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Home » Melquiades Amplifier » Valve Preamplifier for Macondo/DSET (75 posts, 4 pages)

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06-29-2022

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anthony
Posts 338
Joined on 08-18-2014

Post #:	61
Post ID:	26821
Reply to:	26763

Oops

Hi Jarek,

Apologies for missing your post.

To answer your questions:

(1) Yes and no. I've bundled the preamp into its new chassis (that I made from scratch) and it does not sound as good as before. There is a grounding problem with the new installation that I need time to track down and I am only getting volume from even numbered volume settings on the attenuator, not the odd settings, which is weird, but related to my grounding issue. The preamp has sat there for some time waiting for work to calm down a little to give me weekends to myself so that I can do this last little bit of work to get the preamp back into use.

(2) I have been using Ales operating point. However, I have a new source that puts out almost 4V and it will drive the preamp input to audible distortion so I will have to bias the 801a/10y deeper, probably around -10V. Once the grounding issue is sorted I will pull out the audio analyser and figure out just where to bias the valve to suit that high input source.

(3) No decoupling with a new cap...although there is already the series cap at the output of the hybrid mu-follower that rids DC from the output.

(4) Initially just sic filament bias. I do have other options here to try once the preamp is operating correctly. Reading descriptions of sound from other builders I think the sic diodes will probably suit Macondo/Melquiades most appropriately but only time will tell.

However, and this is a big however, I personally need this preamp, or something like it, because I have high input amps (4Vrms) and low output sources (1Vrms) and I like to listen loud which Macondo/Melq does unlike anything else I have heard. If you do not need the gain in your system, there are likely to be better preamps about or even a more conventional DHT preamp using a good output transformer and a suitable tube (not the 10 family: perhaps 71a if you can tame the microphonics).

Entire system gain structure is much more important to good sound than any particular qualities of the preamp. If I didn't need the x8 gain from my preamp I would be using a different pre with just the right amount of gain, no more. The 10y/801a is the right tool for my job, but it may not be so for yours.

Listening to the Placette active linestage with my new high output dac is very nice indeed and I do appreciate what Romy values in this setup, and if my sources all put out 4Vrms then I would have no need for the 10y preamp in its current guise, or the 10y tube at all.
Anthony

06-30-2022

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	62
Post ID:	26822
Reply to:	26821

Some more on my needs

Hi Anthony,
Thank you for your reply & explanations.
I actually need only a buffer, perhaps 2x as my Yamaha B2 is very sensitive, but I need a good one. I have right now Yamaha C2 just to have anything and I suspect it kills the sound ('constipated' sound) although it has ample of gain. Placette in EU is very rare to come by to have a listen. I've been looking at 801A not so much for its gain but for to its very good following as a preamp tube. Spoke about it to Ale, he claims it has some special character and betters all he has heard (incl. 46 which I also have and was thinking to use). You seemed to have seconded that initially but now sounds like you are a bit cooler in your perception? I'm being a bit of a parasite here, trying to copy a known good solution - too little time for experiments recently.

My idea is to make sth along Ale's/your lines with the Slagle autoformer at the output to reduce both the gain and the output impedance (the preamp drives 6m interconects). BTW, which model of the Slagle do you have? Does it handle your 4Vrms output well without distorting?

Cheers, Jarek

Cheers,
Jarek
STACORE

06-30-2022

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anthony
Posts 338
Joined on 08-18-2014

Post #:	63
Post ID:	26823
Reply to:	26822

The known good solution

N-set wrote:
Hi Anthony,
trying to copy a known good solution - too little time for experiments recently.

Well, Romy had great results with the Placette and his Dannoys, so that is the known good solution as far as I am concerned. Sounds like the 10y will introduce far too much gain which you will have to attenuate thus likely ruining the sound. I mentioned system gain structure earlier, and it is very important, more important than the amplification stages themselves.

The 10y is a bitch of a tube. You cannot wind a good output transformer for it...anyone that tells you they can either are deaf or have very low expectations of sound...so for a preamp we are limited to different output topologies including the mu follower which Ale uses. Trouble with the hybrid mu-follower is that unlike an OPT we end up with all the gain of the tube which in my situation is excellent but in yours not so much. Ale does recommend a resistor divider to attenutate some of the gain and perhaps that is an option should you still go with the 10, but it is still attenuation, and resistor attenuation at that which may or may not be better sounding than letting the Slagle Autoformers do all the attenuating work (I have the silver version with the Bent AVC-1 which Dave made for me and John Chapman supplied the control circuitry).

There is talk that thoriated tungsten filaments (as used in most of the 10's along with several other tubes) are where the good sound comes from. I don't know if this is true but all DHT's are very sensitive to the quality of the heater power supply. You are likely limited to using the Coleman regs, which are very good, but I have used a CCS developed locally that is no longer available, and last time anybody checked is better sounding than the previous generation Coleman regs, although the latest version seems to be well regarded but I not heard them. I don't know how much of my sound is due the the over-the-top filament supply, but I reckon a good portion of it.

In terms of me going cool on my preamp, no, that is not true, I've just had trouble putting it in a box. Plus I need to experiment a bit because my one (new) high output source overloads the input of the preamp and I need to bias it deeper. It is still the best sound in my system, but that is my system, and I am not sure it will be the best fit for your system.

07-01-2022

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	64
Post ID:	26825
Reply to:	26823

Yes but...

anthony wrote:
Well, Romy had great results with the Placette and his Dannoys, so that is the known good solution as far as I am concerned.

If I were in US, I'd definitely try it but not here.

anthony wrote:

Sounds like the 10y will introduce far too much gain which you will have to attenuate thus likely ruining the sound. I mentioned system gain structure earlier, and it is very important, more important than the amplification stages themselves.
The 10y is a bitch of a tube. You cannot wind a good output transformer for it...anyone that tells you they can either are deaf or have very low expectations of sound...so for a preamp we are limited to different output topologies including the mu follower which Ale uses. Trouble with the hybrid mu-follower is that unlike an OPT we end up with all the gain of the tube which in my situation is excellent but in yours not so much. Ale does recommend a resistor divider to attenutate some of the gain and perhaps that is an option should you still go with the 10, but it is still attenuation, and resistor attenuation at that which may or may not be better sounding than letting the Slagle Autoformers do all the attenuating work (I have the silver version with the Bent AVC-1 which Dave made for me and John Chapman supplied the control circuitry).

All well understood of course but I'm massaging the idea, possibly wrong, of making effectively a 801A buffer. "Cheating the physics" with: i) the mu follower taking the job of the load and ii) letting the Slagle magnetics do only the stepdown, without the need for the magnetics to do both jobs, which as you mention is an impossible task given the high plate impedance of 801. By that the usual bass/HF compromise that step down transformer have to struggle with is +/- avoided. Autoformer should actually have an excellent HF, at least on paper, as the coupling does not rely on the magnetic flux with leakage inductances limiting the HF. Of course as you point out at the ~18dB attenuation that I'd need from the autoformer, no idea how well would it perform.
How is the performance of your preamp on lower volumes? That might give a hint if what I'm considering makes sense.
Thanks again, Jarek

Cheers,
Jarek
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07-03-2022

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anthony
Posts 338
Joined on 08-18-2014

Post #:	65
Post ID:	26826
Reply to:	26825

Damnable Type 10's

Jarek,
If you would like some help with this please get in contact with me and I'll help out any way I can. Probably best to not do it on Romy's forum lest it become a diy audio site...
Anthony

07-03-2022

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	66
Post ID:	26827
Reply to:	26826

Thanks goodness we are not soldering resistors ;)

rather discussing a potential of building a tube buffer around 801/10. I'd appreciate your help very much, especially your sound impressions under various conditions. My mail phixphi_AT_gmail.com
Thank you

Cheers,
Jarek
STACORE

08-04-2023

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	67
Post ID:	27193
Reply to:	26827

801A preamp

After eons of construction, I've finally completed my version of the 801A premap, based on Ale Moglia /Bartola Valves design with his Gyrator anode loads, SiC bias and Rod Coleman filament supplies. 6 inputs, switched by an Elma switch and Dave Slagle / Intactaudio TVC on the output to better drive the 5m long IC cables to B2. I'm sorry I'm too lazy to upload the pics, you can find some here: https://www.facebook.com/groups/164921830213087/posts/6808017412570129/ Expectedly, it is a night and day from my previous Yamaha C2 that was temporarily doing the job. The pre is still breaking-in, missing a proper power cord, etc but man it makes magic! It also shows more accurately how Dannoys work, uncovered some problems with a bass in my space, but that is a separate subject. PS is Romy-style with 3300uF caps. I made my life harder being too lazy to add a shorting resistor on power down so have to wait about 10mins after switching the HV off for the caps to discharge. If anyone follows the design, do make that little effort.
There is a space in the chassis (and a ready PS) for a twin TDA1541A DAC I've been cooking simultaneously, hope to finish within a few eons.
Big thanks to Anthony for the inspiration and help!

Cheers,
Jarek
STACORE

08-05-2023

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Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #:	68
Post ID:	27194
Reply to:	27193

With Headphones?

Jarek, congrats on getting a project to where you can listen to it! Are you planning to use this with headpones, or have you used it with headphones? I saw it is "limited" to 5V in, but perhaps enough overall gain with buffer for 'phones"? I realize that 'stats have special requirements; just wondered if this new pre-amp would do yoeoman duty.

Best regards,
Paul S

08-05-2023

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	69
Post ID:	27195
Reply to:	27194

Dannoys

Thanks Paul! No, no, it works with Yamaha B2 and my Dannoys. I continue researching this intriguing project. For the Staxes I do not need a preamp. 5V is a plenty enough for B2 which has 1Vmax sensitivity.

Cheers,
Jarek
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08-05-2023

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Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #:	70
Post ID:	27196
Reply to:	27195

Attenuation?

You may remember I also use transformer shunting for attenuation, in my case the taps are selected by "communications" shunts/relays. My output is quite low R, but variable, and only the transformers for isolation (no "active buffer". I was wondering if your new pre would be a "simple attenuator" that would drive headphones. I have not measured output from my radio's headphone jack, but it drives my Sennheiser HD650s well enough, and then some. I have not yet even tried headphones from my TVC/main system.

Paul S

08-05-2023

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	71
Post ID:	27197
Reply to:	27196

Electrostats

Paul, my headphones are electrostats that need a separate driver. I use Blue Hawaii amp with a quad EL34. The preamp has a direct output from the selector switch, which will be connected to the headphone amp.

Cheers,
Jarek
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08-05-2023

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anthony
Posts 338
Joined on 08-18-2014

Post #:	72
Post ID:	27198
Reply to:	27193

It is alive!

Nice one Jarek! Glad that you have it going.

I've now switched my autoformer to the input as one of my new sources puts out over 10Vrms and I did not want to increase the bias. No real change in sound as far as I can tell. Enjoy.

08-05-2023

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	73
Post ID:	27199
Reply to:	27198

Thank you!

It's quite a marvel from what I can tell now. The overall sound is somewhat on the darker side but the preamp is still breaking in (although I gave it 30h benchtop burn in with the frybaby track). I also suppose it reveals the Dannoy and the room interactions, which Yamaha C2 was masking due to inadequate bass and which I have not optimized yet (the Dannoys sit very close to the floor). The bass is great btw, amazing from such moderate-looking speakers. Plus it's power cord is still burning in and not in the place. And I've been using ordinary, cheap speaker cables. I suspect at this level of resolution all that begins to matter. I'm very happy to have the TVC at the output to run my long cables and given that my sources are not as powerful as yours, in particular TU-X1 tuner needs quite some amplification. I used different parts than you do in some locations, in particular Soviet K40Y-9 and Dale resistors on the gyrator board (Rmu is 5W Mills) and Polish Miflex plastic coupling caps, recommended to me by a prominent Polish audio manufacturer whose sound I know and like (initially I had an eye on the V-caps). The tubes are Hytron VT62, pumping 18mA with 204V on the plates and -6V bias. I also have graphite plate Mazda's 801A, which I haven't tried yet.

Cheers,
Jarek
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08-07-2023

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Romy the Cat

Boston, MA
Posts 10,159
Joined on 05-28-2004

Post #:	74
Post ID:	27200
Reply to:	27199

Get more DB from you tuner

N-set wrote:
…in particular TU-X1 tuner needs quite some amplification….

It is not necessary the case. My TU-X1 has nigh output, no different than all of my other front ends. If you look at the schematics of the TU-X1 then you might find a chip per channel that is responsible for output stage. This chip has feedback and right there will be a trimmer resistor that adjusts the depth of that feedback. I lowered the feedback that sent to this chip and got if I remember correctly 10 or 12 dB more from the TU-X1. Whatever I got I made it to be the same as my Bidat DAC. At that time, I did a lot of experiments to ensure that getting more gain from TU-X1 will not impact its sound. I did not detect any meaningful difference, at least in context of FM broadcasts.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

08-07-2023

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	75
Post ID:	27201
Reply to:	27200

Not necessary now

Thanks Romy. Given the power of 801A preamp, this correction is not necessary. I simply increase the volume compared to my clone of 834 RIAA or other sources and the autoformer at the output is still in the attenuation mode, providing increased output current to drive the long IC's. It's the beauty of having the TVC at the output, I learned from Anthony.

Cheers,
Jarek
STACORE

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