Using a turntable with an 800b

Well, I adjusted the phono output pots to maximum and it's still a lot quieter than the other inputs. It's probably time to build a MM preamp. I've been looking at the CNC phono pre, it's got good reviews and it's simple enough to build on a breadboard.

Glenn

Are you sure your phono inputs are connected to phono low?

Only one phono input on my model, so yes?

Even though phono is the format with least dynamic range, most LPs were and are mastered to use more of the dynamic range available on the format than you'd find on compressed radio or digital.
Is it so soft that it's unusable or do you have to turn the volume to 11/12 instead of 9/10?

That crossed my mind too.
I have the volume at about 1:00-2:00, and when I turn the source selector back to FM boy do I get a blast! This is the thing that's bothering me the most. The FM/AM/tape inputs I run at about 10:00-11:00 most of the time.

What do you think about just using a phono preamp? I'm eventually going to switch to a MC cart anyway. Granted the preamp would have to be changed for the difference, but I'm able to do that. I probably want to tune it for the specific cartridge anyway.

Thanks
Glenn

Are your phono stage tubes strong? Those are the two with the shields on them.
If you're going MC, you'll need an outboard phono stage to an aux or tape play (not tape head) input anyway.

What speakers are you using and what's their efficiency?

The V15 Type V has a output voltage of 3.2mV. This is lower than the V15 III @ 3.5mV although the difference shouldn't be that noticable. Compare that to an EMPIRE 2000E/I with a 7mV output and the difference is very noticable.

The "problem" you are having isn't new with SHURE Cartridges. It's a matter of "matching" the output of the cartridge with the input of the receiver. The 800C's "LOW" setting is for Magnetic Carts and the "HIGH" is for Ceramics. The input sensitivity on the receiver is 3.3mV. So the Shure looks to be a decent match. If your phono section hasn't been overhauled (including the P.E.C.'s), it should be. Also the Phono tubes could be weak causing the problem. Shure's on my 800C sound weak compared to my Empire 2000E only because the EMPIRE's output is 7mV. Almost the same as FM input. But I still have to reduce the volume on the 800C when using the Empire and switching to FM. I've found that this is a Brand wide issue with all of my FISHER Receivers (800C, 550-T, 500-TX, 175-T and even the consoles when swapping out from the Pickering V15 ATE types with a 10mV output. You can repeat this with any brand SS or tube unit, so I think it's more a matter of getting the cartridge output to pretty much match or exceed the receiver sensitivity. You can use an external preamp and connect into the AUX as long as the preamp has the RIAA curves built in.

Larry

Thanks guys.
I rebuilt the receiver and tested all the tubes when I purchased it. You'll have to explain to me what the PECS acronym is for. I didn't rebuild everything, so maybe the phono section needs attention. That's a good suggestion.

The 800b I have doesn't have the hi low inputs for the phono. Mine has only one phone input with external pots for level control.

I'm using this design with Fostex 103 drivers:
http://www.tnt-audio.com/casse/tqwp_e.html
I'm not sure of the efficiency, but I built them mainly for use with my SE KT88 amp. Not much power output on that amp but these speakers are plenty loud with it.

I'll take a look at the phono section schematic to see what the design looks like. Thanks for all the suggestions, I appreciate the help.
Glenn

After looking at the schematic, there is a 100k resistor from the phono input to ground. I may try playing around with a different value, unless this resistor controls the impedance?

Ok. Sorry about that. I forgot it was a "B". Anyway a P.E.C. is a PACKAGED ELECTRONICS COMPONENT. Basically it's a precursor to an IC. On your schematic they are listed as PC's. PC1 and PC2 are the ones you are looking for. Looks like an oversized ceramic cap with 3 to 10 legs. PC 1& PC 2 have 3 legs. In this case they are responsible for RIAA curve. New PEC's are not available but the individual component value's are on the schematic so you can breadboard them.

With the Adjustment Pot AFTER the 12ax7, The tube may be showing good, but not good enough.

IIRC the 100K resistor is the loading resistor for the cartridge. The recommended value by Shure for the V15V is 47K but some guys advocate 68K or higher, sometimes as high as 200K. As I use more than 1 brand cart, I just leave it alone. Feel free to experiment with 47K, 68K, and 100K. Note the differences in S.Q.(Sound quality). It'll be very subtle.

Larry

Thanks Larry.
The PEC's look like a simple circuit to build. I did see those in the unit when I was rebuilding it. I assume 1% resistors and silver mica caps are in order since it's for the RIAA circuit? I assume the cap values on the schematic are in pF?

Well I tested all the tubes (in a tester), wouldn't this reveal a weak tube? I have some new 12AX7's so maybe it's worth swapping to see if this has any affect.

Since I think I'm going to build an external preamp anyway, I can play around with adding different resistors in parallel for loading.

Thanks for the suggestions.
Glenn

Here's an update on the turntable issue I'm having. I finished my CNC preamp build this past weekend, and decided to try it out. I attached it to my AUX input, and did get sound out of it but it was VERY low. I swapped-out the gain resistors for the higher gain value. After trying this I get sound out of the system, and it does sound good! Even better than the phono inputs on the receiver. I still however have low output, it requires me to run the volume at about 3:00. This is even higher than when using the phono input.
I'm beginning to wonder if the cartridge is to blame for this issue. I think it's time to make some measurements with the scope to see how much voltage I'm getting out of the cartridge and the preamp. Do these types of cartridges get weak with age? This is a Shure V15 V cart.

Glenn

A V15V should have plenty of output.

Not enough to make the level the same as the other inputs, FM/AM,AUX. I realize that normally the turntable will probably never be the same as those inputs, I'd just like it to be closer if possible.

I actually asked about the preamp gain over on the turntable forum, and apparently I only changed 1/2 the gain resistors. I'm going to change the other two tonight to see how it sounds.

As an alternative, I'm asking around to see if it's possible to re-work the first stage of the phono preamp (12AX7) to get a little more gain out of it. Maybe change the bias of the tube a little.

Glenn