New tape pre-amp king!!

[Ki Choi]

Just picked-up a well-optioned HP 35665A DSA for fun.
Thought you might appreciate it
Oh! Also, met Harry -- very gregarious...thanks for putting us in touch!

With you new big boy toy, I can see you staying up at late nights to take measurements of "power spectral density" of incoming AC power for your Studer.

After several years of emails back and forth, I met Harry in person at one of the RMAFs. Great guy and crazy tapehead like us.

 

[c1ferrari]

With you new big boy toy, I can see you staying up at late nights to take measurements of "power spectral density" of incoming AC power for your Studer.

After several years of emails back and forth, I met Harry in person at one of the RMAFs. Great guy and crazy tapehead like us.

Well, it'll have to do until a reasonable and well-optioned R&S UPV or SRS SR1 become available
A few of us down here are unabashedly, certifiably, tape-endorphin-experiencing, disciples of sound!

 

[Bruce B]

Got the tubes in and umbilicals connected. Love the soft glow of tubes!!

 

[c1ferrari]

Got the tubes in and umbilicals connected. Love the soft glow of tubes!!
View attachment 8596

Ah...that's nice, Bruce.
I'd like to hear Nick's gear, sometime.
Congrats!

 

[Ki Choi]

Got the tubes in and umbilicals connected. Love the soft glow of tubes!!

Here's what the doctor ordered, Dr. Brown that is:

The custom brackets for A80RC made for Neutrik XLRs for the Doshi's "direct differential inputs" and Neutrik RCAs to feed King/Cello's unbalanced tape head preamps.

I think they look like "made up north" as we used to say in North Carolina. They need nice labels next and it will be time to make the house call to the doctor's place.

 

[rockitman]

Here's what the doctor ordered, Dr. Brown that is:

The custom brackets for A80RC made for Neutrik XLRs for the Doshi's "direct differential inputs" and Neutrik RCAs to feed King/Cello's unbalanced tape head preamps.

I think they look like "made up north" as we used to say in North Carolina. They need nice labels next and it will be time to make the house call to the doctor's place.

I don't tweet, but I sure do like !!!!
To have both options is a dream !

 

[rockitman]

Got the tubes in and umbilicals connected. Love the soft glow of tubes!!



View attachment 8596

ahem...so how does it sound ? Still on a honeymoon ?

 

[doshiaudio]

Hello,
Thought I might chime in since there seems to be some interest in this right now. I typically do not interfere in equipment threads because it is the users forum. Anyway .....

The units for Bruce are significantly different from the units that I demoed at RMAF. Bruce's requirements for level and eq calibration required me to figure out a way to achieve his needs and my requirement for audio quality !

So, to specifically answer a couple of issues, the input chip is indeed the ssm2019, I did significant listening to the head amplifier from the RMAF unit which was built around a discrete low noise pair of transistors on the front end and this preamplifier and found that this chip offered sound quality comparable to discrete if properly implemented, additionally, i was able to drive 2 eq sections directly without a follower and coupling caps etc so as in life, there are pros and cons, its just a matter of making a informed choice.
As far as feedback is concerned, even a tube with a cathode resistor has a certain amount of local feedback. The proof should be in what sounds good. I'm not talented enough to build a unit with a lot of feedback so I tend to stay away from it ;-)
Lastly, there have been some posts regarding input transformers, In my experience, I have found that either approach when properly engineered is capable of superlative results, it is however, a little harder to interface transformers to a large variance of head types since the power transfer is optimal around one set of values.
On a personal note, thanks to all on these forums for the kind words over the years. keep listening !!

 

[steve williams]

Hello,
Thought I might chime in since there seems to be some interest in this right now. I typically do not interfere in equipment threads because it is the users forum. Anyway .....

The units for Bruce are significantly different from the units that I demoed at RMAF. Bruce's requirements for level and eq calibration required me to figure out a way to achieve his needs and my requirement for audio quality !

So, to specifically answer a couple of issues, the input chip is indeed the ssm2019, I did significant listening to the head amplifier from the RMAF unit which was built around a discrete low noise pair of transistors on the front end and this preamplifier and found that this chip offered sound quality comparable to discrete if properly implemented, additionally, i was able to drive 2 eq sections directly without a follower and coupling caps etc so as in life, there are pros and cons, its just a matter of making a informed choice.
As far as feedback is concerned, even a tube with a cathode resistor has a certain amount of local feedback. The proof should be in what sounds good. I'm not talented enough to build a unit with a lot of feedback so I tend to stay away from it ;-)
Lastly, there have been some posts regarding input transformers, In my experience, I have found that either approach when properly engineered is capable of superlative results, it is however, a little harder to interface transformers to a large variance of head types since the power transfer is optimal around one set of values.
On a personal note, thanks to all on these forums for the kind words over the years. keep listening !!

Hi Nick and a big welcome to WBF. We value your comments here but we don't want you hanging out too long here because it will take away precious time from building more of these units for those of us who have been waiting

 

[c1ferrari]

Greetings, Nick,

Thanks for the elucidating post.
I hope to have some quality time listening to your gear at some point.

Congratulations!

 

[Bruce B]

Hello,
Thought I might chime in since there seems to be some interest in this right now. I typically do not interfere in equipment threads because it is the users forum. !

Welcome Nick.... thank you so much for educating us mortals. This is your piece so any information you could give would be highly appreciated!

 

[Bruce B]

ahem...so how does it sound ? Still on a honeymoon ?

Waiting for Ki to insert the balanced connections.....

 

[steve williams]

Waiting for Ki to insert the balanced connections.....

curious as to why Nick didn't do this Bruce

 

[Bruce B]

curious as to why Nick didn't do this Bruce

Nick has balanced connections.... the Studer doesn't. Ki put SE connectors on my Studer years ago and I didn't want to use adapters.

 

[steve williams]

Oh on your A80. I thought you meant the new unit

 

[Bruce B]

Oh on your A80. I thought you meant the new unit

Corrrect.... on the A80RC... see Ki's post #45 above.

 

[Bruce B]

HOLY CRAPOLA' BATMAN!!!

Our friend and in-house Studer Guru, Ki , spent the afternoon changing out the back SE connection to an XLR on the A80RC and got the Doshi fired up. He left and I got to calibrating the outputs and HF on the Doshi. This thing has tons of gain and it's QUIET AS A CHURCH MOUSE! For the gain, I set it at 1.25v... I think I could get a maximum of over 3v output! I set the HF for 10k and started doing come critical listening.
Was listening to Ellington/Hodges, Fleetwood Mac, Bob Marley and a few others. On each and every one of them, the gain was matched to within .1db and I can switch between internal and external.
Definitely the Doshi is better in every way. On the Marley and Ellington/Hodges, the internal electronics gives it a little darker sound and the Doshi brings out all the details. It's such a change that anyone could pick it out in a DBT.
Tried something else... Fed a DSD128fs file into the Studer and monitored off the heads spinning tape. I can switch back and forth between the DAC and the tape output and I definitely prefer the tape output. Again, same results! This thing does MAGIC!

 

[rockitman]

soundz like fun man....

 

[c1ferrari]

Tried something else...Fed a DSD128fs file into the Studer and monitored off the heads spinning tape. I can switch back and forth between the DAC and the tape output and I definitely prefer the tape output.

I infer if you recorded a DSD128 file on tape and played it back through the Doshi -- AND you preferred tape, then the transfer wasn't entirely neutral?

 

[doshiaudio]

I infer if you recorded a DSD128 file on tape and played it back through the Doshi -- AND you preferred tape, then the transfer wasn't entirely neutral?

I would not expect a tape pass through to be entirely neutral. Tape will add gentle compression and extremely low level dither to the audio thereby gently compressing dynamic range. This process adds warmth and lifts detail slightly. Those are characteristics that lead a lot of musicians to run their mixes through a tape machine and/or purchase software that emulates several famous tape paths.

In my design, one of the biggest differences over a standard studer electronics path is that (if my memory serves me right) - no input / output transformers and no eq in a feedback loop. The latter, i feel, contributes to a more open/dynamic sound. I observed the same characteristics when auditioning the unit at my listening room with a stock technics RS-1500 head vs my stock Studer A-810 (trafoless outputs) and Sony APR 5003. I was surprised at the amount of detail and resolution existed in tapes that i had heard many times. On a Varese track the effect was spooky and kind of frightening!