A dream came true - R2R.

[Foxbat]

Well, we should not forget the roots of the 12AX7 design - a low cost phonograph solution, hence its high gain, so you could get enough sensitivity with just two tubes.

That particular board documentation also mentions the possibility of using the Russian 6N2 tubes, but I have no experience with those, and the transformer I had fit the 12V filaments better, so I stayed with them, even though I do have some 6N2's. But someone might try them and let us know.

 

[Kcin]

Thank you for this thread. I am going to build this and let you know how I make out. I will compare it to the de Havilland 222 I have and to the stages in the Marantz 1's and 7.

It looks like a very simple project.

 

[Salectric]

An even simpler tape preamp would use two 12ax7 gain stages without a cathode follower, something like a Dyna PAS.

While I haven’t built a tape head preamp, I have built many tube phono preamps including a number with 12ax7 gain stages, both with a CF and without. A circuit using the 12ax7 can sound very good indeed and shouldn’t be dismissed out of hand. A number of companies today still make phono preamps with a topology similar to the Marantz 7 or ARC SP-3 but often with a different tube for the CF such as a 12au7. One which I’ve read about but haven’t heard is the Tron Silver Reference.

Another option is to use the 12ax7 with a different topology. Back in the 1970s, I built several phono preamps where the input stage was a cascode 12ax7, and at the time I thought they sounded better than cascade designs like the Marantz and ARC. Commercial examples include the Paragon 10 and 12.

Yet another option is to combine a 12ax7 with another tube for the gain stages. An example of that is the Artemis PH-1 which used a 6dj8 with battery bias for the first gain stage, followed by a 12ax7 and a choke-loaded 5687 output stage.

My phono preamp in recent years is very simple. It’s a 2-stage with a D3a for the first gain stage followed by a 5687 with an output transformer. Passive eq between the tubes. No global feedback.

 

[adrianywu]

I prefer the 12AT7 to the 6DJ8 as you can run some current on it (unlike the 12AX7) and you get far better bandwidth (than a 12AX7) since less troubles with stray capacitance.

6DJ8s, 6922 and similar, tend to have more troubles with microphonics as they were not intended for audio. If you change the impedance at the output with a different tube the amount of feedback being presented will be altered.

My preamp is all 6922 family. I use 7308 for the phono/tape head input, cascoded wth a JFET. The 7308 is very quiet.

 

[Foxbat]

The tube noise is represented by its noise resistance, the lower it is, the lower the noise, and that resistance is 2.5/Gm, so the 6922 tube with its high transconductance will be about the quietest tube you can find. Of course in a feedback circuit similar to that of M7 it will be further reduced, making the 12AX7 acceptable.

There are tubes with even higher transconductance than the 6922, such as 6C45, with their huge Gm of 45mA/V, but those tend to have other noise sources, such as grid vibration, so I only use them in the output stages, never in the front.

 

[Atmasphere]

My preamp is all 6922 family. I use 7308 for the phono/tape head input, cascoded wth a JFET. The 7308 is very quiet.

If your circuit is a cascode, I think you'll find that 90% of its noise is coming from the JFET (assuming the JFET is on the bottom).

 

[stellavox]

Thanks All,

There was a great article years back in Audio Amateur (or maybe) Glass Audio comparing different CF topology's. If interested, I'll try to look it up when I return from vacation. DO happen to have had very positive "sonic experience" with the DJ8 and its variants - that is until I switched allegiance to solid state.

 

[Foxbat]

Let us know the issue if you find it, I have many of them.

Both worlds can be fun, no need to switch, but today more people are abandoning tubes. 20 years ago everyone wanted them...

If you ask me, I can't blame them. In my system there seems to be a tube that does very intermittent ping. But figuring out which one out of 64 is not great fun. At least I think it is in the right channel, so just 32.

 

[dminches]

It would be nice if there were some lower cost options for tape preamps.

 

[Tapetech]

It would be nice if there were some lower cost options for tape preamps.

There are: https://www.audionirvana.org/forum/...o-reel/tapestages-repros/150302-new-tapestage

 

[Atmasphere]

It would be nice if there were some lower cost options for tape preamps.

We just renovated an old Leak preamp which had CCIR (IEC1) EQ. Its not that hard to convert a phono preamp to do tape EQ unless several curves are needed (such as NAB, IEC1 and IEC2). Switching is where things get tricky.

 

[dminches]

Victor wanted me to do that with one of his older phono preamp models but I couldn’t find one to work on. I would definitely be game if I had a blueprint on how to do it, including which machine to start with.

I would be fine with just IEC for starters. I am not sure how one performs any calibration for the specific head, though. Maybe that isn’t possible with a phono conversion.

 

[Foxbat]

EAR 834 is, apparently, a good alternative, well respected. The feedback there is very different, though, as it is applied to the grid of the second tube, but that can be changed... however, such a change requires knowledge. Still, a good vehicle, but the prices seem to have moved up.

The Chinese copies are available for under $300 fully assembled, in cases.

 

[Kingrex]

I have the nab/iec from the link post #90. Is Tim still making them?

Its a good device. I don't even need to add a gain device. Seems to have enough without one. You can add one, but your adding a little color. A gain device is any preamp, but usually a headphone amp with preamp outputs.

 

[Atmasphere]

EAR 834 is, apparently, a good alternative, well respected. The feedback there is very different, though, as it is applied to the grid of the second tube, but that can be changed... however, such a change requires knowledge. Still, a good vehicle, but the prices seem to have moved up.

The Chinese copies are available for under $300 fully assembled, in cases.

Feedback to a grid of a tube is a good thing! When its applied to a cathode, the cathode distorts the feedback slightly, causing higher ordered harmonic generation and intermodulations. The resistor divider networks needed for applying the feedback to a grid are a lot more linear so the feedback is more effective at its job with less distortion generation.

 

[stellavox]

Feedback to a grid of a tube is a good thing! When its applied to a cathode, the cathode distorts the feedback slightly, causing higher ordered harmonic generation and intermodulations. The resistor divider networks needed for applying the feedback to a grid are a lot more linear so the feedback is more effective at its job with less distortion generation.

Hey Ralph, GLAD you're joining us.

NOT having enough "fun" with OTL that you now have to get into tape also???

 

[Mike Lavigne]

Andrey from ATR Service INC also offers a mid priced ($9k) very high performance plug in HDV-3 transformerless Triode Tape Repro system for the ATR-102, which can do the EQ switching, and head alignment functions from the front panel of the card.

The HDV-3 is a reproduce amplifier designed to provide a transparent musicalsound stage to the sound of a standard ATR102. HDV-3 is a new improved versionof the HDV-2 predecessor module, a tube playback pre-amp for the ATR-102 tape machine engineered and produced over 25 years ago by Dave Hill (Crane Song Ltd.).

The HDV-3 engineered and produced entirely by the ATR Service, Inc. team. is a two-channel playback system consisting of the highest quality
transformerless dual triode tape head preamp coupled to a solid-state final gain stage. The front-end tube stage provides accurate musical depth, presence and focused midrange that compliments many different musical styles. The HDV-3 is a modular design and plugs directly into the ATR100 motherboard cage and is transparent to the operation of the recorder. The HDV-3 channel outputs can be taken directly at low line level or feed the machine's Input / Output Assemblies. HDV-3 systems operate at 15 IPS NAB / CCIR and 30 IPS AES Equalization. Systems are capable of working with standard ATR-102 playback heads at either 1/2 inch or 1/4-inch tape format versions. The HDV-3 was designed to be a musically accurate amplifier without bias of the technology used. The transformerless tube front end came about after listening tests to different front-end designs and determined to sound the most musical. The unit has front panel control over high frequency head damping which allows to align more accurately the mid and high frequency response curves.

 

[Tapetech]

I have the nab/iec [tape preamp] from the link post #90. Is Tim still making them?

It's a good device. I don't even need to add a gain device. Seems to have enough without one. You can add one, but you're adding a little color. A gain device is any preamp, but usually a headphone amp with preamp outputs.

Right now I am not making the tape preamps but I plan to resume production soon. $2400 for the SS model with RCA outs. $2750 for the Hybrid model (SS and tube). $2900 for the SS, XLR balanced out model.

 

[Atmasphere]

Hey Ralph, GLAD you're joining us.

NOT having enough "fun" with OTL that you now have to get into tape also???

Sort of- I started with tape in 1974 when I put a small recording studio in my basement, where a college friend Steve Tibbetts recorded his second LP, Yr (originally with a black and white hand drawn cover; it was later re-issued on ECM). The machine then was a Tascam, with an Ampex 300 transport with 351 electronics for 2-channel mastering. Later added a 350 transport with the same electronics. I added Neumann mics about 1980 or so, supplementing some tube Phillips mics and a set of RCA 44s.

For on location I used an Ampex 350 machine, but refurbished a Magnecord 728 and used that since it was a bit more portable. Later that was replaced by a refurbished Magnecord 1028. I used the Ampex in my home stereo and maintained that until about 2010.

The studio has long since had its own location. These days the tape machines are Studer, Sony, Otari and a 16 channel Tascam.

Tape EQ has been an option on our preamps for the last 10-12 years.

 

[stellavox]

Sort of- I started with tape in 1974 when I put a small recording studio in my basement, where a college friend Steve Tibbetts recorded his second LP, Yr (originally with a black and white hand drawn cover; it was later re-issued on ECM). The machine then was a Tascam, with an Ampex 300 transport with 351 electronics for 2-channel mastering. Later added a 350 transport with the same electronics. I added Neumann mics about 1980 or so, supplementing some tube Phillips mics and a set of RCA 44s.

For on location I used an Ampex 350 machine, but refurbished a Magnecord 728 and used that since it was a bit more portable. Later that was replaced by a refurbished Magnecord 1028. I used the Ampex in my home stereo and maintained that until about 2010.

The studio has long since had its own location. These days the tape machines are Studer, Sony, Otari and a 16 channel Tascam.

Tape EQ has been an option on our preamps for the last 10-12 years.

Thanks for the heads-up that tape EQ is available for/in your preamps - PLUS, if I'm not mistaken, your low-level inputs are all BALANCED (electronic not transformer) - as all magnetic inputs should be!