changes with the day, it also drops slightly as the unit warms up, at first it is slightly high and then settles in closer to 6.3v.

I have found the 5V4GA can sound a little too full, on the recommendation of Jim McShane, http://pages.prodigy.net/jimmcshane/tubes.htm, I tried a 12AU7A GE branded CBS, ANOS black vertical rib plate like a 5814 for $21.50. I like the GE better than the Raytheon 12AU7. The bass stays just as deep, but tightens up and the imaging is more focused.

The money tube is the Sovtek 12AX7LPS, I got a matched pair from Jim and have no desire to try out any others in that spot.