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Groovewatt - tube RIAA phono preamp
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Author:  Snhel5 [ 15 Jul 2018, 09:38 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi

I started my build of a groovewatt.
At the moment I'm still mainly in the design phase.
Some parts have been ordered and others even already received.
Beside that I wanted to use parts which I had on hand.

First PCB (I call that one the high voltage buffer board as it contains the filter section before splitting the power) has come in and is now being build.
Next up are the valve supply board and heater supply board.

I have a question about connecting the heaters.

The ECC83/12AX7 tubes use a 9 pin socket.
The heaters are connected together sharing a common midpoint on pin 9.
You could connect pins 4 and 5 to the 68V (E) using pin 9 as a common for the 62V (F) or connect the 62V (F) to pins 4 and 5 and 68V (E) to pin 9.

Would there be any noticeable difference in sound quality between the both of them.

Author:  gofar99 [ 16 Jul 2018, 15:12 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, I have not been able to hear or measure any difference. The applied lift voltage is enough apparently to swamp any possible differences as to what part of the heater string it is attached to. I imagine in a super high tech environment it might show a difference but lots of other things will mask the difference.

Good listening
Bruce

Author:  Snhel5 [ 17 Jul 2018, 14:33 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Thanks

My system is definitely not super high tech so I will definitely not notice the difference.

F to pin 9 sounds most logical to me and so it will be.

Author:  Snhel5 [ 28 Jul 2018, 07:21 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

If you don’t mind i like to ask you another question (actually 2 questions or 1question and 1 opinion).

I’m selecting the components which will be used in the amplification sections (done with the PSU stuff for now).
Took your advice on using Jantzen cross-cap for the 22µF caps in the tube supply sections and while I was out to buy them picked up cross-caps for all other values I needed.
It turns out that that no such thing exists as a cross-cap with 10nF or 27nF so had to revise my initial plan for the RIAA filter.

First thing that comes to mind when thinking about caps for audio equipment is WIMA.
If I’m not mistaken I also spotted some of the familiar red blocks on your photographs (not sure if this is in the RIAA filter).
But I also dug a little deeper while I was on a world wide web search.

Now the question.

I can get my hands on MKP capacitors with a tolerance of 1%.
WIMA at best offers 5% or even higher.
Considering these caps are not in the signal path what would be preferable to go for a well-known (will sound good) brand or the strict tolerances of 1% (these 1% by the way are Kemet capacitors).


Second thing are the step-up transformers.

I ruled out the use of Lundahl transformers as they are way too complicated for me with 20 different configuration possibilities.
I’m now looking at Softone instead an alternative could be silk audio or Jensen.

On the forums you wrote:
gofar99 wrote:
If you are going to use LOMC with it (I do) then you will need to use step up transformers (most major companies do as it is like free gain without noise). There are a few that I really like. First is Silk Audio's SAC1 (about $200 a pair and available in a nice case assembled for about $100 more - a bargain), then comes Softone PLC-1, after that either Lundahl 1678 ot 9226.

But in Audioxpress you wrote “My present one of choice is the Softone”

What made you change your opinion?

Author:  Bucurescu [ 02 Nov 2018, 07:03 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi all,

I have mine for few months already. I noticed a noise like a wind blowing on one channel after 1-2 hours. It is a tube. So, I’m looking to replace my JJ ECC803 (long plate) with ECC83.

Anybody tried Tung-Sol or Electro-Hamonix instead of JJ?

All the best.

Bogdan

Author:  gofar99 [ 02 Nov 2018, 17:25 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, I have not tried all the possible tube that can go in the preamp. Most with the exception of New production Mullard and Electro Harmonix were pretty quiet. I did not test TS ones as I don't have any. In all the builds I have done the best sound IMO is the long plate tubes. The others didn't seem as "nice". YMMV

I another post....I like the sound of the Softones slightly better than the SAC step ups. It is really close. I am pretty confident that it is my usual LOMC that mates slightly better with them than the other SUTs. All sound quite excellent though. My main LOMC is a Dynavector Karat23MR-RS. It tends to be rather lively and the Softones seem to tame it a bit IMO. When I switch to the AT33PTG/II The SACs seem more suitable. You really can't go wrong with either of the SUTs. BTW I use the lower values of gain for both types.

For components...I have used both Kemit and WIMA in the RIAA section. Both seem to be about equal. To get around the 5% vs 1% I measure them with a LCR meter. I believe I have seem some Vishay ones that are in the 1-2% range from some sources that would be suitable. True the caps in the RIAA are not exactly in the signal path, but they have a key influence on the depth and turn over frequencies of the equalization needed to play LPs according to the RIAA standard. A 5% deviation may not be noticeable though. While accuracy in the playback preamp is quite important, you will find that most cartridges are unable to get the music off the LP to the accuracy level of even modest preamps.

Good listening
Bruce

Author:  eshazen [ 11 Jan 2019, 16:13 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

I am finally through with other projects and ready to start a phono preamp.
I like the looks of the Groovewatt and I'm seriously considering it.

Looking at the 3 versions of the schematic on the project page, I'm curious
whether the plate voltage regulators really add anything. Is there an audible difference
between the initial simple version with only RC filters and the version with the
regulators?

My inclination would be to go "old school" and omit the high voltage regulators,
but if they make an audible improvement I could be convinced otherwise.

(Rest of system currently:
Dual 504/Grado - pyle phono preamp - Forewatt - KT88 Oddblocks - Polk Monitor 10s)

Author:  gofar99 [ 11 Jan 2019, 16:32 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, The regulators improve the S/N about 1-3 db depending on the rest of the power supply and general layout...mostly how the grounds are done. What you can do is try the preamp without them and see if it is quiet enough. Probably will be. But as most on this forum know I am nearly fanatical about hum and noise...any is too much so I go to great lengths to eliminate it. One thing on the various versions that is important is the 47uf (approx) that goes from the heater circuit to the ground. It can make a difference of 2-3 db. Again the layout and grounding seem to matter. Sometimes on one side of the heaters, sometimes on the other and sometimes it makes no difference. I use the type of pin jumpers that you see in PCs and with three pins...the middle to the cap and one on either side to the heater sides so you can check it easily. It is most noticeable with headphones, but a scope or speakers will do.

Good listening
Bruce

Author:  eshazen [ 21 Jan 2019, 16:19 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Starting my build. Decided to use the latest (?) schematic I could find (http://ohm.bu.edu/~hazen/TubeAmp/Groove/Groovewatt_mono_April%202017b.jpg April 3, 2017) with the LR8K4s, mounted on ~ 1 inch square pieces of copper clad as heatsinks. Planning to use 3 turret boards, one for the unregulated part of the PS, and two identical ones with the regulator and one channel each. Omitting the cathode follower stage since it will be driving a Forewatt input.

Did a layout in "diylc". Love this software! At work I use professional-grade CAD: OrCAD, Altium, Cadence, Mentor and have a love-hate relationship with each one. I fell in love with diylc immediately and did the chassis layout. It has a few quirks but perfect for the application. I re-drew the schematics in ExpressPCB schematic editor since I find it easier to use than any of the heavy-hitting stuff. Haven't tried the diylc for schematics yet.

Using a Hammond steel 12x8x3 chassis with another smaller steel box on top for the transformer. I'll float the transformer electrically and run a ground wire into the chassis so I can find the quietest point to connect it to.
I want to see the tubes glowing but still get low noise. Here's the plan: make tube shields out of copper screen wrapped around a cylindrical form and soldered, grounded to signal or PS ground. Recess the tube sockets half an inch or so in the chassis with grommets the right size for the copper screens.

If it turns out nice I'll post photos! If it doesn't, I'll still post photos and be back for advice :)

Layout: Image

My schematic (amp): http://ohm.bu.edu/~hazen/TubeAmp/Groove/groove_4tube_amp.png

My schematic (ps): http://ohm.bu.edu/~hazen/TubeAmp/Groove/groove_4tube_ps.png

Author:  gofar99 [ 21 Jan 2019, 20:25 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, It sounds like an interesting build. Keep us posted

Good listening
Bruce

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