It is interesting you are mentioning RCA BA-21a because such outputs sound pretty different from anode followers. I'm working on something similar, it is fully push-pull preamp. First stage consists of ECC83 i'm going to change for 12AY7 (NFB allows achieving similar level at the output), output has 6N6P although i will try to get 6N30P if price is right. Do you find new production EH or Sovtek matched enough not to cause problems? I see you like RCA BA-21a, how do they sound to you compared to anode follower outputs (Redd47, Ian's TLA, RCA-BA2, etc)? I know this is a bit like apples and oranges because we didn't use same transformers..
I have extensive experiences with Cinemag only (some known Jensens are based on their designs), then some with Sowter and a bit with others. Differences between Cinemag's best or cheapest transformers are pretty big because they have extensive catalogue and wind for a long time. It seems we finally got a source for RCA like transformers (A-10, A-24, etc) because someone from Poland is making them. People who compared them to original so far seem happy, can't wait to try them.
Yes cathode follower with a ccs sound very clean. Even more if you bootstrap another CF on top of the main one.
For me it is the cleanest stage i've heard with small signal tube. Some may argue it is 'cheated' ( ss ccs- depletion mosfet) so let's say it's no more tube but hybrid.
This kind of approach i find interesting when i want headroom and nice transient behavior ( advantage to have high voltage rails for me) with no global feedback.
This is a modern approach.
The historical ones are attractive to me too, they have a different rendering, esthetic. I like it too.
The Ba21a is not very coloured like older Rca design (single ended from 40's and before) but it have a sound still. It's a stange approach in a way: three stage with 20db global nfb ( with a dedicated out from the out transfo), first stage is a transformer input grounded cathode single ended ( nfb entry on cathode) followed by a phase splitter ( 'concertina' circuit iirc) then a push pull transformer coupled out.
Input transformer is close to A10 from what i've read. The output one is the one with 'character' from my experiment with the circuit.
About sound, it remain me from 50's/60's jazz recording ( Miles Davis, Brubeck,...). With ribbon mic on close micing( Coles and AEA) and tube mic (close mic and more distant location -my own version of U47 and M49) it is a wayback machine.
With cartdrige i tried with my mc ( 310mc) but i cheated: i have an SL10 in which there is an integrated preamp to bring the mc out voltage into mm territory in order to attack an mm pre which will take care of riaa and final voltage gain.
I bypassed it and integrated the ba21a in place of it. Sound nice. Different from the SL10 internal one and the RJM's Phonoclone i use the mc with usually. If i had a passive rlc Riaa i could use a whole tube chain with 1xba21a -passive riaa- 1xba21a. It should have more 'sound'.
I still crave for the phonoclone though ( it is good with everything, tube sound more...tubey and is sometime too much for my preference with electronic music).
In this video i identify the sound i like about it ( start at 1mn):
Difference with older Rca design comes from transfo, sure but from general design too: single ended without global nfb have different sound imprint. Especially when they are pushed, distortion sound different. It's nice too and remind from 40's recording. Suit well bluegrass, blues,classic rock'n roll, old school R&B, gospel,... i like them too!
For new prod 6h30p there was some shop which offered balanced and pairing options in UK. I'll try to find them in my bookmark but it's been a while since i ordered them ( maybe Watford Valves?) So i don't know at the moment. The need for this will depend of your circuit, design.
Is it Moby you are talking about (A10/A24)?
For older UTC iron, Cinemag offer their own version. I've been in communication with them about some for a ba2( or another ref but an older one edit: Ba2c) i planned. I agree there is difference in Cinemag i own ( mostly mic tube out). But overall i find older transformers to have stronger character, this was my point.
For me it is the cleanest stage i've heard with small signal tube. Some may argue it is 'cheated' ( ss ccs- depletion mosfet) so let's say it's no more tube but hybrid.
This kind of approach i find interesting when i want headroom and nice transient behavior ( advantage to have high voltage rails for me) with no global feedback.
This is a modern approach.
The historical ones are attractive to me too, they have a different rendering, esthetic. I like it too.
The Ba21a is not very coloured like older Rca design (single ended from 40's and before) but it have a sound still. It's a stange approach in a way: three stage with 20db global nfb ( with a dedicated out from the out transfo), first stage is a transformer input grounded cathode single ended ( nfb entry on cathode) followed by a phase splitter ( 'concertina' circuit iirc) then a push pull transformer coupled out.
Input transformer is close to A10 from what i've read. The output one is the one with 'character' from my experiment with the circuit.
About sound, it remain me from 50's/60's jazz recording ( Miles Davis, Brubeck,...). With ribbon mic on close micing( Coles and AEA) and tube mic (close mic and more distant location -my own version of U47 and M49) it is a wayback machine.
With cartdrige i tried with my mc ( 310mc) but i cheated: i have an SL10 in which there is an integrated preamp to bring the mc out voltage into mm territory in order to attack an mm pre which will take care of riaa and final voltage gain.
I bypassed it and integrated the ba21a in place of it. Sound nice. Different from the SL10 internal one and the RJM's Phonoclone i use the mc with usually. If i had a passive rlc Riaa i could use a whole tube chain with 1xba21a -passive riaa- 1xba21a. It should have more 'sound'.
I still crave for the phonoclone though ( it is good with everything, tube sound more...tubey and is sometime too much for my preference with electronic music).
In this video i identify the sound i like about it ( start at 1mn):
Difference with older Rca design comes from transfo, sure but from general design too: single ended without global nfb have different sound imprint. Especially when they are pushed, distortion sound different. It's nice too and remind from 40's recording. Suit well bluegrass, blues,classic rock'n roll, old school R&B, gospel,... i like them too!
For new prod 6h30p there was some shop which offered balanced and pairing options in UK. I'll try to find them in my bookmark but it's been a while since i ordered them ( maybe Watford Valves?) So i don't know at the moment. The need for this will depend of your circuit, design.
Is it Moby you are talking about (A10/A24)?
For older UTC iron, Cinemag offer their own version. I've been in communication with them about some for a ba2( or another ref but an older one edit: Ba2c) i planned. I agree there is difference in Cinemag i own ( mostly mic tube out). But overall i find older transformers to have stronger character, this was my point.
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Comming back to the price and qualities of NOS tubes, what about e188cc, e288cc,...no personality enough because too much clean for audio signal (not colored)
And about modern design, what about hybrid mu follower Krivium ? quality of sand becomes higher than the tube here when not using DHT but IHT instead?
And about modern design, what about hybrid mu follower Krivium ? quality of sand becomes higher than the tube here when not using DHT but IHT instead?
I don't know these tubes but i don't know if there is such thing as 'too clean for audio'.
I mean it all depends what you are looking for as outcome.
Sure all references have proper set of characteristics for self generated distortion, capacitive behavior, and so on but in fine, the circuit will have a stronger influence in 90% of case.
But there is no rules against trying to optimise with another step by selecting a tube which seems more suited to the task than another one.
'Modern design' sound different from conservative design. Really different. If you are into vintage sound you'll be disapointed. If you look for transparency you'll be pleased.
I don't think sand or solid state takes over in the sound. At least i'm not able to identify any 'sand' sound ( in 'secondary' tasks as ccs or active load) to it but as it become more 'perfect' on some objective parameters you can use the full potential of 'clean' a tube can offer. And as there is much less dynamic interacting bothering parameters i find they (tubes) can sound even more true in same case.
It's a way to approach things and i like to do it with a common grounded cathode ( without cathode bypass) and varying operation point until it sound 'fat' with the iron and brings hd... it all depend what you want.
I mean it all depends what you are looking for as outcome.
Sure all references have proper set of characteristics for self generated distortion, capacitive behavior, and so on but in fine, the circuit will have a stronger influence in 90% of case.
But there is no rules against trying to optimise with another step by selecting a tube which seems more suited to the task than another one.
'Modern design' sound different from conservative design. Really different. If you are into vintage sound you'll be disapointed. If you look for transparency you'll be pleased.
I don't think sand or solid state takes over in the sound. At least i'm not able to identify any 'sand' sound ( in 'secondary' tasks as ccs or active load) to it but as it become more 'perfect' on some objective parameters you can use the full potential of 'clean' a tube can offer. And as there is much less dynamic interacting bothering parameters i find they (tubes) can sound even more true in same case.
It's a way to approach things and i like to do it with a common grounded cathode ( without cathode bypass) and varying operation point until it sound 'fat' with the iron and brings hd... it all depend what you want.
This are great looking preamps, are they yours? I like this clean and wide drum sound, would be interesting to know what they were recorded with and groups tracked with. Bred 806 i built with help of EMI technical engineer to finish my studies used similar output transformer like BA-21a although with completely different circuit.
Beside some other American preamps, i made RCA BA-2 with modern 1:10 input ala Jensen 115-K or UTC A-10 like tr. Output trafos are gapped Fe or 50Ni/50Fe (try 50Ni if you build it, sound more open to me) from Cinemag (no gap they stacked it in a way to take a few mA). This was my first preamp of this kind some people didn't like; as you know many think tube preamps can be easily driven into lots of distotion while sounding good and what not...
I never thought no nfb preamp would be so clean (used EF86 wired as triodes) despite very bad scope pictures compared to others with NFB. It sounds quite dark (i see black and brown color) but highs are there. Depending on transformers used fr. response is fine from ~50Hz-~16kHz. It works well on acoustic instruments because they never come out harsh.
This manufacturer started making UTC-A10 people like, Carnhill also has something close, can't say how good is Igor from Poland: https://www.crimsonaudiotransformers.com/a-10/ I tend to use modern inputs or "UTC like" for replicas, outputs are more problematic because some are not made anymore.
I just found slightly used E182CC to try instead 6N6P, 12BH7 and similar for my push pull output stage, can't wait to build it completely. Btw, 20 years ago a friend got a sleeve of Philips E80CC driver tubes that were so tightly matched in any way possible, we have never seen something like them again. EH might come close if big batch was tested.
Attachments
No these are not mine.
I got the 4 set of iron from modules which were into a dumpster ( whole console).
I rebuilt 2 chanels using russian paper and pio capacitors and tubes from russian origin, ( EH12ay7), carbon resistor ( Koa)... on satellite board the old school way. I discarded the metering on mine. I've had multiple psu, crc, then crc+ 2x vr150 ( i changed one resistor of original circuit from 2700r to 4300r to account for the B+ rise). I used a smps for the heaters when i swapped the first passive psu, and still use it. My musicians friends nicknamed 'coldwar' or 'glatsnozk'' preamp when i described it.
I would like to try crc+ (ccs+ 2xvr150) per chanel to have a nice 'modern' shunt regulated psu with old school parts and tech. And rebuilt the 4 units and had a switching system to have the possibility to change order of them on the fly ( from 4 independant unit to 2x2 in series) and have the choice of transformers loading, insert a constant z attenuator between them or a riaa circuit, etc,etc,.... it would need some relay switching i could use the smps for that too... but i'm short on time and since i'm more onto loudspeakers for some years now... it'll have to wait.
But i must say the idea to have 8x vr150 purple glow and 8x tubes and transfos on a nice chassis have a certain appeal to me.
And it would drive crazy some musicians i work with from time to time who crave for tube gear.
The atribute you give are what i find attractive about this kind of gear, their rendering suit acoustic instruments well despite their flaws and limitation.
I got the 4 set of iron from modules which were into a dumpster ( whole console).
I rebuilt 2 chanels using russian paper and pio capacitors and tubes from russian origin, ( EH12ay7), carbon resistor ( Koa)... on satellite board the old school way. I discarded the metering on mine. I've had multiple psu, crc, then crc+ 2x vr150 ( i changed one resistor of original circuit from 2700r to 4300r to account for the B+ rise). I used a smps for the heaters when i swapped the first passive psu, and still use it. My musicians friends nicknamed 'coldwar' or 'glatsnozk'' preamp when i described it.
I would like to try crc+ (ccs+ 2xvr150) per chanel to have a nice 'modern' shunt regulated psu with old school parts and tech. And rebuilt the 4 units and had a switching system to have the possibility to change order of them on the fly ( from 4 independant unit to 2x2 in series) and have the choice of transformers loading, insert a constant z attenuator between them or a riaa circuit, etc,etc,.... it would need some relay switching i could use the smps for that too... but i'm short on time and since i'm more onto loudspeakers for some years now... it'll have to wait.
But i must say the idea to have 8x vr150 purple glow and 8x tubes and transfos on a nice chassis have a certain appeal to me.
And it would drive crazy some musicians i work with from time to time who crave for tube gear.
The atribute you give are what i find attractive about this kind of gear, their rendering suit acoustic instruments well despite their flaws and limitation.