• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

Introducing Tavish Design

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
T

TavishDad

Member
Joined 2014
Tavish Design Classic Vacuum Tube Phono Stage (MM / MC) Kit

Tavish Design is a small (2-person, father-son, for now) audio component business based in New York State. We make what we sell. We’ve just introduced our first product in kit form, a vacuum tube phono stage (moving magnet & moving coil) that is simple, attractive, and inexpensive, yet offers very high performance. The phono stage is available in a variety of ways; as a bare circuit board with instructions, a complete kit with enclosure, or an assembled product. The assembly and setup manual (including schematics and parts lists) is a free download, even if you don’t buy anything.

There are other products on our website, and we’ll be introducing several more kits in the near future. Please let us know if you’d like to see the kit in other forms (e.g. parts w/o enclosure, etc.), or if there are other kits you’d like to see.

I’m an electrical engineer with more than 25 years of industry experience, and I’ve also been an amateur audiophile and DIYer for more than 35 years. I hope you’ll check out our website and let us know what you think.

Of course, I’ll monitor this thread on diyaudio, but for a faster response you can always contact us at:

info@tavishdesign.com
Tavish Design
Scott
 
Last edited:
T

TavishDad

Member
Joined 2014
In response to a couple of inquiries, we’ve just made our vacuum tube phono stage kit available in an additional format, as a complete kit, but without the enclosure – for those who would like to use their own enclosure.

So, the Classic Phono Stage is now available as a bare circuit board with instructions, as complete kit with or without the enclosure, or as an assembled product.

The assembly and setup manual (including schematics, parts lists, and measurements) is a free download, even if you don’t buy anything.

The assembled product (and kits) now ship to USA & Canada. The circuit board ships anywhere (please contact us if you don’t see a shipping option for your location). We’re also considering an export version of the kits, so contact us (or respond to this forum), if that might be of interest.

Finally, the Classic Phono Stage uses the 5751, 12AX7, and 12AU7 tubes. We considering a variant that uses the popular 6SL7GT – and we’re testing current production 6SL7s to see if they have low enough noise for our product.

How much interest in a 6SL7 – based phono stage?

Classic Vacuum Tube Phono Stage (MM / MC) – Tavish Design

Scott
 
T

TavishDad

Member
Joined 2014
Raffle

We’d like your feedback on our products and website, and so we’re holding a raffle, as other vendors on this forum have done in the past. For the every 20 readers who post a question, constructive feedback, or suggestion for a future product on this thread, we’ll give away a free Classic Phono Stage PCB (including free postal shipping up to $10), up to 4 PCBs. The winner will be selected at random from the 20 posts. And we’ll give away at least 1 board per month, so if there is only one post in a month, that’s the winner (no posts = no winner…….).

Previous customers have been entered into their own “raffle” with even better odds (thanks!).

Classic Vacuum Tube Phono Stage (MM / MC) – Tavish Design

Scott
 
T

TavishDad

Member
Joined 2014
IwanS said:
Very interesting hybrid amplifier. I don't suppose you would post the schematics for that? :)

Iwan
Click to expand...


Thanks. There are lots of hybrid amps out there, but the Minotaur is one of very few on the market that are direct-coupled. But it is a complicated piece of hardware, and I don’t see any practical way to offer it as a kit.

But I have been considering a simpler, lower power, lower cost, direct-coupled hybrid that could be offered in kit form. Of course, I’d post the schematics for that. I opened a thread on diyaudio to discuss the circuit idea (which could be a power amp or headphone amp), but it didn’t get much attention.

http://www.diyaudio.com/forums/tube...d-tube-tube-mosfet-headphone-amp-circuit.html

Scott
 
T

TavishDad

Member
Joined 2014
rayma said:
Can you discuss the decision in your phono stage to have the 75uS after the second stage,
instead of after the first stage?
Click to expand...

Thanks. That’s sort of two questions, and I’m not sure which one you are asking.

I split the RIAA EQ into two sections, instead of one as in the classic RCA circuit, because I found it easier to get consistently accurate equalization over variations in tube characteristics. For a given set of tubes, the equalization can be trimmed as accurately as your inverse RIAA network will allow. But tubes vary in their plate resistance and input impedance (variations in input impedance are less often discussed), and coming up with a set of component values that work well for all tubes is complicated. Splitting the EQ into two parts makes it simpler and gives more freedom for component value selection.

The next question is whether to put the 318us or 75us first. The 318us time constant is a shelving filter that falls at 20dB/decade from 50 to 500Hz, then attenuates signals above 500Hz by a constant 20dB. The 75us circuit is a low-pass filter that attenuates signals above 2.1kHz by 20dB/decade. So signals below 21kHz will be attenuated by less than 20dB. Therefore, putting the 318us section first gives more overload margin for signals in the audio range.

But tubes have a lot of overload margin, and I’ve seen it done successfully both ways.

Scott
 
T

TavishDad

Member
Joined 2014
rayma said:
How about noise in the two cases?
Click to expand...

Another good question. If the RIAA EQ is split into two sections, which one comes first can affect the noise level in some cases.

In the case of the Classic Phono Stage, the first stage has a gain of about 45, or 33dB, so the noise from the passive plate load resistor and RIAA EQ network is suppressed by that amount. And the noise of the second stage is suppressed by 33dB – 20dB = 13dB or 4.5x, where 20dB is the attenuation of the 318us shelving filter. So the overall noise level is dominated by the input-referred noise of the first stage, which is what you want.

But you can see from the above calculation that if you had a low gain first stage combined with the 20dB loss from the 318us shelving filter, the noise of the second stage might become important. So if you have a noisy second stage and/or a low gain first stage, you might want to consider putting the 75us low-pass filter first. But that comes at the expense of poorer overload margin, as I discussed in the earlier post.

The Classic Phono Stage has very low noise. I measured a lot of tubes to find the lowest noise current-production tube to use in the first stage, and I am currently using a JJ 5751 (other 12AX7 types also work fine).

Thanks for the words of support SY!
Scott
 
T

TavishDad

Member
Joined 2014
jackinnj said:
Looking at the schematic -- is the transformer happy in this orientation. I had one which ran hot.
Click to expand...

Hi Jack. Thanks for asking.

The toroidal step-up transformer barely even gets warm. Total current from the HV supply is <15mA, or around 3.3W. The transformer dissipates ~2W as heat, which is very little for a transformer this size.

The overall phono stage consumes ~15W, mostly heater power, with some inefficiency in the linear heater regulator. So it is fairly efficient as vacuum tube circuits go. The wall transformer also runs cool.

Scott
 
T

TavishDad

Member
Joined 2014
Tavish Design Vacation Aug 1 - Aug 9

Quip said:
The Minotaur; was thinking of the graphs for LF distortion and IMD. Is the design cap-coupled or DC-coupled? Just curious.
Click to expand...

Ok, I'll post some plots of distortion vs level and frequency.

The Minotaur is Direct-Coupled, except for a single blocking capacitor at the input. I added that cap to prevent a DC offset from the source from being applied to the amplifier.

The amplifier has the same output DC-offset protection that a standard transistor amp does, and it also has a system microcontroller controlling bias and offset. It has been several years in testing and I believe it has very high reliability. You can even pull a tube out while it is operating, and the output relay opens with no drama or damage.

Thanks for asking!

My son & I will both be away on vacation this week, so I'll post the graphs when we return on Aug 10.

Scott
 
T

TavishDad

Member
Joined 2014
Minotaur Direct Coupled Hybrid Amp

Quip said:
The Minotaur; was thinking of the graphs for LF distortion and IMD. Is the design cap-coupled or DC-coupled? Just curious.
Click to expand...

We're back from vacation. In response to Quip's request, my son measured the Minotaur distortion levels vs power (from 0.1W up to 140W into 8 ohms), at four different frequencies (25 Hz up to 20 kHz). He also captured some distortion spectra using the Picoscope 4262. I've updated the Minotaur owner's manual, adding an appendix to include these plots.

Minotaur Direct-Coupled Hybrid Integrated Amplifier – Tavish Design

For a hybrid amp with a predominantly vacuum tube signal path and only 24 dB of negative feedback, I think the results are pretty good.

Thanks for asking.
Scott
 

Attachments

  • minotaur_thd.jpg
    minotaur_thd.jpg
    426.9 KB · Views: 420
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom