doshi tape pre users?

Just a correction: I emailed with Nick today and his tape preamp DOES have SE inputs (good!!) - but he himself still prefers balanced for the 6db improvement in SN. Maybe one day I'll go balanced all the way with the R2R.
 
Mike said:
Just a correction: I emailed with Nick today and his tape preamp DOES have SE inputs (good!!) - but he himself still prefers balanced for the 6db improvement in SN. Maybe one day I'll go balanced all the way with the R2R.
Click to expand...

You do get 6dB more gain and you do achieve less noise, but I'm not sure the noise drops by the 6dB of extra gain you achieve by going balanced.
 
mep said:
You do get 6dB more gain and you do achieve less noise, but I'm not sure the noise drops by the 6dB of extra gain you achieve by going balanced.
Click to expand...

Here's what Nick said: "The
advantages of 6 db better S/N ratio and common mode noise rejection
are lost if the head is wired SE."


Sent from my iPhone using Tapatalk
 
Mike said:
Here's what Nick said: "The
advantages of 6 db better S/N ratio and common mode noise rejection
are lost if the head is wired SE."


Sent from my iPhone using Tapatalk
Click to expand...

I could be dead wrong and I probably am, but what I think Nick is saying is that you by using balanced connections you have achieved 6dB more gain compared to the unbalanced connections referenced to the same S/N ratio.
 
mep said:
Bruce-It's going to vary by tape head.
Click to expand...


IIRC correctly head inductance will typically vary from 200 to 500 millihenries. (?) (Wish Bruce or Ki was around.)That's why the better tape pres like Nick or Charlies give you adjustable gain. For instance, the King-Cello give one the choice of 40-50-60 dB of gain.

Nick's unit is a bit more sophisticated but even the King-Cello will give you high frequency adjustability to compensate for tape head wear as well as the ability to smooth out the head bump (yes, Bruce and I had a discussion over whether that is an advantage or disadvantage.)
 
My Bottlehead prepro which predates most of the ones being mentioned here has both unbalanced RCA and balanced XLR outputs. They cannot be used at the same time and the balanced is 6db more gain than the RCA's. When ripping my R2R tapes, I feed the balanced lines directly into my PM Model 2.

Larry
 
Doshi Preamp (earlier generation but new to me) has arrived. Pic is of the tape pre. PSU is in a separate stainless chassis with umbilicals to the tape pre
Excited to try it in the system this weekend.
photo.JPG
 
Wow! Congrats! Look forward to your impressions.


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tunes said:
I've a used earlier generation doshi tape pre incoming from nick and wondering if there are other doshi tape pre owners on the forum. Nick has been generous with his efforts to wire up and align the headblock of my nagra t and install a int/ext switch to operate his tape pre or the internal nagra electronics. Super excited to try it out. Couple of pics of Nick's excellent wiring job!
Chris
Click to expand...

Above photos are significant. Nagra's repro head is originally capable of balanced interface to external preamps with balanced inputs. However, their own factory tapehead preamp has unbalanced inputs as you can see the connections to the record head's single conductor shielded cables for both channels. So as Nagra T was originally designed, cold leg of repro head wire was tied to signal shied and works as ground going through the headblock connections and using the same cable all the way to the internal preamp board.

When I sent the machine to Chris, I left the head to the preamp board wiring alone to maintain its original configuration, mounted the switch in the photo, and installed the XLR connectors while connecting signal grounds and shields together in unbalanced configuration. It worked fine with King Cello, Cello Audio Suite P603/P301, and Manley Tapehead preamp and Doshi tape preamp in unbalanced configuration but wasn't technically ideal for Nick's preamp with fully balanced input circuit.

Thus, it is important to note that Nick had gone all the way up to the repro head to separate signal cold wire from signal ground using two conductor shielded cables (see new red and white color cables) to the headblock connectors, then the other side of headblock connectors to the 4PDT switch and then back to the factory board and to XLR connectors for fully balanced interface.

In all of Studer head rewiring work, the head to factory preamp connections are already fully balanced using two conductor shielded cable throughout. Balanced XLR connections from the head to the XLR outputs for Studer A80RC is the cleanest IMO.

Ki
 
Myles B. Astor said:
Mike I double checked with Nick because I thought his units came with balanced and unbalanced inputs. Apparently there was some miscommunication. Here's his response.

That's the beauty of a differential input
It can be used either way , I provide both xlr and RCA inputs on the unit , if the signal from the transport is ground referenced, simply wire the output to an RCA connection and use it that way,
A tape head ( and mc cart) are differential devices in that they respond to changes in magnetic fields by generating a voltage on both ends of the winding that are equal in magnitude and opposite in polarity
When you choose to amplify this signal you can do it by referencing one of the poles to ground ( s.e) or you can chose to do it differentially (amplify only the difference between the two poles)

The advantages of the latter are that any common mode signal induced into the chain via electromagnetic interference is cancelled out, additionally by amplifying the difference voltage you get an additional 6db of gain over referencing one of the poles to ground, lastly any noise carried on the ground (rfi) is isolated from the amplification chain
Click to expand...

Thanks for sharing this info :scholar:
 
Ki Choi said:
In all of Studer head rewiring work, the head to factory preamp connections are already fully balanced using two conductor shielded cable throughout. Balanced XLR connections from the head to the XLR outputs for Studer A80RC is the cleanest IMO. Ki
Click to expand...

I just e-mailed Martin Berner a few questions. Perhaps, I can contribute to this thread upon his reply.
 
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