Preamp for EPC-450CII and semiconductor / strain-gauge carts

[Doug G.]

I wouldn't worry too much about compliance vs. tonearm. I use one of these in a BIC 980 arm which is medium-light and it works fine at 2 - 2.5 grams with CD-4 so it can't be having too much trouble, being CD-4 tracking is much more critical than regular stereo.

If you want to disable the muting on the Duals, all you have to do is put pieces of paper between the contacts so they can't close. Then the signals will not be grounded out during cycle and you aren't drastically or permanently altering the table.

Doug

[williamsunique]

Replacement stylus are being sold on Ebay. 672-DQ Panasonic USA Stylus Needle Cartridge EPS451QD EPS45STQD 46 EPC450CM4
Ebay item 220964530704 US $55.00
Worth a look. Paul.

[Mellowgroovy]

Hi Flavio81 and everybody,


I just finished building my tube strain gauge preamp with EQ inside.

It's sound very good and made me feel happy so much.

But I need to measure frequency response of my preamp for adjust EQ to become flat.

Could anyone suggest me about program and equipment for measuring?


Thanks & regards,

[williamsunique]

Hi Mellowgroovy.
Congratulations on your build. I do not know if this program would be of any use.
Audio DiffMaker.
It is free and looks as if it could be quiet useful. I have not as yet tried it myself.
Paul.

[flavio81]

Hi Flavio81 and everybody,


I just finished building my tube strain gauge preamp with EQ inside.

It's sound very good and made me feel happy so much.

But I need to measure frequency response of my preamp for adjust EQ to become flat.

Could anyone suggest me about program and equipment for measuring?


Thanks & regards,

You need a test record with a frequency sweep from aprox 20 to aprox 20000Hz, or a pink noise track on it.

Then you can record the audio to a PC and do a spectrum analysis on it, for example using audacity.

[Filament2]

Hi Flavio,

What is the output voltage and output impedance of your SG power supply design?

Thanks,
Filament2

[flavio81]

Testing, testing...

[flavio81]

Hi Flavio,

What is the output voltage and output impedance of your SG power supply design?

Thanks,
Filament2

Hi,

It is a complete preamp, not a power supply.

The output voltage is healthy and high, more than enough for connecting to the AUX input of an amplifier. Output impedance is correct for it (50K-100Kohm).

BUT you should delete (bridge) C1 on the circuit, or replace it with a 1uF non-polarized capacitor of good quality.

[flavio81]

What's the compliance of EPC-450CII cartridge? I have several record players and arms and I should make up my mind to which one I mount it. Possibilities are:

Lenco L70 original arm
Thorens TP 16 (version I)
Thorens TP 13 (a bit modified, several grams ligher than in factory condition)
Dual 1019
Dual 701

There's a mute switch in Duals, I guess it can not be used with strain gauge or am I wrong?
What's the current opinion, should I still just make the ultra simple one (page 8 on this chain) or should I go for something more complicated/better one?

1) The L70 arm is way too heavy for it.
2) The TP16 is 16g, too heavy in my opinion.
3) The TP13 is the ugliest thorens arm EVER
4) The Dual 1019, i have no idea.
5) The arm on the Dual 701 is surprisingly good (i have a Dual 701) and should be a good match (haven't tried, though). But you need spacers because that arm doesn't have VTA adjust. Or it does? Please inform me!!

As for the mute switch, it would make a loud "POP" on the preamp. I'd suggest you to bypass the mute switch. This is a good mod for all cartridges!!

[Filament2]

The Professor originally turned me onto the wisdom of these carts and vintage DD TT's about 4 years ago. I have a few 451cII's and a 460, as well as a NOS stylus.

Great, so I take it the output voltage is at least 1.5V and no linestage is required?

I've been following a number of these threads here and on audiokarma for a while, but please refresh my memory: Is this preamp you are referring to the DIY one based around the ebay kit board or is it one built from scratch?

Thanks

[SLA-3]

With a ratio of 100 to 1 on the FB loop the output level is sufficient to drive most power amps directly thru passive level control or simple 50k pot.

[Coffee Phil]

Hi Flavio81,

Oddly enough I just discovered this string. I noticed at the start that you had enough of these cartridges that you might offer some for sale. I don't really imagine that there any could be left but it doesn't hurt to ask.

I haven't read this entire string (as yet) but I did notice some discussion of EQ.

I know that strain gauges are displacement (amplitude) responding as opposed to velocity responding cartridges (all magnetics). I also had heard that Peter (Soundsmith) claims to not use any EQ in his strain gauge electronics. His claim is the slight error in amplitude response is not worth the trade-off with the coloration the added circuitry would add. With RIAA EQ records are recorded constant amplitude from 50 Hz to 500 Hz, then constant velocity from 500 Hz to 2121 Hz, then constant amplitude again from 2121 Hz to the high frequency limit. The difference between constant amplitude and constant velocity is 6 dB / octave. The span from 500 Hz to 2121 Hz is ~ two octaves which works out to be 12 dB. A 12 dB offset in the amplitude from the part of the spectrum below 500 Hz and that above 2121 Hz doesn't strike me as slight.

Last night as I was getting into bed I was pondering the things above so I conceived of an experiment. It turns out that I have a mono phono stage which has selectable EQ for both the bass turn and treble cut. I can select 500 Hz base turn and 2121 Hz treble cut (RIAA). I can also select 700 Hz bass turn and 700 Hz treble cut. This gives a negative slope from 70 Hz (The bass shelf is a decade below the base turn in all settings) to the high frequency limit of 6 dB / octave. This converts the theoretical constant velocity response of my Sonus to the theoretical constant amplitude response of a strain gauge.

I got out of bed and fired up the system and played a mono record with the RIAA settings, then the constant amplitude settings. The constant amplitude settings did not sound bad but it did sound like what I would expect with a 12 dB displacement in amplitude from what is below 500 Hz and what is above 2121 Hz. The constant amplitude did sound OK but it is hard for me to imagine the raves these strain gauges get compared to good magnetic cartridges if what I heard is representative.

What gives? Is there some mechanical thing in the cartridge which gives the points of inflection at 500 Hz and 2121 Hz? Could there be some "secret sauce" the makers of the electronics for these cartridges are not telling us of?

Phil

[SLA-3]

The Matsushita carts can sound pretty good 'naked' but they do lack something compared to a decent conventional cart IMO and the opinion of others. Peter has a product to sell and a living to make and it's likely he hasn't yet found a comp network that doesn't negatively affect the "directness" (for lack of a better term) of the carts he offers that he likes, just my USWAG. Some folk like them just the way they are and are quite satisfied. Me, I'm interested in a good comp network that flattens them out without mucking up their good points.

[Coffee Phil]

Hi SLA-3,

That is pretty much Peter's story and apparently he is sticking to it. I don't fully buy it however. The network should be fairly simple. We are talking 12 dB of compensation here, not the ~ 40 dB of compensation a magnetic cartridge requires.

There is more to this story than has been adequately explained to me. This issue also applies to ceramic cartridges which are also amplitude responding. Most usually they were fed into a line level input with no compensation. I do seem to remember however a ceramic which was touted as in the league with magnetics and it came with an adapter which went between the phono leads and a normal magnetic phono input. Also my Harmon Kardon Citation IV had a ceramic phono input as well as the magnetic input. The ceramic input was simply a 100 pf capacitor connected to the magnetic 47 K Ohm input. The cap and the 47 K Ohm Formed a differentiation network which gave a 6 dB / octave rising response over the entire audio spectrum (amplitude to velocity conversion). The normal RIAA EQ used for magnetic cartridges could then do its thing on the ceramics as well.

Phil

The Matsushita carts can sound pretty good 'naked' but they do lack something compared to a decent conventional cart IMO and the opinion of others. Peter has a product to sell and a living to make and it's likely he hasn't yet found a comp network that doesn't negatively affect the "directness" (for lack of a better term) of the carts he offers that he likes, just my USWAG. Some folk like them just the way they are and are quite satisfied. Me, I'm interested in a good comp network that flattens them out without mucking up their good points.