Amina HD4 Tube Tape Head PreAmp Opening Up But ........

Jazzbo · Sep 20, 2013

Hello and good Friday morning to all,

My HD4 preamp is sounding better as it begins to settle in and that's great. So far, even with the 20 plus year old GE 12AX7 tubes things appear to be rock solid. However, I've read some previous posts that talk about "bass bump" which I have listened for but have not heard yet. While I had good bass reproduction initially, it seems to be getting better as my preamp burns in, if that's a proper term to use. What should I be listening for and is there a real need to be concerned if my music is sounding good? I'm still loving what I am hearing. Thanks for all comments.

jazzbo Bob

tony ky ma · Sep 20, 2013

Bob
Always trust your own ear is better than measurement, as long you can hear the different of break in that you and your system are in a kind of level already, you will find out right away when the sound is going better or worst because you know your system better than any other when you get use of the sound, try change those 12AX7 ( Telefonken) or 6SN7 (RAC red base), you will be surprised by the different change, and the best recording will more easy to hear the different too !
tony ma

RogerD · Sep 20, 2013

Hello Bob,

I always wait 50 to 100 hours before expecting the preamp to stabilise. If it sounded good from the start everything should be fine. The low end should get better,more punch,definition.articulation and with tape sound very good. As Tony suggested,roll some tubes after it stabilises.

Jazzbo · Sep 20, 2013

Good afternoon Mr. Tony Ma,
You make a good point sir. I do try to depend a great deal on what I hear through my music system. However, there are so many great threads posted here on various topics that is a major concern to me as a reel to reel lover. Thank you so much for your continued support.

bob

Steve Williams · Sep 20, 2013

Roll those 12AX7 tubes Bob

MylesBAstor · Sep 20, 2013

Jazzbo said:
Good afternoon Mr. Tony Ma,
You make a good point sir. I do try to depend a great deal on what I hear through my music system. However, there are so many great threads posted here on various topics that is a major concern to me as a reel to reel lover. Thank you so much for your continued support.

bob

What caps were installed in the unit? If they're Teflon, you'll need maybe 2-300 hrs before drawing any meaningful conclusions.

Jazzbo · Sep 20, 2013

Hello everyone,
I've got to say that I have met many friends on this forum and feel more than blessed to be a part of what's going on here. No matter what concerns or major problems I have and will have in the future, everyone of my friends here have come through with "problem reduction" suggestions that really work and work well. Thank you Myles, Steve, Roger and those who will respond later for your input on my latest HD4 thread. Put simply, you guys are just wonderful and I sure appreciate you being here.

jazzbo bob

Steve Williams · Sep 20, 2013

You owe it to yourself to roll those 12AX7's

Ki Choi · Sep 20, 2013

Hi Bob:

Although we have a side conversation about your tape preamp, for the benefits of others here, I would like to suggest you run the MRL Cal tape (if your tech hadn't done already) and tell us how the preamp is responding in HF and LF before spending time and money on better tubes.

Send me a note if you need help.

I have said elsewhere, most of the available tape head preamps (other than Manley), have no means to verify if NAB or IEC EQ frequency responses are correct for the particular head in respect to normal audiophile uses. We all know no two heads are the same electrically or have same wear characteristics mechanically even if they are two exact model heads.

So, if the tape head preamp was made at the factory with anything other than the head you have in your machine (in your case, yes), there's a good chance the preamp will behave differently when you get it home. I truly believe the differences will be greater than any cap upgrades or tube rolling.

It is my opinion, majority of the differences we hear from various tape head preamps are in their built-in inaccuracies or non adjustable EQ responses more than their circuit differences or SS vs Tube challenges. This is why properly adjusted Studer internal audio circuits would sound different or inferior to some of the outboard preamps with exception of superior transparency one gets from simpler outboard repro circuits with tube or well designed SS components.

Thus, we must start from a baseline reference points for all tape preamps to confidently say - this tape preamp is +/- 1dB from 30 - 30K at 15ips on NAB and IEC EQ using MRL cal tape etc. Just as we assume RIAA EQ performance on most of the phono preamps to be correct (or varies very little) and the differences in sonic come from elsewhere. But unfortunately, for tapes preamps, we are not there yet...

Steve Williams · Sep 20, 2013

Ki

IIRC Nick Doshi has algorithms that he uses for each tape head in the production of his tape head preamp. I remember Nick commented on that when he set mine up or am I mistaken

Jazzbo · Sep 20, 2013

Hello again all,
Actually, my preamp was finalized after I ordered the Pro Nortronics playback head. So, the tech was able to match the Nortronics and pre amp so they would complement each other. He in fact did use a Cal tape during this time. While I don't have the specs, it would appear that the pre amp sounds good and supports the Nortronics head very well. I just want to be able to max out what's available from the combination preamp and playback head, but understand the HD4 will have to have some additional playing time before I can move on to what's next. However, so far, the preamp has had a little over 120 hours including playing time at the shop where the unit was constructed. Again, just using my ears, the sound I am getting is good but I am sure could be better. The left and right level controls as well as the trim control on the HD4 has provided plenty of control over what I am hearing.

bob

Ki Choi · Sep 20, 2013

Steve Williams said:
Ki

IIRC Nick Doshi has algorithms that he uses for each tape head in the production of his tape head preamp. I remember Nick commented on that when he set mine up or am I mistaken

Hey Steve:

Your Doshi preamp should've been dialed in not at the factory but at your home! What more can a man ask for? Most of us are not so fortunate.

I can't critic the Doshi preamp circuits or predict how well it would respond to a particular repro head, I do see the preamp having its dedicated gain stage for both IEC and NAB passive EQ. Thus, whatever one does to IEC part won't affect NAB section or the other way around. This is good and Bruce's input may have something to do with it. But unfortunately, I can't say the same for other tape preamps.

However, Doshi provided only HF adjustments. One can argue there's no real needs for adjusting LF in audiophile application (since most of us like the bass boost from head bump)..., I have seen more than 10dB boost in 50Hz region on some other preamps with no way of taming it...

Again, it is only one man's opinion and YMMV.

Ki Choi · Sep 20, 2013

Jazzbo said:
Hello again all,
Actually, my preamp was finalized after I ordered the Pro Nortronics playback head. So, the tech was able to match the Nortronics and pre amp so they would complement each other. He in fact did use a Cal tape during this time. While I don't have the specs, it would appear that the pre amp sounds good and supports the Nortronics head very well. I just want to be able to max out what's available from the combination preamp and playback head, but understand the HD4 will have to have some additional playing time before I can move on to what's next. However, so far, the preamp has had a little over 120 hours including playing time at the shop where the unit was constructed. Again, just using my ears, the sound I am getting is good but I am sure could be better. The left and right level controls as well as the trim control on the HD4 has provided plenty of control over what I am hearing.

bob

Good for you Bob that your tech had adjusted the preamp's responses to your Nortronics repro head using MRL cal tape before delivery. As you use the machine for a long time and the head would start to wear, you would need to have him re-adjust mainly the HF to compensate for eventual loss of HF response from the worn head.

Bruce B · Sep 20, 2013

Ki Choi said:
However, Doshi provided only HF adjustments. One can argue there's no real needs for adjusting LF in audiophile application (since most of us like the bass boost from head bump)..., I have seen more than 10dB boost in 50Hz region on some other preamps with no way of taming it...

Again, it is only one man's opinion and YMMV.

This shouldn't be hard to do. Set up the tape pre with the MRL tape and then record some 20-20k sweeps and do FFT.

Ki Choi · Sep 20, 2013

Bruce B said:
This shouldn't be hard to do. Set up the tape pre with the MRL tape and then record some 20-20k sweeps and do FFT.

Yes, Bruce it should be easy to check if any tape head preamps are properly sweeping 20 - 20Khz but the challenge is what to do next if the test shows it is way off...especially if there are no LF adjustments in the preamp... In addition, depends on head/preamp combination, the adjustments that worked at the factory may not be wide enough with some preamps when the head is electrically different than the reference head used at the factory, I have found.

There's no EQ needed for IEC @15 ips in the bass region (one of the main reasons to go with IEC, IMHO) but NAB EQ setting needs to be boosted close to 8dB at 20Hz and would need some adjustments, IMO.

Bruce B · Sep 20, 2013

Ki Choi said:
Yes, Bruce it should be easy to check if any tape head preamps are properly sweeping 20 - 20Khz but the challenge is what to do next if the test shows it is way off...especially if there are no LF adjustments in the preamp... In addition, depends on head/preamp combination, the adjustments that worked at the factory may not be wide enough with some preamps when the head is electrically different than the reference head used at the factory, I have found.

There's no EQ needed for IEC @15 ips in the bass region (one of the main reasons to go with IEC, IMHO) but NAB EQ setting needs to be boosted close to 8dB at 20Hz and would need some adjustments, IMO.

It would at least show how close these tape pre's are to the IEC and NAB standards. It's the manufacturer's problem to fix it!

Ki Choi · Sep 20, 2013

Bruce B said:
It would at least show how close these tape pre's are to the IEC and NAB standards. It's the manufacturer's problem to fix it!

My guess is that the test will disappoint few people and ruffle many manufacturers' feathers...

On the other hand, "ignorance is bliss." - It applies to most of us audiophile hobby people here as long as the preamp sounds good to our ears. I assume you have different requirements for your work.

Jazzbo · Sep 20, 2013

Thanks Ki,
So far so good. I'm hoping that this Nortronics head will continue to do its thing for a long time without need for any additional adjustments. I am happy that not many here worries about bass bump which I have not been able to hear anyway. As has been said, at least some of us don't have major problems with a little help below 50hz.

bob

Jazzbo · Sep 20, 2013

After thinking about what I've read, it would appear that the purchase of any tape head preamp, other than one that was designed to work with a particular tape deck would be considered an adventure. How would one know which preamp to buy to work with his/her tape deck since it would not be perfectly matched?

bob

tony ky ma · Sep 20, 2013

Bob
Match ideas from other people may not work same in your system (amp + speaker), for recording is better to adjust the recorder in perfect condition because they are recording into tape so we check before record every time, but for repro listening I don't think we need a very flat frequency respond on play back of the deck ,it will depend how it combine with the whole system, and I believe that it is not too easy to hear the different between a flat and not too flat frequency respond but when you switch to another tape head preamp then you will find out very easy of the difference, also this will cost too much money, for up grade if you are a DIYER you can change some cap in the sound path of the circuit or more easy way of changing tubes. using more filters to make a flat frequency respond will down grade the transparency and emotions that is the choice of give and take
tony ma

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