[paradoxper]

I gladly will, BUT...the SR1a that you own (thank you!) need the open baffle EQ.
There was no plan to provide the built-in passive EQ inside the transformer interface box, as that would introduce a drop of 4.5dB of SPL and there's not enough power available (except with your amp) to have this drop and still have a rewarding SPL.
The idea is to offer the transformer interface only without EQ circuit, basically limit it's usability to SR2a only, as there will be no penalty in SPL with 5-6W/32 Ohms amps.

However, you could use a passive line-level EQ circuit at your RCA input. Can be made as a female-male RCA adapter that you plug into your amp's input and then plug you RCA interconnecting cable in it.

if that would be a product thatpeople might be interested in, I'm willing to work on it.

Yes, the interface is used with CFA3 for SR1a. The transformer interface will only be used for SR2a. Aside from direct-drive amplification alternatives that negate any interface.

 

[normie610]

I gladly will, BUT...the SR1a that you own (thank you!) need the open baffle EQ.
There was no plan to provide the built-in passive EQ inside the transformer interface box, as that would introduce a drop of 4.5dB of SPL and there's not enough power available (except with your amp) to have this drop and still have a rewarding SPL.
The idea is to offer the transformer interface only without EQ circuit, basically limit it's usability to SR2a only, as there will be no penalty in SPL with 5-6W/32 Ohms amps.

However, you could use a passive line-level EQ circuit at your RCA input. Can be made as a female-male RCA adapter that you plug into your amp's input and then plug you RCA interconnecting cable in it.

if that would be a product thatpeople might be interested in, I'm willing to work on it.

Using PEQ in the digital domain really elevates SR1a even higher. Best sound I’ve ever heard….ribbon is definitely THE way

 

[Aleksandar R.]

Yes, the interface is used with CFA3 for SR1a. The transformer interface will only be used for SR2a. Aside from direct-drive amplification alternatives that negate any interface.

Then we have a deal!

 

[paradoxper]

Then we have a deal!

Obliged. If you didn't mind, a U.S. sample may be tested by various people as we've established a fair CFA3 base. A few more overseas if the more help establish a baseline. It's your show.

 

[deafenears]

There was no plan to provide the built-in passive EQ inside the transformer interface box, as that would introduce a drop of 4.5dB of SPL and there's not enough power available (except with your amp) to have this drop and still have a rewarding SPL.
The idea is to offer the transformer interface only without EQ circuit, basically limit it's usability to SR2a only, as there will be no penalty in SPL with 5-6W/32 Ohms amps.

However, you could use a passive line-level EQ circuit at your RCA input. Can be made as a female-male RCA adapter that you plug into your amp's input and then plug you RCA interconnecting cable in it.

if that would be a product thatpeople might be interested in, I'm willing to work on it.

Yes, I would be interested in something like that where the transformer interface box is without the EQ circuit for use with just the SR2a only and option for passive line-level EQ circuit at the RCA input.

 

[BBBpin]

No manual adjustment, all auto. Has to be like that, as toroidal output transformers are very easy to saturate with bias unsymmetry. The transformers are designed by Menno van der Veen and we have strictly followed the recommendation about autobias.

I can say about Vandeveen transformers is that they have the least sound of "iron" I've ever experienced! Also, the response at the end of the bandwidth (~32kHz) is a very nice and wide low-Q knee, without any traces of ringing. A very remarkable achievement for a 100 :1 transformer (10000x impedance conversion) for both bandwidth and lack of parasitic reactive components. It's bonkers and it sounds like an OTL with ba..s!
As the loading of the transformers is basically the cable resistance of 0.4 Ohms, we've made sure that cable parasitic Inductance is kept to a minimum, the same requirement as for the JotR. Not recommended to use with any other cables, as the cable is the actual load (ribbon is only 0.018 ohms) and you don't want unknown inductance to be multiplied 10000x and load the anodes as voltage-spiking reactance.

The amp is Class AB (70% of possible swing is class A) Push-Pull with a pair of EL34's, driven with high current/voltage swing capability of another EL34 that doubles as a phase splitter.
The input tube is 6SL7 triode, loaded with a CCS.
No overall feedback.
Output power at 0.4 Ohms is 21 Watts, about 3dB higher than what SR1a and SR2a can use cleanly, so basically, it all works in Class A, until you overload the headphones.
Input is only XLR with awesome Cinemag transformers, for audio ground isolation from source gnd and best possible CMRR.

Initially, we've had the speaker output, BUT...the sound of the feedbackless amp was so enchanting on SR1a that we ditched the speaker output as that can't work without feedback.
So, audio purity at it's finest all the way!
The one that got broken in shipping to the show was my piece and I'm still weeping over it's sudden death! However, it's martyrdom made me redesign the transformers mounting and it will be rock solid, worthy of MIL-spec hardware. Also, packaging is getting redesigned so it will arrive safely to any point on the planet, with all modes of transport.

We're really rushing to get the VM-1a into sales, and we'll do everything humanly possible to shorten that amount of time!

Again, circuitry is designed by Solaja Audio, with parts choice input by Danny and me and the sound is brought to the very summit through several iterations. And I'm so glad we all did it!

Can you add speaker output function if you make feedback on off switch?
And can the VM-1a be used with conventional headphones?

 

[Aleksandar R.]

The trouble with that is if you flip the feedback switch while the amp is on, you'll get large pops and bangs and you are likely to do damage to speakers or headphones.

Also, we're not fond on having any type of feedback to depend on switch reliability. If there would be any deposit on contacts after a while, things may go drifting, making noises, even channel imbalance...We prefer normally soldered traces and component leads with anything feedback related.

Now, even if this is not a real issue, that we're just too cautious, there is a problem of open loop vs. closed loop amplifier gain.
With feedback on, and if it's 20dB, the amp will loose 20dB of gain, so we would need another voltage gain stage stage to get the gain back...

With feedback off, you have too much gain, the volume pot never above 9 o'clock, and there is one stage too many in the circuit.

I mean, all of that can be made to work correctly, but it just didn't seem to be a nice, simple and pure concept, with that unnecessary extra stage in the circuit, when we're focusing on ribbon headphones.

As for conventional headphones, it doesn't work right, simply because of the noise. This is actually a kind of a "loudspeaker" power output, designed to pump out 7+ Amps of current into the headphones. Because it's a normal power amp, it doesn't have low enough noise floor for highly senstitive transducer that you stick close to your ear.
It would literally be like connecting a speaker that has 130dB/W to a speaker tube amp, so the hum and buzz would be ever-present and very annoying.

Granted, feedback would reduce that to a very low level, but then the point is lost. You're listening to ribbon headphones without feedback, but have to use it for all other headphones. It wouldn't be the same sound at all.

So, it comes down to horses for courses, and this is a one trick pony...but no other pony can do that trick and that's just the trick we need

 

[Aleksandar R.]

Yes, I would be interested in something like that where the transformer interface box is without the EQ circuit for use with just the SR2a only and option for passive line-level EQ circuit at the RCA input.

Okay, Sir! We'll make that a product.
For now, I see no reason that balanced XLR version couldn't be made, so that's another option.
It will provide the SR1a owners the opportunity to explore the transformer interface.
It will prevent the need to use an inductor/resistor EQ at power level in the primary circuit of the transformer and a reliable switch that turns it on and off.
It will keep the amp in direct connection to the transformer without a reactive circuit in between.

 

[FLTWS]

"The input tube is 6SL7 triode, loaded with a CCS."

Constant Current Source(?)

 

[Aleksandar R.]

"The input tube is 6SL7 triode, loaded with a CCS."

Constant Current Source(?)

Yes.

 

[FLTWS]

Something else I'm thinking. Output transformers on all tube amps I have familiarity over the years with do not like to be operated without a load across their outputs, could cause damage to them.
That scenario will apply to the VM-1a as well?

 

[Aleksandar R.]

Yes, as a general precaution. Point being to not send signal into unloaded xfmr, so just bringing the attenuator down is enough to be completely safe. Don't need to completely turn it off when plugging/unplugging headphones or turning it on. It can be turned on without the headphones plugged in if the Att. is all the way down.
When switching the Vari-Mode, it has to be off before you make the change. Unfortunately, Auto-bias takes about one minute to get up and running, so there's that delay when comparing the sound of different modes.

 

[dolstein]

Yes, as a general precaution. Point being to not send signal into unloaded xfmr, so just bringing the attenuator down is enough to be completely safe. Don't need to completely turn it off when plugging/unplugging headphones or turning it on. It can be turned on without the headphones plugged in if the Att. is all the way down.
When switching the Vari-Mode, it has to be off before you make the change. Unfortunately, Auto-bias takes about one minute to get up and running, so there's that delay when comparing the sound of different modes.

Aleksandar -

I understand that the HSA-1b has an improved volume control as compared to the discontinued HSA-1a amplifier, and works with both the SR1a's and conventional headphones. But one thing I liked about the HSA-1a feature set was the ability to drive two pairs of SRA1a's. When the HSA-1b is switched to SR1 playback, is the headphone output marked "Conventional HP" capable of driving a second pair of SRA1a's with a XLR Female to XLR Male adapter? If not, have you considered offering a direct drive amp that has the improved volume control of the HSA-1b but, like the HSA-1a, was designed to drive two pairs fo SRA1a's?

 

[jlbrach]

I cannot imagine there is enough of a market to produce a product simply to drive 2 pairs of sr1a at once

 

[Aleksandar R.]

Aleksandar -

I understand that the HSA-1b has an improved volume control as compared to the discontinued HSA-1a amplifier, and works with both the SR1a's and conventional headphones. But one thing I liked about the HSA-1a feature set was the ability to drive two pairs of SRA1a's. When the HSA-1b is switched to SR1 playback, is the headphone output marked "Conventional HP" capable of driving a second pair of SRA1a's with a XLR Female to XLR Male adapter? If not, have you considered offering a direct drive amp that has the improved volume control of the HSA-1b but, like the HSA-1a, was designed to drive two pairs fo SRA1a's?

Hi dolstein,

Sure, HSA-1b can drive two or more sets of ribbon headphones with a paralleling adapter.
We've had a number of requests to drive conventional headphones besides our ribbons, increasing the functionality of the amp. Actually, for a significant number of people that was a condition for purchase, so it was a no brainer.